Direct Solar Power-Driven Durable Ammonia Electrosynthesis From Nitrate Under Fluctuating Voltage Conditions.

Nitrate electroreduction (NO3RR) powered by solar energy offers a sustainable platform for ammonia (NH3) synthesis. However, the variability of solar energy, leads to fluctuating voltages and frequent start-stop of the system, presents significant challenges for catalysts in maintaining high efficiency and stability. In this work, the symmetry of charge distribution across distinct Cu facets was manipulated, achieving high NH3 faradaic efficiencies (FEs) above 90% across a wide potential window of 800 mV in an H-cell condition. Moreover, the membrane electrode assembly directly powered by a commercial silicon-based solar panel operated for 8 days at a current density of 300 mA cm-2 under fluctuating natural solar conditions (1.6 V-2.9 V), maintaining high NH3 FE between 81%-94%. Mechanistic studies reveal that incorporating isolated Sn on the Cu (111) facet triggers a highly asymmetric charge distribution, which not only induces a weak field-dipole interaction between NO3 - and SnCu111 surface but also promotes water dissociation kinetics and key intermediate hydrogenation, maximizing the free energy differentiation from the competing HER. This work provides a blueprint for practical catalyst design, offering a proof of concept for direct solar power-driven NH3 electrosynthesis.