Binder-Focused Approaches to Improve the Stability of Cathodes for CO₂ Electroreduction

While the use of flow electrolyzers has enabled high selectivity (>80%) and activity (>200 mA cm–2) in the reduction of CO2 to value-added chemicals, the durability of these systems is still insufficient for feasibility at scale. A key component of flow electrolyzers, the gas diffusion electrode, must be hydrophobic and stable to maintain the triple phase boundary at the catalyst layer. The catalyst layer consists of an active catalyst and a binder to augment hydrophobicity and stability. Many CO2 electrolysis systems utilize Nafion as the binder, yet, these cathodes are prone to carbonate formation and are often not stable beyond 20 h. Inspired by knowledge from other electrocatalysis applications, this paper explores alternatives to Nafion in the catalyst layer as well as different methods of catalyst layer preparation. Cathodes with a poly(tetrafluoroethylene) (PTFE) binder elude carbonate formation, although their performance still decreases over time. However, the addition of PTFE to Nafion (mixed binders) limited carbonate formation. Furthermore, we found that coating cathodes with a Sustainion ionomer over layer extends lifetimes, presumably by hindering carbonate formation. The characteristics of cathodes with these binders are further explored using surface-enhanced Raman spectroscopy to help explain their effect on the electroreduction of CO2.