Membrane-less electrocatalytic ammonia synthesis coupled with selective methanol oxidation via porous Ni2+-doped Co3O4 nanosheets

Porous Ni 2+ -doped Co 3 O 4 nanosheets were prepared by a combination method of electrodeposition and post-calcination. The catalytic activities of the as-prepared samples for the electrocatalytic nitrate reduction to ammonia were evaluated. It was found that the Ni 2+ -doped Co 3 O 4 sample with a Ni 2+ doping content of 20 % exhibited higher catalytic activity as compared with other samples. The outstanding catalytic activity of the 20 % Ni 2+ -doped Co 3 O 4 sample could be attributed to its porous nanosheet structure with rich oxygen vacancies, which was confirmed by SEM, XPS, TEM, EPR and operando EIS analyses. The DFT results further revealed that the increased hydrogen generation energy and nitrate adsorption, and the diminished rate-determining step energy barrier ensured Ni 2+ -doped Co 3 O 4 exhibited outstanding activity for the electrocatalytic nitrate reduction. Moreover, membrane-less electrocatalytic nitrate reduction was coupled with methanol oxidation by using the oxygen vacancies-rich Co 3 O 4 electrocatalyst. The Faradic efficiencies for the electroreduction of nitrate to ammonia and the electrooxidation of methanol to formate could keep at 98 % and 99 % after multiple cycles, respectively, revealing a good stability of the reported hybrid system for the membrane-less electrocatalytic ammonia synthesis.