Promoting Hydrogen Evolution and Oxidation by Reconstructing Hydrogen-Bonding Network of Interfacial Water

Abstract

The hydrogen evolution and oxidation reactions (HER/HOR) at the electrode-water control the performance of water electrolyzers and hydrogen fuel cells, two important devices for deep decarbonization of our economy (1). Platinum (Pt) catalyzes the HER/HOR with exceptional activity and stability across a wide pH range. However, its activity progressively decreases by about two orders of magnitude as the pH increases from 0 to 13 (2, 3). The lack of understanding of this pH dependence reflects our fundamental knowledge gaps in electrochemistry and has hindered the advancement of alkaline electrolyzers and fuel cells.Herein, we promoted the HER/HOR of Pt in base by introducing N-methylimidazoles in the Pt-water interface. In situ spectroscopic characterization of the interface together with computations showed that the N-methylimidazoles form strong hydrogen-bonding with neighboring water molecules thereby reconstructing the H-bond network of interfacial water. We accordingly established a unified mechanism by which the HER/HOR in acid and base proceeds via diffusion of protons and hydroxides, respectively through the H-bond network of interfacial water by the Grotthuss mechanism. This mechanism accounts for the pH-dependent HER/HOR kinetics of platinum, a long-standing puzzle. Utilization of N-methylimidazoles as the HER/HOR probes and promoters not only leads to the elucidation of the HER/HOR mechanism but also holds great promise for applications. We have demonstrated 40% performance improvement of an anion exchange membrane water electrolyzer by adding 10-5 M 1,2-dimethylimidazole into the 0.1 M potassium hydroxide solution fed into its Pt cathode. Acknowledgements This work was supported by the Office of Naval Research (ONR) grant N000141712608 (Q.J.)This research used beamline 7-BM (QAS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory Contract DE-SC0012704. Beamline operations were supported in part by the Synchrotron Catalysis Consortium Grant DE-SC0012335. V. R. Stamenkovic, D. Strmcnik, P. P. Lopes and N. M. Markovic, Nat. Mater., 16, 57 (2017). J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz and H. A. Gasteiger, Energy Environ. Sci., 7, 2255 (2014). W. Sheng, Z. Zhuang, M. Gao, J. Zheng, J. G. Chen and Y. Yan, Nat. Commun., 6 (2015). Figure 1