High-Efficiency Electrochemical Nitrate Reduction to Ammonia on a Co3O4 Nanoarray Catalyst with Cobalt Vacancies

Electrocatalytic nitrate reduction reaction (NO3RR) affords a bifunctional character in the carbon-free ammonia synthesis and remission of nitrate pollution in water. Here, we fabricated the Co3O4 nanosheet array with cobalt vacancies on carbon cloth (vCo-Co3O4/CC) by in situ etching aluminum-doped Co3O4/CC, which exhibits an excellent Faradaic efficiency of 97.2% and a large NH3 yield as high as 517.5 μmol h-1 cm-2, better than the pristine Co3O4/CC. Theoretical calculative results imply that the cobalt vacancies can tune the local electronic environment around Co sites of Co3O4, increasing the charge and reducing the electron cloud density of Co sites, which is thus conducive to adsorption of NO3- on Co sites for greatly enhanced nitrate reduction. Furthermore, the vCo-Co3O4 (311) facet presents excellent NO3RR activity with a low energy barrier of about 0.63 eV on a potential-determining step, which is much smaller than pristine Co3O4 (1.3 eV).