Patent Application
20220105498
This invention relates to, inter alia, a catalytically active particle comprising a ruthenium (Ru) transition metal (M) alloy, and to devices and processes employing the same.
Alkaline-exchange membrane fuel cells (AEMFC's, also known as anion exchange membrane fuel cells), which operate in basic media, have the potential to exhibit higher efficiencies and better performance than proton exchange membrane fuel cells (PEMFC's), which operate in an acidic environment, in that the oxygen reduction reaction (ORR) kinetics can be significantly enhanced. However, while in acid media H2 oxidation reaction (HOR) kinetics on platinum (Pt) are very facile, in alkaline media, the HOR kinetics on Pt are very sluggish, being over 100 times slower than in acidic media. Other Pt-group metals also exhibit a similar trend when going from acidic media to alkaline media. Thus, a need exists for improved materials to better enable AEMFC's as viable alternatives to other commercial fuel cells, such as PEMFC's.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicant in no way disclaims these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.
Briefly, the present invention satisfies the need for improved materials to improve and better enable, inter alia, AEMFC's.
The invention provides, inter alia, catalytically active particles comprising a RuM (M=Co, Ni, Fe, or a combination thereof) alloy, said alloy comprising at least 50 atomic % Ru and 1 to 50 atomic % of M. The catalytically active particles find use as, e.g., catalysts for HOR and ORR (for example, in electrolyzers and fuel cells, such as AEMFC's).
Embodiments of the invention may address one or more of the problems and deficiencies discussed above. However, it is contemplated that the invention may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed invention should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.
Certain embodiments of the presently-disclosed catalytically active particles and related devices and processes/methods have several features, no single one of which is solely responsible for their desirable attributes. Without limiting the scope of the catalytically active particles and related compositions, devices and processes as defined by the claims that follow, their more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section of this specification entitled “Detailed Description of the Invention,” one will understand how the features of the various embodiments disclosed herein provide a number of advantages over the current state of the art. These advantages may include, without limitation, providing alloys and compositions that have enhanced electrocatalytic activity toward HOR and/or ORR, providing alloys, compositions, and devices having improved HOR and/or ORR kinetics, providing low or lower cost catalysts (e.g., as compared to commercial catalysts such at Pt catalysts), providing improved fuel cells, e.g., providing improved anion-exchange membrane fuel cells, providing improved anode or cathode catalysts for fuel cell (e.g., AEMFC) applications, etc.
In a first aspect, the invention provides a catalytically active particle comprising an alloy, said alloy comprising:
In a second aspect, the invention provides a device comprising the catalytically active particle according to the first aspect of the invention.
In a third aspect, the invention provides an electrocatalytic process, wherein said process comprises use of the catalytically active particle according to the first aspect of the invention.
These and other objects, features, and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings.
The present invention will hereinafter be described in conjunction with the following drawing figures. The depicted figures serve to illustrate various embodiments of the invention. However, the invention is not limited to the precise arrangements and instrumentalities of the embodiments in the drawings.
The present invention relates to, inter alia, a catalytically active particle comprising a ruthenium (Ru) transition metal (M) alloy, and to devices and processes employing the same.
Aspects of the present invention and certain features, advantages, and details thereof are explained more fully below with reference to the non-limiting embodiments discussed and illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as to not unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions and/or arrangements within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure.
In a first aspect, the invention provides a catalytically active particle comprising an alloy, said alloy comprising:
As is known in the art, an alloy is a mixture of the elements comprised within it.
In some embodiments, the elements in the alloy of the catalytically active particle are homogeneously mixed.
In some embodiments, the alloy of the catalytically active particle is a single phase alloy.
Also as known in the art, atomic % (at. %) refers to the percentage of one or more atom(s) of an indicated kind relative to the total number of atoms present in an alloy.
As indicated above, embodiments of the catalytically active particle comprise a ruthenium-transition metal (Co, Ni, and/or Fe) alloy. The alloy may be referred to herein as the “alloy” or the “RuM alloy”.
In some embodiments, M is Co.
In some embodiments, M is Ni.
In some embodiments, M is Fe.
In some embodiments, the RuM alloy accounts for greater than or equal to 80 wt. % of the catalytically active particle. For example, in some embodiments, the RuM alloy accounts for greater than or equal to 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.1, or 99.5 wt. % of the catalytically active particle. In some embodiments, the catalytically active particle consists of the alloy.
