Patent Application
20210147240
The present invention is in the field of material science and electrocatalysis.
Today's human transportation is based on fossil fuels, which are inefficient and polluting. A promising alternative is using fuel cells as a clean and energy-efficient transportation power source. Fuel cells separate fuel oxidation and oxidant reduction, so usable electricity is generated. However, the most researched fuel for fuel cells, hydrogen (H2) gas, is hard to transport and store. Moreover, fuel cells are expensive because their electrode materials are made from precious metals. There is a need for alternative fuel sources with easier and safer transportation, and more stable electrodes made of cheaper and more abundant materials.
Oxygen redox catalysis, including the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is crucial in determining the electrochemical performance of energy conversion and storage devices such as fuel cells, metal-air batteries and electrolyzers. At the current stage of technology, platinum (Pt)-based materials are the most practical catalysts. Because these Pt-based catalysts are too expensive for making commercially viable fuel cells.
The oxidation of hydrazine (N2H4) is an important challenge in electrocatalysis, with applications in direct hydrazine fuel cells and in medical and environmental sensing. Noble metals such as palladium (Pd) and gold (Au) catalyze the HzOR effectively, yet their scarcity calls for earth-abundant alternatives.
Therefore, there is still a great need for new materials that have the ability to compete with the known precious metals in the reduction of oxygen, and hydrazine oxidation, as a practical alternative to the expensive metals.
According to one aspect, there is provided a composition comprising a porous carbon material comprising mesopores, micropores, macropores, or any combination thereof, wherein the composition is characterized by (i) a total pore volume between of 0.01 cm3 g−1 and 4 cm3 g−1 and (ii) a specific surface area (SSA) between 50 m2 g−1 and 2000 m2 g−1.
In some embodiments, the micropores are characterized by a total volume between 0.01 and 0.6 cm3 g−1.
In some embodiments, the mesopores and the macropores are characterized by a total volume between 0.09 and 4 cm3 g−1.
In some embodiments, the carbon material is doped with 0.2 at. % to 5 at. % nitrogen.
In some embodiments, the pores are void.
In some embodiments, the pores comprise an alkaline earth metal compound comprising magnesium, calcium, strontium, barium, or any combination thereof.
In some embodiments, the alkaline earth metal compound is in the form of nanoparticles.
In some embodiments, the nanoparticles are characterized by a diameter in the range of 1 nm to 60 nm.
In some embodiments, the alkaline earth metal compound is characterized by crystallite size in the range of 3 nm to 40 nm, as determined by the Scherrer method.
In some embodiments, the carbon material comprises graphite, carbon black, graphene, reduced graphene oxide, graphene oxide, carbon microfibers, carbon nanofibers, carbon nanotubes, carbon nanowires, glassy carbon, amorphous carbon, or any combination thereof.
In some embodiments, the composition is for use in hydrazine oxidation reaction (HzOR), oxygen reduction reaction (ORR), or both.
According to another aspect, there is provided an article comprising the composition of the present invention, wherein the composition is deposited on at least one surface of the article.
In some embodiments, the article is in the form of a cathode. In some embodiments, the article is in the form of an anode.
In some embodiments, the loading of the composition is in the range of 0.01 mg cm−2 to 0.3 mg cm−2.
According to another aspect, there is provided an electrochemical cell comprising the article of the present invention.
In some embodiments, the electrochemical cell is configured to oxidize hydrazine at onset potentials in the range of 0.2 V vs. reversible hydrogen electrode (RHE) to 0.8 V vs. RHE.
In some embodiments, the electrochemical cell operates in alkaline environment. In some embodiments, the electrochemical cell operates in acidic environment.
According to another aspect, there is provided a process of oxidizing hydrazine, the process comprising: (i) contacting a hydrazine containing solution with the electrochemical cell of the present invention, and (ii) applying an anodic electric potential to the electrochemical cell, thereby oxidizing the hydrazine.
According to another aspect, there is provided a method for preparing the composition of the present invention, comprising: (i) providing one or more earth metal-coordination polymer precursor comprising magnesium, calcium, strontium, barium, or any combination thereof; and (ii) pyrolysing the earth metal-coordination polymer precursor, thereby obtaining the porous carbon material.
In some embodiments, the method further comprises step (iii) of washing the doped earth metal-carbon material, thereby obtaining the porous carbon material.
In some embodiments, pyrolysing is at a temperature ranging from of 450° C. to 1000° C.
Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention, in some embodiments thereof, is directed to a composition comprising a porous carbon material.
In some embodiments, the present invention provides a porous carbon material comprising a network of pores. In some embodiments, the present invention provides a hierarchically porous carbon material comprising micropores, mesopores, macropores, or any combination thereof. In some embodiments, the composition comprises a nitrogen doped hierarchically porous carbon material.
As used herein, the terms “hierarchically porous” and “hierarchical porosity” refer to the presence of at least two different pore sizes in the carbon material, i.e., at least one set of pores being microporous (d<2 nm), mesoporous (2 nm<d<50 nm and at least one set of pores being macroporous (50 nm<d). The mesopores, micropores and macropores may be arranged, with respect to each other, in any of several different ways. In some embodiments, at least one (or both, or all) of the mesopores micropores and macropores are arranged in an ordered (i.e., patterned) manner.
In some embodiments, a composition comprising a porous carbon material as described herein is a catalyst. In some embodiments, a composition comprising a porous carbon material as described herein is characterized by an improved catalytic activity towards hydrazine oxidation reaction (HzOR), oxygen reduction reaction (ORR), or both. In some embodiments, a composition comprising a porous carbon material comprising micropores, mesopores, macropores, or any combination thereof, is characterized by an increased exposure of the catalytic sites to an efficient flow of reactants and products.
In some embodiments, the present invention is directed to a method for preparing a composition comprising a porous carbon material comprising micropores, mesopores, and macropores, as described herein.
In some embodiments, the hierarchical porosity in the porous carbon material is obtained by the pyrolysis of well-designed metal-organic precursors, comprising earth metal-coordination polymer (MOCP).
As used herein “coordination polymer” refers to an infinite array composed of metal ions which are bridged by certain ligands among them. This incorporates a wide range of architectures including simple one-dimensional chains with small ligands to large mesoporous frameworks. In some embodiments, the formation process proceeds automatically and, therefore, is called a self-assembly process. Various coordination polymers are well-known in the art and would be will be apparent to those skilled in the art.
As used herein, the term “alkaline earth metal” refers to the series of elements comprising Group 2 of the Periodic Table of the Elements. “Alkaline earth metal” refers to beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). In some embodiments, the composition comprises an alkaline earth metal oxide. The term “alkaline earth metal oxide” refers to an oxide of an alkaline earth metal, including BeO, MgO, CaO, SrO, and BaO. In some embodiments, the composition comprises an alkaline earth metal carbonate. The term “alkaline earth metal carbonate” refers to a carbonate of an alkaline earth metal, e.g. SrC3, BaC3, CaCO3. In some embodiments, the composition comprises an alkaline earth metal hydroxide. The term “alkaline earth metal hydroxide” refers to a hydroxide of an alkaline earth metal, e.g. Ca(OH)2, Sr(OH)2. In some embodiments, the composition comprises an alkaline earth metal compound(s), complex(es) and/or salt(s) thereof. In some embodiments, the composition comprises mixtures of alkaline earth metal compounds. As used herein, the term “mixtures of alkaline earth metal compounds” refers to the use of two or more compounds of alkaline earth metals. In some embodiments, a mixture of alkaline earth metal compounds provides an enhanced catalytic activity.
In some embodiments, the composition comprises an alkaline earth metal compound. In some embodiments, the carbon material is a porous carbon material. In some embodiments, the composition is in the form of a catalyst. In some embodiments, the composition comprises a catalyst with hydrazine oxidation reaction (HzOR) activity. In some embodiments, the composition comprises a catalyst with oxygen reduction reaction (ORR) activity. In some embodiments, the composition has catalytic activity towards HzOR, ORR, or both. In some embodiments, the composition described herein has enhanced activity towards HzOR, ORR, or both. In some embodiments, the catalyst described herein has catalytic activity towards HzOR, ORR, or both, operating at low overpotentials and in a wide pH rage.
According to some embodiments, the present invention provides a composition comprising 90% to 99.9% (w/w) of a porous carbon material and less than 5% (w/w) of an alkaline earth metal. According to some embodiments, the present invention provides a composition comprising at least 95% (w/w) of a porous carbon material. According to some embodiments, the present invention provides a composition comprising at least 97% (w/w) of a porous carbon material. According to some embodiments, the present invention provides a composition comprising at least 99% (w/w) of a porous carbon material. In some embodiments, the present invention provides a composition comprising less than 5% (w/w) of an alkaline earth metal. In some embodiments, the present invention provides a composition comprising less than 2% (w/w) of an alkaline earth metal. In some embodiments, the present invention provides a composition comprising less than 1% (w/w) of an alkaline earth metal. In some embodiments, the present invention provides a composition comprising less than 0.5% (w/w) of an alkaline earth metal. In some embodiments, the present invention provides a composition comprising less than 0.1% (w/w) of an alkaline earth metal. In some embodiments, the composition is devoid of an alkaline earth metal compound.
