CuS-Decorated GaN Nanowires on Silicon Photocathodes for Converting CO2 Mixture Gas to HCOOH.

Hybrid materials consisting of semiconductors and cocatalysts have been widely used for photoelectrochemical (PEC) conversion of CO2 gas to value-added chemicals such as formic acid (HCOOH). To date, however, the rational design of catalytic architecture enabling the reduction of real CO2 gas to chemical has remained a grand challenge. Here, we report a unique photocathode consisting of CuS-decorated GaN nanowires (NWs) integrated on planar silicon (Si) for the conversion of H2S-containing CO2 mixture gas to HCOOH. It was discovered that H2S impurity in the modeled industrial CO2 gas could lead to the spontaneous transformation of Cu to CuS NPs, which resulted in significantly increased faradaic efficiency of HCOOH generation. The CuS/GaN/Si photocathode exhibited superior faradaic efficiency of HCOOH = 70.2% and partial current density = 7.07 mA/cm2 at -1.0 VRHE under AM1.5G 1 sun illumination. To our knowledge, this is the first demonstration that impurity mixed in the CO2 gas can enhance, rather than degrade, the performance of the PEC CO2 reduction reaction.