Photoelectrochemical Urea Synthesis from Nitrate and Carbon Dioxide on GaN Nanowires

Semiconductor photoelectrodes can be used to synthesize urea from carbon dioxide and nitrate under solar light. We find that GaN nanowires (NWs) have inherent catalytic activity for nitrate conversion to nitrite, while Ag cocatalysts loaded onto GaN NWs further promote the performance of photoelectrochemical urea synthesis. Under optimized conditions, a high faradaic efficiency of 75.6 +/- 2.6% was achieved at a potential of -0.3 vs reversible hydrogen electrode. Control experiments and theoretical calculations suggest that the high selectivity of urea originates from the facilitated C-N coupling between key intermediates of NO2 and COO- at an early stage of the reduction reaction. This work demonstrates the potential of GaN NWs with loaded Ag cocatalysts to achieve solar-powered urea synthesis with an efficiency higher than that of previously reported methods.