Effect of boron on the structural and electrochemical properties of nanocrystalline Ti2RuFeBx electrodes

The effect of the boron content on the structural and electrochemical properties of nanocrystalline Ti₂RuFeB_x (with x varying from 0 to 12) was studied. The nanocrystalline materials were prepared by high energy ball milling and their structural evolution was analyzed by X-ray and neutron diffraction. Through a detailed Rietveld refinement analysis of the structural data, it is shown that the nanocrystalline materials are mainly composed of a B2 structure at low boron content (0 < x < 2). At higher boron content, TiB₂ is mainly formed and the B2 structure disappears with the concurrent formation of a highly disordered Ru-rich phase. These electrodes were tested for the hydrogen evolution reaction in both NaOH and chlorate solutions. The best results are obtained for 4 ≤ x ≤ 6, with a cathodic overpotential at −250 mA/cm², η₂₅₀, of ∼−575 mV. Accelerated aging tests and continuous electrolysis tests show that η₂₅₀ does not vary with time, contrary to the case of Ti₂RuFe, which shows a rapid deterioration of the cathodic overpotential after a few hours of continuous electrolysis. This is explained by the lower solubility of hydrogen in Ti₂RuFeB₄ as opposed to Ti₂RuFe.