Abstract
Ammonia is a key chemical feedstock for industry as well as future carbon‐free fuel and transportable vector for renewable energy. Photoelectrochemical (PEC) ammonia synthesis from NOx reduction reaction (NOxRR) provides not only a promising alternative to the energy‐intensive Haber–Bosch process through direct solar‐to‐ammonia conversion, but a sustainable solution for balancing the global nitrogen cycle by restoring ammonia from wastewater. In this work, selective ammonia synthesis from PEC NOxRR by a kesterite (Cu2ZnSnS4 [CZTS]) photocathode through loading defect‐engineered TiOx cocatalyst on a CdS/CZTS photocathode (TiOx/CdS/CZTS) is demonstrated. The uniquely designed photocathode enables selective ammonia production from NOxRR, yielding up to 89.1% Faradaic efficiency (FE) (0.1 V vs reversible hydrogen electrode (RHE)) with a remarkable positive onset potential (0.38 V vs RHE). By tailoring the amount of surface defective Ti3+ species, the adsorption of reactant NO3− and *NO2 intermediate is significantly promoted while the full coverage of TiOx also suppresses NO2− liberation as a by‐product, contributing to high ammonia selectivity. Further attempts on PEC ammonia synthesis from simulated wastewater show good FE of 64.9%, unveiling the potential of using the kesterite‐based photocathode for sustainably restoring ammonia from nitrate‐rich wastewater.
A rationally designed defect‐engineered TiOx cocatalyst on a kesterite‐based photocathode (CdS/Cu2ZnSnS4) for selective photoelectrochemical ammonia synthesis directly from NOx reduction is established. Synergistically outstanding light‐absorption capability, efficient photogenerated charge transfer, and selective surface catalytic reaction are successfully unified, contributing to maximum 89.1% Faradaic efficiency (at 0.1 V vs reversible hydrogen electrode) toward ammonia.