Alkaline membrane electrolyzer and fuel cell technologies are attractive alternatives to their more mature acidic counterparts. Alkaline conditions are advantageous for the electrocatalysis of the oxygen electrode reactions, but the opposite holds for the hydrogen electrode. In acidic electrolyte, the kinetics of the hydrogen oxidation and evolution reactions (HOR and HER) on platinum catalyst are very fast, thus enabling ultra-low platinum loadings (≪ 0.1 mg Pt cm -2 ) in proton-exchange membrane (PEM) fuel cells and electrolyzers. In fact, the acidic hydrogen reaction is so fast that it is rather challenging to study its kinetics without mass-transport phenomena dominating the measured data and special approaches, like H 2 -pump experiments or floating electrode configurations have to be used. In alkaline conditions, on the other hand, the HOR/HER kinetics are about two orders of magnitude slower than in acid, thus requiring significantly larger platinum loadings in alkaline fuel cell and electrolyzer technologies. It is therefore of great interest to better understand the kinetics and mechanism of the HOR/HER in basic media: Alkaline HOR/HER: