Fig. 2: Pseudo-capacitive discharge kinetics on polycrystalline Pt.

a Cyclic voltammogram (50 mVs⁻¹) of a polycrystalline Pt foil in 0.1 M KOH. Temperature dependent potential jumps were performed between the starting potential (V_S) and positive potentials up to 800 mV_RHE. In anodic direction, the electrosorption processes include H desorption, OH adsorption and the onset of Pt oxidation, all of which involve water formation and hydroxide desolvation, as indicated. b Potential dependent (dis)charge current transients after the potential jumps. After ~10 ms, the discharge currents start to resolve the potential dependent (dis)charge peaks, including the onset of Pt oxidation at higher potentials. c Bias dependent pre-exponential factor (logA(η)) and activation energy (\({E}_{A}(\eta )\)) for (dis)charge currents at different times after the potential jumps (Supplementary Fig. 3). We observe a decreasing logA(η) and \({E}_{A}(\eta )\), since higher temperatures (T) lead to lower currents (J) (\({E}_{A}\propto -d\log {JdT} < 0\)). Note, here, a lower slope dlog\(A\left(\eta \right){E}_{A}{\left(\eta \right)}^{-1}\) represents faster discharge kinetics, in contrast to the kinetics at Faradaic currents. At longer times and higher potentials, we observe a reversal of the slope for the onset of Pt oxidation, where currents increase with temperature. For a full video with 1 ms time resolution see Supplementary Movie 1. E_A and A are means and error bars show standard deviation for E_A (slope) and A (intercept) from Arrhenius analysis, based on five observations (temperatures). d, e Time dependence of logA(η) and \({E}_{A}(\eta )\), respectively. After 10–20 ms, the electrosorption peaks in Fig. 2a appear. These potential dependent variations around 300–600 mV are not apparent in panel c, as logA(η) and \({E}_{A}(\eta )\) compensate along the same line. The bias dependent compensation of logA(η) and \({E}_{A}(\eta )\) in (d, e) is likely related to the impact of bias dependent build-up of excess charge at local surface motifs on the solvation kinetics. For (d, e) E_A and A are means. Error bars are not shown for clarity. R² values based on five observations are shown in Supplementary Fig. 4. For more discussion on the linear fit see Supplementary Note 2. All potentials are referenced vs. the reversible hydrogen electrode (RHE).