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.