Tailoring the hierarchical porous nitrogen-doped carbon structures loaded single-atomic Ni catalyst for promoting CO2 electrochemical reduction at low CO2 concentration

Although direct reduction of exhaust gases into CO can enable significant economic benefits, the poor activity of CO2 reduction reaction (CO2RR) at low CO2 concentration seriously impedes its application. Herein, a series of Ni single atom sites/nitrogen doped porous carbon materials with different pore sizes were prepared to explore the effect of porosity on the local CO2 concentration in the electrocatalytic process of CO2RR. The results of characterization and experiments demonstrate that surface micropores generated by KOH activation are the key to creating the high local concentration of CO2 around active sites, helping facilitate the reaction kinetics at low CO2 concentration. Therefore, when the reaction is conducted under 20% diluted CO2 condition, the optimal activated macroporous sample exhibits up to nearly 1.3-fold higher faradaic efficiency of CO (FE(CO)) and a 1.7-fold higher of partial current density of CO (jCO) than similar samples without activation. These results offer new insight for designing efficient electrocatalysts for low-concentration CO2 reduction by constructing advanced porous structures.