Patent Application
20180171493
The present disclosure relates to an improved method for synthesizing Cobalt Molybdenum disulfide (CoMoS2) using alkyl-containing thiomolybdate precursors. Still more particularly, the present disclosure relates to a method for synthesizing Cobalt Molybdenum disulfide (CoMoS2) having a high surface area and number of catalytically active exposed edge sites.
Growing concerns about global warming and energy security demand the expansion of renewable energy sources as viable alternatives to fossil-fuel-based technologies, in conjunction with improved energy storage options. In many of the innovative approaches to address these challenges, the production of hydrogen in various (photo)-electrolysis systems plays a pivotal role. Electrocatalytic generation of molecular hydrogen through hydrogen evolution reactions (HERs) is a promising alternative for the development of clean-energy technologies. Research on HERs is focused on the implementation of robust, efficient, and cheap catalysts able to lower the activation energy required for producing hydrogen gas (Turner, Science 2004, 305(5686):972; Walter et al., Chem. Rev. 2010, 110(11):6446). Platinum metal is well suited as the most active catalyst for the electrocatalytic reduction of water to produce molecular hydrogen. This is due to the large cathodic current density generated at practically zero overpotential (Lewis and Nocera, Proc. Natl. Acad. Sci. 2006, 103(43):15729; Gray, Nat. Chem. 2009, 1(1):7; Merki and Hu, Energy Environ. Sci. 2011, 4(10):3878). However, its utilization is impeded by its high cost and rarity (Gray, Nat. Chem. 2009, 1(1):7). Thus, replacement of platinum with cost-effective and highly efficient catalysts is crucial to achieve a more sustainable way for hydrogen evolution (Du and Eisenberg, Energy Environ. Sci. 2012, 5(3):6012; Eckenhoff et al., Biochim. Biophys. Acta BBA—Bioenerg. 2013, 1827(8-9):958; Wang et al., Energy Environ. Sci. 2012, 5(5):6763).
Recently, complexes of earth-abundant metals such as Co, Mo, Ni, and Fe have emerged as alternative HER electrocatalysts to platinum (Du and Eisenberg, Energy Environ. Sci. 2012, 5(3):6012; Eckenhoff et al., Biochim. Biophys. Acta BBA—Bioenerg. 2013, 1827(8-9):95; Wang et al., Energy Environ. Sci. 2012, 5(5):6763; Callejas et al., ACS Nano 2014, 8(11):11101; Popczun et al., Angew. Chem. 2014, 126(21):5531; Hinnemann et al., J. Am. Chem. Soc. 2005, 127(15):5308). Transition metal sulfides (TMSs) have been extensively studied as catalysts for hydrodesulfurization (HDS) processes in the petroleum industry (Staszak-Jirkovský et al., Nat Mater. 2016, 15(2):197; Füchtbauer et al., Top. Catal. 2013, 57(1-4):207; Bag et al., Nat. Chem. 2009, 1(3):217; Prins et al., Catal. Rev. 1989, 31(1-2):1). Molybdenum disulfide (MoS2) is one of the most widely used industrial catalyst for HDS, and has been suggested as a possible HER catalyst through experimental and computational studies (Hinnemann et al., J. Am. Chem. Soc. 2005, 127(15):5308; Jaramillo et al., Science 2007, 317(5834):100; Karunadasa et al., Science 2012, 335(6069):698; Laursen et al., Energy Environ. Sci. 2012, 5(2):5577). However, the efficiency of MoS2 as HER electrocatalysts is hindered due to the limited number of exposed edge sites, which are important for catalytic activity (Staszak-Jirkovský et al., Nat. Mater. 2016, 15(2):197; Lukowski et al., J. Am. Chem. Soc. 2013, 135(28):10274). It has been well established that presence of Co to MoS2 will act as a promoter to increase the reactivity of MoS2 as a HDS catalyst (Popczun et al., Angew. Chem. 2014, 126(21):5531; Prins et al., Catal. Rev. 1989, 31(1-2):1; Nava et al., Catal. Lett. 86(4):257). Co—Mo—S materials are also used in the process of hydrogen production (Merki and Hu, Energy Environ. Sci. 2011, 4(10):3878).
