Influence of Synthesis Gas Components on Hydrogen Storage Properties of Sodium Aluminium Hexahydride

A systematic study of different ratios of CO, CO₂, N₂ gas components on the hydrogen storage properties of the Na₃AlH₆ complex hydride with 4 mol% TiCl3, 8 mol% aluminum and 8 mol% activated carbon is presented in this paper. The different concentrations of CO and CO₂in H₂ and CO, CO₂, N₂ in H₂ mixture were investigated. Both CO and CO₂gas react with the complex hydride forming Al oxy-compounds, NaOH and Na₂CO₃ that consequently cause serious decline in hydrogen storage capacity. These reactions lead to irreversible damage of complex hydride under the current experimental condition. Thus, after 10 cycles with 0.1 vol % CO + 99.9 vol %H₂ and 1 vol % CO + 99 vol %H₂, the dehydrogenation storage capacity of the composite material decreased by 17.2% and 57.3%, respectively. In the case of investigation of 10 cycles with 1 vol % CO₂ + 99 vol % H₂ gas mixture, the capacity degradation was 53.5%. After 2 cycles with 10 vol % CO +90 vol % H₂ , full degradation was observed, whereas after 6 cycles with 10 vol % CO₂+ 90 vol % H₂, degradation of 86.8% was measured. While testing with the gas mixture of 1.5 vol % CO + 10 vol % CO₂+ 27 vol % H₂ + 61.5 vol % N2, the degradation of 94% after 6 cycles was shown. According to these results, it must be concluded that complex aluminum hydrides cannot be used for the absorption of hydrogen from syngas mixtures without thorough purification.