(Invited) Influence of Hydrogen Bond Networks on Hydrogen Evolution Reaction in Aqueous Systems

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Hydrogen evolution reaction (HER) is one of the key issues to achieve “carbon neutrality”. Driving the electrocatalytic HER in aqueous solutions with solar-energy cells is considered as a green and sustainable way to produce hydrogen molecules (H2). To achieve effective H2 production, it is required to reduce HER overpotential using appropriate heterogeneous electrocatalysts such as Pt. The HER activities of catalytic metals have a strong correlation with the hydrogen adsorption free energies on their surfaces, which is known as a so-called volcano-like relation. Because the optimum adsorption energy and hence maximum HER activity are found at the top of the volcano, most of the studies to develop electrocatalysts focus on tuning of the adsorption energy. However, the hydrogen adsorption step, i.e., discharge reaction of proton, at the surface is strongly influenced by hydrogen bonding with the bulk phase of liquid water. Recently, we have developed a surface-selective THz-vibrational spectroscopy based on surface-enhanced Raman scattering, which can obtain dynamical and structural information on hydrogen bond networks of water at interfaces with the frequency range of 10 - 100 cm-1 (0.3 – 3 THz) [1-6]. Using this technique, we have examined the potential-induced behavior of interfacial hydrogen bonds under the HER process on various metal surfaces with different HER activities and found that there is a correlation between the HER activities and hydrogen bond structures at interface. The details will be discussed in the presentation. We will also present a new strategy to produce hydrogen gas more efficiently using a non-traditional electrochemical cell structure.[1] M. Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 4236-4240 (2017).[2] M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807-9717 (2020).[3] M. Inagaki, K. Motobayashi, K. Ikeda, Nanoscale, 12, 22988-22994 (2020).[4] R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 2100589 (2022).[5] T. Kondo, M. Inagaki, K. Motobayashi, K. Ikeda, Catal. Sci. Technol., 12, 2670-2676 (2022).[6] T. Isogai, M. Inagaki, M. Uranagase, K. Motobayashi, S. Ogata, K. Ikeda, Chem. Sci. 14, 6531-6537 (2023).