An embodiment of the present disclosure provides a method for producing cobalt-promoted molybdenum disulfide (CoMoS2). The method comprises alkylating ammonium thiomolybdate (ATM) with one the group consisting of C4 to C16 amines, C4 to C16 ammonium salts, and combinations thereof, to form an alkylated thiosalt precursor. The method further comprises synthesizing the CoMoS2 from the alkylated thiosalt precursor. The CoMoS2 has a surface area greater than about 35 square meters per gram (m2/g).
Another embodiment of the present disclosure provides a hydrogen evolution catalyst. The hydrogen evolution catalyst comprises cobalt-promoted molybdenum disulfide (CoMoS2) having a surface area greater than about 35 square meters per gram (m2/g).
Yet another embodiment of the present disclosure provides an electrolytic cell. The electrolytic cell comprises an electrode at which a hydrogen evolution reaction occurs. The electrode comprises a metallic base cobalt-promoted molybdenum disulfide (CoMoS2). The CoMoS2 has a surface area greater than about 35 square meters per gram (m2/g).
A further embodiment of the present disclosure provides a method of generating hydrogen. The method comprises forming an electrolytic cell having an electrode at which a hydrogen evolution reaction occurs. The method further comprises applying a current to the cell facilitating disassociation of water and the production of hydrogen. The electrode comprises cobalt-promoted molybdenum sulfide (CoMoS2) having a surface area greater than about 35 square meters per gram (m2/g).
The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives, and features thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
The illustrative embodiments described herein provide for the synthesis and characterization of CoMoS2 materials with different surface areas using different alkyl containing ammonium thiomolybdate precursors. These of CoMoS2 materials were evaluated as HER catalysts in a 0.5 M H2SO4 aqueous solution.
ATM was treated with C4 to C16 amines and C4 to C16 ammonium salts in aqueous solution to prepare the alkyl-containing ammonium thiomolybdate precursors for CoMoS2 catalysts. Specifically, ATM was treated with 1-dodecylamine (DDA), diethylenetriamine (DETA), tetradecyltrimethylammonium (TDTA) bromide, and cetyltrimethylammonium (CTA) bromide.
Electrochemical studies, including linear scanning voltammetry and bulk electrolysis, were carried out to characterize HER electrocatalytic activity of the prepared CoMoS2 materials. Long-term chronoamperometric measurements were carried out to characterize the tolerance of the prepared CoMoS2 materials to strongly acidic media.
Synthesis of CoMoS2 catalysts using ATM form different alkyl-containing ATM precursors when treated with different amines and ammonium bromide salts including 1-dodecylamine, diethylenetriamine, tetradecyltrimethylammonium bromide, and cetyltrimethylammoniumb bromide. These materials are amorphous and with porous surfaces that show reasonable big surface area. Electrochemical studies along with hydrogen gas analysis in 0.5 M H2SO4 aqueous media indicate that these materials are active electrocatalysts for hydrogen generation and show good stability in acid during long-term electrolysis.
Preparation of alky-containing ATM was followed by a simple synthetic technique in aqueous solution to form the different CoMoS2 materials. This method involves a one-step substitution of the NH4+ from ATM by the alkyl containing amines or ammonium salts.
ATM (5.0 g, 19.2 mmol) was dissolved in 10 mL deionized water (DIW). A solution of 2 equivalents (38.4 mmol) amine or ammonium bromide salt in 50 mL DIW was added to form a black slurry. A solution of CoCl2 (2.5 g, 19.2 mmol) in 10 ml DIW was added to the reaction mixture. The reactor vessel was then heated at 300° C. for 2 hours.
It should be noted that the amines were evaporated off during the reaction which built up the pressure. Thus, pressure was held constant at 1300 Psi to prevent an explosion. After completion, the resultant products were filtered and washed with water and isopropyl alcohol and then dried under reduced pressure.
All the CoMoS2 samples were characterized by means of Brunauer-Emmett-Teller (BET) analyses. Surface area analyses were obtained on a Micromeritics Accelerated Surface Area and Porosity System (ASAP 2020).
All CoMoS2 samples were characterized by means of scanning electron microscopy (SEM) to reveal the morphology of the CoMoS2 using different alkyl-containing ATM precursors. SEM experiments were performed using a Hitachi S-4800 SEM instrument.
The surface areas of the synthesized CoMoS2 samples range from 43-69 m2/g (Table 1). CoMoS2 prepared from DDA (Sample 1) shows the highest surface area while CoMoS2 prepared from DDA (DETA) exhibits the lowest.
