Hydrogen evolution reaction of microwave-synthesized pristine and metal-doped molybdenum carbides: Insights from electrochemical modeling and in situ visualization

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Increasing energy demands, combined with urgency to decrease greenhouse gas emissions, has spurred research and development of sustainable chemical and fuels technologies. Hydrogen is an essential component of many fuels and chemicals. Catalysts play a central role in the sustainable production of hydrogen by facilitating hydrogen generation via electrochemical splitting of water molecules, by a process known as the Hydrogen Evolution Reaction (HER). Over the past few years, rapid progress has been made in catalyzing hydrogen evolution using low-cost molybdenum carbide materials, with recently reported activities rivaling those of the optimum, but precious, platinum catalysts. The project will continue to advance research and development of molybdenum carbide catalysts through a coordinated theoretical and experimental approach supported by advanced characterization techniques. Specific goals include 1) deeper mechanistic understanding of the surface-catalyzed hydrogen evolution reaction as promoted by both pure and metal-doped metal carbide materials, 2) elucidation of catalyst surface structure and composition under reaction conditions, and 3) identification of catalyst structures and compositions that demonstrate exceptional stability and durability with time-in-service. Project outcomes will extend beyond the hydrogen evolution reaction to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations related to applications such as battery technology and fuel cells. The project will promote training of new generations of scientists and engineers by offering opportunities for both graduate and undergraduate students - particularly for those from underrepresented groups - to participate in “green” energy research. Molybdenum carbide nanoparticles of various stoichiometry (i.e., Mo(y)C) will be synthesized using a microwave reaction and sol-gel process. The electrochemical performance with and without metal dopants will be systematically examined. Transmission electron microscopy imaging, diffraction, and spectroscopy - energy-dispersive X-ray (EDS) and electron energy-loss (EELS) - will be employed to elucidate the reactivity-structure relationships of the catalysts down to the atomic scale. Environmental transmission electron microscopy (ETEM) will enable these structural dynamics to be studied in real-time under relevant reaction conditions. Ambient-pressure X-ray photoelectron spectroscopy (AP­XPS) and Raman spectroscopy will be utilized to establish a correlation between surface chemistry and reactivity. In situ characterization will be closely coordinated with kinetic measurements, and experimental conditions for lowering the anodic overpotential of the water electrolysis reaction. This will provide critical input for density functional theory (DFT) electrochemical simulations employing constrained thermodynamics to determine the surface composition/structure of the catalyst under the HER conditions including thermodynamic/kinetic limitations. Furthermore, the theory will complement the experiments by elucidating the HER mechanisms, active sites, and rate-limiting steps, which will guide the design of catalysts for water electrolysis. The research will be integrated into educational efforts via development of new course components and novel education modules that emphasize the importance of integrated theoretical and experimental efforts to design new materials tailored for the sustainable manufacturing of fuels and chemicals. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.