Co-N bond promotes the H* pathway for the electrocatalytic reduction of nitrate (NO3RR) to ammonia

Electrocatalytic reduction of nitrate to ammonia is an effective method for the recycling of NO3--N in the field of nitrate polluted water treatment. In this work, Co-N-C was prepared in this work by pyrolysis of Co-based metal organic framework at 700 °C and it can achieve 100 % selectivity to ammonia under the optimum experiment conditions. Impressively, no harmful nitrite generated in the reduction process because the reduction rate constant of Co-N-C for NO2--N is higher than that of NO3--N. Experiment results show that the chemical adsorption rather than electrostatic adsorption dominated among Co-N-C and free NO3-, which is significant for the subsequent electronic reduction process. Mechanism analysis indicated the active hydrogen (H*) reduction mechanism is predominate for Co-N-C but the direct electron mechanism is predominate for Co-C during the reduction from NO3- to NO2-. While for Co-N-C and Co-C, the subsequent reduction of NO2- to NH4+ was conducted by the direct electron mechanism. The present work not only explores high performance for the selectively electrocatalytic reduction from nitrate to ammonia but also promote new inspiration for the preparation of other Co-based functional materials for reducing the production of nitrite.