Polymer Binder-Regulated Microenvironments of Nickel Single-Atom Catalyst Layers for CO ₂ Reduction in Zero-Gap Membrane Electrode Assemblies

Researchers are currently conducting investigations at the membrane electrode assembly (MEA) level to obtain insights into conditions pertinent to industrially relevant CO 2 electrolyzers. However, the effects of polymer binders on nickel single-atom catalysts (Ni SACs) are insufficient, despite the outstanding performance of the catalysts. In this study, we systematically investigate the roles of different polymer binders in MEA structures during the CO 2 reduction reaction (CO 2 RR). Three representative binders─Nafion, Sustainion XA-9, and polytetrafluoroethylene (PTFE)─were used to fabricate Ni SAC electrodes, and their CO 2 RR performance was evaluated in a zero-gap cell. N20P20, a mixed-binder combining Nafion and PTFE, achieved a high current density of 245 mA cm –2 with 91.65% CO Faradaic efficiency (FE CO ) and 59.53% CO energy efficiency at 2.3 V. Furthermore, it demonstrated superior long-term stability at 100 mA cm –2 for 140 h while maintaining high FE CO values of 93%–99% compared with single binders. This enhanced CO 2 RR performance is attributed to the synergistic effects of the mixed-binder, which regulates the microenvironment of the catalyst layer. The mixed-binder exhibited high hydrophobicity, suppressed salt formation, enhanced gas transport, and improved the overall electrode functionality in MEAs.