In Situ Facet Transformation Engineering over Co3O4 for Highly Efficient Electroreduction of Nitrate to Ammonia

Various exposed facets can cause a huge difference in the catalytic activity. Here we prepared Co₃O₄ hexagonal nanosheets with exposed {112}, {112}&{111}, and {111} facets for the electrochemical nitrate reduction reactions (NO₃RR). The reaction pathways of the NO₃RR on Co₃O₄ {111} and {112} facets are clarified through in situ electrochemical characterizations and theoretical analysis. As the dominating facet of Co₃O₄ transforms from {112} to {111}, the rate-determining step changes from *NO₂ → *NO₂H to *NO₃H → *NO₂, with the energy barrier decreasing to 0.48 eV. And the {111} facet promotes the hydrogenation of NO_x and NH_x intermediates. Notably, the Co₃O₄-{111} catalyst shows exceptional NO₃RR performance, achieving an NH₃ yield of 5.73 mg mg_cat.^–1 h^–1, surpassing the majority of the reported activities.