Molybdenum Sulfide for Hydrogen Evolution Reaction: The Importance of Solution Dynamic Wetting Behavior in The Drying Process.

Abstract

MoSx serving as a hydrogen evolution reaction electrocatalyst is known for its morphology sensitive characteristic. The low temperature thermo-decomposition method provides an easy and energy saving pathway to produce highly active MoSx on carbon paper substrates. However, during the precursor solution drying process, the dynamics of liquid wetting behavior dominates the morphology of the precursor salt and eventually the morphology of MoSx. As a result, here, for the first time, by carefully pairing the substrate hydrophobicity and solvent polarity, the cohesive force between solvent molecules and adhesive force between solvent and carbon substrate can be tuned, and thus the MoSx morphology can be controlled. Pairing hydrophilic carbon paper with DMF + H2O mixing solvent results in a relatively strong adhesive force, as a result, we are able to lower the overpotential required at the benchmark current density, 10 mA/cm2, to as low as 0.160 V and boost the current density to 40 mA/cm2 at -0.2 V vs RHE. This mainly results from the low charge transfer resistance and the well wrapped MoSx on carbon paper fiber structure. Furthermore, this well wrapped MoSx on hydrophilic carbon paper was proved to be comparably stable for constant voltage electrolysis operation.