Fabrication of inverse opal molybdenum sulfide and its use as a catalyst for H₂ evolution

Amorphous molybdenum sulfide (MoS_x) and crystalline molybdenum disulfide (MoS₂) are attractive noble-metal-free electrocatalysts for the H₂ evolution reaction from water. Their actual activities depend on the quantity of active sites which are exposed to the electrolyte, which in turn, is influenced by their specific electrochemical surface area. Herein we report on the fabrication of regular inverse opal MoS_x and MoS₂ films by employing polystyrene nanoparticles with diameters in the range of 30-90 nm as hard templates. The use of these catalysts for the H₂ evolution reaction in an acidic electrolyte solution is also presented. Impacts of the regular porous structure, the film thickness as well as the chemical nature of the catalyst (MoS₂versus MoS_x) are discussed. It shows a catalytically-effective-thickness of ca. 300 nm where the electrolyte can fully penetrate the catalyst macropores, thus all the catalytic active sites can be exposed to the electrolyte to achieve the maximal catalytic operation.