Role of Binders on the Performance of SnO2-Based Gas Diffusion Electrodes for Electrochemical CO2 Reduction to Formic Acid

Abstract

Binders play a key role in fabricating efficient gas diffusion electrodes (GDEs), where catalyst layers are sprayed onto hydrophobic gas diffusion layers (GDLs). In a previous work, we investigated the use of a dry-pressed single-layer GDE composed of Polytetrafluoroethylene (PTFE) and SnO₂ supported on carbon black for CO₂ reduction to formic acid (FA) with high Faradaic efficiencies (FEs) of 80%–90% at current densities of 200 mA cm⁻². However, dry-pressed single-layer electrodes suffer from progressive electrowetting and flooding during the reduction. To address these limitations, we transferred this approach to catalyst-coated hydrophobic GDLs, which require suitable binders/ionomers. We examined Nafion, Sustainion, PTFE, and an imidazolium-based polymeric ionic liquid (PIL), specifically poly(1-vinyl-3-dodecylimidazolium bromide) (PIL1-d), which was anticipated to provide enhanced performance. The results demonstrated that incorporation of the PIL significantly improved electrode performance for electrochemical CO₂ reduction (eCO₂RR). This improvement was most pronounced for unsupported SnO₂ and for larger SnO₂ nanoparticles (>100 nm). Dynamic light scattering measurements indicated that the PIL already stabilized the SnO₂ dispersion in the catalyst ink during spray coating through interactions with the oxide nanoparticles. An ionomer loading of 5 wt.% PIL in the catalyst layer was optimal, yielding a maximum FE of 92% FA at 200 mA cm⁻².