Continuous Flow Photoelectrochemical Reactor with Gas Permeable Photocathode: Enhanced Photocurrent and Partial Current Density for CO 2 Reduction

Abstract Photoelectrochemical (PEC) CO 2 reduction using a photocathode is an attractive method for making valuable chemical products due to its simplicity and lower overpotential requirements. However, previous PEC processes have often been diffusion‐limited leading to low production rates of the CO 2 reduction reaction, due to inefficient gas diffusion through the liquid electrolyte to the catalyst surface, particularly at high current densities. In this study, a gas‐permeable photocathode in a continuous flow PEC reactor is incorporated, which facilitates the direct supply of CO 2 gas to the photocathode‐electrolyte interface, unlike dark reaction‐based flow reactors. This concept is demonstrated using Ag‐TiO 2 on carbon paper, illuminated through a quartz window and flowing liquid electrolyte. CO 2 supply is managed via pressure and flow control on the non‐illuminated side of the carbon paper. The photocurrent density is significantly influenced by the flow rates and pressure of CO 2 gas, and the electrolyte flow rates. Compared to the traditional H‐cell, the continuous PEC flow reactor achieves ≈10‐fold increase in CO faradaic efficiency, 30‐fold increase in production rate and 16‐fold increase in stability without catalyst modifications. This work provides essential insights into the design and application of continuous gas‐liquid flow PEC reactor systems, highlighting their potential for other PEC reactions.