In the catalytically active particle, the alloy is not fully or partially encapsulated by a layer (i.e., one or more layers) of platinum atoms. Thus, the alloy is not coated with a layer of platinum atoms.
In some embodiments, the catalytically active particle does not comprise a coating on all or a portion of the alloy, other than an optional Ru coating (e.g., one or more atomic layers of Ru). In some embodiments, the catalytically active particle does not comprise a coating containing another platinum-group metal (besides Ru) on all or a portion of the alloy.
In some embodiments, the catalytically active particle is of substantially uniform (i.e., 90 - 100% uniform, e.g., at least 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 99.5% uniform) composition.
In some embodiments, the catalytically active particle is in the form of a core-shell particle. In some embodiments, the core is the inventive alloy, and the shell is Ru. In some embodiments, the catalytically active particle is in the form of a core-shell particle, and the shell does not comprise Pt and/or Pd. In some embodiments, the catalytically active particle is not in the form of a core-shell particle.
In some embodiments, all or a portion of the exterior surface of the catalytically active particle is comprised of the RuM alloy. In some embodiments, at least 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% of the exterior surface area of the catalytically active particle is comprised of the RuM alloy.
The alloy comprises greater than or equal to 50 atomic % Ru (e.g., 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 at. %, including any and all ranges and subranges therein). In some embodiments, the alloy comprises greater than or equal to 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, or 95 atomic % Ru.
The alloy comprises 1 to 50 atomic % (e.g., 0.25, 0.50, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 at%, including any and all ranges and subranges therein) of one or more transition metals (M) selected from cobalt (Co), nickel (Ni), and iron (Fe).
In some embodiments, the sum of the atomic percentages of Ru and M in the alloy is greater than or equal to 65 atomic % of the alloy (e.g., 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 at. %, including any and all ranges and subranges therein). For example, in some embodiments, the sum of the atomic percentages of Ru and M in the alloy is greater than or equal to 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, or 99.9 atomic % of the alloy.
In some embodiments, the alloy does not comprise greater than 5 atomic % (e.g., greater than 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0 at. %) of rhodium, palladium, osmium, iridium, platinum, or any combination thereof. In some embodiments, the alloy does not comprise rhodium, palladium, osmium, iridium, and/or platinum.
In some embodiments, at least 90 volume % (e.g., at least 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 99.5 vol%) of the alloy has a hexagonal close packed (hcp) crystal structure.
In some embodiments, the alloy is a binary alloy.
In some embodiments, the alloy is a ternary (or higher) alloy.
In some embodiments, the alloy is of formula (I):
Ru100−xMx (I),
wherein x is the atomic % of one or more transition metals (M) present, wherein M is selected from Co, Ni, Fe, and a combination thereof, and 1≤x≤50 (e.g., x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, including any and all ranges and subranges therein). For example, in some embodiments, x is 4-50, 1-30, 3-40, etc.
In some embodiments, the alloy is of formula (I) and M is Co, Ni, or Fe.
In some embodiments, the catalytically active particle consists of:
In some embodiments, the catalytically active particle has a size of 1 to 50 nm (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nm), including any and all ranges and subranges therein (e.g., 1.5 to 30 nm, 2 to 10 nm, etc.).
In some embodiments, the catalytically active particle is spherical in shape.
In some embodiments, the catalytically active particle is substantially spherical in shape. For example, in some embodiments, the catalytically active particle deviates from spherical by less than or equal to 10% (e.g., by less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1%).
In some embodiments, the invention provides a plurality of catalytically active particles as described herein.
In some embodiments, the plurality of catalytically active particles have an average particle size of 1 to 50 nm (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nm), including any and all ranges and subranges therein (e.g., 1.5 to 30 nm, 2 to 10 nm, etc.).
In some embodiments, the plurality of catalytically active particles, on average, deviate from spherical by less than or equal to 10% (e.g., by less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1%).
In a second aspect, the invention provides a device comprising the catalytically active particle according to the first aspect of the invention.
In some embodiments, the device is a fuel cell.
The device can comprise any embodiment according to the first aspect of the invention, optionally in combination with properties of any other embodiment(s) according to the first aspect of the invention.
