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 NOx and NHx intermediates. Notably, the Co3O4-{111} catalyst shows exceptional NO3RR performance, achieving an NH3 yield of 5.73 mg mgcat.–1 h–1, surpassing the majority of the reported activities.