Improving the performance of CuO in electrocatalytic nitrite reduction to ammonia (NIRA) is the priority for designing efficient NIRA electrocatalysts. The electrocatalytic activity of CuO was enhanced by growing Co 3 O 4 nanospheres on it. By comparing Co 3 O 4 @CuO with the mechanically mixed CuO and Co 3 O 4 on a rotating ring-disk electrode, we discovered that the enhancement was attributed to a dual-site catalytic pathway.