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Cu2 MoS4 is a ternary transition-metal sulfide that shows great potential in the field of energy conversion and storage, namely catalytic H2 evolution in water and Li-, Na- or Mg-ion battery. In this work, we report on a growth mechanism of the single-crystalline Cu2 MoS4 nanotube from (NH4 )2 MoS4 salt and Cu2 O nanoparticle. By probing the nature and morphology of solid products generated in function of reaction conditions we find that the crystalline Cu(NH4 )MoS4 nanorod is first generated at ambient conditions. The nanorod is then converted into Cu2 MoS4 nanotube under hydrothermal treatment due to the Kirkendall effect or a selective etching of the Cu2 MoS4 core. Extending the hydrothermal treatment causes a collapse of nanotube generating Cu2 MoS4 nanoplate. The catalytic activities of these sulfides are investigated. The Cu2 MoS4 shows superior catalytic activity to that of Cu(NH4 )MoS4 . Catalytic performance of the former largely depends on its morphology. The nanoplate shows superior catalytic activity to the nanotube, thanks to its higher specific electrochemical surface area.

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p-type Cu2O (p-Cu2O) is a promising candidate for engineering of photocathodes for solar H2 generation but it suffers from the photo-induced corrosion process. In this work, we report on the two new strategies to overcome the photo-induced corrosion and to enhance the photocatalytic activity of the p-Cu2O photocathode: (i) a 60-to-300-nm-thick Au layer prepared by sputtering was used as a protective layer to the p-Cu2O electrode; (ii) a thin layer of n-type Cu2O was deposited onto the p-Cu2O electrode surface before sputtering the Au protective layer. For the latter, as a direct result, a pn-Cu2O homojunction was formed that was then protected by the Au thin layer. The pn-Cu2O homojunction helps to enhance the charge separation within the Cu2O electrode, consequently contributes to the enhancement of the photocatalytic activity. Under the standard 1 Sun irradiation, the best Au-protected pn-Cu2O photocathode showed an onset photovoltage of +0.55 V vs. Reversible Hydrogen Electrode (RHE), and a photocurrent density of 0.76 mA/cm2 at an applied potential of 0 V vs. RHE that remained more than 50% after 3 min of operation. Whereas, the bare p-Cu2O showed a photocurrent density of 0.3 mA/cm2 that was completely degraded after 1 min of operation under the identical conditions.

Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO)6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm2. Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.