In one embodiment, a composition, a particle, an article or a cell as described herein is characterized by a graphitization content as measured by a Raman IG/ID ratio of 0.2-2. In one embodiment, a composition, a particle, an article or a cell as described herein is identified by a graphitization content as measured by a Raman IG/ID ratio of 0.2-2. In one embodiment, a composition, a particle, an article or a cell as described herein is identified by a graphitization content as measured by a Raman IG/ID ratio of 0.2-1. In one embodiment, a composition, a particle, an article or a cell as described herein is identified by a graphitization content as measured by a Raman IG/ID ratio of 0.8-2.
According to some embodiments, the present invention provides a composition comprising a porous carbon material comprising mesopores, micropores, macropores, or any combination thereof.
In some embodiments, the carbon material comprises: graphite, carbon black, graphene, reduced graphene oxide, graphene oxide, carbon microfibers, carbon nanofibers, carbon nanotubes, carbon nanowires, glassy carbon, amorphous carbon, or any combination thereof. As used herein, the term “carbon material” refers to carbon containing structures. “Carbon material” according to the present invention refers to a material or substance comprised substantially of carbon. Carbon materials include ultrapure as well as amorphous and crystalline carbon materials. Example of carbon materials comprise activated carbon, mesoporous carbon, templated carbon, carbide-derived carbon, porous carbon sphere, and carbon onion. In some embodiments, carbon materials according to the present invention comprise activated carbons, i.e. materials prepared by pyrolysis. In some embodiments, carbon materials according to the present invention are prepared by pyrolysis of carbon precursors. In some embodiments, carbon precursors comprise one or more polymers, small organic molecules or small molecular weight saccharides. In some embodiments, compositions according to the present invention comprise porous carbon materials. Porous carbon materials can be classified according to their pore diameters: microporous (<2 nm), mesoporous (2-50 nm), and macroporous (>50 nm). The structure of the porous carbon material can take various forms depending on the starting material, and the manufacturing method.
As used herein, the terms “pore” and “porous” refer to an opening or depression in the surface of a catalyst or catalyst support.
In some embodiments, the composition is characterized by a total pore volume between of 0.01 cm3 g−1 and 4 cm3 g−1. In some embodiments, the composition is characterized by a total pore volume in the range of 0.01 cm3 g−1 to 5 cm3 g−1, 0.01 cm3 g−1 to 4 cm3 g−1, 0.05 cm3 g−1 to 5 cm3 g−1, 0.09 cm3 g−1 to 4 cm3 g−1, 0.01 cm3 g−1 to 2 cm3 g−1, 0.05 cm3 g−1 to 2 cm3 g−1, 0.09 cm3 g−1 to 2 cm3 g−1, 0.1 cm3 g−1 to 5 cm3 g−1, 0.2 cm3 g−1 to 2.5 cm3 g−1, 0.5 cm3 g−1 to 2.5 cm3 g−1, 0.7 cm3 g−1 to 5 cm3 g−1, 0.9 cm3 g−1 to 2.5 cm3 g−1, 1 cm3 g−1 to 2.5 cm3 g−1, 1.2 cm3 g−1 to 2.5 cm3 g−1, 1.5 cm3 g−1 to 2.5 cm3 g−1, 1.9 cm3 g−1 to 5 cm3 g−1, 2.0 cm3 g−1 to 5 cm3 g−1, 0.1 cm3 g−1 to 2.0 cm3 g−1, 0.2 cm3 g−1 to 2.0 cm3 g−1, 0.5 cm3 g−1 to 2.0 cm3 g−1, 0.7 cm3 g−1 to 2.0 cm3 g−1, 0.9 cm3 g−1 to 2.0 cm3 g−1, 1 cm3 g−1 to 2.0 cm3 g−1, 1.2 cm3 g−1 to 2.0 cm3 g−1, 1.5 cm3 g−1 to 2.0 cm3 g−1, 1.9 cm3 g−1 to 2.0 cm3 g−1, 0.1 cm3 g−1 to 1.6 cm3 g−1, 0.2 cm3 g−1 to 1.6 cm3 g−1, 0.5 cm3 g−1 to 1.6 cm3 g−1, 0.7 cm3 g−1 to 1.6 cm3 g−1, 0.9 cm3 g−1 to 1.6 cm3 g−1, 1.0 cm3 g−1 to 1.6 cm3 g−1, or 1.2 cm3 g−1 to 1.6 cm3 g−1, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the composition is characterized by a specific surface area (SSA) between 50 m2 g−1 and 2000 m2 g−1. In some embodiments, the composition is characterized by a surface area in the range of 70 m2 g−1 to 2000 m2 g−1, 100 m2 g−1 to 2000 m2 g−1, 200 m2 g−1 to 2000 m2 g−1, 300 m2 g−1 to 2000 m2 g−1, 500 m2 g−1 to 2000 m2 g−1, 700 m2 g−1 to 2000 m2 g−1, 800 m2 g−1 to 2000 m2 g−1, 900 m2 g−1 to 2000 m2 g−1, 1000 m2 g−1 to 2000 m2 g−1, 1200 m2 g−1 to 2000 m2 g−1, 50 m2 g−1 to 1300 m2 g−1, 70 m2 g−1 to 1300 m2 g−1, 100 m2 g−1 to 1300 m2 g−1, 200 m2 g−1 to 1300 m2 g−1, 300 m2 g−1 to 1300 m2 g−1, 500 m2 g−1 to 1300 m2 g−1, 700 m2 g−1 to 1300 m2 g−1, 800 m2 g−1 to 1300 m2 g−1, 900 m2 g−1 to 1300 m2 g−1, 1000 m2 g−1 to 1300 m2 g−1, 1200 m2 g−1 to 1300 m2 g−1, 50 m2 g−1 to 500 m2 g−1, 70 m2 g−1 to 500 m2 g−1, 100 m2 g−1 to 500 m2 g−1, 200 m2 g−1 to 500 m2 g−1, 300 m2 g−1 to 500 m2 g−1, 50 m2 g−1 to 900 m2 g−1, 70 m2 g−1 to 900 m2 g−1, 100 m2 g−1 to 900 m2 g−1, 200 m2 g−1 to 900 m2 g−1, 300 m2 g−1 to 900 m2 g−1, 500 m2 g−1 to 900 m2 g−1, 700 m2 g−1 to 900 m2 g−1, or 800 m2 g−1 to 900 m2 g−1, including any range therebetween. Each possibility represents a separate embodiment of the invention.
As used herein, the term “surface area” refers to the total surface area of a substance measurable by the BET technique.
In some embodiments, the composition comprises a porous carbon material comprising mesopores, micropores, macropores, or any combination thereof. In some embodiments, the composition comprises mesopores, micropores, macropores, or any combination thereof.
In some embodiments, the micropores are characterized by a size in the range of 0.2 nm to 5 nm, 0.5 nm to 5 nm, 0.9 nm to 5 nm, 1.0 nm to 5 nm, 0.2 nm to 3 nm, 0.5 nm to 3 nm, 0.9 nm to 3 nm, 1.0 nm to 3 nm, 1.0 nm to 2.5 nm, 1.2 nm to 5 nm, 1.5 nm to 5 nm, 1.9 nm to 5 nm, 2.0 nm to 5 nm, 0.2 nm to 2.0 nm, 0.5 nm to 2.0 nm, 0.9 nm to 2.0 nm, 1.0 nm to 2.0 nm, 1.0 nm to 2.0 nm, 1.2 nm to 2.0 nm, 1.5 nm to 2.0 nm, 1.9 nm to 2.0 nm, 2.0 nm to 2.0 nm, 0.2 nm to 1.5 nm, 0.5 nm to 1.5 nm, 0.9 nm to 1.5 nm, 1.0 nm to 1.5 nm, 1.0 nm to 1.5 nm, 1.2 nm to 1.5 nm, 0.2 nm to 1.0 nm, 0.5 nm to 1.0 nm, 2.5 nm to 5.0 nm, 0.5 nm to 2.5 nm, or 0.9 nm to 1.0 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the mesopores are characterized by a size in the range of 3 nm to 60 nm, 5 nm to 60 nm, 10 nm to 60 nm, 15 nm to 60 nm, 20 nm to 60 nm, 3 nm to 40 nm, 5 nm to 40 nm, 10 nm to 40 nm, 15 nm to 40 nm, 20 nm to 40 nm, 25 nm to 40 nm, 30 nm to 40 nm, 35 nm to 40 nm, 3 nm to 30 nm, 5 nm to 30 nm, 10 nm to 30 nm, 15 nm to 30 nm, 20 nm to 30 nm, 25 nm to 30 nm, 3 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, 15 nm to 20 nm, 3 nm to 10 nm, 5 nm to 10 nm, or 3 nm to 5 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the macropores are characterized by a size in the rage of 60 nm to 500 nm, 70 nm to 500 nm, 90 nm to 500 nm, 100 nm to 500 nm, 60 nm to 250 nm, 70 nm to 250 nm, 90 nm to 250 nm, 100 nm to 250 nm, 60 nm to 150 nm, 70 nm to 150 nm, 90 nm to 150 nm, 60 nm to 100 nm, or 70 nm to 100 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the micropores are characterized by a total volume between 0.01 cm3 g−1 and 0.6 cm3 g−1, 0.05 cm3 g−1 and 0.6 cm3 g−1, 0.09 cm3 g−1 and 0.6 cm3 g−1, 0.1 cm3 g−1 and 0.6 cm3 g−1, 0.12 cm3 gland 0.6 cm3 g−1, 0.01 cm3 g−1 and 0.5 cm3 g−1, 0.05 cm3 g−1 and 0.5 cm3 g−1, 0.09 cm3 g−1 and 0.5 cm3 g−1, 0.1 cm3 g−1 and 0.5 cm3 g−1, 0.12 cm3 g−1 and 0.5 cm3 g−1, 0.01 cm3 g−1 and 0.4 cm3 g−1, 0.05 cm3 g−1 and 0.4 cm3 g−1, 0.09 cm3 g−1 and 0.4 cm3 g−1, 0.1 cm3 g−1 and 0.4 cm3 g−1, or 0.12 cm3 g−1 and 0.4 cm3 g−1, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the mesopores