In some embodiments, the device comprises a plurality of catalytically active particles according to the first aspect of the invention.
In some embodiments, the device comprises two electrodes.
In some embodiments, the device is configured to transport hydroxide anions (OH−) from one electrode to the other.
In some embodiments, the device is a fuel cell.
In some embodiments, the device is a fuel cell, for example, an anion-exchange membrane fuel cell (AEMFC), comprising an anode and a cathode, wherein at least one of the anode or the cathode comprises the catalytically active particle according to the first aspect of the invention.
AEMFC's are alkaline fuel cells that comprise a solid polymer electrolyte, i.e., an alkaline exchange membrane. Currently, the most popular commercialized fuel cells are proton exchange membrane fuel cells (PEMFC's). PEMFC's and AEMFC's both generate electricity, but PEMFC's operate in acidic media, and comprise a proton-conducting polymer electrolyte membrane (PEM), whereas AEMFC's operate in alkaline media and comprise an anion exchange membrane (AEM) that conducts anions (such as OH−). In addition to the fact that the solid membrane in AEMFC's is an alkaline AEM instead of an acidic PEM, AEMFC's can be further distinguished from PEMFC's in that, for AEMFC's, the AEM transports ions (e.g., hydroxide ions, OH−) from the cathode to the anode, whereas proton (H+) conduction in a PEMFC goes from anode to cathode. The use of the AEM in the AEMFC creates an alkaline pH cell environment, thereby attractively opening up the possibilities for, inter alia, enhanced oxygen reduction catalysis (which could allow for the use of less expensive, e.g., platinum—(Pt) free catalysts, or catalysts that do not require Pt), extended range of fuel cell materials to be used (e.g., stable in the AEMFC, but that may not have sufficient stability in an acidic environment), and different range of possible membrane materials.
Depending on, e.g., the cathode oxidant gas, different anions are present in different amounts during the operation of an AEMFC. For example, when ambient air is used, anions present during operation of the AEMFC can include HCO3−, CO32−, and OH−. Typically, though, when operated at high current densities, the most common anion species present across the AEM membrane is the hydroxide anion (OH−), initially present and also generated via electrochemical ORR at the cathode of the AEMFC.
During operation of an AEMFC, the OH− is transported from the cathode to the anode. If hydrogen is used as fuel, the following oxidation reaction takes place at the anode:
2OH−+H2→2H2O+2e−
Thus, similar to PEMFC's, AEMFC's also produce water as a byproduct, but the water generated in an AEMFC is twice as much as in a PEMFC, per electron. Further, water is a reactant at the cathode.
The above discussion demonstrates various significant differences between AEMFC's and PEMFC's. Indeed, the alkaline environment and AEM, and different ORR and HOR mechanisms result in AEMFC's being significantly different from PEMFC's. Environmental and electrochemical differences between AEMFC's and PEMFC's are such that entirely different materials are used in the fuel cells, and materials useful for one type of fuel cell cannot be expected to be (and are often not) useful in the other. This point is exemplified, for example, by the fact that, while in acidic media H2 oxidation kinetics on platinum (Pt) are very facile, in alkaline media, H2 oxidation kinetics on Pt are very sluggish, being over 100 times slower than in acidic media. Thus, a need exists for improved materials that are specifically useful in alkaline conditions and for the development of improved AEMFC's. The Applicant has found that the catalytically active particle described herein offers such use, including, for example, as new anode and cathode catalysts for AEMFC's.
In some embodiments, the invention provides an AEMFC comprising:
In some embodiments, the anode comprises the inventive catalytically active particle, and the particle is supported on an electrically conductive carrier (e.g., the catalytically active particle is carbon-supported (e.g., carbon black supported)).
In some embodiments, the AEMFC anode does not comprise platinum and/or copper.
In some embodiments, the AEMFC does not comprise platinum and/or copper.
In some embodiments, the AEMFC is configured to use pure oxygen or air as a cathode oxidant gas. In some embodiments, the air is ambient air, CO2-free air (also known as synthetic, or pure air), or CO2-filtered air.
In some embodiments, the AEMFC is configured to use, as fuel, hydrogen or methanol. In particular embodiments, the AEMFC is configured to use hydrogen.
