Molybdenum disulfide microparticles in suspension in an aqueous acidic solution adsorb at the interface with an organic electrolyte solution containing the reducing agent, decamethylferrocene, to catalyse hydrogen evolution. This catalytic process has been investigated by voltammetry at the water/1,2-dichloroethane interface and by biphasic reactions monitored by gas chromatography and UV-visible spectroscopy. © 2011 The Royal Society of Chemistry.