Tetraalkyl/Alkyltriphenylphosphonium Hexatungstates for Efficient Electrocatalytic Hydrogen Evolution Reaction in Alkaline Media: An Experimental and In Silico-Based Synchronization Approach

Abstract

The development of stable, cost-effective, noble metal-free, and highly efficient electrocatalysts embraces great potential for efficient hydrogen production through water electrolysis. Herein, tetraalkyl/alkyltriphenylphosphonium hexatungstate-based Lindqvist polyoxometalates named HTC-1 and HTC-2, respectively, have been synthesized and characterized as promising electrocatalysts for effectual water-splitting reactions. The inclusion of tetrabutyl- and allyltriphenylphosphonium bromides as precursors into hexatungstate ions (W6O192-) exhibited a synergistic effect that promoted a notable improvement in the hydrogen evolution reaction (HER) performance. It also imposes extra surface-active sites and facilitates the electronic transition to boost HER activity in alkaline medium with a lower overpotential value of 136 and 185 mV at benchmark current density and a Tafel slope of 88 and 121 mV dec(-1), respectively. Density functional theory (DFT) calculations also corroborated the experimental finding that HTC-1 acts as a more efficient electrocatalyst due to the presence of a more electron-rich center than HTC-2. The experimental results are further unequivocally corroborated by the in silico approaches, which include density functional theory, reactive site analysis, electronic property analysis, and Gibbs free energy analysis. These results conclusively demonstrate that HTC-1 exhibits a lower energy barrier in promoting the adsorption of HER intermediates, particularly, hydrogen adsorption. These observations represent an auspicious proof of concept for developing more efficient hexatungstate-based electrocatalysts in the future.