In Situ Measurement of Local pH at Working Electrodes in Neutral pH Solutions by the Rotating Ring-Disk Electrode Technique

When electrochemical reactions that generate/consume protons or hydroxide ions take place, the local pH in the vicinity of an electrode becomes considerably different from the bulk pH. However, measuring the local pH is very difficult, and the idea of using a rotating ring-disk electrode (RRDE) is not applicable to solutions with neutral pH. Herein, we extend the theory of local pH measurement using a RRDE and make it applicable to solutions with a wide pH range. This extended theory is corroborated by measurements of hydrogen oxidation/evolution reactions in solutions with near-neutral pH. In addition, the local pH change in a highly concentrated solution is also measured, and the results show that this local pH measurement method can be used regardless of the solution concentration.