Role of Binders on the Performance of SnO 2 ‐Based Gas Diffusion Electrodes for Electrochemical CO 2 Reduction to Formic Acid

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 SnO 2 supported on carbon black for CO 2 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 CO 2 reduction (eCO 2 RR). This improvement was most pronounced for unsupported SnO 2 and for larger SnO 2 nanoparticles (>100 nm). Dynamic light scattering measurements indicated that the PIL already stabilized the SnO 2 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 .