Nitrate-to-ammonia conversion with a plasmonic antenna–reactor catalyst†

Abstract

Electrochemical conversion of nitrate to ammonia is an appealing route to efficiently synthesize ammonia under ambient conditions while reducing environmental nitrate pollutants. However, this approach is obstructed by the limited yield and selectivity of ammonia because the electrochemical nitrate-to-ammonia conversion involves multi-electron/proton transfer and faces competition from the hydrogen evolution reaction. Here, we demonstrate a plasmon-assisted strategy to improve the performance of nitrate-to-ammonia electrochemical conversion by constructing plasmonic antenna–reactor catalysts, where Au and Pd nanoparticles/hydrogen substituted graphdiyne (Pd/HsGDY) work as the light antenna and reaction site, respectively. Plasmonic excitation of Au–Pd/HsGDY catalysts can remarkably accelerate the nitrate reduction, with the yield rate, selectivity, and Faradaic efficiency of ammonia respectively increased by 14.3, 2.1, and 1.8 times under optimal conditions. Mechanistic investigations unveil that Au plasmon-induced hot electrons facilitate nitrate-to-ammonia reaction by regulating the adsorption of reaction intermediates on Pd/HsGDY, wherein the rate-determining step was shifted from nitrate adsorption to *NH protonation and the overall apparent activation was reduced. Moreover, hot electrons suppress the competing hydrogen evolution by enlarging the Gibbs free energy of hydrogen formation. These results open a way to develop desirable catalysts for producing value-added ammonia from environmentally hazardous nitrate by a synergistic combination of electricity and light.