The electrochemical reduction of CO₂ (eCO₂RR) is a promising eco-friendly alternative to fossil-fuel-based processes used for the production of chemicals. Currently, the conversion of CO₂ to CO is a more industrially appealing process than the eCO₂RR to multicarbon products, as it requires lower energy consumption and presents high product selectivity.[1] Also, the concomitant hydrogen evolution reaction (HER) occurring at the same potential window is not a serious setback in this case since the mixture of H₂ and CO (known as syngas) is a valuable product, which can be directly utilized in established industrial processes such as the Fischer-Tropsch to produce energy-dense chemicals. [2] Silver- and gold-based materials are hitherto considered the state-of-the-art of CO-forming catalysts but their cost and scarcity impede their industrial application. In this regard, composite materials based on transition metal oxide nanoparticles supported on metal-nitrogen-doped carbons (MOx/M-N-C) have been recently explored as inexpensive and efficient electrocatalysts for the eCO₂RR-to-syngas process. Several works in literature have reported the synergistic effect between MOx nanoparticles and M-N-Cs, which results in an enhanced eCO₂RR electrocatalysis with respect to each one of the materials separately. [3,4] The research of MOx/M-N-Cs for eCO₂RR is still in its infancy and, therefore, further development is needed to reach the application of these materials in industrial CO₂ electrolyzers.

In this contribution, we introduce several approaches for the preparation of effective MOx/M-N-C-based GDEs. On the one hand, we demonstrate the potential of polybenzoxazine (pBO) resins to synthesize active MOx/M-N-Cs materials, most likely due to the unique properties of the resins. In doing so, we report that gas diffusion electrodes (GDEs) prepared with pBO-derived MOx/M-N-Cs (M= Ni, Fe) exhibited higher activity and CO selectivity in 1 M KOH than the pBO-free ones. On the other hand, we explore the optimization of GDEs in terms of eCO₂RR electrocatalysis by the addition of binders into the catalyst layer (CL). The addition of PTFE to the catalyst layer was proved to favor the production of CO over HER, disclosing the essential role of hydrophobicity in the CL for eCO₂RR. The GDE fabricated with pBO-derived NiOx/Ni-N-C and PTFE displayed suitable syngas production at industrial current densities, with an H₂/CO ratio of ~0.9 at -200 mA cm^-2 and ~-0.6 V vs RHE. Finally, we also conclude that the combination of PTFE and Sustainion in the CL has a synergistic effect that confers stability to the pBO-derived NiOx/Ni-N-C-based GDE while keeping intact the hydrophobicity, activity, and CO selectivity, with respect to the GDE with only PTFE. The results of this work provide relevant insight into both the development of MOx/M-N-C materials as syngas-forming electrocatalysts and the engineering of eCO₂RR-to-CO GDEs aiming for the industrial implementation.