Kinetics study on the generation of hydrogen from an aluminum/water system using synthesized aluminum hydroxides

Abstract

Kinetics study on the generation of hydrogen from an Al/water system is performed. The reaction is affected by three major factors such as the concentration of hydroxyl ions (pH values), catalysts, and temperature. However, these factors are interacted and sometimes difficult to separate. This study demonstrates how these factors affect the generation of hydrogen in an Al/water system. Aluminum hydroxide, Al(OH)3 (bayerite phase), synthesized using a chemical solution method, is proved to be a very effective catalyst for the reaction of Al and water. Approximately 95% yield (1300 mL) of hydrogen is produced from 1 g Al in 10 mL water using 3 g Al(OH)3 catalyst at room temperature within 1 minute. The generation rate of hydrogen is accelerated due to the catalyst Al(OH)3 and the exothermic heat. In this report, a ball-mixing process, the ratio of Al:Al(OH)3:H2O, and the reacting temperatures are investigated to clarify the effect of catalyst Al(OH)3. The synthesized Al(OH)3 catalyst is found to reduce the activation energy of Al/water reaction from 158 kJ/mol to 73.3~76.9 kJ/mol. The roles of hydroxyl ions (ie, pH values), temperature, and catalyst on this phenomenal reaction are explained using a kinetics study and the concept of Fick first law. The 3 factors all improve the flux of hydroxyl ions through the passive Al2O3 layer; therefore, the generation of hydrogen is enhanced.