3 Ni-N-C catalysts
Currently, according to the diversity of nickel species, the reported Ni-N-C electrode materials for ECR can be divided into three types of Ni nanoparticles (Ni NPs), Ni single atom (Ni SA), as well the co-existence of NPs and SA. The performance of some typical catalysts is listed in Table 1 .
Table 1. Summary of representative Ni-N-C electrocatalysts toward CO2 reduction.