Dynamic vs. Stationary Analysis of Electrochemical Carbon Dioxide Reduction: Strong Differences in Local State

Experimental Details:
All electrochemical measurements were conducted in a three-electrode. As a working electrode, a planar silver rotating disk electrode (surface area A = 0.1963 cm²), and as counter electrode, a spiral platinum wire was used. All potentials were measured and plotted against a reversible hydrogen electrode reference electrode (RHE). The potentials were corrected for uncompensated resistance afterward. The electrolyte was purged with CO₂ for 15 min before starting the experiment to ensure saturation with CO₂.
Cyclic voltammetry was performed in a potential window of -0.5 to -2.0 V vs. RHE with rotation speeds between 50 and 150 rpm and between -0.5 to -2.5 V vs. RHE for 300 rpm. The scan rate of the potential sweep was set to values of 50, 100, 200 and 300 mV/s. The number of cycles was eight for each scan rate to guarantee a quasi-steady state. In the figures, only the last cycle is displayed.
The stationary polarization curve was measured by holding a constant potential for 200 s. The step size of the applied potential was 0.1 V. The uncompensated resistance was measured after each holding time. Figures show the corrected mean potential and mean error, determined from the last 20 s of each measured potential.

Numerical Details:
The model was implemented in MATLAB R2020b, and differential equations were solved with ode15s solver. Spatial discretization was done with an equidistant grid and applying finite volume method and central differential quotients. Grid size was set to a value of Δx=1 µm and convergence of the solution regarding grid parameters was confirmed as refining the parameters lead to no visual changes of the cyclic voltammograms and concentration profiles. The system was initialized by holding the starting potential of -0.5 V, where no significant electrochemical reactions take place, until a stationary state was reached. Initial surface coverages and initial potential of the electrode were adapted from the stationary state. Initial concentrations were set to electrolyte bulk concentrations, where equilibrium of carbonate species and dissolved CO₂ is adjusted. For more information about experimental details, see Experimental Section in the manuscript.
For more information about experimental details and the model, see Method section in the manuscript.