Designing effective Si/Ag interface via controlled chemical etching for photoelectrochemical CO2 reduction

Photoelectrochemical reduction of CO2 to value-added chemicals represents a promising approach for artificial photosynthesis, but often suffers from limited selectivity and stability. Improving its performance would require proper design of semiconductor and cocatalyst materials, along with a strategy for effective coupling. Here, we report that controlled chemical etching of Si wafer by Ag+ ions yields effective semiconductor/co-catalyst interface for photoelectrochemical CO2 reduction. Resultant photocathodes exhibit large photocurrent density (similar to 10 mA cm(-2) under 0.5 sun), great CO faradaic efficiency (90% at -0.5 V versus reversible hydrogen electrode), and impressive operational stability (little activity or selectivity loss within 8 h). Further enhancement (by similar to 20%) of photocurrent density is achieved by combining photolithography patterning with chemical etching. Our study applies long-known chemistry as an unexpected solution and may provide a new strategy for highperformance photoelectrochemical CO2 reduction.