The AEM separates the anode and the cathode, and conducts OH−ions from the cathode to the anode. The AEM may be any anion exchange membrane configured for use in an AEMFC.
In some embodiments, the AEM is a polymeric anion exchange membrane comprising cationic moieties that are fixed to or within polymeric chains (vs., e.g., a liquid electrolyte, within which the cationic moieties would be freely mobile). In some embodiments, the AEM comprises a polymer backbone having cationic groups incorporated therein (e.g., alkylated poly(benzimidazoles)). In some embodiments, the AEM comprises a polymer backbone having cationic groups pendant/tethered thereto. For example, in some embodiments, the AEM comprises a hydroxide-conducting functionalized polysulfone (e.g., functionalized via chloromethylation, followed by reaction with a phosphine or quaternization with an amine to yield a phosphonium or ammonium salt that can be alkalinized, e.g., with KOH, to yield a hydroxide-conducting AEM). In some embodiments, the AEM comprises a quaternary ammonium polysulfone. In some embodiments, the AEM is based on a xylylene ionene.
In some embodiments, the inventive device is an alkaline electrolyzer.
In some embodiments, the alkaline electrolyzer comprises two electrodes configured to operate in a liquid alkaline electrolyte solution (e.g., of potassium hydroxide or sodium hydroxide). In some embodiments, the electrodes are separated by a diaphragm that separates product gases and transports hydroxide ions from one electrode to the other.
In some embodiments, the alkaline electrolyzer is a nickel-based electrolyzer.
In some embodiments, the alkaline electrolyzer is a water electrolyzer.
In some embodiments, the inventive catalytically active particle is comprised within an electrode of the electrolyzer. In some embodiments, the inventive alloy or electrocatalyst is comprised within the anode of the electrolyzer. In some embodiments, the inventive alloy or electrocatalyst is comprised within the cathode of the electrolyzer.
In a third aspect, the invention provides an electrocatalytic process, wherein said process comprises use of the catalytically active particle according to the first aspect of the invention.
In some embodiments the electrocatalytic process entails a method of electrocatalysis comprising use of the inventive catalytically active particle (e.g., as an anode or cathode catalyst).
The electrocatalytic process can comprise use of any embodiment according to the first aspect of the invention, optionally in combination with properties of any other embodiment(s) according to the first aspect of the invention.
Likewise, embodiments of the electrocatalytic process can comprise use or operation of a device according to the second aspect of the invention, optionally in combination with properties of any other embodiment(s) according to the first or second aspects of the invention.
In some embodiments, the electrocatalytic process comprises operating a device according to the third aspect of the invention.
In some embodiments, the electrocatalytic process is performed at a pH>7.
In some embodiments, the electrocatalytic process comprises transporting OH− ions from a cathode to an anode, wherein the anode comprises the catalytically active particle according to the first aspect of the invention.
In some embodiments, the electrocatalytic process comprises an H2 oxidation reaction (HOR). In some embodiments, the HOR takes place at the anode of a fuel cell, e.g., an AEMFC.
In some embodiments, the electrocatalytic process comprises both HOR and ORR.
In some embodiments, the electrocatalytic process does not comprise use of a platinum (Pt)-containing catalyst. In some embodiments, the electrocatalytic process does not comprise use of a platinum (Pt)-containing catalyst for the HOR reaction.
In some embodiments, the electrocatalytic process comprises a hydrogen evolution reaction. In some embodiments, the inventive catalytically active particle catalyzes the hydrogen evolution reaction. In some embodiments, the hydrogen evolution reaction is performed in alkaline media.
In some embodiments, the invention is as described in one or more of the following clauses.
Clause 1. A catalytically active particle comprising an alloy, said alloy comprising:
Clause 2. The catalytically active particle according to clause 1, wherein the sum of the atomic percentages of Ru and M is greater than or equal to 85 atomic % of the alloy.
Clause 3. The catalytically active particle according to clause 1 or clause 2, consisting of:
Clause 4. The catalytically active particle according to any one of clauses 1 to 3, wherein at least 90 volume % of the alloy has a hexagonal close packed (hcp) crystal structure.
Clause 5. The catalytically active particle according to any one of the preceding clauses, wherein the alloy is a single phase alloy.
