Proton-Coupled Electron Transfer
Proton coupled electron transfer (PCET) is a redox process in which electron transfer is accompanied by proton transfer, either in a concerted step or stepwise. Quinone/hydroquinone couples are classic examples, undergoing two electron, two proton reactions in water, and the local pH at the electrode and the identity of the available proton acceptor or donor strongly shape their voltammetry.
Quinone PCET as an electrochemical proton pump (2015)
Watkins et al. studied hydroquinone/benzoquinone and 2,6-dimethylbenzoquinone/hydroquinone in sulfate and bicarbonate electrolytes and attributed extra oxidation peaks in weakly buffered media to local pH drops that change the proton acceptor from water to sulfate or bicarbonate, rather than to a change away from PCET (Watkins et al. 2015). The oxidation peak shifted with pH while the reduction peak did not (peak separation about 206 mV at pH 7.5 rising to about 499 mV at pH 6.5), and 1.0 M NaHCO3 buffered the system enough to give single peaks. They then used the PCET reaction to pump protons between two electrodes and drive CO2 separation. Summary: watkins2015.