Enhancing the selectivity of C2 hydrocarbons over Fe-based catalysts by controlling nitrogen doping in electrocatalytic CO2 reduction

Abstract

Rational design of cost-effective materials as highly efficient catalysts for the electrochemical CO₂ reduction reaction (CO₂RR) to produce multi-carbon (C₂₊) hydrocarbons is highly desirable. Cu-based catalysts are widely recognized as effective for the electrosynthesis of multi-carbon products. Exploration of non-copper-based catalysts for C₂₊ products is very interesting and challenging. In this work, using ethylenediaminetetraacetic acid disodium salt and ethylenediamine as the ligands and N source, N-doped Fe₂O₃ catalysts containing FeO_1−xN_x (0.34 < x < 0.54) sites with and without a FeN₄ structure were fabricated. It was found that the catalyst without a FeN₄ structure converted CO₂ to C₂ hydrocarbons (ethane and ethylene). The faradaic efficiency (FE) of C₂ products and the current density of C₂ products reached 60.8% and 39.1 mA cm⁻², respectively, which is currently the best result for non-copper catalysts in an H-cell. However, the FE of the catalyst with a FeN₄ structure was much lower when producing C₂ products. Detailed study showed that the FeO_1−xN_x sites with suitable coordination of N with Fe was pivotal to the high FE of C₂ products. A combination of experimental and density functional theory studies indicated that the feasible coordination of N with Fe resulted in the deformation of the electron cloud around the Fe nucleus, which facilitated the charge transfer and promoted the production of C₂ products. This work provides a successful example of designing non-copper catalysts for producing C₂₊ products in the CO₂RR.