Hydrogen Generation By Reaction Of Aluminum With Water

Hydrogen, a regenerative and environmentally friendly fuel with high calorific value, has attracted much attention. The hydrogen economy concept envisions that the future global energy demands will be mainly satisfied by hydrogen fuel instead of fossil fuels. Hydrogen generation by hydrolysis of aluminum in NaOH solution is concerned in the past ten years, because the dense aluminum oxide film is dissolved into alkaline solution, exposing fresh aluminum continue to react with water. However, the corrosion of the alkaline solution is strong. The aluminum-water reaction in weak acid solution, water and alkaline solution was studied. X-ray diffraction (XRD),scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the microstructure of the products.The main results are included as following:(1) The hydrogen generation of aluminum in AICl3, FeCl3, NiCl2and CoCl2solution was investigated. The discharge current of hydrogen-oxygen reaction was related to the hydrogen generation rate and the hydrogen generation amount. The hydrogen generation amount linearly increased with increasing CoCl2concentration from0.5M to2.5M, and it reached the maximum in1M CoCl2. It dramatically decreased with further increasing CoCl2and NiCl2concentration. The formation of Co/Al and Ni/Al galvanic cell, the decrease of pH and the permeation of chloride into oxide layer benefited hydrogen evolution. Besides these factors, the amorphous Co with higher specific surface area acted as the catalyst to quicken hydrogen evolution. The hydrogen evolution in1M CoCl2increased from30℃to45℃, and then it obviously slowed down above60℃.(2) Al/NaCl composites were prepared using the melting of Al. The hydrogen generation of Al/NaCl in water, NaOH and NiCl2solution was discussed. The results showed that hydrogen generation amount was enhanced with increasing NaCl content. Increasing temperature, both the induction time and hydrogen generation amount were enhanced. The reaction of Al/NaCl with water in weak acid or alkaline media was improved. The induction time was shorted in NaOH solution and the hydrogen generation amount in NiCl2was higher.(3) Al/Ni/NaCl mixture prepared by ball milling was effective to improve hydrogen generation. Varying the ratio of Ni and Al, hydrogen generation amount improved from 720ml·g-1to1170ml·g-1at45℃. The particles size of Al decreased by ball milling. Meanwhile, the dissolution of NaCl enhanced the conductivity and strengthened the function of Al/Ni micro-galvanic cell. Value of pH in the media was important for hydrogen evolution. Therefore, the hydrogen generation of Al/Ni/NaCl mixture in water, NaOH and NiCl2was investigated. It is to note that the synergism cooperation of the fresh Ni and the decrease of pH value in NiCl2aqueous solution accelerate hydrogen generation.