Hydrogen production from aluminum-water reactions subject to varied pressures and temperatures

Abstract

The production of hydrogen via an aluminum-water reaction is explored at temperatures and pressures ranging from 273.15 to 600 K and 0.1–10 MPa, respectively. Across this range, aluminum and water can react to form different aluminum oxide and hydroxide species, resulting in differences in the release of thermal energy, as well as the amount of water required stoichiometrically for the reaction to proceed. A model presented in this work uses the Gibbs free energy to predict the favorability of these byproducts as a function of temperature and pressure. At 0.1 MPa, this model predicts the primary favorability of Al(OH)₃ (gibbsite)below 294 K, AlOOH (boehmite)from 294 to 578 K, and Al₂O₃ (corundum)above 578 K. The results of this model were tested using a previously established technique for activating bulk aluminum via infusion of a gallium-indium eutectic into its grain boundary network. Reaction tests were performed at the extremities of the operating range of interest, and the composition of the byproducts from each test, determined via Fourier transform infrared spectroscopy (FTIR)and X-ray diffraction (XRD)analysis, were all in alignment with the model. Furthermore, reaction tests above 423 K at 0.1 MPa indicate limited reactivity of steam with aluminum activated in this manner. Consequently, the model is modified accordingly to show that Al₂O₃ cannot be achieved in practice with this method as its transition remains above the saturation temperature of water at the pressures studied here.