are characterized by a total volume between 0.01 cm3 g−1 and 6 cm3 g−1, 0.05 cm3 g−1 and 6 cm3 g−1, 0.09 cm3 g−1 and 6 cm3 g−1, 0.1 cm3 g−1 and 6 cm3 g−1, 0.12 cm3 g−1 and 6 cm3 g−1, 0.01 cm3 g−1 and 5 cm3 g−1, 0.05 cm3 g−1 and 5 cm3 g−1, 0.09 cm3 g−1 and 5 cm3 g−1, 0.1 cm3 g−1 and 5 cm3 g−1, 0.12 cm3 g−1 and 5 cm3 g−1, 0.01 cm3 g−1 and 0.3 cm3 g−1, 0.05 cm3 g−1 and 0.3 cm3 g−1, 0.09 cm3 g−1 and 0.3 cm3 g−1, 0.1 cm3 g−1 and 0.3 cm3 g−1, or 0.12 cm3 g−1 and 0.3 cm3 g−1, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the mesopores and the macropores are characterized by a total volume between 0.09 cm3 g−1 and 4 cm3 g−1, 0.1 cm3 g−1 and 4 cm3 g−1, 0.12 cm3 g−1 and 4 cm3 g−1, 0.5 cm3 g−1 and 4 cm3 g−1, 0.9 cm3 g−1 and 4 cm3 g−1, 0.1 cm3 g−1 and 4 cm3 g−1, 2 cm3 g−1 and 4 cm3 g−1, 0.09 cm3 g−1 and 3 cm3 g−1, 0.1 cm3 g−1 and 3 cm g−1, 0.12 cm3 g−1 and 3 cm3 g−1, 0.5 cm3 g−1 and 3 cm3 g−1, 0.9 cm3 g−1 and 3 cm3 g−1, 0.1 cm3 g−1 and 3 cm3 g−1, 2 cm3 g−1 and 3 cm3 g−1, 0.09 cm3 g−1 and 2 cm3 g−1, 0.1 cm3 g−1 and 2 cm3 g−1, 0.12 cm3 g−1 and 2 cm3 g−1, 0.5 cm3 g−1 and 2 cm3 g−1, 0.9 cm3 g−1 and 2 cm3 g−1, 0.1 cm3 g−1 and 2 cm3 g−1, 2 cm3 g−1 and 2 cm3 g−1, 0.09 cm3 g−1 and 1 cm3 g−1, 0.1 cm3 g−1 and 1 cm3 g−1, 0.12 cm3 g−1 and 1 cm3 g−1, 0.5 cm3 g−1 and 1 cm3 g−1, 0.9 cm3 g−1 and 1 cm3 g−1, 0.1 cm3 g−1 and 1 cm3 g−1, or 2 cm3 g−1 and 1 cm3 g−1, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the volume fraction of the micropores is 5% to 50%, 10% to 50%, 15% to 50%, 20% to 50%, 25% to 50%, 30% to 50%, 25% to 50%, 40% to 50%, 5% to 45%, 10% to 45%, 15% to 45%, 20% to 45%, 25% to 45%, 30% to 45%, 25% to 45%, 5% to 25%, 10% to 25%, 15% to 25%, 20% to 25%, 5% to 15%, or 10% to 15%, relative to the volume of the mesopores, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, microporosity is introduced in the composition by the metal doping. In some embodiments, the metal ions oxidize the carbon material. In some embodiments, mesoporosity is introduced in the composition through self-templating. In some embodiments, the composition comprises a hierarchical pore structure. In some embodiments, the hierarchical pore structure exposes the active sites of the composition allowing a better flow of reagents and products.
In some embodiments, porous carbon material is doped with 0.2 at. % to 5 at. %, 0.5 at. % to 5 at. %, 0.9 at. % to 5 at. %, 1.0 at. % to 5 at. %, 1.5 at. % to 5 at. %, 1.9 at. % to 5 at. %, 2 at. % to 5 at. %, 2.5 at. % to 5 at. %, 2.9 at. % to 5 at. %, 3 at. % to 5 at. %, 3.5 at. % to 5 at. %, 0.2 at. % to 4 at. %, 0.5 at. % to 4 at. %, 0.9 at. % to 4 at. %, 1.0 at. % to 4 at. %, 1.5 at. % to 4 at. %, 1.9 at. % to 4 at. %, 2 at. % to 4 at. %, 2.5 at. % to 4 at. %, 2.9 at. % to 4 at. %, 3 at. % to 4 at. %, 3.5 at. % to 4 at. %, 0.2 at. % to 3 at. %, 0.5 at. % to 3 at. %, 0.9 at. % to 3 at. %, 1.0 at. % to 3 at. %, 1.5 at. % to 3 at. %, 1.9 at. % to 3 at. %, 2 at. % to 3 at. %, or 2.5 at. % to 3 at. %, nitrogen, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the nitrogen is present in pyridinic form, pyrrolic form, pyrimidonic form, graphitic form metal-bound form, oxidized form, or any combination thereof. In some embodiments, the nitrogen is covalently bound. In some embodiments, the nitrogen is present in graphitic (Ng) form, pyridinic (Np) form, pyrrolic (Npy) form, oxidized (Nox) form, or any combination thereof.
In some embodiments, the composition comprises a porous carbon material comprising mesopores, micropores, macropores, or any combination thereof, wherein the pores are void.
In some embodiments, the composition comprises a porous carbon material comprising mesopores, micropores, macropores, or any combination thereof, wherein the pores comprise an alkaline earth metal compound comprising magnesium, calcium, strontium, barium, or any combination thereof. In some embodiments, the earth metal compound is in the form of nanoparticles. In some embodiments, the nanoparticles are characterized by a diameter in the range of 1 nm to 60 nm, 2 nm to 60 nm, 5 nm to 60 nm, 6 nm to 60 nm, 7 nm to 60 nm, 8 nm to 60 nm, 9 nm to 60 nm, 10 nm to 60 nm, 15 nm to 60 nm, 20 nm to 60 nm, 25 nm to 60 nm, 30 nm to 60 nm, 35 nm to 60 nm, 1 nm to 50 nm, 2 nm to 50 nm, 5 nm to 50 nm, 6 nm to 50 nm, 7 nm to 50 nm, 8 nm to 50 nm, 9 nm to 50 nm, 10 nm to 50 nm, 15 nm to 50 nm, 20 nm to 50 nm, 25 nm to 50 nm, 30 nm to 50 nm, 35 nm to 50 nm, 5 nm to 45 nm, 6 nm to 45 nm, 7 nm to 45 nm, 8 nm to 45 nm, 9 nm to 45 nm, 10 nm to 45 nm, 15 nm to 45 nm, 20 nm to 45 nm, 25 nm to 45 nm, 30 nm to 45 nm, 35 nm to 45 nm, 5 nm to 40 nm, 6 nm to 40 nm, 7 nm to 40 nm, 8 nm to 40 nm, 9 nm to 40 nm, 10 nm to 40 nm, 15 nm to 40 nm, 20 nm to 40 nm, 25 nm to 40 nm, 30 nm to 40 nm, 35 nm to 40 nm, 5 nm to 35 nm, 6 nm to 35 nm, 7 nm to 35 nm, 8 nm to 35 nm, 9 nm to 35 nm, 10 nm to 35 nm, 15 nm to 35 nm, 20 nm to 35 nm, 25 nm to 35 nm, 5 nm to 20 nm, 6 nm to 20 nm, 7 nm to 20 nm, 8 nm to 20 nm, 9 nm to 20 nm, or 10 nm to 20 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention. In some embodiments, the nanoparticles are characterized by a size in the range of 1 nm to 60 nm, 2 nm to 60 nm, 5 nm to 60 nm, 6 nm to 60 nm, 7 nm to 60 nm, 8 nm to 60 nm, 9 nm to 60 nm, 10 nm to 60 nm, 15 nm to 60 nm, 20 nm to 60 nm, 25 nm to 60 nm, 30 nm to 60 nm, 35 nm to 60 nm, 1 nm to 50 nm, 2 nm to 50 nm, 5 nm to 50 nm, 6 nm to 50 nm, 7 nm to 50 nm, 8 nm to 50 nm, 9 nm to 50 nm, 10 nm to 50 nm, 15 nm to 50 nm, 20 nm to 50 nm, 25 nm to 50 nm, 30 nm to 50 nm, 35 nm to 50 nm, 5 nm to 45 nm, 6 nm to 45 nm, 7 nm to 45 nm, 8 nm to 45 nm, 9 nm to 45 nm, 10 nm to 45 nm, 15 nm to 45 nm, 20 nm to 45 nm, 25 nm to 45 nm, 30 nm to 45 nm, 35 nm to 45 nm, 5 nm to 40 nm, 6 nm to 40 nm, 7 nm to 40 nm, 8 nm to 40 nm, 9 nm to 40 nm, 10 nm to 40 nm, 15 nm to 40 nm, 20 nm to 40 nm, 25 nm to 40 nm, 30 nm to 40 nm, 35 nm to 40 nm, 5 nm to 35 nm, 6 nm to 35 nm, 7 nm to 35 nm, 8 nm to 35 nm, 9 nm to 35 nm, 10 nm to 35 nm, 15 nm to 35 nm, 20 nm to 35 nm, 25 nm to 35 nm, 5 nm to 20 nm, 6 nm to 20 nm, 7 nm to 20 nm, 8 nm to 20 nm, 9 nm to 20 nm, or 10 nm to 20 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the composition comprises a porous carbon material and a plurality of embedded nanoparticles. In some embodiments, the nanoparticles are discrete. In some embodiments, the nanoparticles are agglomerated. In some embodiments, the agglomerates are ordered. In some embodiments, the agglomerates are disordered. In some embodiments, the agglomerates are spherical. In some embodiments, the agglomerates are characterized by a size in the range of 1 s to 300 s of nm, 3 s to 300 s of nm, 4 s to 300 s of nm, 5 s to 300 s of nm, 9 s to 300 s of nm, 10 s to 300 s of nm, 1 s to 250 s of nm, 3 s to 250 s of nm, 4 s to 250 s of nm, 5 s to 250 s of nm, 9 s to 250 s of nm, 10 s to 250 s of nm, 1 s to 120 s of nm, 3 s to 120 s of nm, 4 s to 120 s of nm, 5 s to 120 s of nm, 9 s to 120 s of nm, 10 s to 120 s of nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
Herein throughout, the terms “nanoparticles”, “nanoparticle”, “nano”, “nanosized”, and any grammatical derivative thereof, which are used herein interchangeably, describe a particle featuring a size of at least one dimension thereof (e.g., diameter, length) that ranges from about 1 nanometer to 100 nanometers. Herein throughout, “NP(s)” designates nanoparticle(s).
