Effect of Temperature Gradients on the Selectivity of the Electrocatalytic CO₂ Reduction Reaction

The impact of a temperature gradient at the electrode-electrolyte interface on the activity and selectivity of electrochemical reactions was investigated using the electrocatalytic CO₂ reduction reaction in an aqueous solvent as a model system. A heated electrode setup, coupled with a thermostated bath, was employed to establish and control a temperature gradient across the electrode surface, which enables comparing the reaction under isothermal vs nonisothermal conditions at various temperatures. Results show that natural convection induced by a relatively modest temperature gradient increases the activity and selectivity of CO₂ reduction over H₂O reduction. Finite-element analyses support the experimental findings by demonstrating that a temperature gradient in the electrochemical cell can increase fluid velocity, thereby improving mass transport. Simulations and experiments were further extended to evaluate different lab-scale electrolyzer configurations and a representative flow cell design. In H-cell configurations, the velocity distribution was found to be dependent on the orientation, size, and position of the electrocatalyst surface inside the cell. In the flow cell model, a temperature gradient was able to alter the flow profile, but this effect was limited to either low flow rates or steep temperature gradients. These findings underscore the importance of considering not only absolute temperature but also temperature gradients and thermally induced convection in the design and interpretation of electrochemical experiments. Moreover, they suggest that heat sources and heat flow may serve as handles to tune reaction performance in electrolyzers.