Some progress has been recently made in understanding the sluggish kinetics of hydrogen evolution and oxidation reactions (HER/HOR) of Pt in alkaline solutions. The pH dependence of the HER/HOR activity of Pt was reasonably accounted for by the potential of zero free charge (pzfc) theory.¹ We lately proposed the 2B theory to account for the alkali cation effects on the HER/HOR activity of Pt and the beneficial roles of the second metal such as the Ni on the HER/HOR activity of Pt.^2,3 Meanwhile, the Ru-induced improvement of the HOR activity of Pt was ascribed to the bifunctional mechanism^4,5 or the hydrogen binding energy.^6,7 However, these different theories often conflict with each other, and have not been unified into a coherent picture depicting the kinetics of HER/HOR in alkaline solutions. Herein, we propose a new theory to account for the Ni and Ru induced improvement of the HOR activity of Pt in alkaline solutions, on the basis of combined electrochemical and in situ spectroscopic data. The combination of this new theory with the pzfc and 2B theories appears to give a coherent picture of the HER/HOR kinetics of Pt in alkaline solutions.

Acknowledgements

This work was supported by the Office of Naval Research (ONR) under award number N00014-18-1-2155. The authors declare no competing financial interests. Use of Beamline ISS 8-ID of the National Synchrotron Light Source (NSLS) II was supported by the NSLS-II, Brookhaven National Laboratory, under U.S. DOE Contract No. DE-SC0012704. Use of beamline 5-BM-D at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31–109-Eng-38. Jia acknowledged the help from Eli Stavitski, Klaus Attenkofer from ISS, NSLS-II; Qing Ma from DND-CAT, APS at ANL; and Todd E Miller, Lynne LaRochelle Richard from Northeastern University on the XAS data collection.

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