Regulating the Connectivity of Hydrogen Bonding Networks on Pt for Alkaline Hydrogen Oxidation

Abstract

The hydrogen bonding network at the electrochemical interface plays a critical role in determining alkaline hydrogen oxidation reaction (HOR) kinetics. However, strategies for regulating this network are limited, and there is a lack of systematic understanding regarding the regulatory mechanisms. In this study, 16 small organic molecules with varying functional groups were employed to systematically adjust the contact angle between the Pt/C surface and water. Density functional theory (DFT) calculations revealed that the electrostatic potential range (ESP_range) of these molecules can be used as a descriptor to correlate their properties with the hydrophilicity of the modified Pt/C surfaces. The ESP_range also demonstrated a volcanic relationship with HOR exchange current densities (i_0,HOR) on the modified Pt/C surfaces. Ab initio molecular dynamics simulations (AIMD) further highlighted that the molecule modifications can increase the potential of zero charge (PZC) of Pt surface and regulate its double-layer capacitance (C_dl). These combined effects influence the crowding of K⁺ cations in double-layer, thereby impacting the connectivity of the interfacial hydrogen bonding network and the HOR kinetics. The experimental results suggest the i_0,HOR of Pt/C can be doubled by appropriately increasing the hydrophilicity and decreasing the C_dl of the Pt surface. The methodology presented in this study is also applicable to investigating hydrophilicity and connectivity of the interfacial hydrogen bonding network regulation on other electrode surfaces.