Facile Synthesis of Iron- and Nitrogen-Doped Porous Carbon for Selective CO₂ Electroreduction

A general and simple solvent-free procedure using direct heating of a ball-milled mixture of l-histidine–Fe₂O₃–FeCl₃ is developed for the synthesis of iron- and nitrogen-doped porous carbon electrocatalysts. Through adjustment of the reactant ratios and the pyrolysis temperature, a series of electrocatalysts are easily obtained with varying activities for electrochemical CO₂ reduction reaction (CO₂RR). The electrocatalyst synthesized from l-histidine–Fe₂O₃–FeCl₃ at a 4:1:0.25 component ratio at 1000 °C exhibits the highest Faradaic efficiency of 83% for CO₂-to-CO conversion at a small overpotential (360 mV) in aqueous media. The use of a number of characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, electron microscopy, and nitrogen sorption experiments, reveals that both Fe₂O₃ and FeCl₃ contribute to the iron doping and formation of porosity. As a result, they are both crucial to produce the optimal CO₂RR electrocatalyst. Correlation of the CO₂RR activity with the carbon structure suggests that the degree of graphitization of the carbon electrocatalysts plays an important role in their CO₂RR performance.