Promoting effects of potassium on ammonia production from electrochemical nitrate reduction over nano-crystal nickel

Abstract

Potassium ions (K⁺) in electrolyte can stimulate the electrochemical nitrate reduction to ammonia (NRA) while the mechanism behind this improvement is still underexamined. Here, the effects of K⁺ on regulating the NRA over a nano-crystal nickel catalyst are thoroughly investigated. The catalyst exhibits excellent NRA performance with an NH₃ yield rate of 167.98 ± 1.41 μmol h⁻¹ cm⁻², selectivity of 95.56%, and faradaic efficiency of 89.23%. The NH₃ yield rate can further increase to 214.10 ± 4.22 μmol h⁻¹ cm⁻² with 50% K⁺. In situ Raman and density functional theory (DFT) revealed that K⁺ facilitates NO₃⁻ adsorption but hinders sulfate (SO₄²⁻) adsorption on the catalyst. In addition, the efficiency of active hydrogen (*H) generation is elevated, which facilitates the NRA pathway with *NH as the intermediate over the catalyst. The present result is beneficial for gaining a mechanistic understanding of the promoting effects of ions on NRA and developing electrolyte engineering to improve the performance of NH₃ production.