(324g) Role of Reaction Environments in Shaping Charge Transfer at Nanoscale Electrocatalyst/Semiconductor Junctions for Solar Water Splitting

Photo(electro)catalytic water splitting offers a promising route to clean and renewable hydrogen production. A widely studied approach couples metal nanoparticle electrocatalysts (np-ECs) with semiconductor (SC) light absorbers, where the SC harvests solar energy to generate charge carriers, which are separated and move to np-ECs that drive the hydrogen (HER) and oxygen (OER) evolution half-reactions. Despite significant progress, the fundamental mechanisms governing charge transfer efficiencies (i.e., photovoltage) at np-EC/SC interfaces remain poorly understood, especially under dynamic reaction conditions. In addition, classical theories, such as the Schottky model for metal/semiconductor contacts, fall far short of accurately describing and explaining the performance of these systems. As a result, even well-studied systems, such as Pt nanoparticles anchored on p-Si (np-Pt/p-Si) for the photoelectrochemical hydrogen evolution, lack physical models that fully explain their significant performance gap when compared to their Pt thin-film counterparts.

In this study, we shine light on the complexities associated with the physical mechanisms underlying the operation of these complex photo(electro)catalysts. Specifically, we investigate how reaction environments influence charge transfer at np-EC/SC junctions, offering new insights into the fundamental physics that govern their performance. Through a series of in-depth investigations of various Pt/p-Si model systems, we reveal that molecular adsorption processes involving H₂ and O₂ interactions with the metal electrocatalyst play a decisive role in modulating charge transfer across the EC/SC junction. Our findings demonstrate that an initially non-selective (i.e., Ohmic) np-EC/SC contact can dynamically transform into one that is highly selective for the desired charge carrier (i.e., electrons) by simply altering the nature of the species adsorbed on the electrocatalyst. We also developed a comprehensive digital twin model to describe the experimentally observed behavior and quantified the impact of different interfacial mechanisms on the performance. These findings help guide the rational design of interfaces in practical photoelectrochemical devices.