Enhancing hydrogenation with Co/Cu foam electrode to achieve wide-range electroreduction of nitrate to ammonia

Abstract

Electroreduction of nitrate to ammonia (ERNA) is an attractive option to achieve green conversion of renewable energy sources. However, most of the current catalysts for ERNA have poor applicability over a wide potential range and display high selectivity only at fixed potentials. In this work, Co/Cu foam electrode was prepared using electrodeposition method for ERNA. The Faradaic efficiency of this electrode for ammonia production was 92.8 %-97.1 % over a wide potential range from -0.49 V to -0.79 V (ERHE), demonstrating a high degree of stability under potential fluctuation scenarios. NH3 yield rate significantly increased to a peak of 5615.1 μg·h–1·cm−2 at -0.59 V. Density functional theory calculations showed that Co nanosheets reduce the Gibbs free energy of hydrogenation pathway for nitrogen-related intermediates on copper sites. The energy barrier of *N to *NH step on Co/Cu foam is only 0.01 eV, which is 1.12 eV lower than that on Cu foam without Co. The enhanced hydrogenation process significantly reduces the energy barrier of NH3 evolution step from 1.73 eV to 0.2 eV.