Performance assessment of photoelectrochemical CO2 reduction photocathodes with patterned electrocatalysts: a multi-physical model-based approach

Abstract

Photoelectrochemical (PEC) carbon dioxide reduction (CO₂R) devices stand as a promising route for converting intermittent solar energy into storable fuels. The performance of the PEC CO₂R device requires simultaneous minimization of optical obstruction by the catalyst and maximization of the junction barrier height to facilitate charge separation. A photocathode coated with patterned electrocatalysts is a promising solution due to its flexibility in tuning optics and interfacial charge separation by size and coverage. This study reports typical p-Si photocathodes coated with patterned Ag electrocatalysts for efficient CO₂R under various catalyst sizes and coverage designs. Notably, we investigated the effects of patterned electrocatalysts on optical absorption due to obstruction and interfacial barrier height rectification due to the pinch-off effect. A coupled multi-physical model-based framework was developed to quantitatively analyze the trade-offs among optical propagation, charge transport, mass transfer, and electrochemical reactions in a PEC CO₂R photocathode. We found that an optimal catalyst coverage of 0.4 can reconcile the interplay between optical reduction and the catalyst's available surface area, leading to an achievable solar-to-carbon monoxide conversion efficiency (η_CO) of up to 9.6%, and decreasing the boundary layer thickness of the electrolyte to 25 μm can achieve a η_CO of 11.2%. This modeling framework offers valuable insights into the intricate interplay between optics, charge transport, and electrochemical behavior and provides a potent tool for guiding the engineering of high-performance CO₂R photocathodes featuring patterned electrocatalysts.