Peculiarities of the electrolytic hydrogenation of Pd as revealed by resistivity measurements

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Abstract

In this work, the electrochemical hydrogen doping and withdrawal process of Pd metal was examined with respect to the applicability of Faraday's law. It was found that after a suitable electrolytic pre-treatment, the normalized resistivity (R/R0) versus hydrogen concentration (cF = H/M) curves where CF was determined from Faraday's law by assuming that the 100% current efficiency is independent of the value of the applied charging current density in a wide range. In the α-Pd(H) phase (up to c(αmax) = 0.015H/M), a good quantitative agreement was found with previous resistivity studies by both electrolytic and gas-phase charging. However, for c > c(αmax) our R/R0 versus C F data did not agree with the R/R0 versus CH curve from previously reported electrochemical charging experiments of Pd metal where the doped amount of hydrogen, CH, was determined by direct methods. The two sets of resistivity data can be brought into good agreement by assuming that the current efficiency for the absorption process is ηa = 1.55. Similarly, for the electrolytic desorption process, an agreement with the previously reported R/R0 versus CH curve could be achieved by taking ηa = 1.9. These current efficiency values higher than unity would imply that each hydrogen absorbed/desorbed by electrolytic charge/discharge processes is accompanied by the absorption/desorption of some excess H atoms by processes not requiring electric charge transfer (i.e., only neutral H atoms are involved). At present, we do not have a physical/chemical picture about the nature of such processes.

Original languageEnglish
Pages (from-to)172-178
Number of pages7
JournalJournal of Alloys and Compounds
Volume387
Issue number1-2
DOIs
Publication statusPublished - Jan 25 2005

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Keywords

  • Electrochemical reactions
  • Electronic transport
  • Gas-solid reactions
  • Hydrogen storage materials
  • Metals

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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