Carbon-Modified Bismuth Catalysts for CO₂ Electrolysis at Elevated Temperature: Insights and Challenges

The electrochemical CO 2 reduction (CO 2 RR) holds promise for sustainable fuel and chemical production, but faces challenges in maintaining catalyst stability under industrial conditions, particularly at elevated temperatures. This study investigates CO 2 RR performance at 85 °C using three types of carbon-based bismuth catalyst in a flow-by electrolyzer. Elevated temperatures accelerate degradation processes, making long-term operation difficult. We synthesized and tested catalysts where carbon serves as a structural support to disperse and stabilize Bi-based particles. While commercial bismuth oxide nanoparticles initially exhibit high selectivity toward formate (85%), their faradaic efficiency (FE) declined by 20% over 24 h. In contrast, Bi@C, where carbon acts as a porous support material to anchor nanoparticles and enhance dispersion, showed greater structural resilience, maintaining 75% initial selectivity with only a 10% drop over the same period. Post-electrolysis scanning electron microscopy (SEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) further confirmed that Bi@C underwent only minor morphological changes compared to its carbon-free counterpart, thereby explaining its enhanced stability. These findings provide insights into the role of carbon in stabilizing electrocatalysts at elevated temperatures, underscoring the required advancements to enable long-term CO 2 electrolysis under industrially relevant conditions of temperature and current density.