Interfacial polarization in ultra-small Co3S4−MoS2 heterostructure for efficient electrocatalytic hydrogen evolution reaction

Constructing suitable heterostructured electrocatalysts and understanding their interfacial effects have been considered as an effective strategy to improve the intrinsic activity of electrocatalytic hydrogen evolution reaction (HER). In this work, ultra-small Co3S4-MoS2 heterostructure was synthesized using a precursor solubility controlling method. It is found that the electrocatalytic HER performance of the heterostructured catalysts exhibited a low overpotential of 260 mV at 100 mA cm−2 in 1.0 M KOH and possessed remarkable stability over 100 h continuous electrolysis at high current density (100 mA cm−2). Besides, Co3S4-MoS2 electrocatalyst is applied as the cathode material for a homemade membrane electrode device for water electrolysis to produce hydrogen. It shows that the electrocatalyst has a comparable catalytic activity to that of 20% Pt/C catalyst at 70 °C. The outstanding performance of the ultra-small Co3S4-MoS2 heterostructure is attributed to the efficient mass transport benefitting from its unique ultra-small hollow structure and the rapid electron transfer at the interface between Co3S4 and MoS2. XPS characterizations and DFT calculations confirm that the interfacial polarization and the corresponding electron transfer from Co3S4 to MoS2 at the interface optimizes the charge state of the catalyst and tunes the binding strength to the intermediates during each elementary step of the HER process. To be exact, the electron transfer promotes the adsorption of OH* on the charge-depleted Co3S4 sites and the adsorption of H* on the charge-enriched MoS2 sites, respectively, thereby reducing the free energy barrier of the water dissociation step (rate-limiting step) and improving the reaction kinetics. The solubility controlling strategy may provide a novel idea for rational design and synthesis of superior stability transition metal sulfides HER electrocatalysts.