Scanning electron micrographs of CoMoS2 catalysts for Samples 1 and 2 are shown in
Scanning electron micrographs of CoMoS2 catalysts for Samples 3 and 4 are shown in
All CoMoS2 samples were characterized by means of X-Ray Diffraction. XRD data were obtained on a Bruker D8 Discover X-ray Diffractometer.
As shown in
Catalysts CoMoS2 prepared according to each of Samples 1-4 were coated on fluorine-doped tin oxide (FTO) glass substrates with silver paste prior to the electrochemical measurements and employed as working electrodes in electrochemical studies.
10 mg CoMoS2 was dispersed in 10 mL ethanol and ultrasonicated for 30 minutes to generate a homogenous suspension. FTO glass was cleaned with water and acetone before a thin layer of silver paste was coated on top of the active side of the FTO glass with an area of 1 cm2. 0.5 mL of the prepared suspension containing the CoMoS2 sample material was spin-coated on the silver paste using a spin coater. (Spin rate: 1000 rpm; Time: 1 minute). The CoMoS2/FTO substrates were then allowed to dry prior to use.
Bulk electrolysis and chronoamperometric measurements were performed in a custom-built two-compartment gas-tight electrochemical cell under argon atmosphere. The working and counter electrodes of the two-compartments are separated through a fine glass frit.
A first compartment of the cell contains: (i) CoMoS2/FTO working electrode (1 cm2); (ii) saturated calomel electrode (SCE) reference electrode; and (iii) gas inlet and gas outlet. The electrolyte solution in the first compartment was kept stirring to remove the in situ-generated H2 bubbles. The second compartment of the cell contains: (i) a platinum mesh auxiliary counter electrode; and (ii) a gas outlet.
Electrochemical measurements were obtained using a CHI760D potentiostat. The potentials displayed were referred to reversible hydrogen electrode (RHE). All potentials obtained referenced to SCE were calibrated with respect to reversible hydrogen electrode (RHE). A 2 mm diameter platinum working electrode was used for cyclic voltammogram in 0.5 M H2SO4 solution at a scan rate of 50 mV/s. The potential at which the cathodic current increase was constantly observed to be −0.27 V vs. SCE. Thus, the potentials obtained using a SCE reference electrode were added by +0.27 V in order to be referred to RHE.
The electrocatalytic HER behaviours of the prepared CoMoS2 samples were studied in a 0.5 M H2SO4 aqueous solution.
A control working electrode of platinum metal was used as a benchmark electrocatalyst for hydrogen generation. Platinum shows an immediate enhancement of catalytic current at 0 V vs. RHE. A blank FTO glass coated with silver paste, which is the substrate for preparing the CoMoS2 electrode, was also tested, and it shows negligible current increase at potentials between 0 V to −0.5 V vs RHE. The corresponding current densities generated at −0.5 V vs. RHE are 17.2, 16.7, 12.1, 11.5, mA/cm2.
To quantify the hydrogen gas generated, bulk electrolysis along with gas detection was performed.
The passages of charge of Samples 1, 2, 3, and 4 for one hour are 81.7, 76.6, 64.2, and 46.6 C, respectively. The blank silver-coated FTO glass generates negligible charge at the same potential. The amount of H2 gas evolved shows between 98% to 100% faradaic yield, which implies a quantitative faradaic yield for hydrogen generation. The blank silver-coated FTO glass shows no H2 generation at the same potential.
Electrochemical studies of these four CoMoS2 HER catalysts synthesized using different alkyl-containing ammonium thiomolybdate precursors show different electrocatalytic behaviors. Samples 3 and 4, which are synthesized using ATM treating with amines with longer carbon chains and more branches as compared to Samples 1 and 2, are less active CoMoS2 HER catalysts with higher overpotential and less current density at the same potential.
The description of the different illustrative embodiments has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different features as compared to other desirable embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/436,574 filed Dec. 20, 2016, and entitled “Electrocatalytic Hydrogen Gas Generation by Cobalt Molybdenum Disulfide (CoMoS2) Synthesized Using Alkyl-Containing Thiomolybdate Precursors.”
| Number | Date | Country | |
|---|---|---|---|
| 62436574 | Dec 2016 | US |
