Isolated single-atom platinum (Pt) embedded in the sub-nanoporosity of 2D g-C3 N4 as a new form of co-catalyst is reported. The highly stable single-atom co-catalyst maximizes the atom efficiency and alters the surface trap states of g-C3 N4 , leading to significantly enhanced photocatalytic H2 evolution activity, 8.6 times higher than that of Pt nanoparticles and up to 50 times that for bare g-C3 N4 .

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.