Heterogeneous electrochemical processes, including photoelectrochemical water splitting to evolve hydrogen using electrocatalyst-coated semiconductors, 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 or semiconductor ohmic contact, but are unable to isolate processes and electrochemical potentials at the surface during operation. In this talk I will show how a nanoelectrode tip of an atomic force microscope cantilever can effectively sense the surface electrochemical potential of electrocatalysts in operando. First, I will discuss fundamental aspects and capabilities of the probes used. I will then show how the technique allows for measurement of the surface potential and thickness-dependent electronic properties of cobalt (oxy)hydroxide phosphate (CoPi) deposited on illuminated photoanodes such as hematite (α-Fe2O3) and bismuth vanadate (BiVO4) where it acts as both a hole collector and an oxygen evolution catalyst. I will further show how the technique can be used to directly measure the spatially varying junction properties of nanoparticle catalysts on photoactive semiconductor surfaces where so-called “pinch-off” effects have a dramatic influence.

Nanoscale probing of carrier-selective catalyst-semiconductor contacts in water-splitting photoelectrodes

2019 Fall National Meeting

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