A Cu–Co₃O₄ Tandem Catalyst for Efficient Electrocatalytic Nitrate Reduction at Low Concentration

Electrocatalytic reduction of nitrate (NO3–) in waste streams to valuable ammonia under ambient conditions is a green route for nitrate remediation. However, efficient catalysts are required for this multistep proton coupled electron transfer reaction. This work presented a tandem catalyst composed of N-doped carbon layer coated Co3O4 coupled with CuOx as a highly efficient and selective electrocatalyst for NO3– reduction to NH3 at low onset potential. The tandem catalysis of NO3– → NO2– → NH3 over the two synergistical sites of in situ generated metallic Cu and Co3O4 was verified by experiments and theoretical calculations. Benefiting from the two coupled active sites, the catalyst exhibited an ammonia yield rate of 3.23 mg h–1 cm–2 and a Faradaic efficiency of 93.77% at an ultralow potential of −0.1 V versus RHE. This work opens a new avenue for the design of highly efficient tandem catalysts for electrocatalytic nitrate reduction.