A Journey to the Center of the Earth Abundant Metal Oxide Catalysts

Abstract

The oxygen evolution (OER) and hydrogen evolution reactions (HER) compose the process of water splitting: an electrochemical route to sustainable hydrogen production. The OER is the more complex and challenging of these reactions, relying upon bespoke electrocatalysts to effect necessary intermediates and drive desired pathways. Among the most promising catalysts for this reaction are heterogeneous metal oxides composed of earth-abundant metals (e.g, Co, Ni). Despite their com- petency for the OER, these materials lack long-range order (i.e., they are not crystalline) or defined stoichiometries [i.e., they form CoOx(OH)y species not Co3O4] complicating how we understand this activity and how we go about designing increasingly active materials.

This thesis is concerned with resolving how the morphologies and compositions of heterogeneous electrocatalysts affect their activity for the OER. We first explore how proton accumulation during operation and the localized pH environments thereby generated may dampen the kinetics and stability of these catalysts. We apply these studies to the design of acid-stable electrochemical systems that may effectively drive the OER under practically relevant conditions. We finally interrogate the composition of active sites on heterogeneous electrocatalysts by selectively obscuring their inactive regions with exogenous overlayers. In these systems, we spatially resolve unobscured regions where the OER is still able to proceed effectively and champion this approach as a means of discerning the active sites of these heterogeneous catalysts. Cumulatively, the works described herein explore fundamental and practical aspects of the OER to expand our understanding and aspirations for this field of research.