Utilizing spatial confinement effect of N atoms in micropores of coal-based metal-free material for efficiently electrochemical reduction of carbon dioxide

Abstract

Nitrogen-doped carbon metal-free materials are widely used in electrochemical reduction of carbon dioxide due to high earth abundance, structural tunability, and excellent catalytic performance. Although specific surface area and nitrogen content are considered as the two most important factors in affecting the electrochemical performance of nitrogen-doped porous carbon catalysts, it does not always mean that the larger they are, the better the catalytic performance is. Tailoring pore structures and maximizing the catalytic effect of a limited number of nitrogen atoms are the keys to the improvement in the electrochemical performance. Herein, we develop a solvent evaporation induced self-assembly method to synthesize a coal-based nitrogen-doped porous carbon as an efficient metal-free electrocatalyst for CO2 electroreduction. Under the effect of pore shrinkage induced by high temperatures, nitrogen atoms derived from dicyandiamide are inserted into the carbon matrix of coal, and confined in the micropores produced by KOH activation. The stable nitrogen atoms restricted in the micropores can efficiently convert CO2 into CO due to the spatial confinement effect. The electrocatalyst shows a negligible onset overpotential (–0.16 V) for CO product, a maximum CO Faradaic efficiency of 95 % and a large CO production rate of 36.1 μmol h–1 cm–2 at a low potential of –0.67 V versus the reversible hydrogen electrode (vs. RHE). Moreover, its current density can remain stable after 10 h of potentiostatic electrolysis. This work not only provides a promising earth-abundant electrocatalyst for CO2 electroreduction, but would open up a new avenue for improving the electrochemical performance by coordinating the pore structures and active components.