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