For selected systems we performed measurements of the positions of the H-upd features, notably peak 2, at different hydrogen partial pressures. While both mechanisms predict an effect from molecular hydrogen on the peak position of the H-upd, in the case of the H-V path the peak position is expected to reach a sharp maximum with hydrogen partial pressure and then decrease (Fig. ) towards a potential associated with the Heyrovský step (being relatively accelerated to the Volmer step by the increased molecular hydrogen activity). We never observed such behavior, instead, the peak positions behave closely to what can be described by the T-V path. A similar analysis shows that peak 1 exhibits the same behavior, while the effect of molecular hydrogen activity on peak 3 can only be determined with substantial uncertainty and we are not able to provide conclusive information on this matter.