Electrochemical conversion of nitrate to NH3 not only eliminates nitrate pollution in the environment, but also produces highly valuable NH3. Herein, Cu-doped Co3O4 with abundant oxygen vacancies (Cu-Co3O4-x) was prepared on carbon cloth. The as-fabricated Cu-Co3O4-x can selectively reduce nitrate to NH3 with high Faraday efficiencies (around 90%) and a large NH3 yield of 0.83 mmol h-1 cm-2 in a neutral electrolyte.