In some embodiments, the size of the particles described herein represents an average or median size of a plurality of nanoparticle composites or nanoparticles.
In some embodiments, the average or the median size of at least e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of the particles, ranges from: about 1 nanometer to 1000 nanometers, or, in other embodiments from 1 nm to 500 nm, or, in other embodiments, from 5 nm to 200 nm. In some embodiments, the average or the median size ranges from about 1 nanometer to about 300 nanometers. In some embodiments, the average or the median size ranges from about 1 nanometer to about 200 nanometers. In some embodiments, the average or the median size ranges from about 1 nanometer to about 100 nanometers. In some embodiments, the average or the median size ranges from about 1 nanometer to 50 nanometers, and in some embodiments, it is lower than 35 nm.
In some embodiments, a plurality of the particles has a uniform size.
By “uniform” or “homogenous” it is meant to refer to size distribution that varies within a range of less than e.g., ±60%, ±50%, ±40%, ±30%, ±20%, or ±10%, including any value therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, plurality of the particles is characterized by an average hydrodynamic diameter of less than 30 nm with a size distribution of that varies within a range of less than e.g., 60%, 50%, 40%, 30%, 20%, or 10%, including any value therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the particles size is about 1 nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm, about 25 nm, about 26 nm, about 27 nm, about 28 nm, about 29 nm, about 30 nm, about 31 nm, about 32 nm, about 33 nm, about 34 nm, about 35 nm, about 36 nm, about 37 nm, about 38 nm, about 40 nm, about 42 nm, about 44 nm, about 46 nm, about 48 nm, or 50 nm, including any value therebetween. Each possibility represents a separate embodiment of the invention.
As used herein the terms “average” or “median” size refer to diameter of the particles. The term “diameter” is art-recognized and is used herein to refer to either of the physical diameter (also termed “dry diameter”) or the hydrodynamic diameter. As used herein, the “hydrodynamic diameter” refers to a size determination for the composition in solution (e.g., aqueous solution) using any technique known in the art, e.g., dynamic light scattering (DLS).
As exemplified in the Example section that follows, the dry diameter of the particles, as prepared according to some embodiments of the invention, may be evaluated using transmission electron microscopy (TEM) or scanning electron microscopy (SEM) imaging.
The particle(s) can be generally shaped as a sphere, incomplete-sphere, particularly the size attached to the substrate, a rod, a cylinder, a ribbon, a sponge, and any other shape, or can be in a form of a cluster of any of these shapes, or can comprises a mixture of one or more shapes.
In some embodiments, the alkaline earth metal compound is characterized by crystallite size in the range of 3 nm to 40 nm, 4 nm to 40 nm, 5 nm to 40 nm, 10 nm to 40 nm, 15 nm to 40 nm, 20 nm to 40 nm, 3 nm to 30 nm, 4 nm to 30 nm, 5 nm to 30 nm, 10 nm to 30 nm, 15 nm to 30 nm, 20 nm to 30 nm, 3 nm to 20 nm, 4 nm to 20 nm, 5 nm to 20 nm, or 10 nm to 20 nm, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the composition comprises 60 at %. to 95 at %. carbon. In some embodiments, the composition comprises 60 at %. to 95 at., 65 at %. to 95 at %., 70 at %. to 95 at %., 80 at %. to 95 at %., 83 at %. to 95 at %., 85 at %. to 95 at %., 89 at %. to 95 at %., 60 at %. to 90 at %., 65 at %. to 90 at %., 70 at %. to 90 at %., 80 at %. to 90 at %., 83 at %. to 90 at %., 85 at %. to 90 at %., or 89 at %. to 90 at %., carbon, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the composition comprises a first alkaline earth metal. In some embodiments, the composition comprises a second alkaline earth metal. In some embodiments, the composition comprises a first alkaline earth metal, and optionally a second alkaline earth metal. In some embodiments, the first alkaline earth metal is selected from the group consisting of magnesium, calcium, strontium, barium, and radium. In some embodiments, the second alkaline earth metal is selected from the group consisting of magnesium, calcium, strontium, barium, radium, or any combination thereof. In some embodiments, the second alkaline earth metal is present at a concentration of 0.1% to 75%, 0.3% to 75%, 0.5% to 75%, 0.8% to 75%, 0.9% to 75%, 1% to 75%, 3% to 75%, 5% to 75%, 10% to 75%, 15% to 75%, 20% to 75%, 25% to 75%, 30% to 75%, 40% to 75%, 50% to 75%, 60% to 75%, 0.1% to 50%, 0.3% to 50%, 0.5% to 50%, 0.8% to 50%, 0.9% to 50%, 1% to 50%, 3% to 50%, 5% to 50%, 10% to 50%, 15% to 50%, 20% to 50%, 25% to 50%, 30% to 50%, 0.1% to 30%, 0.3% to 30%, 0.5% to 30%, 0.8% to 30%, 0.9% to 30%, 1% to 30%, 3% to 30%, 5% to 30%, 10% to 30%, 15% to 30%, 20% to 30%, 0.1% to 10%, 0.3% to 10%, 0.5% to 10%, 0.8% to 10%, 0.9% to 10%, 1% to 10%, 3% to 10%, or 5% to 10%, relative to the first alkaline earth metal, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the composition comprises an alkaline earth metal in its elemental form. In some embodiments, the composition comprises alkaline earth metals resulting from reduction by the carbon material matrix. In some embodiments, an alkaline earth metal is discretely dispersed in the carbon matrix. In some embodiments, an alkaline earth metal is agglomerated in the carbon matrix.
One of skill in the art will appreciate that the order of the metals may be altered in various embodiments and that the nomenclature “first alkaline earth metal” and “second alkaline earth metal” is used herein for ease of reference.
In some embodiments, the composition is for use in hydrazine oxidation reaction (HzOR), oxygen reduction reaction (ORR), or both.
In some embodiments, the composition is a catalyst. As used herein, the term “catalyst” refers to a substance which alters the rate of a chemical reaction. Catalysts participate in a reaction in a cyclic fashion such that the catalyst is cyclically regenerated. In some embodiments, the catalyst is for use in hydrazine oxidation reaction (HzOR). In some embodiments, the catalyst is for use in oxygen reduction reaction (ORR). In some embodiments, the catalyst is configured to oxidize hydrazine in solutions with a pH ranging from 0 to 14 with good to excellent activity.
In some embodiments, the catalyst is characterized by a faradaic efficiency in the range of 50% to 100%, 55% to 100%, 60% to 100%, 65% to 100%, 70% to 100%, 75% to 100%, 80% to 100%, 85% to 100%, 50% to 98%, 55% to 98%, 60% to 98%, 65% to 98%, 70% to 98%, 75% to 98%, 80% to 98%, 85% to 98%, 50% to 95%, 55% to 95%, 60% to 95%, 65% to 95%, 70% to 95%, 75% to 95%, 80% to 95%, 85% to 95%, 50% to 85%, 55% to 85%, 60% to 85%, 65% to 85%, 70% to 85%, 75% to 85%, or 80% to 85%, including any range therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the catalyst is stable for at least 2000 cycles, at least 2500 cycles, at least 3000 cycles, at least 3500 cycles, at least 4000 cycles, at least 4500 cycles, at least 5000 cycles, at least 10000 cycles, or at least 15000 cycles, as measured by CV, including any value therebetween. Each possibility represents a separate embodiment of the invention.
In some embodiments, the electrochemical cell is stable for 2000 cycles to 50000 cycles, 2500 cycles to 50000 cycles, 5000 cycles to 50000 cycles, 9000 cycles to 50000 cycles, 10000 cycles to 50000 cycles, 15000 cycles to 50000 cycles, 20000 cycles to 50000 cycles, 25000 cycles to 50000 cycles, 35000 cycles to 50000 cycles, 2500 cycles to 50000 cycles, or 5000 cycles to 9000 cycles, as measured by CV, including any range therebetween. Each possibility represents a separate embodiment of the invention.
