Hollow carbon spheres with isolated Ni atoms on both external and internal surfaces for efficient CO2 electroreduction

Electrochemical CO2 reduction is a promising method to mitigate excessive CO2 emission and realize CO2 valorization. However, the lacking of efficient catalysts hinders the practical applications of this important process. Here, we report a new type of hollow carbon spheres containing isolated Ni atoms on both external and internal surfaces by an integrated bottom-up and top-down strategy. For such unique structure, the material exhibits good activity for electrochemical CO2 reduction with much higher current density and Faradaic efficiency for CO production than the materials with common structures (i.e., the solid spheres with Ni sites only on external surface). The enhanced activity of the material is attributed to the favored mass transport and charge transfer guaranteed by the presence of hollow structure as well as active Ni sites on both external and internal surfaces. Furthermore, we demonstrate that a secondary pyrolysis of the material can improve its activity and stability for CO2 reduction. Such treatment can increase the degree of graphitization and reaction kinetics of the material during electrocatalysis. The final material exhibits a large current density (150 mA cm−2) and a high Faradaic efficiency for CO production (94%) in a flow cell, showing good potential for practical applications. This work extends the concept of structural regulation of catalysts and provides the guidance for the design of high-performance catalysts for electrochemical CO2 reduction.