Electrode characteristics of two-phase glass-forming Ni-Nb-Y alloys

Two-phase amorphous and two-phase crystalline Ni58.2Nb20.25Y21.25 alloy samples with coexisting Y-rich and Nb-rich phase fractions were produced by melt-spinning and copper mould casting. Their electrochemical reactivity in the as-quenched or mechanically polished state and after HNO3/HF solution treatment was investigated in nitrogen-purged 0.1 M NaOH solution (pH = 13) by means of potentiodynamic polarisation experiments. In the as-quenched state the two-phase amorphous samples are blocked by a strong passive layer. The main effect of a HNO3/HF treatment is a selective dissolution of Y-rich phases leading to an excavation of Nb-rich phase regions, i.e. amorphous Ni-Nb-(Y) spheres or Nb6Ni7 grains. The enhanced reactivity of etched Ni58.2Nb0.25Y21.25 ribbons is mainly related to the high reactivity of the residual Y-rich matrix phase, while the Nb-rich spheres with smooth and non-defective surface appear quite inactive. In contrast, in the case of the etched crystalline counterpart the Nb6Ni7 grains provide a highly defective and thus, active surface, which can contribute to an enhanced electrochemical reactivity. The high cathodic performance of a commercial Ni foam for the hydrogen evolution reaction is reached for etched two-phase amorphous and crystalline Ni58.2Nb20.25Y21.25 alloys. (c) 2007 Elsevier Ltd. All rights reserved.