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.