CAS: Bimetallic Transition Metal Phosphide Nanostructures as High-Efficiency, Earth-Abundant, and Durable Catalysts for Electrochemical Water Splitting

Virginia Commonwealth University, Richmond VA

Investigators

Abstract

With the support of the Chemical Catalysis program in the Division of Chemistry, Professors Indika Arachchige and Ka Un Lao of the Virginia Commonwealth University are studying the fundamental properties of metal phosphide nanoparticles as effective catalysts for splitting water into environmentally friendly hydrogen and oxygen fuel. The inexpensive generation of hydrogen from water using electricity (electrochemical water splitting) would provide an abundant source of renewable fuel. Currently, the most active catalysts used in water splitting are comprised of expensive and rare metals such as platinum. This project will develop new chemical syntheses to produce efficient catalysts from metal phosphides that are less expensive and abundant. The activity of the phosphide catalysts is improved by modifying the surface of the particles by incorporating multiple metal atoms. The research team combines synthesis and catalysis expertise with quantum chemistry calculations and artificial intelligence to garner a thorough understanding of the effects of particle size, shape, and composition on key catalytic properties and chemical stability. The collaborative nature of this project provides multidisciplinary training and mentoring for graduate and undergraduate students, to develop skills in catalyst design and synthesis, computational chemistry, and nanoscience. The summer outreach to Richmond Public Schools exposes K-12 students to cutting-edge nanochemistry and catalysis projects, and develops age-appropriate nanoscience educational modules impacting hundreds of underrepresented minority students. Electrocatalysis enabled water splitting presents an exciting opportunity to produce environmentally benign fuel to power human activities. Transition metal phosphides (TMPs) have emerged as earth abundant catalysts for water electrolysis and their activity can be enormously augmented by admixing synergistic metals to modify the surface affinity and the kinetics and mechanisms of hydrogen (HER) and oxygen evolution (OER) reactions. Underpinning their efficient application is the ability to rationally and predictably achieve precisely controlled catalyst features, including specific catalyst structures, surface facets, morphologies, and compositions, that directly impact the HER/OER activity, stability, and durability. The objective of this program is to exploit a comprehensive theoretical and experimental approach to produce bimetallic TMP nanostructures with control over intrinsic features as high efficiency electrocatalysts for HER and OER. A series of TMP nanostructures having various sizes, compositions, and morphologies are produced by colloidal chemistry methods. The influences of synergistic metal alloying on charge distribution, ion adsorption, oxidation/reduction kinetics and mechanisms, and stability are thoroughly probed with experiments guided by density functional theory simulations and machine learning models. The theory-guided experiments are designed to probe specific catalyst structures, crystal facets, surface terminations, and compositions that show superior water splitting activity and stability, which are correlated to underlying kinetics and mechanisms of HER and OER. These efforts reveal the fundamental influences of simultaneous control over nanostructure, crystal facets, morphology, and composition on water splitting activity and develop roadmaps that guide researchers to produce highly efficient, robust TMP nanocatalysts for the rational design of electrochemical reactors. 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.