The Re values decrease with more negative potentials and exhibit even smaller values in the presence of CA. Notably, the Cdl of IO-TiO2|FDH electrodes increases from 0.2 V vs. RHE to -0.4 V vs. RHE, indicating a rise in local ion concentration due to CO2-to-formate conversion. The introduction of CA, which consumes H + and HCO3 -to compensate for CO2 depletion during formate production, effectively balances Cdl values across the voltage range.