Surface and Subsurface Effects in Electrochemical Water Splitting

Abstract

We will report on the surface and subsurface electrode processes in aqueous solutions. We are particularly focused on anode and cathode processes in electrochemical water splitting. Well-defined model electrode materials of oxides and noble metal alloys are prepared to investigate structural and mechanistic details of water splitting. Gas phase synthesis and controlled atmosphere electrochemical analysis of oxygen evolution electrocatalysis of CaxSr1-xFe2O6-δ perovskites where δ = 0-1, will be discussed. This system exhibits a wide range of activity depending on the A site composition. Our results suggest that surface and subsurface oxygen content controls the oxygen evolution catalysis. Although, current understanding from the d-orbital electron count (eg occupancy) predicts low OER activities for such a system, under specific solution conditions, some of the compounds in the Sr2-xCaxFe2O6-δ series exhibit higher activity than LaCoO3. We particularly use results of in-situ vibrational spectroscopy and electrochemical analysis to elucidate vacancy content and ordering effects on catalysis. We will also discuss the influence of surface and subsurface structures of model Pt-M (M = Cu and Ni) surface alloys and bilayers during hydrogen adsorption relevant to hydrogen evolution reaction (HER). We use electrochemical measurements and in-situ surface stress analysis of these systems to elucidate activity trends from hydrogen adsorption affinities. Our results exhibit a correlation between the energetics of hydrogen underpotential deposition and HER catalytic activity.