Clause 6. The catalytically active particle according to any one of clauses 1, 2, 4, or 5, wherein the alloy is of formula (I):
Ru100−xMx (I),
wherein x is the atomic % of one or more transition metals (M) present, wherein M is selected from Co, Ni, Fe, and a combination thereof, and 1≤x≤50.
Clause 7. The catalytically active particle according to clause 6, wherein M is Co, Ni, or Fe.
Clause 8. The catalytically active particle according to any one of the preceding clauses, wherein M is Co.
Clause 9. The catalytically active particle according to any one of clauses 1 to 7, wherein M is Fe.
Clause 10. The catalytically active particle according to any one of clauses 1 to 7, wherein M is Ni.
Clause 11. The catalytically active particle according to clause 10, comprising 1 to 30 atomic % Ni.
Clause 12. The catalytically active particle according to any one of clauses 1 to 11, wherein at least 99 wt. % of the catalytically active particle consists of Ru and M.
Clause 13. The catalytically active particle according to any one of clauses 1 to 12, wherein the particle has a size of 1 to 50 nm.
Clause 14. A device comprising the catalytically active particle according to any one of clauses 1 to 13.
Clause 15. The device according to clause 14, wherein the device is an electrolyzer comprising an anode and a cathode, wherein said catalytically active particle is in direct electrical contact with at least one of the anode or the cathode.
Clause 16. A fuel cell comprising the catalytically active particle according to any one of clauses 1 to 13.
Clause 17. The fuel cell according to clause 16, wherein the fuel cell is an anion-exchange membrane fuel cell (AEMFC).
Clause 18. The AEMFC according to clause 17, comprising:
Clause 19. An electrocatalytic process, wherein said process comprises use of the catalytically active particle according to any one of clauses 1 to 13.
Clause 20. The electrocatalytic process according to clause 19, wherein the process comprises a H2 oxidation reaction (HOR), H2 evolution reaction (HER), O2 reduction reaction (ORR), or oxygen evolution reaction (OER).
Clause 21. The electrocatalytic process according to clause 19 or clause 20, wherein the process is performed at a pH >7.
Clause 22. The electrocatalytic process according to any one of clauses 19 to 21, wherein the process takes place in an anion-exchange membrane fuel cell (AEMFC).
Clause 23. The electrocatalytic process according to any one of clauses 19 to 21, wherein the process takes place in an anion-exchange membrane water electrolyzer (AEMWE).
The invention will now be illustrated, but not limited, by reference to the specific embodiments described in the following examples.
Synthesis of Carbon Supported Nanoparticles. Electrocatalyst nanoparticles were prepared according to embodiments of the invention and comparative non-inventive embodiments. A series of Ru1−xCox (11 wt. %), Ru1−xNix (11 wt. %) and Ru1−xFex (11 wt. %) nanoparticles supported on Vulcan XC-72R conductive carbon black with a metal loading of 11 wt. were synthesized by a wet impregnation method followed by subsequent forming gas reduction. This synthesis method yields surfactant-free carbon supported nanoparticles. The nanoparticles were well dispersed on the carbon support and exhibited mostly spherical shape. The reduction and annealing temperatures were selected to control the size of nanoparticle catalysts. Specified amounts of metal chlorides (RuCl3, CoCl2, NiCl2 and FeCl3) or metal nitrates (Ru(NO)(NO3)3, Co(NO3)2, Ni(NO3)2, and Fe(NO3)3) were dissolved in 10 mL of water, to which 40 mg of Vulcan XC-72R (oxidized at 400° C. for 12 hours to enhance hydrophilicity) were added. After 30 minutes of ultrasonication, the solution was heated and magnetically stirred on a heating plate to form a slurry. The slurry was then ultrasonicated for 10 minutes. Afterwards, the slurry was dried at 60° C. in air overnight. Finally, the dried powders were reduced at 300° C. for 2 hours in a flow furnace under a forming gas atmosphere (5% H2, 95% Ar, Airgas, Ultrapure), and were then annealed under a forming gas atmosphere at different temperatures (shown in Table I) for 2 hours. The resulting nanoparticle size increased with increasing annealing temperatures. The flow furnace temperature was raised at a heating rate of 3 K/min. Ru/C (20 wt. %), Pt/C (20 wt. %) and Ru9Pt1/C (20 wt. %) and Ru9Ir1/C (20 wt. %) were also synthesized using the same procedure for comparison.