According to some embodiments, the present invention provides an article comprising a composition as described herein. In some embodiments, the composition is deposited on at least one surface of the article. In some embodiments, the article is in the form of an anode.
In some embodiments, the loading of the composition is in the range of 0.01 mg cm−2 to 0.3 mg cm−2, 0.02 mg cm−2 to 0.3 mg cm−2, 0.03 mg cm−2 to 0.3 mg cm−2, 0.05 mg cm−2 to 0.3 mg cm−2, 0.09 mg cm−2 to 0.3 mg cm−2, 0.1 mg cm−2 to 0.3 mg cm−2, 0.01 mg cm−2 to 0.2 mg cm−2, 0.02 mg cm−2 to 0.2 mg cm−2, 0.02 mg cm−2 to 0.2 mg cm−2, 0.05 mg cm−2 to 0.2 mg cm−2, 0.09 mg cm−2 to 0.2 mg cm−2, 0.1 mg cm−2 to 0.2 mg cm−2, 0.01 mg cm−2 to 0.1 mg cm−2, 0.02 mg cm−2 to 0.1 mg cm−2, or 0.03 mg cm2 to 0.1 mg cm−2, including any range therebetween. Each possibility represents a separate embodiment of the invention.
According to some embodiments, the present invention provides an electrochemical cell comprising the article described herein. In some embodiments, the electrochemical cell is configured to oxidize hydrazine at onset potentials in the range of 0.20 V vs. reversible hydrogen electrode (RHE) to 0.8 V vs. RHE.
In some embodiments, the onset potentials is pH depended. In some embodiments, the electrochemical cell comprising the article described herein is configured to oxidize hydrazine in solutions with a pH ranging from 0 to 14 with good to excellent activity.
According to some embodiments, the present invention provides a process of oxidizing hydrazine. In some embodiments, the process comprises contacting a hydrazine containing solution with the electrochemical cell described herein, and applying an anodic electric potential to the electrochemical cell, thereby oxidizing the hydrazine.
In some embodiments, the solution comprises an electrolyte selected from sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution, lithium hydroxide (LiOH) solution, phosphate-buffered saline (PBS) solution, sulfuric acid (H2SO4), perchloric acid (HClO4) or any combination thereof. In some embodiments, the concentration of the electrolyte in the solution is 0.01 M to 5 M, 0.02 M to 5 M, 0.05 M to 5 M, 0.09 M to 5 M, 0.1 M to 5 M, 0.5 M to 5 M, 0.9 M to 5 M, 1M to 5M, 2M to 5M, 3 M to 5 M, 4 M to 5 M, 0.01 M to 4.5 M, 0.02 M to 4.5 M, 0.05 M to 4.5 M, 0.09 M to 4.5 M, 0.1 M to 4.5 M, 0.5 M to 4.5 M, 0.9 M to 4.5 M, 1M to 4.5M, 2M to 4.5M, 3M to 4.5 M, 0.01 M to 2.5 M, 0.02 M to 2.5 M, 0.05 M to 2.5 M, 0.09 M to 2.5 M, 0.1 M to 2.5 M, 0.5M to 2.5M, 0.9M to 2.5M, 1M to 2.5M, 2M to 2.5M, 0.01M to 1M, 0.02M to 1M, 0.05M to 1M, 0.09M to 1M, 0.1M to 1M, 0.5M to 1M, or 0.9M to 1M, including any range therebetween.
In some embodiments, the solution has a pH of 0 to 14, 1 to 14, 2 to 14, 3 to 14, 4 to 14, 5 to 14, 6 to 14, 7 to 14, 8 to 14, 0 to 12, 1 to 12, 2 to 12, 3 to 12, 4 to 12, 5 to 12, 6 to 12, 7 to 12, 8 to 12, 0 to 8, 1 to 8, 2 to 8, 3 to 8, 4 to 8, 5 to 8, 6 to 8, 7 to 8, 0 to 6, 1 to 6, 2 to 6, 3 to 6, or 4 to 6, including any range therebetween.
In some embodiments, the process is performed at a temperature of 20° C. to 95° C., 23° C. to 55° C., 25° C. to 55° C., 30° C. to 55° C., 32° C. to 55° C., 35° C. to 55° C., 40° C. to 55° C., 20° C. to 45° C., 23° C. to 45° C., 25° C. to 45° C., 30° C. to 45° C., 32° C. to 45° C., 35° C. to 45° C., 40° C. to 45° C., 20° C. to 35° C., 23° C. to 35° C., 25° C. to 35° C., 45° C. to 95° C., 35° C. to 85° C., 60° C. to 90° C. or 30° C. to 35° C., including any range therebetween.
In some embodiments, the process is characterized by a faradaic efficiency in the range of 50% to 100%, 55% to 100%, 60% to 100%, 65% to 100%, 70% to 100%, 75% to 100%, 80% to 100%, 85% to 100%, 50% to 98%, 55% to 98%, 60% to 98%, 65% to 98%, 70% to 98%, 75% to 98%, 80% to 98%, 85% to 98%, 50% to 95%, 55% to 95%, 60% to 95%, 65% to 95%, 70% to 95%, 75% to 95%, 80% to 95%, 85% to 95%, 50% to 85%, 55% to 85%, 60% to 85%, 65% to 85%, 70% to 85%, 75% to 85%, or 80% to 85%, including any range therebetween.
In some embodiments, the electrochemical cell is stable for at least 2000 cycles, at least 2500 cycles, at least 3000 cycles, at least 3500 cycles, at least 4000 cycles, at least 4500 cycles, at least 5000 cycles, at least 10000 cycles, or at least 15000 cycles, as measured by CV, including any value therebetween.
In some embodiments, the electrochemical cell is stable for 2000 cycles to 50000 cycles, 2500 cycles to 50000 cycles, 5000 cycles to 50000 cycles, 9000 cycles to 50000 cycles, 10000 cycles to 50000 cycles, 15000 cycles to 50000 cycles, 20000 cycles to 50000 cycles, 25000 cycles to 50000 cycles, 35000 cycles to 50000 cycles, 2500 cycles to 50000 cycles, or 5000 cycles to 9000 cycles, as measured by CV, including any range therebetween.
According to some embodiments, the present invention provides a method for making a templated porous carbon material with hierarchical porosity.
In some embodiments, the method comprises: providing one or more earth metal-coordination polymer precursor comprising magnesium, calcium, strontium, barium, or any combination thereof, and pyrolysing the earth metal-coordination polymer precursor, thereby obtaining the porous carbon material. In some embodiments, the carbon material comprises a carbon matrix doped with nitrogen atoms and comprising embedded inorganic nanoparticles comprising an earth metal compound comprising magnesium, calcium, strontium, barium, or any combination thereof. In some embodiments, the composition is formed by a self-templating mechanism. In some embodiments, the nanoparticles are spontaneously formed, and template micropores, mesopores and/or macropores in the carbon material.
In some embodiments, the porosity and characteristics of the obtained porous carbon material can be tuned by choosing an appropriate metal-organic coordination polymer (MOCP).
In some embodiments, the MOCP comprises a Group 2 metal. In some embodiments, the MOCP are based on Mg2+, Ca2+, Sr2+ or Ba2+, and nitrilotriacetic acid (H3NTA), as ligand. In some embodiments, the MOCP is characterized by a formula M(NTA)3, wherein M is a Group 2 metal.
In some embodiments, the MOCP serve as both a source and a spontaneous template for the final carbon material.
In some embodiments, during pyrolysis, the precursor ligand is carbonized, yielding a carbon matrix doped with nitrogen atoms and embedded with inorganic nanoparticles.
In some embodiments, the organic ligands of the MOCP are carbonized to yield a carbon matrix, doped by atomic or nanoparticulate metal sites. In some embodiments, inorganic particles form inside the carbon material. In some embodiments, the inorganic particles are oxide particles MO (e.g. MgO, CaO). In some embodiments, the inorganic particles are carbonate particles MCO3 (e.g. SrCO3, BaCO3).
In some embodiments, the obtained inorganic/carbon composites are characterized by a formula MX@NC, wherein where M=Mg, Ca, Sr, Ba, and X=the anion(s). In some embodiments, inorganic particles are washed away, serving as in situ templates for meso-, micro- and macropores. In some embodiments, the final porous carbon material is characterized by a formula NC-M.
In some embodiments, pyrolysing comprises heating the composition in an inert atmosphere. In some embodiments, heating is at a temperature in the range of 450° C. to 1100° C., 450° C. to 1000° C., 500° C. to 1100° C., 800° C. to 1000° C., 600° C. to 900° C., 650° C. to 900° C., 700° C. to 900° C., 750° C. to 900° C., or 800° C. to 900° C., including any range therebetween.
In some embodiments, the inorganic particles formed during pyrolysis are temperature dependent. In some embodiments, the size of the inorganic particles formed during pyrolysis is temperature dependent.
In some embodiments, the method further comprises a third step of washing the doped earth metal carbon material. In some embodiments, the method further comprises a third step of washing the doped earth metal carbon material, thereby obtaining the porous carbon material. In some embodiments, the porous carbon material is devoid of inorganic particles. In some embodiments the inorganic particles are washed out. In some embodiments, the washing is done using an acid. In some embodiments, washing is with hydrochloric acid (HCl).
