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| Hauptseite > Publikationsdatenbank > Raney multi-metallic electrodes from regular crystalline and quasi-crystalline precursors : I. Cu-stabilized Ni/Mo cathodes for hydrogen evolution in acid |
| Hauptseite > Publikationsdatenbank > Raney multi-metallic electrodes from regular crystalline and quasi-crystalline precursors : I. Cu-stabilized Ni/Mo cathodes for hydrogen evolution in acid |
| Journal Article | PreJuSER-37839 |
; ;
2001
Elsevier
New York, NY [u.a.]
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Please use a persistent id in citations: doi:10.1016/S0013-4686(01)00727-7
Abstract: 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 H2SO4. RC precursors are multi-phase mixtures with a predominant hexagonal Ni2-xCuxAl3 structure. Increasing Cu level exacerbates the intrinsic resistance of Ni2Al3 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 Ni16Mo10Al74. Before cathodic polarization, the active (leached) form consists of fcc Ni/Cu (or Ni/Cu/Co) mesoporous alloy with a grain size of similar to 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 < 1 mA cm(-2)) up to a breakdown potential beyond + 200 mV/NHE. Post-alkali vacuum annealing at 400 degreesC markedly improves the resistance to corrosion. XPS shows surface enrichment of Cu and Mo, present mainly in oxidation states I and IV, respectively, after etching. The route from novel QC precursors is of practical benefit in leading to more efficient leaching, and yields active forms with somewhat higher resistance to corrosion in acid. (C) 2001 Elsevier Science Ltd. All rights reserved.
Keyword(s): J ; Raney electrocatalysts (auto) ; Ni/Mo synergy (auto) ; decagonal quasicrystals (auto) ; multi-metallic alloys (auto) ; passivation (auto)
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