Efficient generation of H₂ as a clean energy source from water constitutes one of the cornerstones of the so-called hydrogen economy. We are currently limited to precious metal such as Pt as effective HER catalysts in acid owing to the stability issue, but also in alkaline owing to the slow kinetics of HER in high pH environment. The origin of the slow HER rate in alkaline, and how to overcome this fundamental limitation have been under extensive debatable. By far there are three schools of thoughts led by Markovic, Gasteiger, and Koper, and their respective collaborators, although they all agree that the HER kinetics in alkaline is limited by the Volmer step M + H₂O + eˉ ↔ M-H_ads + OHˉ. Markovic et al.¹ stated that and the reactive hydroxyl species (OH_ads) accomondated by the surface oxophilic sites is responsible for the acceleration of this step. We recently provided the first experimental evidence of OH_ads accommodated by the Ru in both Pt-Ru and Ru systems within the HER/HOR potential region, and its promoting role on the HER/HOR kinetics in alkaline media.² Gasteiger et al.³ and Yushan () argued that H-binding energy (M-H) is the sole descriptor for the HER rate in a broad range of pH environments, although the origin of the difference in H-binding energy is not clear. Most recently, Koper’s group⁴ proposed a model that states a possible pH dependence of surface water (H₂O) orientation and highlights the role of the reorganization of interfacial water for the HER kinetics to accommodate charge transfer through the electric double layer. In this talk, all the three mechanisms will be discussed in the context of new experimental and computational results achieved by us and others to update our understanding of the HER kinetics in alkaline pH.

Acknowledgements:

The authors gratefully acknowledge the financial support of the Department of Energy (DOE) via Energy Efficiency and Renewable Energy (EERE), under the auspices of an incubator effort lead by Proton On-Site and a new grant (grant #.. ) under the HydroGen initiative. Authors also acknowledge the support from arpa.e under their open initiative via a grant lead by Pajarito Powders, Albuquerque (grant # ). The support from (DOE) office of science under contract no DE-SC0012704 for building and maintaining the National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Laboratory (BNL), Upton, NY and Thermo Fisher for instrumental support is gratefully acknowledged.

References

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(2) Li, J.; Ghoshal, S.; Bates, M. K.; Miller, T. E.; Davies, V.; Stavitski, E.; Attenkofer, K.; Mukerjee, S.; Ma, Z.-F.; Jia, Q. Angew. Chem. Int. Ed., n/a.

(3) Durst, J.; Siebel, A.; Simon, C.; Hasche, F.; Herranz, J.; Gasteiger, H. A. Energy Environ. Sci. 2014, 7, 2255.

(4) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M. Nat. Energy 2017, 2, 17031.