Plasma-sprayed nanocrystalline Ti–Ru–Fe–O coatings for the electrocatalysis of hydrogen evolution reaction

Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) was prepared by mechanical alloying in a ZOZ attritor. Vacuum plasma spray (VPS) was then used to deposit coatings of this material on a substrate. Energy dispersive X-ray fluorescence and X-ray diffraction analysis was used to follow the change in the chemical composition and crystalline structure of the powder upon deposition by VPS. Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) prepared by the ZOZ attritor contains more than 50 wt.% of hexagonal Fe ₂Ti and a smaller amount (<10 wt.%) of a cubic phase. Iron contamination coming from the attrition of the milling tools yields [Fe] ∼38 wt.%, almost twice as much as the nominal composition of the powder. When it is used for VPS, reaction between Fe ₂ Ti and Ru results in the formation of several cubic phases with lattice parameters ranging from 2.96 to 3.02 Å. This reflects a change in the Ru content on the 1 a ( 1 2 , 1 2 , 1 2 ) site of the cubic lattice. The deposition process also results in the formation of Ti ₂O ₃ . This phase is present in excess at the surface of the coating but can be efficiently dissolved through etching in an acid solution. The cathodic overpotential for hydrogen evolution of such activated coatings in typical chlorate electrolysis conditions is η ₂₅₀=−550 mV.