Free-Standing Porous Composite Polyelectrolyte for Efficient CO ₂ Electrolysis

Conventional CO 2 reduction electrolyzers typically employ liquid-based electrolytes, resulting in expensive postsynthesis purification steps to recover the product. Solid-state reactors address product separation challenges, but current particle-based solid electrolytes face issues with long-term stability, scalability, reusability, and challenging cell assembly. Here, we report a free-standing and highly conductive porous composite polyelectrolyte for CO 2 electrolysis produced by combining ion-exchange particles with sulfonated polysulfone as a binder. The resulting composite polyelectrolyte achieves an ionic conductivity as high as 10.4 mS cm –1 while maintaining excellent mechanical properties. When used in a CO 2 electrolyzer, formate selectivity consistently exceeded 90% at current densities up to 200 mA cm –2, and the electrolyzer maintained a cell potential close to 3.5 V over 220 h at 100 mA cm –2 . Technoeconomic and life cycle assessments further highlight the scalability and sustainability of this approach, advancing the development of large-scale, energy-efficient solid-state CO 2 electrolyzers.