In some embodiments, the method further comprises a step of heating the washed porous carbon material at a temperature in the range of 900° C. to 1100° C., for a period of time between 45 minutes (min) and 3 hours (h).
In some embodiments, the conductivity of the porous carbon material is temperature dependent. In some embodiments, the surface area of the porous carbon material is temperature dependent. In some embodiments, the pore volume is temperature dependent. In some embodiments, the nitrogen content is temperature dependent. In some embodiments, conductivity, surface area, pore volume, or any combination thereof increases with temperature increase. In some embodiments, nitrogen content decreases with temperature increase.
As used herein the term “about” refers to ±10%.
The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to”.
The term “consisting of means “including and limited to”.
The term “consisting essentially of” means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.
The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.
The word “optionally” is used herein to mean “is provided in some embodiments and not provided in other embodiments”. Any particular embodiment of the invention may include a plurality of “optional” features unless such features conflict.
As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof.
Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging/ranges between” a first indicate number and a second indicate number and “ranging/ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.
As used herein the term “method” refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.
As used herein, the term “treating” includes abrogating, substantially inhibiting, slowing or reversing the progression of a condition, substantially ameliorating clinical or aesthetical symptoms of a condition or substantially preventing the appearance of clinical or aesthetical symptoms of a condition.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.
Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non-limiting fashion.
The Ba-NTA metal coordination polymer was prepared as reported earlier. Briefly, 22.93 gr (120 mmol) of nitrilotriacetic acid (N(CH2COOH)3, H3NTA) were added to 300 mL DI water at 85° C., followed by 18.95 gr (96 mmol) of BaCO3 and 7.57 gr (24 mmol) of Ba(OH)2.8H2O. A white precipitate formed; to complete precipitation, the beaker was placed in an ice bath after 15 minutes, and 1.5 L of ethanol were added. The final precipitate was filtered and vacuum-dried at 50° C. for three days.
5 gr of Ba-NTA were placed in a quartz boat inside a tube furnace under a flow of argon (150 cm3 min−1). The sample was heated to 70° C. for 3 hours, then heated to temperature T at 10° C. min−1, soaked at T for 1 hour, then allowed to cool naturally. The resulting black powder was stirred with 100 mL of 1 M hydrochloric acid for 72 hours, filtered, washed with 800 mL DI water, and vacuum-dried at 50° C. overnight. The washed carbon was annealed again in argon at 1000° C. (dwell time 1 hr, heating rate 5° C. min−1).
Thermal gravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC) was performed in a Netzch Jupiter® STA 449F3 instrument, under argon flow (20 mL min−1). X-ray diffraction (XRD) was carried out on a powder X-ray diffractometer (Rigaku, SmartLab). Scherrer analysis of the sizes of coherently scattering domains was performed using the PDXL software. High resolution scanning electron microscopy (HR-SEM) was done on a Zeiss Ultra+ microscope, using an accelerating voltage of 4 keV. Transmission electron microscopy (TEM) was conducted using FEI Tecnai G2 T20 S-Twin TEM instrument, using an accelerating voltage of 200 keV. N2 adsorption-desorption isotherms at 77 K were measured on a Quantachrome Autosorb iQ instrument, using vacuum-dried samples (200° C. for 10 h−1). The isotherms were analyzed using the Brunauer-Emmett-Teller (BET) model for specific surface area, and quenched solid state density functional theory (QSDFT) isotherm fitting for meso-micropore size distribution. In the latter, the model used was N2/carbon at 77 K, with slit-shaped pores, in equilibrium. X-Ray photoelectron spectroscopy (XPS) measurements were carried out using a PHI VersaProbe III scanning XPS microprobe (Physical Instruments AG). Analysis was performed using a monochromatic Al Kα X-ray source of 1486.6 eV, with a beam size of 200 μm. Survey spectra were recorded with a pass energy of 140 eV (step size 0.5 eV), and surface concentrations of the elements were calculated by peak integration. The core level binding energies of the different peaks were normalized by setting the binding energy for the C is peak at 285.0 eV. The atomic concentrations were calculated using elemental sensitivity factors without applying any standardization procedure. Curve fitting was done using CasaXPS 2.3.19PR1.0. Elemental analysis was performed using Flash 2000 Organic Elemental Analyzer (Thermo Scientific) at 950° C., on 2-3 mg of sample in a tin crucible, with 8-10 mg of vanadium as a combustion aid (except for the C-700 sample, where vanadium was not employed). Raman spectroscopy was performed on a LabRam micro-Raman instrument with 532 nm laser excitation, 1800 grating, two acquisitions of 50 seconds each. The spectra were fit with four components, based on literature assignments. The in-plane (a direction) lengths of graphitic crystallites (La) were calculated from the intensity ratios of fitted D and G bands, according to the relation determined by Cangado et al.
Inks of the carbon powders (0.80 mL DI water, 0.20 mL ethanol, 10 μL Nafion® 5 wt % dispersion (Alfa Aesar), 1.0 mg carbon powder) were sonicated and dropcast (20 μL) on a polished glassy carbon electrode (5 mm diameter) and dried at 50° C. Total catalyst loading was 0.02 mg, or 0.1 mg cm2. Electrochemical experiments were performed in 1 M KOH at 25.0±0.1° C., using a BioLogic VSP multichannel potentiostat. Saturated calomel electrode (SCE), separated by a 10 mm frit was used as a reference electrode, and a graphite rod as a counter electrode. Potentials were reported vs. reversible hydrogen electrode (RHE) by adding 1.0708 for pH 14. N2 (99.999%) was bubbled for >30 min, and was flowed above the solution during the experiments. Measurements were carried out in 10 mM of hydrazine unless stated otherwise. Cyclic voltammograms (CVs) were collected from 0.17 V to 1.17 V vs. RHE with a scan rate of 10 mV s−1. Rotating disk electrode (RDE) voltammograms were collected at rotating speed of 1600 rpm. A positive feedback automatic iR correction of 80% was used, with an AV amplitude of 5 mV. Before measurements, the electrode was cycled between 0.1708 and 0.4708 V vs. RHE for 20 cycles at 100 mV s−1 to reduce surface-adsorbed oxygen and improve wetting. Electrochemical surface area (ECSA) was calculated from the non-faradaic charging current, as determined from CV cycles at 8 scan rates (2, 5, 10, 15, 20, 40, 60 mV s−1) at a small potential window of 0.1708 V to 0.4708 V (vs. RHE) in 1 M KOH:
This calculation assumes a reasonable value of 40 μF cm−2 for the surface-area normalized capacitance associated with double-layer charging.
The preparation of the various N-doped self-templating carbons proceeds according to a three-step procedure (
To study the self-templating process by Ba2+ ions, the inventors chose a range of temperatures where Ba-based particles may exist and vary in size and crystal phase. Thermal gravimetric analysis (TGA) provides charts the course of the pyrolytic synthesis (
To understand the evolution of inorganic particles inside the carbon matrix—and thus, their templating role in the nanostructure of the final catalyst—the inventors analyzed the crystalline phases by X-ray diffraction (XRD). BaC-500 contains a rare, lattice-substituted δ-BaCO3 phase. This meta-stable phase forms when small inorganic oxide molecules (e.g. SO42−, CrO42−) substitute a γ-BaCO3 lattice. Interestingly, barium acetate forms from BaNTA at 320° C., immediately before BaCO3 formation. Thus, the inventors propose that at these low pyrolysis temperature, acetate occupies lattice positions, yielding the unique lattice-substituted δ-BaCO3 phase. At higher temperatures, the lattice substituents were released, leaving behind a pure γ-BaCO3 (witherite) in BaC-600 and BaC-700. The γ-BaCO3 phase undergoes a phase transition at 811° C. (under standard conditions) to yield α-BaCO3. However, this phase was unquenchable, and couldn't be observed at room temperature. Rather, Ba(OH)2 peaks appeared in BaC-800, growing further in BaC-900. These peaks reflect the continuous CO2 removal from the carbonate.
Sizes of the crystalline particles are traditionally estimated by Scherrer analysis, which correlates peak broadening to quantum effects visible on the nanoscale. By following several diffraction peaks at each pyrolysis temperature, the inventors could obtain reliable information on their broadening. Importantly, this analysis determines the size of coherently scattering crystallites, rather than ‘particle size’. Such crystallites are often smaller than the entire nanoparticle, due to the presence of various defects. In the BaCO3-carbon composites studied, the crystalline domains were 20-30 nm in size along four different lattice directions (α-BaCO3 phase transition, which necessarily introduces crystal defects—rather than to an actual decrease in particle size.
