Study On Rapid Hydrolysis Of Hydrogen From Al-based Materials

With the deterioration of the environment, hydrogen, one of regenrative and ultimate secondary energy, has been attracting much attention by scientists. Aluminium, abundant in earth,has the characteristics such as low density, high capacity and good activity, also on the trend of thermodynamics is easy to react with water to generate hydrogen.Aluminium as hydrogen production material can effectively solve the bottleneck of the hydrogen in the transport and use,will greatly reduce the cost of the hydrogen use.In this thesis,bases on the review of the research and development of hydrogen generation from borohydride 、 photoelectro-catalysis 、 water electrolysis and metal-based material, the Al-based materials were selected as the object of this article. The effects of alloy composition,hydrolysis temperature and alkali concentration on the hydrolysis of Al-based alloys performance were studied. By means of X-ray diffractometer and microscope analyses the phase and the surface morphology of the alloy, and by CS310 testing electrochemical corrosion of alloys.Effect of alloys composition on the hydrogen generation: the results showed that the addition of Ni could significantly improve the hydrolysis rate of Al-Ni alloys. As the Ni content of Al-Ni alloys increased from 0(pure Al) to 4wt.%, the average hydrogen generation rate increased dramatically from 15.16mL·min-1·g-1 to 27.71mL·min-1·g-1. The X-ray diffraction analysis indicated that Al3 Ni phase appeared during melting process, and the micro-structure observation showed that Al3 Ni phase uniformly distributed around the Al phase, which can effectively destroy the integrity of the oxide film on the surface of the Al alloy.The study on the effect of different Fe content on Al-Fe alloys hydrolysis ability founded that Al-1wt.%Fe alloy showed the fastest hydrogen generation rate and preferable hydrogen yield. In 25%KOH solution, hydrogen generation rate was 22.15 m L·min-1·g-1, hydrogen yield was 98.1%. The X-ray diffraction analysis indicated that Al3 Fe phase appeared in Al-1wt.%Fe alloy. The micro-structure observation showed that Al3 Fe phase in Al-1wt.%Fe alloy distributed in grain boundaries, which increased the contact area between the Al and the solution, on the other hand, Al3 Fe and Al can form a miniature battery. All of these help to improve the hydrogen generation rate and hydrogen yield.The study on the effect of different LaNi3 content on Al-LaNi3 alloys hydrolysis ability founded that Al-3wt.%LaNi3 alloy showed the fastest hydrogen generation rate and preferable hydrogen yield. In 25%KOH solution, hydrogen generation rate was 19.0mL·min-1·g-1, hydrogen yield was 95.0%.Effect of KOH concentration on the hydrogen generation. Experiments showed that the change of KOH concentration mainly influence the hydrogen generation rate and reaction time.With the increased of the KOH concentration, the hydrogen generation rate of the Al-based alloys significantly increase. With the reaction processing, OH- continually decrease, it will slow down the hydrogen evolution from corrosion of aluminum. The increase of KOH concentration,meas much more OH- in solution, which can directly accelerate the hydrolysis rate.Studies suggested that lye as a catalyst for the hydrolysis reaction of Al also participated in the hydrolysis reaction. The intermediate KAl(OH)4 rapidly decomposed into KOH and Al(OH)3,this is the first step to determine the hydrolysis kinetics of aluminum. So increasing the alkali concentration can conducive to improve the hydrogen generation rate.Effect of temperature on the hydrogen generation: Increasing the temperature can improve the dynamic performance of the hydrolysis reaction of aluminum, and the higher the temperature,the more obvious improvement. Since the hydrolysis reaction was an exothermic reaction, the reaction once started, and would generate a lot of heat, so that the hydrolysis of the ambient temperature would rise.Galvanic corrosion of Al-based alloys during hydrogen generation. Electrochemical test on Al-Ni alloys showed that, as the Ni content added, alloy corrosion potential reduced from-0.803 VSCE of pure Al to-0.950 VSCE of Al-4wt.%Ni. Electrochemical test on Al-Fe alloys showed that, alloy corrosion first decreased from-0.803 VSCE of pure Al to-0.982 VSCE of Al-1wt.%Fe, and then increased from-0.890 VSCE of Al-3wt.%Fe to-0.851 VSCE of Al-6wt.%Fe.As is known to all, the lower corrosion potential, the faster the rate of hydrogen generation rate,so the appropriate Ni and Fe were added as a second phase, can decrease the corrosion potential of the alloy, so as to achieve the purpose of speeding up the rate of hydrogen generation by hydrolysis.