Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.

Electrochemical reduction of carbon dioxide (CO) to value-added carbon products is a promising approach to reduce CO levels and mitigate the energy crisis. However, poor product selectivity is still a major obstacle to the development of CO reduction. Here we demonstrate exclusive Ni-N sites through a topo-chemical transformation strategy, bringing unprecedentedly high activity and selectivity for CO reduction. Topo-chemical transformation by carbon layer coating successfully ensures preservation of the Ni-N structure to a maximum extent and avoids the agglomeration of Ni atoms to particles, providing abundant active sites for the catalytic reaction. The Ni-N structure exhibits excellent activity for electrochemical reduction of CO with particularly high selectivity, achieving high faradaic efficiency over 90% for CO in the potential range from -0.5 to -0.9 V and gives a maximum faradaic efficiency of 99% at -0.81 V with a current density of 28.6 mA cm. We anticipate exclusive catalytic sites will shed new light on the design of high-efficiency electrocatalysts for CO reduction.