A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.

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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.