High-Efficiency Electrochemical Nitrate Reduction to Ammonia on a Co 3 O 4 Nanoarray Catalyst with Cobalt Vacancies.

Electrocatalytic nitrate reduction reaction (NO 3 RR) affords a bifunctional character in the carbon-free ammonia synthesis and remission of nitrate pollution in water. Here, we fabricated the Co 3 O 4 nanosheet array with cobalt vacancies on carbon cloth (v Co -Co 3 O 4 /CC) by in situ etching aluminum-doped Co 3 O 4 /CC, which exhibits an excellent Faradaic efficiency of 97.2% and a large NH 3 yield as high as 517.5 μmol h -1 cm -2 , better than the pristine Co 3 O 4 /CC. Theoretical calculative results imply that the cobalt vacancies can tune the local electronic environment around Co sites of Co 3 O 4 , increasing the charge and reducing the electron cloud density of Co sites, which is thus conducive to adsorption of NO 3 - on Co sites for greatly enhanced nitrate reduction. Furthermore, the v Co -Co 3 O 4 (311) facet presents excellent NO 3 RR activity with a low energy barrier of about 0.63 eV on a potential-determining step, which is much smaller than pristine Co 3 O 4 (1.3 eV).