Multiphysics Modeling of Heat and Mass Transfer for Photoelectrochemical CO₂ Reduction to CO

Photoelectrochemical (PEC) CO2 reduction (CO2R) offers a promising pathway for converting CO2 into high-value-added chemicals and fuels using solar energy. However, PEC CO2R involves multiple interrelated steps, including light transmission and absorption, heat transfer, mass transfer of chemical species, the equilibrium reaction, and photoelectrochemical reactions. Understanding these processes necessitates a multiphysics approach that integrates the above-coupled steps. In this work, we develop a theoretical model for PEC CO2R that involves essential physical and chemical processes. The effect of light intensity, bicarbonate concentration, electrolyte flow speed, electrode surface properties on the heat/mass transport, and CO2R performance are investigated. The results reveal that forming a two-phase flow plays a vital role in prompting the transport of chemical species and mitigating the pH shift. Increasing the bicarbonate concentration and electrolyte flow velocity can facilitate the bubble removal and mass transport of chemical species, thereby improving the CO2R performance. Furthermore, a superoleophobicity surface design effectively prompts bubble detachment and ion transport, consequently increasing the CO2R performance of the photoelectrode. Overall, this research highlights the complex interactions among various physical and chemical processes, and the developed mathematical model enables a deeper understanding of the fundamental processes for the PEC CO2R.