Sizes and shapes of the inorganic nanoparticles were analyzed by high resolution scanning electron microscopy (HR-SEM), revealing densely packed BaCO3 particles in the BaC-T composites (
In the final, BaCO3-free carbons, HR-SEM reveals a developed, near-organized nanostructure (
The carbon with the finest mesopores (C-800) was further analyzed by transmission electron microscopy (TEM,
To determine the specific surface area (SSA) and the pore size distribution—crucial parameters in determining active site exposure and mass transfer—the inventors measured the physisorption of N2 on the different carbons (
Doping plays a central part in carbon electrocatalysis, since dopants typically serve as active catalytic sites. Moreover, dopants such as nitrogen improve conductivity, wettability and modify the work function of the carbon. The inventors have quantified the nitrogen content both at the surface and in the bulk of the carbon, using X-ray photoelectron spectroscopy (XPS) and elemental analysis (
The last important microstructural parameter of a carbon electrocatalysts, is its electronic conductivity. In addition to the turnover number and mass-transfer requirements of the catalyst, the catalytic sites must be electrically wired to the external circuit, in order to shuttle charge to and from these sites. The conductivity of a carbon material is correlated to its degree of graphitization, namely the size, concentration and connectivity of graphitic domains. This, in turn, is described by Raman spectra, which reveal vibrational modes in the carbon structure. The most typical vibrations are the D band at 1350 cm−1, related to inter-plane defects and G band at 1600 cm−1, related to the tangential stretching vibration mode58. The degree of graphitization was correlated to the intensity ratio between the D and G Raman peaks (ID/IG). Moreover, this ratio allows one to estimate the characteristic length of graphitic domains in the a direction (La). The inventors measured the Raman spectra of carbons C-500 to C-800 (
Tailoring the microstructure of a carbon electrocatalyst is a challenging task, as seen in the complex temperature dependencies. With rising temperature, the BaNTA-derived carbons change along wide-ranging trends (Table 1
Table): surface area rises and falls, with a peak at 700° C. (
Small mesopores shrink gradually (
Carbons C-500 to C-800 were all active towards hydrazine oxidation electrocatalysis (
Bubbles formed on all electrodes at high applied potentials and grew with each cycle. To test whether they correspond to N2 (from complete, 4e oxidation of hydrazine) or to O2 from the oxidation of water (4OH−→2O2+2H2O+4e−), the inventors varied the concentration of hydrazine during the CV (
The electrochemical surface area (ECSA) of C-700, the best performing electrocatalyst, was calculated from double layer capacitance charging. Based on 10 separate measurements, the ECSA was found to be 208±43 m2 g−1 (
The cyclic voltammetry for C-600 to C-800 exhibits two oxidation waves. Peak I (0.5-0.6 V vs. RHE) is highest on C-800 both in a non-stirred solution, and during electrode rotation at 1600 rpm. Peak II (˜1 V vs. RHE), on the other hand, is higher on C-700 at both conditions. By varying the scan rate during CV, the inventors could study the dependence of current density on diffusion. The inventors varied the scan rate between 5 and 100 mV s−1 and plotted the peak current density (jpeak, corrected for baseline current) versus square root of the scan rate (
Overall, C-700 and C-800 displayed the best electrocatalytic activity towards the HzOR at pH 14, while varying slightly in the current densities they can drive for the first and second oxidation waves. These high oxidation currents correlate well with the superior structure and composition of these materials. Both contain the highest specific surface areas and mesopore volumes. Interestingly, C-700 is richer in nitrogen than C-800: nitrogen was 30% more concentrated at the surface, and over 300% richer in the bulk (
The inventors delve deeper into the self-templating mechanism, and expand the synthesis to Ca2+, Sr2+ and Ba2+-based coordination polymers. Briefly, metal carbonate, metal hydroxide and nitrilotriacetic acid were mixed in water at a 4:1:5 molar ratio (based on metal ions and NTA units). A clear solution was obtained and stirred for 10 min at 85° C., then left to cool to room temperature. To complete the precipitation, ethanol was gradually added and the solution was ice-cooled. The resulting white precipitate was vacuum filtered, washed with cold ethanol, and vacuum dried at 50° C. for 2 days. The synthesis has been repeated >3 times for each precursor, with identical results.
The MOCP powders were pyrolyzed at 750° C. in Ar atmosphere for 1 h (heating rate 10° C. min−1). These inorganic/carbon composites are denoted as MX@NC, where M=Mg, Ca, Sr, Ba, and X is the anion(s). The inorganic phase was dissolved in hydrochloric acid (1 M, 72 hours), and the resulting carbon (denoted NC-M) was vacuum dried, and annealed again in Ar (1000° C./1 h, heating rate 5° C. min−1).
Powder X-ray diffraction (XRD) was recorded on a Rigaku SmartLab instrument operating at 45 kV and 150 mA, at a wavelength of 1.54 Å. ICDD cards used for powder XRD assignment: MgO (00-004-0829), CaCO3 (01-075-6049), Ca(OH)2 (00-044-1481), CaO (01-070-5490), SrCO3 (00-052-1526), Sr(OH)2 (00-018-1273), Sr(OH)2.H2O (00-028-1222), and BaCO3 (01-074-2663). Ritveld fitting of different phases showed sufficiently low fitting figures-of-merit (wR<10, GOF˜1). High-resolution scanning electron microscope was done on a Zeiss-ultra+ at 4 kV and in-lens detector, on the NC-M samples prior to the final annealing (samples after the final annealing showed identical morphologies). Energy dispersive spectroscopy (EDS) was measured with a Quantax spectrometer (Bruker) at 7 kV. High-resolution transmission electron microscopy (HRTEM) was performed on FEI Talos 200C, at an acceleration voltage of 200 kV. N2 adsorption-desorption isotherms were measured on a Micromeritics 3Flex instrument at 77 K, using vacuum-dried samples. The isotherms were analyzed using the two-parameter Brunauer-Emmett-Teller (BET) model for specific surface area (SSA, at P/P0 values of 0.01-0.15) and by non-local density functional theory (NLDFT) isotherm fitting for pore size distribution (using the adsorption branch of the isotherm). Raman spectroscopy was performed on a Horiba LabRam HR Evolution Raman microscope using ×10 lens, 532 nm laser excitation wavelength, and 1800 grating. First-order Raman spectra were fitted iteratively with four Lorentzian components. X-Ray photoelectron spectroscopy (XPS) was collected on a PHI VersaProbe III scanning microprobe supplied from Physical Instruments at UHV˜10−10 torr, step size 0.05 eV. Peaks were calibrated using the C1s position (284.5 eV), and deconvluted in CasaXPS.
The oxygen reduction reaction voltammograms were recorded on a BioLogic VSP bipotentiostat, combined with a Pine rotating electrode setup. Carbon powder inks were prepared by sonicating 1 mg of carbon, 300 μL of deionized water, 180 μL ethanol and 20 μL of Nafion 5 wt % dispersion (Alfa Aesar). 10 μL of the ink were dropcast onto a rotating ring-disk electrode (RRDE; glassy carbon disc ϕ=5.61 mm, Pt ring, loading 81 μg cm−2), and dried at 50° C. Experiments were conducted in 0.1 M KOH at 25.0° C., saturated by O2 (for ORR measurements) or N2 (for baseline measurements) by bubbling for 30 minutes, and kept under a gas blanket. Currents in N2-purged solutions were subtracted from those in the O2-purged solutions, to account for capacitive currents. Graphite and saturated calomel (SCE) were used as counter and reference electrodes, respectively. Potentials were applied using an automatic 85% iR correction. Reported potentials were converted to RHE by adding 0.242 V and 0.0592 V for every pH unit, a total of 1.011 V. Before measurement, the electrode was wetted by 20 cycles between 0.1 V and −0.7 V vs. SCE at 100 mV s−1. The number of electrons transferred per 02 molecule (n) was calculated by the Koutecký-Levich method from linear sweep voltammograms performed on a rotating disk at rotation speeds of 200-2400 rpm, as described elsewhere.22 The yield of H2O2 (%) was calculated by Eq. 1, where iring is the ring current, and idisc is the disc current. The collection efficiency was determined experimentally to be N=0.35, using 4 mM of the Ru(III)/Ru(II) hexamine couple in N2-purged 0.1 M KCl.
The self-templating, or endo-templating synthetic strategy combines advantages from both approaches (
The inventors report a systematic study of the self-templating synthesis of carbon materials, using Group 2 MOCP precursors. Alkaline earth metal ions are highly abundant: Mg2+, Ca2+, Sr2+ and Ba2+ are the 7th, 5th, 14th and 16th most abundant elements in the earth's crust, respectively. Importantly for electrocatalysis research, Group 2 metal ions are electrocatalytically inactive, allowing them to direct structure formation without masking the catalytic activity. Nevertheless, these promising elements are under-represented in the field of MOCP-derived carbons, dominated by precursors based on Fe2+/3+, C2+, Zn2+, and Al3+ salts.
To understand in detail how the carbon microstructure evolves during the self-templating synthesis, to explore the expected richness of Group 2-derived precursors, and to try and correlate structure to electrocatalytic activity, the inventors took a systematic approach. The inventors prepared a homologous series of MOCPs based on Mg2+, Ca2+, Sr2+ and Ba2+ with a single common ligand, nitrilotriacetic acid (H3NTA). The ligand is both cheap and flexible, providing high binding versatility to different ion sizes. By combining a broad range of material characterization techniques with oxygen reduction reaction (ORR) electrocatalytic studies, the inventors investigated the effect of the metal ion on the material morphology throughout the self-templating pathway. The carbons produced by this method spanned the full porosity range between pure microporosity to rich hierarchical porosity. The pore size distribution was found to determine both ORR activity (through boosting flow) and selectivity (through confinement of intermediates).
The Group 2 nitrilotriacetates are crystalline powders, as determined by XRD and electron microscopy. Their single crystal X-ray diffractograms show well-defined crystals of metal-organic coordination polymers, sharing a common M(NTA)3(H2O)x composition: MgNH(CH2COO)3(H2O)3, CaNH(CH2COO)3(H2O)2, SrNH(CH2COO)3(H2O)1.5, and BaNH(CH2COO)3.
