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

Electrocatalytic nitrate reduction reaction (NORR) affords a bifunctional character in the carbon-free ammonia synthesis and remission of nitrate pollution in water. Here, we fabricated the CoO nanosheet array with cobalt vacancies on carbon cloth (v-CoO/CC) by in situ etching aluminum-doped CoO/CC, which exhibits an excellent Faradaic efficiency of 97.2% and a large NH yield as high as 517.5 μmol h cm, better than the pristine CoO/CC. Theoretical calculative results imply that the cobalt vacancies can tune the local electronic environment around Co sites of CoO, increasing the charge and reducing the electron cloud density of Co sites, which is thus conducive to adsorption of NO on Co sites for greatly enhanced nitrate reduction. Furthermore, the v-CoO (311) facet presents excellent NORR activity with a low energy barrier of about 0.63 eV on a potential-determining step, which is much smaller than pristine CoO (1.3 eV).