(668c) Exploring the Performance Limits of Nanoscale Electrocatalysts on Planar Semiconductor Light Absorbers for the Oxygen Evolution Reaction

Photoelectrochemical water splitting is a promising solution for converting solar energy directly into hydrogen fuel. High-efficiency devices consist of a tandem system with two semiconductor light absorbers coupled to electrocatalysts to perform the hydrogen and oxygen evolution half reactions. Efficiency analyses of these systems shows that the bottom semiconductor ideal band gap is between 1-1.4 eV¹. Silicon (Si) has emerged as a prized material for this application due to its earth abundance and ideal band gap (1.1 eV) but suffers from instability under reaction conditions. Metal-insulator-semiconductor (MIS) systems have been shown to increase stability by protecting Si from corrosion². Alternatively, nanoparticle catalysts deposited on bare Si have demonstrated reasonable stability without an additional protection layer. However, these systems remain poorly understood as the nanoparticle/semiconductor interface is complex on atomic scales, dynamic under reaction conditions, and difficult to probe directly using experimental methods.

We performed rigorous electrochemical experiments coupled with interfacial atomic characterization and computational modeling to study the interface of a functioning semiconductor (Si) and Nickel nanoparticle electrocatalysts under oxygen evolution reaction conditions. We found that an advantageous Si oxide insulator layer is formed at the nanoparticle/semiconductor interface, creating a MIS junction which significantly enhances the performance.³ Specifically, the interface impacts the performance by (1) minimizing the electron/hole recombination by influencing the charge carrier fluxes (2) increasing the barrier height of the junction, and (3) improving the stability. Additionally, we explored the critical roles of non-idealities and electrocatalyst coverage due to interfacial geometry to deconvolute photo- and catalytic effects in these systems. Each of these factors must be considered to optimize metal/semiconductor interfaces, which are which are ubiquitous in photoelectrocatalysts.

References:

[1] Seitz, L. C. et al. ChemSusChem 2014

[2] Quinn, J.; Hemmerling, J.; Linic, S. ACS Energy Lett. 2019

[3] Hemmerling,J.; Mathur,A.;Linic,S. Adv. Energy Mat 2022