Polymerized Tungstate-Molybdenum Sulfide Electrocatalysts for Hydrogen Evolution Reaction under acidic conditions

Abstract

Polyoxometalate-based electrocatalysts represent a promising class of earth-abundant electrocatalysts for hydrogen production; however, their large-scale synthesis remains challenging due to the multi-step procedures. Inspired by the effectiveness of {Mo₃S₄}-containing polyoxometalates in catalyzing the hydrogen evolution reaction (HER) under acidic conditions, we have developed a one-pot synthetic strategy to design efficient heterogeneous HER electrocatalysts. This approach leverages the self-condensation properties of tungstate ions in the presence of the [Mo₃S₄(H₂O)₉]⁴⁺ aqua cluster in aqueous solution. The nature of the resulting polymeric tungstate-molybdenum sulfide materials is strongly pH-dependent, as revealed by elemental analysis, infrared and Raman spectroscopies, nitrogen adsorption-desorption, small-angle X-ray scattering, and transmission electron microscopy. The evaluation of the electrochemical performance revealed that all polymeric inorganic materials exhibit low overpotentials, small Tafel slopes, and small charge transfer resistances. Importantly, incorporating carbon nanotubes during synthesis modulates the HER activity. This leads to enhanced performance for materials prepared under acidic conditions, while a negative effect is observed for those in alkaline media. Atomic force microscopy combined with scanning electrochemical microscopy suggests that this contrasting behavior arises from variations in adhesion between the inorganic framework and the carbon nanotubes. As a proof of concept, the best catalyst has been implemented at the cathode of a proton exchange membrane (PEM) water electrolysis cell, revealing it as a promising candidate to replace platinum in water electrolysis technology. These findings offer valuable insights into the rational design of scalable and high-performance electrocatalysts, drawing inspiration from the molecular engineering principles of polyoxometalate chemistry.