The structure–activity correlation of single-site Ni catalysts dispersed onto porous carbon spheres toward electrochemical CO2 reduction

Single-site metal catalysts (SSMCs) with high activity and stability have been widely applied as electrocatalysts for electrochemical CO2 reduction reaction (CO2RR) process. However, it remains challenging for precise controlling the nanoarchitectures and atomic metal sites of SSMCs to investigate their corresponding structural and related catalytic properties toward CO2RR. In this work, four categories of Ni based SSMCs with different nanoarchitectures were successfully synthesized, including Ni-N doped solid carbon spheres with micropore (Ni-N/C-S-Micro), Ni-N doped hollow carbon spheres with micropore (Ni-N/C–H-Micro), Ni-N doped hollow carbon spheres with mesopore (Ni-N/C–H-Meso), and Ni-N doped hollow carbon spheres with micropore and mesopore (Ni-N/C–H-Micro/Meso). Ni-N/C-S-Micro and Ni-N/C–H-Micro were favorable for the generation of atomic Ni sites in SSMCs, resulting in higher loading amount of Ni, while Ni-N/C–H-Meso with open structure leads to the aggregation of Ni species during pyrolysis. In comparison with Ni-N/C-S-Micro, carbon spheres with hollow and mesoporous structures can enhance the diffusion of CO2 and improve the catalytic activity of per Ni site toward CO2RR process. Thus, Ni-N/C–H-Meso shows the highest turnover frequencies (TOF) value for CO2RR to CO. This study provides a SSMCs design protocol for investigation the SSMCs correlation of structure and properties toward electrochemical conversions.