TechnicalRemarks: Experimental Details: Cyclic voltammetry (CV) experiments were conducted under both ambient conditions (25°C, 101.3 kPa) and elevated pressures (5 bar, 10 bar, and 25 bar). For ambient conditions, a three-electrode glass cell filled with CO2-saturated 0.1 M TBABF4 in acetonitrile electrolyte solution was employed. A polished planar copper disk served as the working electrode. A coiled Pt-wire inserted in a glass tube with a porous glass frit at the bottom acted as the counter electrode and Ag/AgCl as a reference electrode. At elevated pressure, a 316L stainless steel cell was used. Inside the cell, a three-electrode setup consisting of a Cu-foil working electrode, an AgBF4-coated silver wire as quasi-reference, and a platinum gauze counter-electrode was employed. Before the experiment, the cell was filled with the electrolyte (0.1 M TBABF4 in acetonitrile) and purged five times with CO2 (until 6 atm) under constant stirring with a magnet-operated stirrer. Afterward, the cell was filled with CO2 until the desired absolute pressure. The reference potential was adjusted to account for the different Ag/Ag+ reference systems employed in the ambient and high-pressure setups. Cyclic voltammograms were collected for five consecutive cycles for each scan rate between –0.8 V and –2.4 V. Data of the third cycle is provided. Post-iR correction was applied to all CV data to eliminate solution resistance effects.
Computational Details: The model was implemented and simulated with the MATLAB 2022b software. The set of differential equations was solved using the ode15 ODE solver function. A finite volume discretization scheme with central difference quotients was applied to discretize the spatial domain into 100 segments with logarithmically increasing cell width. The total thickness of the simulation domain was set to 6 mm. The initial concentrations for each species were set to their bulk concentrations. The *CO2 surface coverage was initially set to equilibrium with the liquid phase.
For further details regarding the experimental and computational procedures, please refer to the Supporting Information.
