Electrochemical CO2 reduction at elevated temperatures

Promovendus/a: Alana Rossen

Promotor(en): prof. dr. Tom Breugelmans

The rapid rise in atmospheric carbon dioxide CO2 concentrations necessitated by anthropogenic activity requires the development of robust carbon capture and utilization (CCU) technologies. Among these, electrochemical CO2 reduction (CO2RR) offers a promising pathway to synthesize value-added chemicals and fuels using renewable energy. While laboratory research typically occurs at ambient conditions, industrial-scale electrolyzers will inevitably operate at elevated temperatures due to internal ohmic heating. This dissertation investigates the influence of thermal intensification on the performance, stability, and transport phenomena of electrochemical CO2 and carbon monoxide (CO) reduction.
One major challenge at 85°C is the morphological degradation of catalysts. To address this, a bismuth-based catalyst integrated with a mesoporous carbon shell was developed. This architecture effectively suppressed bismuth sintering and surface degradation, maintaining high selectivity toward formate for twenty-four hours of continuous operation. Beyond catalyst stability, elevated temperatures exacerbate gas diffusion electrode (GDE) flooding, which disrupts the triple-phase boundary necessary for efficient gas conversion. By implementing precise differential pressure control between the gas and liquid phases, the reaction interface was stabilized, increasing the Faradaic efficiency for formate from 40% to 65% under thermally intensified conditions.
The research further transitioned to electrochemical CO reduction within a zero-gap electrolyzer configuration. This architecture circumvents the carbonate salt precipitation issues inherent to CO2 feeds, allowing for a clearer decoupling of thermal effects from bulk electrolyte chemistry. This study revealed that while temperature has a secondary effect on the intrinsic product distribution on copper catalysts, it drastically reduces the crossover of liquid products through the ion-exchange membrane. This reduction in crossover is a critical finding for industrial process design, as it simplifies downstream separation and enhances product recovery.
Ultimately, this work demonstrates that elevated temperature operation fundamentally alters the electrochemical environment, influencing parameters ranging from CO2 solubility and local pH to membrane permeability and catalyst longevity. By exploring the interplay between catalyst design, mass transport, and reactor architecture, this dissertation provides a comprehensive framework for the design of next-generation electrolyzers. These insights are essential for the deployment of thermally intensified systems capable of operating at the scales required for global carbon mitigation.