As one of the key reactions of electrocatalysis, hydrogen oxidation reaction (HOR) has been extensively investigated to understand its sluggish kinetics in alkaline. Elucidation of the mechanism of HOR in alkaline can not only deepen our understandings of alkaline electrochemistry, but also help to rationalize the design of highly active catalysts for alkaline fuel cells. Recent research of bimetallic catalysts for the HOR shed some light on the HOR mechanism in alkaline1. It was shown that alloying Pt with oxophilic metals (Ni, Ru, Ir) or depositing those metals on Pt surface can largely accelerate the HOR kinetics of Pt2. However, the beneficial roles of the second metals are under extensive debate. Herein, we investigate the HOR kinetics of Pt-M bimetallic catalysts by using electrochemical characterization and in situx-ray absorption spectroscopy. We propose that the oxidation state of the second surface metal is the governing factor for the hydroxide transportation between the surface and the bulk solution in alkaline, thereby controlling the HOR kinetics of Pt-M bimetallic catalysts. Liu E, Li J, Jiao L, Doan HT, Liu Z, Zhao Z, Huang Y, Abraham KM, Mukerjee S, Jia Q. Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation. Journal of the American Chemical Society. 2019 Feb 20. Strmcnik D, Uchimura M, Wang C, Subbaraman R, Danilovic N, Van Der Vliet D, Paulikas AP, Stamenkovic VR, Markovic NM. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nature chemistry. 2013 Apr;5(4):300.