Perovskite oxide LaMO3-δ (M = Fe, Co, Ni and Cu) cathode for efficient electroreduction of nitrate

•Perovskite oxide LaMO3-δ cathodes were applied for NO3–-N electroreduction.•La2CuO4 exhibited best catalytic performance as its super electrochemical property.•The selectivity of NH4+-N and N2 were 82.4 ± 2.2% and 9.4 ± 2.4%, respectively.•Both electron- and H*-mediated pathway occurred for NO3–-N electroreduction.•Oxygen vacancies and redox cycle of Cu(I)-Cu(II)-Cu(I) worked for NO3–-N reduction.