Wide-pH-range adaptable ammonia electrosynthesis from nitrate on Cu-Pd interfaces.

Ammonia production via electrochemical nitrate reduction is essential for environmental protection and the emerging hydrogen economy. Complex nitrate wastewater with a wide pH range calls for flexible catalysts with high selectivity. A high Faradaic efficiency (FE) of NH₃ cannot be obtained under strong acid or alkaline conditions due to the uncontrollable adsorption energy and coverage of hydrogen species (H*) on active sites. This article describes the design and fabrication of a copper-palladium (Cu-Pd) alloy nanocrystal catalyst that inhibits H₂ and nitrite generation in electrolytes with different nitrate concentrations and varied pH. The interfacial sites of Cu-Pd alloys could enhance the adsorption energy and coverage of H* while increasing the reaction rate constant of NO₂*-to-NO*, which achieves a rapid conversion of NO₂* along with a decreased FE of NO₂⁻. Under ambient conditions, optimal FE(NH₃) is close to 100% at a wide pH range, with the solar-to-chemical conversion efficiency approaching 4.29%. The combination of thermodynamics and kinetics investigations would offer new insights into the reduction mechanism of NO₂* for further development of nitrate reduction. [ABSTRACT FROM AUTHOR]