The first objective is addressed by using a supporting electrolyte like in the study of the HOR/HER. Figure -b compares the CVs in acid and base in the supporting electrolyte, finding that the characteristic CV features are maintained. For the second objective we supply a controlled amount of molecular hydrogen, ranging from just below 100 mbar to 1 bar. In such a case we achieve a controlled current contribution of the HOR/HER and knowledge of the bulk pH through the Nernstian shift of the open-circuit potential. Lastly, to accurately determine the H-upd, its current must be much greater than the background contribution of the HOR/HER. This is achieved by using substantially higher scan rates than is common in the electrochemical literature; 50 mV/s for the HOR/HER background current scans and 200mV/s, 500 mV/s, 1000 mV/s, and 2000mV/s for the H-upd scans. Still, we cannot probe the full CV below pH 3 where the proton acceptor limiting current is too high.