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

Abstract

Electrochemical Nitrate Reduction (NO3−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 NO3−→NO2− step may serve as the rate‐determining step, posing a critical bottleneck for efficient NH3 synthesis. In this paper, the emulsion hydrothermal method is used to synthesize spherical and nanoflower‐like CuO/CuCo2O4 catalysts with small particle stacking. Among them, CuCo2O4 perfectly inherits the advantages of CuO and Co3O4, and successfully connects the two‐step reactions of NO3−→NO2− and NO2−→NH3 in series. The CuO formed by excess copper doping is reduced to monomeric copper during electrolysis. Cu is able to synergize with CuCo2O4 to break through the bottleneck of the rate‐limiting step of NO3−→NO2−, exhibiting almost the same ammonia production efficiency in both NO3−RR and nitrite reduction reaction (NO2−RR). The NH3 yield of Cu/CuCo2O4 at −0.70 V (vs RHE) reached a maximum of 24.58 mg h−1 mgcat−1 under neutral electrolyte conditions and exhibited 100% Faraday efficiency for NH3. Under the same conditions (where the reaction substrate is NO2−), Cu/CuCo2O4 reached an NH3 yield of 24.34 mg h−1 mgcat−1 in NO2−RR.