X-ray diffraction. The prepared catalysts were characterized by powder XRD in a Rigaku Ultima VI diffractometer with a Cu Ka source. Data were collected at a scan rate of 5°/min and with an increment of 0.02.
Energy dispersive X-ray absorption (EDX) spectroscopy. A LEO 1550 FESEM instrument, in which a field emission scanning electron microscopy (FESEM) is equipped with an energy dispersive X-ray spectrometer (EDX), was used to perform EDX spectroscopy.
Transmission Electron Microscopy (TEM). TEM was performed using a FEI Tecnai 12 BioTwin operated at 120 kV, which was equipped with a LaB6 filament, and a high-resolution, high-contrast, thermoelectrically (TE) cooled Gatan Orius® 1000 dual-scan CCD camera. The fully motorized eucentric goniometer stage (CompuStage) could be tilted to ±80°.
Scanning Transmission Electron Microscopy (STEM) and EELS mapping. STEM images and electron energy loss spectroscopy (EELS) elemental maps were acquired using a fifth-order aberration-corrected FEI Titan Themis STEM operated at 300 keV with a sub-ångstrom spatial resolution. In order to detect the low Co content in Ru0.95Co0.05/C, the new K2 summit direct electron detector camera was employed to acquire EELS spectral images with a much higher signal-to-noise ratio and energy resolution than a regular CCD camera. EELS elemental mapping indicates that Ru and M are well distributed in nanoparticle embodiments, and no surface preferential distribution enrichment is observed.
Electrode preparation. First, Ru1−xCox/C (11 wt. %), Ru1−xNix/C (11 wt. %) and Ru1−xFex/C (11 wt. %) catalyst inks were prepared by mixing 7.2 mg of catalyst powder, 0.8 mg of Vulcan XC-72R, 3.16 mL of Millipore water, 0.8 mL of isopropanol and 40 μL of Nafion solution (5 wt. %, Fuel Cell Store), and subsequent sonication for 15 minutes. Ru/C (20 wt. %) and Ru9Pt1/C (20 wt. %) and Ru9Ir1/C (20 wt. %) catalyst inks were prepared by mixing 4 mg of catalyst powder, 4 mg of Vulcan XC-72R, 3.16 mL of Millipore water, 0.8 mL of isopropanol and 40 μL of Nafion solution (5 wt. %, Fuel Cell Store), and subsequently sonicated for 15 minutes. A glassy carbon (GC) rotating disk electrode (RDE) with a diameter of 6 mm was polished with 1 μm diamond paste (Buehler), and then rinsed with acetone and Millipore water, respectively. Afterwards, 20 μL of catalyst ink were pipetted onto the GC electrode, and subsequently dried in air. An evenly dispersed thin film of catalyst was formed on the GC electrode with a catalyst loading of 14 μgmetal/cm2.
Electrochemical tests. Electrochemical experiments were carried out with a WaveDriver 20 Bipotentiostat/Galvanostat, and AfterMath software (Pine Research Instrumentation). A three-electrode electrochemical cell made of Kel-F was used for alkaline media to avoid contamination from glass. An AFMSRCE Rotator (Pine Research Instrumentation) was used for H2 oxidation/evolution, and oxygen reduction/evolution measurements. A Ag/AgCl (1M NaCl) electrode was used as the reference electrode, and all potentials are referred to a RHE (0.1 M KOH). The supporting electrolyte was prepared using Millipore water (18.2 MΩ·cm) and potassium hydroxide (99.99%, Sigma-Aldrich). Ar, H2 and O2 (high purity) were obtained from Airgas. For blank cyclic voltammogram measurements, all solutions were deaerated with high-purity Ar. All experiments were carried out at room temperature (20±1° C.).
Extraction of the mass activity, specific activity and the exchange current density. The kinetic currents for the HOR and ORR in alkaline media were calculated based on the Koutecky-Levich equation.
where I is the measured current, and ID indicates the diffusion limited current.
The kinetic currents for the HOR, HER, ORR and OER in alkaline media were normalized to the mass of metals to obtain the mass activity.
where Mm is the metal mass of the catalysts.
