Advancing Electrochemical Nitrate Reduction: Overcoming Rate-Limiting Bottlenecks with Copper/Cobalt Catalysts

Electrochemical Nitrate Reduction (NO 3 − RR) is a promising green process for producing ammonia and treating waste water. The nitrate-to-ammonia reduction involves multi-step electron/proton-transfer processes, where the NO 3 − →NO 2 − step may serve as the rate-determining step, posing a critical bottleneck for efficient NH 3 synthesis. In this paper, the emulsion hydrothermal method is used to synthesize spherical and nanoflower-like CuO/CuCo 2 O 4 catalysts with small particle stacking. Among them, CuCo 2 O 4 perfectly inherits the advantages of CuO and Co 3 O 4 , and successfully connects the two-step reactions of NO 3 − →NO 2 − and NO 2 − →NH 3 in series. The CuO formed by excess copper doping is reduced to monomeric copper during electrolysis. Cu is able to synergize with CuCo 2 O 4 to break through the bottleneck of the rate-limiting step of NO 3 − →NO 2 − , exhibiting almost the same ammonia production efficiency in both NO 3 − RR and nitrite reduction reaction (NO 2 − RR). The NH 3 yield of Cu/CuCo 2 O 4 at −0.70 V (vs RHE) reached a maximum of 24.58 mg h −1 mg cat −1 under neutral electrolyte conditions and exhibited 100% Faraday efficiency for NH 3 . Under the same conditions (where the reaction substrate is NO 2 − ), Cu/CuCo 2 O 4 reached an NH 3 yield of 24.34 mg h −1 mg cat −1 in NO 2 − RR.