463736 Effects of Temperature and Gas-Liquid Mass Transfer on the Operation of Small Electrochemical Cells for the Quantitative Evaluation of CO2 Reduction Electrocatalysts
Both effects were evaluated quantitatively in high S/V cells using Cu electrodes and a bicarbonate buffer electrolyte. Electrolyte temperature is a function of the current and total voltage passed through the cell as well as the cell geometry. Even at very high current density, 20 mA cm-2, the measured temperature rise was less than 4 °C and a decrease of <10% in the dissolved CO2 concentration is predicted. In contrast, limits on the CO2 gas-liquid mass transfer into the cells produce much larger effects. By using the pH in the cell to measure the dissolved CO2 concentration, significant undersaturation of CO2 is observed, even at more modest current densities of 10 mA cm-2.
Importantly, undersaturation of CO2 produces large changes in the faradaic efficiency product distribution observed on Cu electrodes, with H2 production becoming increasingly favored as the CO2 undersaturation worsens. We show that the size of the CO2 bubbles being introduced into the cell is critical for maintaining the equilibrium CO2 concentration in the electrolyte, and we have designed a high S/V cell that is able to maintain the equilibrium CO2 concentration at current densities up to 15 mA cm-2.
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