Chemical equilibrium analysis for hydrolysis of magnesium hydride to generate hydrogen

Takehito Hiraki, Shun Hiroi, Takuya Akashi, Noriyuki Okinaka, Tomohiro Akiyama

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Magnesium hydride is a promising hydrogen source because of its high mass density of hydrogen, 15.2%, when it is hydrolyzed; MgH 2 + 2H 2O = Mg(OH) 2 + 2H 2 + 277 kJ. However, a magnesium hydroxide, Mg(OH) 2, layer forms rapidly on the surface of the unreacted MgH 2 as the pH increases, hindering further reaction. The purpose of this study is to find acids that could effectively accelerate the reaction by using a chemical equilibrium analysis where the relationships of pH to concentration of ionized Mg were calculated. For the best performing acid, the calculated and measured relationships were compared, and the effects of acid concentration on hydrogen release were measured. The analysis revealed that citric acid and ethylenediamine-tetraacetic acid were good buffering agents. The calculated and measured relationships between pH and concentration of ionized Mg were in good accord. Hydrogen release improved considerably in a relatively dilute citric acid solution instead of pure distilled water. The maximum amount of hydrogen generated was 1.7 × 10 3 cm 3 g -1 at STP after 30 min. We estimated the exact concentration of citric acid solution for complete MgH 2 hydrolysis by a chemical equilibrium analysis method.

Original languageEnglish
Pages (from-to)12114-12119
Number of pages6
JournalInternational Journal of Hydrogen Energy
Volume37
Issue number17
DOIs
Publication statusPublished - 2012 Sep 1

Keywords

  • Buffer capacity
  • Equilibrium analysis
  • Hydrogen
  • Hydrolysis
  • Magnesium hydride

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Condensed Matter Physics
  • Energy Engineering and Power Technology

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