Structural rule of N-coordinated single-atom catalysts for electrochemical CO2 reduction

Abstract

Metal single-atom catalysts (SACs) on nitrogen-doped carbons exhibit an attractive prospect in catalysis. However, how to quickly collocate various metal centers with diverse N-coordination topological structures to maximize the catalytic performance is still vague and always challenging in practice, and cannot be easily realized using the traditional descriptors. Herein, a new descriptor, i.e., the cohesive energy (E_c) of a metal that corresponds to the intrinsic property of the metal center, is put forward, which facilitates assessing the catalytic performance of SACs expediently. Taking the electrochemical CO₂ reduction to CO (CO₂RR) on transition metal (TM) SACs anchored on different N-doped graphenes (GN_x, local N-coordination x = 2, 3 and 4) as an example, we reveal the general rule of “TM-N_x” combinations in SACs for the CO₂RR from the obtained activity trends in terms of E_c, which interestingly shows that GN₂ and GN₄ generally provide a superior structural platform for a majority of metal centers and exhibit better catalytic activities than GN₃. In particular, SACs anchored by the least N-coordinated GN₂ can hold an outstanding catalytic activity for the most common metal centers and simultaneously keep a high selectivity of the CO₂RR. Accordingly, we proposed that Co (or Ni, Fe, Cr, Mn, Cu, Pd) anchored on GN₂ could be potential SACs for the CO₂RR through high-throughput calculations, where the high catalytic efficiencies of some candidates such as GN₂-anchored Ni (or Co, Fe and Cu) SACs for the CO₂RR have been demonstrated in the experiments. This work provides a significant insight into the structural origin of different N_x-coordinations modulating the catalytic performances of single-atom metal centers, and we believe that the obtained design rule could pave the way to rapidly designing efficient TM SACs for the CO₂RR and other reactions.