Engineering a Kesterite‐Based Photocathode for Photoelectrochemical Ammonia Synthesis from NO_x Reduction

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.

Designing idealised devices for bias-free solar water splitting

“…Finally, a monolithic PEC tandem structure embedded within a membrane can enable the energy-dense storage of solar energy directly as a chemical fuel. Given the similarities in the mechanism, including the light absorption and ion/electron transport, the success of the ideal device design for solar hydrogen production can be expanded toward other types of “artificial leaf,” such as producing chemical fuels from solar energy via CO 2 reduction, 46 PEC ammonia synthesis, 47 and biomass valorisation. 48…”

Efficient ammonia photosynthesis from nitrate by graphene/Si Schottky junction integrated with Ni–Fe LDH catalyst

“…Although the promising progress of the EC NTRR based on the abovementioned catalysts has been demonstrated, there are only a few reports on the synthesis of ammonia from nitrate based on the PEC approach, such as using Au-decorated ordered silicon nanowires 15 and TiO x /CdS/Cu 2 ZnSnS 4 (CZTS) photocathodes. 16 However, their current densities and NH 3 yield rates haven't caught up with the reported values by EC methods. There is still a lot of room for further development.…”

Recent progress in ammonia synthesis based on photoelectrocatalysis

“…3). 58 Photocatalytic N 2 fixation is completed under the action of chemical bias induced by pH. Oshikiri's group was committed to research chemical bias-driven PEC N 2 fixation over Au/SrTiO 3 to improve NH 3 selectivity.…”