CAREER: Probing and Controlling Acidic Electrocatalytic Oxidation Mechanisms and Catalyst Degradation Processes

Northwestern University, Evanston IL

Investigators

Abstract

As our global energy landscape evolves to incorporate a greater fraction of renewable electricity from sources such as wind, solar, and hydroelectric technologies, electrochemical processes will become a major source of fuels and chemicals. Hydrogen is a critical component of many fuels and chemicals, such that hydrogen demand in the US is projected to increase 2-5 times over the next 30 years. Proton exchange membrane (PEM) electrolyzers are a promising technology for large-scale, sustainable production of hydrogen from water, but development of efficient and stable catalysts for water oxidation in acidic conditions has been a longstanding roadblock for widespread implementation. The project will 1) investigate a class of precisely tuned catalyst materials that are designed to withstand the harsh oxidative and acidic conditions of PEM electrolyzers with minimal use of expensive and strategic precious metals, and 2) characterize critical relationships between catalyst structures and reaction mechanisms, as related to reaction rates and efficient utilization of electrical energy. The scientific outcomes of this work will lead to improved technological feasibility of sustainable processes for production of fuels and chemicals from renewable electricity sources. Furthermore, the research will be integrated with a sustainable plan for collaborative development and implementation of new curriculum and classroom activities that emphasize student engagement to improve retention of students from diverse backgrounds and fulfill Next Generation Science Standards, via work with Chicago Public High School teachers. This project focuses on water oxidation in acidic conditions as a critical, yet comparatively simple, electrochemical oxidation reaction for fundamental study of reaction mechanisms, surface structure evolution, and deactivation processes for perovskite oxide catalysts as a function of their electronic and geometric structure properties. Perovskite oxide structures provide a tunable platform for systematically modulating properties of catalysts both at the surface and in the bulk, while utilizing lower loadings of iridium compared to IrO2 and Ir/C benchmark catalysts. In situ spectroscopy and kinetic isotope studies will probe trends in reaction mechanisms and assess extent of catalyst surface reorganization with relation to material properties (oxidation states, metal-oxygen bond covalency, metal-oxygen-metal bond angle, etc.) and reaction conditions. Microscopy, electrochemical quartz crystal microbalance, and impedance spectroscopy will monitor morphology, mass changes, and charge transport effects as a result of long-term testing to provide insights to various deactivation processes. This work will also establish intrinsic catalyst material stability metrics to complement more ubiquitous performance stability metrics to guide development of high performance electrocatalytic systems. Fundamental mechanistic insights and structural understanding arising from this work will fill major knowledge gaps for design and systematic control of metal oxide catalysts that drive a wide range of selective electrochemical oxidation reactions. 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.