In a paper to be published in an upcoming issue of Energy & Environmental Science (now available online), researchers at the U.S. Department of Energy's Brookhaven National Laboratory describe details of a low-cost, stable, effective catalyst that could replace costly platinum in the production of hydrogen.
Fig 1: Splitting hydrogen from water.
- New material is a promising alternative to costly platinum catalyst
The catalyst, made from renewable soybeans and abundant molybdenum metal, produces hydrogen in an environmentally friendly, cost-effective manner, potentially increasing the use of this clean energy source.
The project branches off from the Brookhaven group's research into using sunlight to develop alternative fuels. Their ultimate goal is to find ways to use solar energy—either directly or via electricity generated by solar cells—to convert the end products of hydrocarbon combustion, water and carbon dioxide, back into a carbon-based fuel. Dubbed "artificial photosynthesis," this process mimics how plants convert those same ingredients to energy in the form of sugars. One key step is splitting water, or water electrolysis.
This form of hydrogen production could help the scientists achieve their ultimate goal.
"A very promising route to making a carbon-containing fuel is to hydrogenate carbon dioxide (or carbon monoxide) using solar-produced hydrogen," said Fujita, who leads the artificial photosynthesis group in the Brookhaven Chemistry Department.
But with platinum as the main ingredient in the most effective water-splitting catalysts, the process is currently too costly to be economically viable.
Comsewogue High School students Shweta and Shilpa Iyer entered the lab as the search for a cost-effective replacement was on.
Fig 1: Splitting hydrogen from water: This illustration depicts the synthesis of a new hydrogen-production catalyst from soybean proteins and ammonium molybdate. Mixing and heating the ingredients leads to a solid-state reaction and the formation of nanostructured molybdenum carbide and molybdenum nitride crystals. The hybrid material effectively catalyzes the conversion of liquid water to hydrogen gas while remaining stable in an acidic environment.
The Brookhaven team had already identified some promising leads with experiments demonstrating the potential effectiveness of low-cost molybdenum paired with carbon, as well as the use of nitrogen to confer some resistance to the corrosive, acidic environment required in proton exchange membrane water electrolysis cells. But these two approaches had not yet been tried together.
To make the catalyst the team ground the soybeans into a powder, mixed the powder with ammonium molybdate in water, then dried and heated the samples in the presence of inert argon gas. "A subsequent high temperature treatment (carburization) induced a reaction between molybdenum and the carbon and nitrogen components of the soybeans to produce molybdenum carbides and molybdenum nitrides," Chen explained. "The process is simple, economical, and environmentally friendly."
Electrochemical tests of the separate ingredients showed that molybdenum carbide is effective for converting H2O to H2, but not stable in acidic solution, while molybdenum nitride is corrosion-resistant but not efficient for hydrogen production. A nanostructured hybrid of these two materials, however, remained active and stable even after 500 hours of testing in a highly acidic environment.
Structural and chemical studies of the new catalyst conducted at Brookhaven's National Synchrotron Light Source (NSLS) and the Center for Functional Nanomaterials (CFN) are also reported in the paper, and provide further details underlying the high performance of this new catalyst.
The scientists also tested the MoSoy catalyst anchored on sheets of graphene—an approach that has proven effective for enhancing catalyst performance in electrochemical devices such as batteries, supercapacitors, fuel cells, and water electrolyzers. Using a high-resolution transmission microscope in Brookhven's Condensed Matter Physics and Materials Science Department, the scientists were able to observe the anchored MoSoy nanocrystals on 2D graphene sheets.
The graphene-anchored MoSoy catalyst surpassed the performance of pure platinum metal. Though not quite as active as commercially available platinum catalysts, the high performance of graphene-anchored MoSoy was extremely encouraging to the scientific team.
The scientists are conducting additional studies to gain a deeper understanding of the nature of the interaction at the catalyst-graphene interface, and exploring ways to further improve its performance.