Tunable Syngas Formation at Industrially Relevant Current Densities via CO2 Electroreduction and Hydrogen Evolution over Ni and Fe-derived Catalysts obtained via One-Step Pyrolysis of Polybenzoxazine Based Composites

Abstract

Simultaneous electroreduction of CO₂ and H₂ O to syngas can provide a sustainable feed for established processes used to synthesize carbon-based chemicals. The synthesis of MO_x /M-N-Cs (M = Ni, Fe) electrocatalysts reported via one-step pyrolysis that shows increased performance during syngas electrosynthesis at high current densities with adaptable H₂ /CO ratios, e.g., for the Fischer-Tropsch process. When embedded in gas diffusion electrodes (GDEs) with optimized hydrophobicity, the NiO_x /Ni-N-C catalyst produces syngas (H₂ /CO = 0.67) at -200 mA cm^-2 while for the FeO_x /Fe-N-C syngas production occurs at ≈-150 mA cm^-2 . By tuning the electrocatalyst's microenvironment, stable operation for >3 h at -200 mA cm^-2 is achieved with the NiO_x /Ni-N-C GDE. Post-electrolysis characterization revealed that the restructuring of the catalyst via reduction of NiO_x to metallic Ni NPs still enables stable operation of the electrode at -200 mA cm^-2 , when embedded in an optimized microenvironment. The ionomer and additives used in the catalyst layer are important for the observed stable operation. Operando Raman measurements confirm the presence of NiO_x during CO formation and indicate weak adsorption of CO on the catalyst surface.

Keywords: CO2 electroreduction; M-N-C; Syngas; gas diffusion electrodes; polybenzoxazine.