Electrocatalytic Performance of Titania Nanotube Arrays Coated with MoS₂ by ALD toward the Hydrogen Evolution Reaction

The electrochemical splitting of water provides an elegant way to store renewable energy, but it is limited by the cost of the noble metals used as catalysts. Among the catalysts used for the reduction of water to hydrogen, MoS2 has been identified as one of the most promising materials as it can be engineered to provide not only a large surface area but also an abundance of unsaturated and reactive coordination sites. Using Mo­[NMe2]4 and H2S as precursors, a desired thickness of amorphous MoS2 can be deposited on TiO2 nanotubes by atomic layer deposition. The identity and structure of the MoS2 film are confirmed by spectroscopic ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The electrocatalytic performance of MoS2 is quantified as it depends on the tube length and the MoS2 layer thickness through voltammetry, steady-state chronoamperometry, and electrochemical impedance spectroscopy. The best sample reaches 10 mA/cm2 current density at 189 mV overpotential in 0.5 M H2SO4. All of the various geometries of our nanostructured electrodes reach an electrocatalytic proficiency comparable with the state-of-the-art MoS2 electrodes, and the dependence of performance parameters on geometry suggests that the system can even be improved further