Understanding the key role of vanadium in p-type BiVO4 for photoelectrochemical N2 fixation

The photoelectrochemical N2 reduction reaction (PEC NRR) is extremely charming to the synthetic ammonia (NH3), for its mild operating conditions and low carbon footprint. Taking account of the strong chemical inertness of N2 and competitive hydrogen evolution reaction, it is necessary to explore a robust and stable photoelectrocatalyst. Herein, a robust p-type BiVO4 (p-BiVO4) photocathode is firstly reported for NRR under ambient conditions. Interestingly, V sites are proved as the mainly ideal active center for N2 adsorption/activation based on the density functional theory (DFT) calculations. The ammonia evolution rate (VNH3:11.6 ? 10-8 mol h-1 cm- 2) and Faradaic efficiency (16.2%) were obtained at -0.1 V vs. RHE in 0.1 M Li2SO4 solution, outperforming most of the photoelectrocatalysts reported thus far. Moreover, the 1H nuclear magnetic resonance result confirmed that the source of N was completely from the feeding N2 gas. This work provided a new opportunity to tap the V-based photocathode in the field of PEC NRR.