Whether or not trace metals are present in the IL, which can be deposited on the surface, can for example be studied by in-situ scanning tunnelling microscopy (STM), which allows depicting structural changes of the surface upon their deposition. In a former in-situ STM study using the same batches of ILs as used in the present work, we could not find evidence of metal deposition. The presence of residual halides has been shown to decrease the stability of the IL at high positive potentials at the anode. For the ILs used in this work the suppliers stated a halide content below 100 ppm for all batches. We did not verify the stability of the ILs at high decomposition potentials, to elucidate a possible difference in halide content in the different batches. Thus, its impact still remains unknown in our case. Additionally, the IL could contain different organic impurities, which could equally influence the electrochemical behaviour.