hydrogen gas electrode

A thin foil of platinum electrolytically coated with a finely divided deposit of platinum or palladium metal, which catalyses the electrode reaction: \[\text{H}^{+}+\text{e}\rightarrow \frac{1}{2}\text{H}_{2}\] in solutions saturated with hydrogen gas.
PAC, 1985, 57, 531. 'Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)' on page 540 (https://doi.org/10.1351/pac198557030531)