Raney multi-metallic electrodes from regular crystalline and quasi-crystalline precursors: I. Cu-stabilized Ni/Mo cathodes for hydrogen evolution in acid

Multi-metallic alloys comprising Al (65–75 at.%), Ni, Cu (Co), and Mo, were prepared in regular crystalline (RC) and quasicrystalline (QC) forms, and subjected to alkali leaching to create Ni-rich Raney electrocatalysts. After acid-conditioning, these were tested as cathodes in pressed-powder form for hydrogen evolution and for corrosion resistance in 0.5 M aqueous H 2SO 4. RC precursors are multi-phase mixtures with a predominant hexagonal Ni 2− x Cu x Al 3 structure. Increasing Cu level exacerbates the intrinsic resistance of Ni 2Al 3 to leaching in alkali. In contrast, QCs are mainly single-phase materials which are readily leached regardless of Cu content. Only Mo-containing samples have mass-specific activities for H 2 evolution which approach those of ‘platinized’, and carbon-supported, Pt control electrodes. A current density benchmark of 70 mA cm −2 was attained at modest overpotentials, viz., −115 to −220 mV/NHE. Since there is no evidence for Ni/Mo alloy after leaching, it appears that the synergy operates merely by intimate physical contact of these components. Mo is not incorporated in either of the main RC or QC phases, but forms instead a separate ternary phase of provisional composition Ni 16Mo 10Al 74. Before cathodic polarization, the active (leached) form consists of fcc Ni/Cu (or Ni/Cu/Co) mesoporous alloy with a grain size of ∼2 microns, interpenetrated by an ultra-fine dispersion of oxidized Mo. The presence of minor levels of Cu and Mo together impart respectable stability, though not yet sufficient for technical application. The alloys have slightly positive rest potentials, and passivate (corrosion currents