Tuning the Properties of N-Doped Biochar for Selective CO2 Electroreduction to CO

Nitrogen-doped (N-doped) carbon catalysts have been widely studied for electrochemical CO2 reduction to CO. However, the correlation between the physicochemical properties of N-doped carbon catalysts and their electrocatalytic performance for the CO2RR is still unclear. Herein, a series of N-doped biochar catalysts with different physicochemical properties were synthesized by tuning the carbonization temperature and N-doping level and used for the CO2RR to analyze the structure–performance relationship. The prepared catalysts exhibited massive differences in maximum faradaic efficiency to CO from 26.8 to 94.9% at around −0.8 to −0.9 V vs RHE. In addition, we find that simply increasing the specific surface area and N-doping level of the catalysts does not effectively improve the catalytic performance for the CO2RR. A multivariate correlation analysis reveals a negative correlation between the N-doping content and the electrochemical performance. The porous structural properties exhibit a positive correlation to the FECO but almost no correlation to jCO. Interestingly, improving the degree of graphitization, surface hydrophobicity, the abundance of defects, and optimizing the porosity of the N-doped biochar catalyst can efficiently enhance the catalytic performance for the CO2RR. We conclude that comprehensively analyzing the synergistic effect of various properties of N-doped biochar is critical to reveal structure–activity relationships.