Understanding and controlling factors that restrict the rates of fuel-forming reactions are essential to designing effective catalyst-modified semiconductors for applications in solar-to-fuel technologies. During this presentation, I will describe GaAs semiconductors featuring polymeric coatings containing cobaloxime-type catalysts for photoelectrochemically powering the hydrogen evolution reaction. The activities of these electrodes (achieving limiting current densities &gt;20 mA cm<sup>-2</sup> under 1-sun illumination) enable identification of fundamental performance-limiting bottlenecks encountered at relatively high rates of fuel formation. Experiments conducted under varying bias potential, pH, illumination intensity, and scan rate reveal two distinct mechanisms of photoelectrochemical hydrogen production. At relatively low polarization and pH, the limiting photoactivity is independent of illumination conditions and is attributed to a mechanism involving reduction of substrate protons. At relatively high polarization or pH, the limiting photoactivity shows a linear response to increasing photon flux and is attributed to a mechanism involving reduction of substrate water. This work illustrates the complex interplay between transport of photons, electrons, and chemical substrates during photoelectrosynthetic reactions and highlights diagnostic tools for better understanding these processes.

Understanding and controlling the performance-limiting steps of catalyst-modified semiconductors

ACS Fall 2021

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