Tunable kinetics of nanoaluminum and microaluminum powders reacting with water to produce hydrogen

Abstract

Summary This paper reports on the kinetics and reaction processes of 40‐nm and 1‐μm aluminum powders with water to produce hydrogen at atmospheric pressure. This reaction produces aluminum hydroxide with irregular morphologies as by‐products. It was found that the nucleation and growth of the aluminum hydroxides affect the kinetics of the reaction and thus the hydrogen production. The heat release in isothermal microcalorimetry and hydrogen production in a nonisothermal batch reactor were used to determine the rate‐determining steps of the reaction mechanism and the corresponding activation energies. Model and model‐free methods have been implemented to describe the reaction sequence between aluminum particle and water while the phase of newly produced aluminum hydroxide in the system plays an important role. The reaction of nanoaluminum particles and water, being more sensitive to temperature, goes to completion to produce bayerite, Al (OH)3 at 30°C, and boehmite, AlOOH at 50°C, whereas the microaluminum particles do not react completely and produce only bayerite at 30°C and also low‐amount boehmite at 50°C. Nevertheless, these processes exhibit two distinct and sequential stages: a kinetically controlled stage with the apparent activation energy (Ea) of 100 to 110 kJ/mol, where nucleation and growth are limited by the chemical reactions on the surface of aluminum, and a diffusion controlled stage with Ea of 44 kJ/mol for the 40‐nm Al/water reaction and 86 kJ/mol for the 1‐μm Al/water reaction, where growth is limited by the mass diffusion through the aluminum hydroxide by‐products. The separation of these two stages is more obvious under isothermal conditions. For nonisothermal conditions, two stages are overlapped, and the one with a lower Ea dominates.

Hydrothermal Oxidation of Coarse Aluminum Granules with Hydrogen and Aluminum Hydroxide Production: The Influence of Aluminum Purity

“…Oxidizing a kilogram of aluminum in water yields approximately 15.5 MJ of thermal energy and 111 g of hydrogen, with an additional energy potential of 15.5 MJ. A challenge in this process is the formation of an oxide film on the aluminum surface during oxidation, which impedes efficiency [5]. Most of the previous research has been devoted to the search for chemical additives to solve this issue in order to enhance the oxidation rate and the aluminum conversion degree.…”

Investigation on the Al/low‐melting‐point metals/salt composites for hydrogen generation

“…with water in the recent years. [19][20][21][22][23][24][25] Especially, aluminum is being considered to be a very promising hydrogen storage material due to the following advantages: (a) aluminum metal, which is abundant in nature and has low cost, has high energy density. (b) the byproduct of aluminum hydrolysis is the basic raw material for the electrolytic aluminum industry; (c) recycling of the metallic aluminum can take place via the Hall-Heroult process; (d) hydrogen production via reaction between aluminum and water is very convenient for the transportation and storage of hydrogen to meet the real-time hydrogen supply at certain places.…”

“…Ability to solve the problem of hydrogen storage and transportation has led to increasing attention being paid to the in‐situ hydrogen generation via the reaction of metals (Al, Mg, Li, etc.) with water in the recent years 19‐25 . Especially, aluminum is being considered to be a very promising hydrogen storage material due to the following advantages: (a) aluminum metal, which is abundant in nature and has low cost, has high energy density.…”

Generation of hydrogen upon immersion of Mg in Mn(Ac) 2 and the reaction mechanism

“…Hydrolysis of metals (eg, Al‐based and Mg‐based materials) with water has been reported as one of the approaches to produce real‐time hydrogen 3‐9 . Nonetheless, the reaction between metal and water is often hindered by the presence of an oxide film.…”

“…Hydrolysis of metals (eg, Al-based and Mg-based materials) with water has been reported as one of the approaches to produce real-time hydrogen. [3][4][5][6][7][8][9] Nonetheless, the reaction between metal and water is often hindered by the presence of an oxide film. Despite the low activity of Mg with water at ambient temperature, the oxide film on the Mg surface is easier to remove than the oxide film on Al.…”