The electrochemical surface areas of the catalysts (Sm) were determined using the H adsorption charge. The kinetic currents for the HOR, HER, ORR and OER in alkaline media were normalized to the electrochemical surface area to obtain the specific activity.
The Exchange current densities for the HOR/HER were obtained using the Butler-Volmer equation.
was plotted vs. η, then the exchange current density was obtained from the intercept.
DFT calculations. Calculations were performed using a periodic DFT with the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE). Ultrasoft pseudopotentials and a plane-wave basis set with an energy cutoff of 30 Ry were used for all calculations. In order to improve convergence, a Methfessel-Paxton smearing function with a width of 0.02 Ry was used. The code used for the calculations was the Quantum-ESPRESSO 6.0 package. For lattice parameter calculations, an 8×8×8 Monkhorst-Pack k-point mesh sampling was used for Brillouin zone integration. The lattice constants of Ru (hcp) were calculated to be 2.7444, 2.7444 and 4.3446 Å, respectively, which are close to experimental values (2.7059, 2.7059 and 4.2815 Å).
A slab model was constructed from a 2×2 surface unit cell and consisted of four layers of metal atoms and a vacuum region of more than 10 Å. A 4×4×1 Monkhorst-Pack k-point mesh sampling was used for Brillouin zone integration. The metal atoms in the top two layers were allowed to relax, while the atoms in the bottom two layers were fixed to positions derived from DFT calculated lattice constants. To model Ru3M1 (M=Co, Ni, or Fe) alloys, one of the 4 Ru atoms in each layer was replaced by the second element M. To calculate the adsorption energy of H and O, a ¼ ML coverage was used. The adsorption energy of the adsorbates was obtained as Eads=Etotal−Eslab−Eadsorbate, in which Etotal is the total energy of the slab with adsorbates, Eslab is the energy of the slab, and Eadsorbate is the energy of adsorbed species in the gas phase.
Synthesized nanoparticle catalysts and their properties are summarized in Table I.
metal)
)
2)
/C
/C
/C
/C
/C
/C
/C
/C
.05/C
/C
/C
/C
/C
/C
/C
/C
Fe0.3/C
/C
/C
indicates data missing or illegible when filed
Hydrogen Oxidation Reaction. The effects of Co, Ni and Fe alloying with Ru on the hydrogen adsorption/desorption kinetics are shown in
PtRu/C and IrRu/C are among the best binary catalysts for the HOR, and the HOR activity of Ru0.95Co0.05/C and Ru0.9Co0.1/C are compared to that of Ru0.9Pt0.1/C and Ru0.9Ir0.1/C in
Hydrogen Evolution Reaction. Similar to the HOR, the HER activity was also enhanced for all the studied Ru1−xMx/C (M=Co, Ni, Fe, 0<x≤0.5) catalysts, when compared to pure Ru/C (
Oxygen Reduction Reaction.
Oxygen Evolution Reaction.
Understanding the enhancement of the HOR, HER, ORR and OER activities of Ru1−xMx (x=Co, Ni, or Fe). Both the HOR and HER involve the formation of adsorbed H atoms as intermediates. According to the Sabatier principle, a plot of HOR or HER activity vs. H binding energy should exhibit a “volcano plot” shape.” Thus, the H binding energy can be used as a descriptor of electrocatalytic activity for the HOR and HER.
As established by data for embodiments of the inventive catalysts, alloying Ru with Co, Fe, Ni, Pt or Ir results in a down-shift of the Ru d-band center and, thus, a weakening of the H adsorption energy on Ru sites. This results in an enhancement of the reversibility of H adsorption/desorption processes in the cyclic voltammograms (
Embodiments of the inventive Ru1−xMx (M=Co, Ni or Fe) alloys have a hexagonal close packed (HCP) structure, in which each atom has a coordination number of 12. Ru1−xMx alloys with a M content of 5-10% exhibit the highest activity towards the HOR and HER. This suggests that in the most active Ru1−xMx catalysts, on average, each Ru atom has only one neighboring M atom, and meanwhile the amount of Ru surface sites is not significantly reduced, but the electronic structure of Ru could significantly be modified. Further increasing the Co, Ni or Fe content in Ru alloys results in a decrease of the catalytic activity likely due to the decrease in the amount of Ru surface sites.
