Solar-Driven Ammonia Production via Acidic Nitrate Reduction Coupled with Glucose Oxidation on a GeSe Photocathode

Abstract Photoelectrochemical nitrate reduction (PEC NO3RR) enables nitrate remediation and ammonia synthesis under light irradiation. However, most reported systems operate under neutral or alkaline conditions to suppress the competing hydrogen evolution reaction (HER), which compromises product separation and overall energy efficiency. Although acidic NO3RR is intrinsically favorable for stabilizing the ammonia product in the nonvolatile NH4+ form and suppressing ammonia loss, it remains fundamentally challenged by severe proton competition and HER dominance. Here, acidic NO3RR is intentionally established as a stringent design target rather than merely an operational condition. An electronically reconstructed CuNi cocatalyst is electrodeposited onto a TiO2-protected GeSe photocathode to steer the reaction selectively toward NO3RR under acidic conditions (10 mM H2SO4, pH ≈ 1.8). Ni-induced electronic modulation of Cu active sites positively shifts the onset potential, suppresses HER, and enhances nitrate-to-ammonia selectivity, achieving a Faradaic efficiency of 82.07% and an ammonia production rate of 14.32 μmol h–1 cm–2 at –0.1 V vs. RHE. To translate this selectivity to the system level, a solar-driven tandem PEC device couples the acidic NO3RR photocathode with an alkaline glucose oxidation anode via a bipolar membrane, enabling solar-driven ammonia synthesis.