The electrochemical cells for ex situ experiments were assembled in a 1/4'' Swagelok T-shaped-cell. The electrolyte applied was tetraethylphosphonium tetrafluoroborate (PEt4BF4, >95% purity, Tokyo Chemical Industry UK), 0.5 M, in propylene carbonate (PC) (≥99.0 %, Sigma-Aldrich). Carbon electrodes were cut with a "3/16" inch puncher with mass difference of less than 0.2 mg. The symmetric Swagelok cell was assembled the same way as coin cells with two identical electrodes and an excess amount of electrolyte of 200 µL in a N2-filled glovebox. The third hole was filled by another stainless-steel plunger to seal the cell and avoid H2O and O2 from entering the cell.