Ensemble effects can also weaken H adsorption on Ru alloys, and thus could also contribute to the activity enhancement for the HOR and HER on Ru1−xMx alloys (M=Co, Ni, Fe, Pt and Ir). Adsorbed H on Ru prefers to occupy hcp and fcc sites, and the addition of a second element may reduce the ensembles of three adjacent Ru atoms. Since H adsorption on these second elements is much weaker than on Ru, and since surface Co, Ni and Fe sites can be covered by oxygen-containing species in the H region, some H atoms can only adsorb at the bridge sites of two-Ru-atom ensembles, and their adsorption would be anticipated to be much weaker than at the hcp and fcc sites. In contrast, Pd adsorbs H quite strongly (
As established by data presented herein, Ru alloying with Co, Fe or Ni can also enhance ORR activity. The enhancement of the ORR on Ru alloy catalysts can also be attributed to electronic effects, i.e. a down-shift of the d band center of Ru, and/or the ensemble effect, which weakens O adsorption.
A synergistic effect for the OER on Ru1−xMx (M=Co, Ni or Fe) nanoparticle catalysts can also be attributed to a weakening of O binding by doping with Co, Ni or Fe. However, an oxide layer can be formed on the surfaces of Ru and Ru1−xMx (M=Co, Ni or Fe) nanoparticles at potentials relevant to the OER, and thus the surface properties may be quite different from the bulk.
In summary, a series of Ru1−xCox/C, Ru1−xNix/C and Ru1−xFex/C alloy nanoparticle catalysts have been synthesized via an impregnation method and characterized by XRD, EDX, TEM, STEM and EELS elemental mapping. RDE voltammetry was performed to study the catalytic activity of these materials for the HOR, HER, ORR and OER. A synergistic effect for the HOR, HER, ORR and OER on RuCo/C, RuNi/C and RuFe/C alloy nanoparticle catalysts was observed due to electronic effects and/or the ensemble effect. All the studied Ru1−xCox/C, Ru1−xNix/C and Ru1−xFex/C alloy nanoparticle catalysts were more active than pure Ru/C towards the HOR, HER, ORR and OER. Ru0.95Co0.05/C was the most active among all the studied carbon supported Ru alloy catalysts for the HOR, HER and ORR, while Ru0.7Co0.3/C exhibited the highest activity towards the OER. In particular, as for the HER and HOR, Ru0.95Co0.05/C was more active than Pt/C in terms of mass activity, and was comparable to or even more active than Ru0.9Pt0.1/C and Ru0.9Ir0.1/C. Moreover, Ru0.95Co0.05/C is much less expensive than Pt and Ir, and thus is a promising catalyst for the HOR and HER in alkaline media. DFT calculations indicate that the Ru d-band center of Ru alloys is down shifted, when compared to pure Ru, and thus H and O adsorption on Ru alloys becomes weaker.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), “contain” (and any form contain, such as “contains” and “containing”), and any other grammatical variant thereof, are open-ended linking verbs. As a result, a method or device that “comprises”, “has”, “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a composition or article that “comprises”, “has”, “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features.
As used herein, the terms “comprising,” “has,” “including,” “containing,” and other grammatical variants thereof encompass the terms “consisting of” and “consisting essentially of.”
The phrase “consisting essentially of” or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method.
All publications cited in this specification are herein incorporated by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein as though fully set forth.
Subject matter incorporated by reference is not considered to be an alternative to any claim limitations, unless otherwise explicitly indicated.
Where one or more ranges are referred to throughout this specification, each range is intended to be a shorthand format for presenting information, where the range is understood to encompass each discrete point within the range as if the same were fully set forth herein.
While several aspects and embodiments of the present invention have been described and depicted herein, alternative aspects and embodiments may be affected by those skilled in the art to accomplish the same objectives. Accordingly, this disclosure and the appended claims are intended to cover all such further and alternative aspects and embodiments as fall within the true spirit and scope of the invention.
This application claims priority to U.S. Provisional Patent Application No. 62/820,029, filed Mar. 18, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.
This invention was made with government support under DESC0019445 awarded by the Office of Science (DOE), and under DMR-1120296 awarded by the National Science Foundation. The United States Government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/023114 | 3/17/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62820029 | Mar 2019 | US |
