Regenerative Electrocatalytic Redox Cycle of Copper Sulfide for Sustainable NH3 Production under Ambient Conditions

Electrochemical nitrogen reduction reaction (NRR) is a promising method for energy-efficient and low-emission NH3 production. Herein, we report electrochemical NH3 production using a copper sulfide-based electrocatalyst. A solid-state synthesis is employed to prepare the Cu9S5 catalyst for artificial N2 fixation in a neutral aqueous electrolyte. Despite an excellent NRR activity of 10.8 ± 0.4 μg/hcm2 at −0.5 VRHE, however, the catalyst itself is reductively degraded during the NRR. To achieve continuous electrochemical NH3 production, a regenerative electrochemical sulfur cycle is introduced that revives the Cu9S5 crystal structure and NRR activities. The electrochemical regeneration process reconstructing the metal–sulfur bond in between sequential NH3 production processes restores the NRR activity. Importantly, catalytic surfaces providing a labile sulfhydryl functional group attached to the N2-adsorption metal center are required to achieve efficient NRR activity under ambient conditions.