Thermal treatment of the four MOCPs in argon atmosphere (750° C./1 hr, heat rate 10° C. min-1) converted them into black powders. While MgX@NC and BaX@NC are light and fluffy, SrX@NC is somewhat denser, and CaX@NC is a dense and hard powder. The crystalline phases in each composite were identified by XRD (
To explain the phase composition along the oxide-hydroxide-carbonate sequence, the inventors consider the possible inorganic reactions during pyrolysis (Eq. 2-5). At the pyrolysis temperature of 750° C., the oxides are expected to be more stable than the hydroxides, and less stable than the carbonates. However, the composition is unlikely to be under thermodynamic control. First, the reducing, carbon-rich matrix may shift the equilibria towards hydroxides and carbonates. Second, atom diffusion is slow: only two of the phases are liquid at this temperature (Ca(OH)2 mp 580° C., Sr(OH)2 mp 375° C.), while all others are solids far from their melting points (ranging 1340-2570° C.). This will slow down diffusion in these materials, making dynamic equilibration of the MOM(OH)2
MCO3 mixtures unlikely after only one hour at the pyrolysis temperature. Finally, the presence of Ca(OH)2 and Sr(OH)2 may also result from rapid re-hydration of the oxides,40,41 at any time during or after pyrolysis. Such hydroxide phases are often extended (rather than particulate), possibly leading to loss of pore-templating abilities. Overall, precise tuning of the pyrolysis temperatures and times could prove a highly efficient method for tweaking the composition of the templating phases.
CaO + H2O
CaO + CO2
SrO + H2O
SrO + CO2
The sizes, shapes, and agglomeration of the inorganic particles were studied by HRSEM with elemental mapping by EDS (
a)Obtained by Ritveld analysis of the XRD.
b)Determined by Scherrer analysis of the XRD broadening, average between several peaks. This analysis could not be performed for the Sr2+-based phases,
c)Obtained by image analysis of many particles in the HRSEM or HRTEM images, aggl. denotes sizes of agglomerates.
Well-dispersed particles were also found at the other extreme of the alkaline-earth series, in the case of BaCO3@NC (
In CaX@NC, the Ca-based particles are larger (10s-100s of nm,
Overall, the homologous series of alkaline-earth MOCPs yields various carbon-embedded inorganic phases, ranging in size, shape, crystallinity, and degree of agglomeration. These are expected to template a broad variety of pore size distributions.
To understand the evolution of hierarchical porosity in this series of self-templated materials, the inventors examined both the quantitative (N2-sorption derived) and qualitative (electron microscopy-derived) pore size distributions. Adsorption-desorption isotherms of N2 at 77K were collected for all four NC-M carbons (
a)Determined by N2 adsorption at 77 K, fitted by BET model.
b)Volume of N2 adsorbed at P/P0 = 0.99.
c)Vtotal − Vmicropore.
The simplest morphology is found in NC-Ca, featuring a type I isotherm, typical for strictly microporous materials. Indeed, the pore size distribution reveals no significant mesoporosity, especially in comparison with the other carbons. Thus, no self-templating occurred in NC-Ca, despite the presence of Ca-based inorganic phases in the material. Micropores in the bulk, typically formed homogeneously in pyrolyzed polymers, were inaccessible; rather, only the surface micropores of NC-Ca are accessible to N2.
Crystallites of CaNTA, the carbon precursor, are tabular and smooth, ranging tens of micrometers in size (
After washing the material in acid, the NC-Ca particles retained the original macroscopic dimensions of the CaNTA crystals (
Efficient self-templating by Ca salts strongly depends on the pyrolysis conditions (affecting carbonate decomposition) and on the linker. Overall, the microporosity observed in
The next carbon examined, NC-Sr, shows N2 sorption isotherms of the H4 type (
To test this hypothesis, the inventors first examine the SrNTA crystals: platy, smooth, and around ten microns across (
Unlike NC-Ca (microporous) and NC-Sr (micro- and macroporous), the next two carbons have fully hierarchical porosities, spanning the micro-, meso- and macropore range. The MgNTA precursor is already different, composed of large aggregates (10s of micrometers) of prismatic crystallites (˜1 μm long and tens of nanometers wide (
The spherical meso- and macro-pores were perfectly retained during the acid wash, with diameters up to 40 nm according to N2 sorption porosimetry (
The effect of crystallite size in the metal-organic precursor has not been reported previously, and the exsolution of MgO templates was never directly observed. Overall, magnesium-based self-templating is excellent for hierarchical porosity, since the MgO spheres span a broad distribution of sizes, and easily leave behind a stable network of pores.
Similarly to MgNTA, the BaNTA MOCP yields a carbon with fully hierarchical porosity. The pathway, however, is quite different. The original BaNTA crystals are tabular and tens of microns large, like those of CaNTA and SrNTA (
After the acid wash, the particle retained its overall shape, yet became highly porous, showing a homogeneous array of similarly sized macropores (˜80-150 nm,
The pore size distribution in NC-Ba, calculated from N2 sorption, revealed a distribution of small mesopores (>2 nm), and two peaks at 25 and 40 nm (
Overall, this homologous series of carbons covers the full range of pore modalities. Starting from a microporous carbon with only surface micropores (NC-Ca), to a cracked macroporous carbon exposing some bulk micropores (NC-Sr), and finally to fully hierarchical micro-meso-macro-porosities in NC-Mg and NC-Ba, differing in mesopore size (˜20-40 nm and ˜80-150 nm, respectively). An interesting control experiment would be a non-templated carbon derived from pure, non-complexing NTA. However, nitrilotriacetic acid is volatile and does not carbonize.
This structural richness is expected to be crucial for electrocatalytic activity, as the optimal balance between void network and carbon network is sought. First, the variance in the exposure of bulk micropores will affect the availability of catalytic sites, and the flow rates for the replenishment of reactant (O2) and the removal of products (OH−) and intermediates (HO2−). Second, excessive porosity may lead to undesirably thick catalyst layers, to provide enough catalytic sites within the catalyst volume.
Importantly for the understanding of self-templating mechanisms, the inventors hypothesize that such well-dispersed mesoporosity as in NC-Mg and NC-Ba depends critically on the small size of the crystallites in the MOCP precursors. The sub-micronic dimensions of the MgNTA prismatic crystallites, and of the homogeneous cracks in BaNTA crystals, limit the sizes of inorganic particles as they nucleate during pyrolysis. This opens new avenues in porosity design, suggesting that the fine-tuning of MOCP crystallization conditions can control the self-templating behavior during pyrolysis.
Since the N-doped carbons were all derived from a similar M(NTA)3 precursor composition, the inventors hypothesized that the carbon composition will be constant along the series. To test this hypothesis, the inventors studied the NC-M carbons by Raman spectroscopy (
Transmission electron micrographs of NC-M carbons show similar graphitic regions, ˜3-10 layer thick. For NC-Mg and NC-Ba, these graphitic layers form shells around the inorganic particles. This is the first report of a Ba-based inorganic phase that can catalyze mild graphitization during pyrolysis. Mild graphitization is important for avoiding the uncontrolled growth of carbon nanotubes or large graphite blocks, as many electronic and electrochemical applications seek low dimensional carbon materials.
The NC-M carbons have a high nitrogen content (4.5-7.7 wt %), and very low trace metal content after the acid wash (0.04-0.21 wt %), as determined by ICP-MS (Table 4).
a)Elemental analysis by ICP-MS, in duplicate.
b)at %, by deconvolution of the N 1s XPS.
The distribution of binding states of surface nitrogen and carbon atoms was further analyzed by XPS in the N 1s and C 1s regions (
The similarities in carbon composition along the series, in contrast to the far-swinging differences in porosity, suggest that the ORR activity of these catalysts will depend chiefly on their microstructure. To investigate this dependence, the inventors studied the activity of NC-M carbons towards the ORR, using a rotating ring-disc electrode in an O2(g)-saturated 0.1 M KOH electrolyte. All carbons demonstrated cathodic currents on the disc under mass-transport controlled conditions (1600 rpm,
In N-doped carbons, the nitrogen dopants typically contribute most of the ORR activity, well ahead of the catalytic activity of carbon defect sites. Thus, the ORR current densities catalyzed by the carbons depend on the number of exposed nitrogens. To estimate this value, the inventors can multiply the surface N content by the BET SSA. The number of exposed N atoms, although a rough estimate, is in perfect linear correlation with the ORR activity, as measured by the limiting current density at E=−0.6 V vs. RHE and rotation rate 1600 rpm (
Alkaline ORR on N-doped carbons begins with a 2e electro-reduction yielding a peroxide intermediate (Eq. 6). The peroxide can either (1) escape, (2) be reduced further by another 2e (Eq. 7), or (3) be disproportionated (Eq. 8). Interestingly, the carbons' microstructure has a striking effect on the ORR selectivity (2e− vs. 4e−), as gauged by their different peroxide yields. On each of the NC-M carbons, the disc and ring reactions start at the same onset potential, suggesting they begin producing the HO2 intermediate simultaneously with O2 reduction (
O2+2e−+H2OHO2−+OH− Eq. 6
HO2−+2e−+H2O3OH− Eq. 7
HO2−→½O2+OH− Eq. 8
The inventors propose that the differences in ORR selectivity stem from a competition between the kinetics and mass transfer of peroxide intermediates in the mesopores (as described schematically in
The pore-confinement mechanism can explain how morphology governs ORR activity across the series (
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.
This application claims the benefit of priority of U.S. provisional patent application No. 62/936,707 filed Nov. 18, 2019, and entitled “CARBON-ALKALINE EARTH METAL CATALYSTS FOR HYDRAZINE OXIDATION,” which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62936707 | Nov 2019 | US |
