Abstract
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 CO2 in H2 and CO, CO2, N2 in H2 mixture were investigated. Both CO and CO2 gas 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.
Highlights
Hydrogen storage is a key enabling technology for bringing forward hydrogen and fuel cell technologies in applications including transportation, stationary and portable power
Hydrogen which can be used for recharging metal hydrides is a constituent of synthesis gas that is usually generated by the endothermic steam reforming of hydrocarbons, partial oxidation of methane, or gasification of coal and biomass [4,5]
Activated carbon (8 mol%) and aluminum (8 mol%) were added to Na3AlH6 and TiCl3 (4 mol%) to enhance heat transfer of the composite material, which could improve the hydrogenation and dehydrogenation kinetic as well as dispersion, which can prevent the material from sintering during long time cycling
Summary
Hydrogen storage is a key enabling technology for bringing forward hydrogen and fuel cell technologies in applications including transportation, stationary and portable power. Hydrogen which can be used for recharging metal hydrides is a constituent of synthesis gas that is usually generated by the endothermic steam reforming of hydrocarbons, partial oxidation of methane, or gasification of coal and biomass [4,5]. Partial oxidation of methane occurs when a sub-stoichiometric fuel–air mixture combusted forming a hydrogen-rich synthesis gas in an exothermic process according to Equation (2) [7]: CH4 + 0.5 O2 CO + 2H2 ∆HR = −38 kJ molCH4−1. The influence of different ratios of CO, CO2, N2 on the hydrogen storage performance of the complex metal hydride Na3AlH6 with 4 mol% TiCl3, 8 mol% aluminum and 8 mol% activated carbon is explored
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