Thermal Induction-Driven Optimization of Nafion Structures for Enhanced Triple Phase Interfaces in CO2 Reduction Reaction

Abstract

Cobalt phthalocyanine (CoPc) is a widely utilized molecular catalyst for converting CO₂ to CO in the CO₂ reduction reaction (CO₂RR). However, achieving high selectivity at high current densities remains significant challenges, such as mass transport and interfacial microenvironment. In this study, CoPc-based gas diffusion electrodes with thermal induction treatments are investigated to reach high performance and stability. At a current density of 300 mA/cm², the cell voltage is 2.9 V, with a CO selectivity of 95%, representing nearly a 5-fold improvement compared to the pristine electrode. Additionally, at a current density of 150 mA/cm², the electrode demonstrates long-term durability, maintaining stable performance for 45 h. The structural changes and underlying mechanisms of the Nafion ionomer induced by thermal treatment are investigated via microscopic characterization and molecular dynamics simulations. It is revealed that thermal induction at temperatures slightly above Nafion’s glass transition point could enhance ionomer phase separation, resulting in the formation of additional hydrophilic–hydrophobic interfaces that facilitate CO₂ mass transport. Moreover, the rearrangement of Nafion chains during thermal induction produces a denser structure that restricts OH^– release. This localized retention of OH^– raises the pH near the catalyst, thereby improving the efficiency of the CO₂RR. This work offers valuable insights into the design of CoPc-based gas diffusion electrodes with high selectivity at elevated current densities and provides guidance for post-treatment processes in the field of CO₂RR.