Polarization Impact On CO2 Reduction Overpotentials On Copper Electrodes.pdf

The supplementary information discusses the effect of polarization on kinetic overpotential during CO2 reduction reactions (CO2R) on copper. The intrinsic activity or overpotentials were determined by subtracting computed polarization losses and equilibrium potentials from the applied potential, as shown in Figure S1a. These plots are horizontally shifted based on equilibrium potentials depicted in another figure.

The onset overpotentials for various products at a current density of 0.056 mA cm^-2 include -0.668 V for hydrogen, -1.114 V for methane, -0.972 V for ethylene, -0.8692 V for ethanol, -0.666 V for formate, and -0.676 V for CO.

Figure S1b illustrates the equilibrium potential of methane (solid red line), which is not parallel to hydrogen due to a decrease in CO2 concentration at the cathode. The polarization loss at the cathode results from a net decrease in reaction equilibrium potential caused by increased pH. Consequently, applied voltage comprises both polarization loss and kinetic overpotential, with kinetic overpotential decreasing as applied voltage increases beyond -1 V.

Figure S1a shows partial current density versus kinetic overpotential for CO2RRs on Cu after accounting for polarization losses and equilibrium potentials. Figure S1b plots methane's equilibrium potential against cathode pH, noting a decrease in kinetic overpotential with increasing negative bias (past -1.4 V vs SHE) due to rising polarization losses. A slight drop in methane formation's equilibrium potential is attributed to reduced CO2 concentration at the cathode.