Nanoelectrode Atomic Force Microscopy Probes Enable the in-Operando Measurement of Surface Electrochemical Potentials during Oxygen Evolution Catalysis

Abstract

Heterogeneous electrochemical processes, including (photo)electrochemical water splitting to evolve hydrogen via semiconductors and/or electrocatalysts, are driven by the accumulation of charge carriers and thus the interfacial electrochemical potential gradients that promote charge transfer. Conventional electrochemical techniques measure/control potentials at the conductive substrate, but are unable to isolate processes and electrochemical potentials at the surface during operation.1 In this talk, we will show that a nanoelectrode tip of an atomic force microscope cantilever can effectively sense the surface electrochemical potential of electrocatalysts in operando.2 First, we will discuss fundamental aspects and capabilities of the probes used.3 We then will show how the technique allows for measurement of the surface potential and thickness-dependent electronic properties of cobalt (oxy)hydroxide phosphate (CoPi). We show that when CoPi is deposited on illuminated photoanodes like hematite (a-Fe2O3), it acts as both a hole collector and an oxygen evolution catalyst. We highlight the versatility of the technique by comparing surface potentials of CoPi-decorated planar and mesoporous hematite, as well as bismuth vanadate photoelectrodes.