In all experiments conducted with the EC-MS cell, a Pt film (99.99%, Goodfellow) and Hg/Hg2SO4 (K2SO4 0.6 mol/l, B 3610+, VMR) was used as the counter and reference electrode, respectively. The carrier gas was CO (> 99.9999%, Air Liquid), He (> 99.999%, Air Liquid), or Ar (> 99.999%, Air Liquid) for different purposes. The flow rate of employed carrier gas was kept at 1 sccm in all measurements.