The effect of the boron content on the structural and electrochemical properties of nanocrystalline Ti2RuFeBx, (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 132 structure at low boron content (0 < x < 2). At higher boron content, TiB2 is mainly formed and the 132 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/cm(2), eta(250), of similar to-575 mV. Accelerated aging tests and continuous electrolysis tests show that eta(250) 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. Crown Copyright (c) 2007 Published by Elsevier Ltd. All rights reserved.