A NOVEL STUDY OF HYDROGEN STORAGE IN (Ni-)Mg-Al HYDROTALCITE-DERIVED MIXED OXIDES

Hydrogen was adsorbed using mixed oxides adsorbents derived from (Ni) Mg-Al hydrotalcite-like compounds (HTlcs). This is a novel study on the use of these mixed oxides to adsorb hydrogen as these materials have never been investigated for use as hydrogen storage media. A previous study has only used the as-synthesized HTlcs to adsorb hydrogen and no hydrogen adsorption was observed in the study. In this study the HTlcs were synthesized via the coprecipitation method and were calcined at various temperatures to obtain the corresponding mixed oxides. Characterizations of the as-synthesized and calcined samples were also conducted. XRD characterizations of the as-synthesized samples showed that the hydrotalcite-like phase was obtained and MgO and NiO (only for Ni-Mg-Al HTlcs) were formed after the calcination step. Furthermore, the FTIR showed that the HTlcs contained water and carbonate ions before and after calcination. However, calcination at high temperatures (750°C and 900°C) caused destruction of the hydrotalcite structure which cannot be reconstructed via rehydration. Meanwhile, it was found that the BET specific surface area generally increases after calcinations at moderate temperatures but decreases at higher calcination temperature. Additionally, TPR showed that only a small amount of hydrogen uptake (1.4mmol/g) occurred when the Mg-Al HTlcs were used which may be due to the low reducibility of the material while addition of Ni showed increase in H2 uptake of Ni-Mg-Al HTlcs (3.3mmol/g) with the same Mg/Al molar ratio. The adsorption of hydrogen following the material reduction in the TPR experiments is indicated by tailings in the reduction profile. Meanwhile, the hydrogen adsorption capacity determined by thermogravimetric analysis conducted at temperatures of 400°C, 200°C and 100°C indicated that Ni-Mg-Al HTlcs with Ni/Mg/Al molar ratio of 1:2:1 adsorbed the highest amount of hydrogen (3 wt% at 100°C). In conclusion, the high reducibility and the hydrotalcite-like structure of the Ni-Mg-Al HTlc make it the most favourable material for hydrogen storage in this study.