Jun-Jie Shi, Xin-Ming Hu , Monica Rohde Madsen, Paolo Lamagni, Emil Tveden Bjerglund, Steen Uttrup Pedersen, Troels Skrydstrup, and Kim Daasbjerg
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.