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 Co 3 O 4 hexagonal nanosheets with exposed {112}, {112}&{111}, and {111} facets for the electrochemical nitrate reduction reactions (NO 3 RR). The reaction pathways of the NO 3 RR on Co 3 O 4 {111} and {112} facets are clarified through in situ electrochemical characterizations and theoretical analysis. As the dominating facet of Co 3 O 4 transforms from {112} to {111}, the rate-determining step changes from *NO 2 → *NO 2 H to *NO 3 H → *NO 2, 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 Co 3 O 4 -{111} catalyst shows exceptional NO 3 RR performance, achieving an NH 3 yield of 5.73 mg mg cat. –1 h –1, surpassing the majority of the reported activities.