In-situ facet transformation engineering over Co 3 O 4 for highly efficient electro-reduction of nitrate to ammonia

The catalytic performance on the various exposed facets has a huge difference for electrochemical nitrate reduction reactions (NO 3 RR). Herein, we fabricate Co 3 O 4 hexagonal nanosheets with various exposed facets, including {112}, {112}&{111}, and {111} facet. The reaction pathways of NO 3 RR on various facets are elucidated via in-situ electrochemical characterizations and density functional theory (DFT) investigations. Interestingly, as the dominated facet of Co 3 O 4 transform from {112} to {111}, the rate-determining step (RDS) changes from *NO 2 →*NO 2 H to *NO 3 H→*NO 2 , and the energy barrier also decreases to 0.48 eV. And {111} facet promotes the hydrogenation of NO x and NH x intermediates. Notably, Co 3 O 4 -{111} catalyst shows an excellent NO 3 RR performance with the NH 3 yield of 5.73 mg mg cat. -1 h -1 , which outperforms most of the reported activities.