Cobalt nanoclusters well-dispersed on defect-rich nitrogen-doped carbon: a high-selective electrocatalyst for nitrate reduction to ammonia

The electrocatalytic reduction of nitrate to ammonia represents a promising process with significant potential applications. Its importance extends beyond closing the nitrogen cycle to establishing an efficient “ammonia energy storage” system. Catalysts with enhanced selectivity, stability, and mass-specific catalytic activity are essential for these processes. In this study, we have successfully synthesized a scalable catalytic material consisting of cobalt clusters supported on nitrogen-doped carbon (Co/NC) via a ball milling method. The Co/NC catalyst exhibits remarkable catalytic activity and selectivity for ammonia synthesis that at an applied potential of −0.7 V vs. RHE (RHE: reversible hydrogen electrode), the Faradaic efficiency for NH 3 generation exceeds 96 %, with a maximum NH 3 yield of 2715.32 mmol h −1 g cat −1 . In situ Raman investigations reveal that metallic cobalt, rather than cobalt oxides or nitrides, constitutes the primary active site in the Co/NC catalyst during the reaction. The ball milling process introduces additional defect sites, which are proposed to prevent the Co nanoclusters from agglomerating, thus exposing more reactive sites and enhancing the catalyst's electrocatalytic activity for nitrate reduction (NO 3 RR).