Aluminum composites for rapid green hydrogen generation and their reaction rate enhancement mechanisms

Aluminum powder can react directly with water to form hydrogen, but the presence of a dense oxide layer on its surface prevents this reaction from occurring efficiently. This study synthesizes an activated aluminum composite (Al-Bi-NaCl-GF) using a novel mechanical ball milling technique, combining activated aluminum powder, bismuth (Bi) powder, graphite fluoride, and sodium chloride (NaCl). The ball milling process disrupts the composite's oxide layer, while the combined catalytic effect of Bi powder, graphite fluoride, and NaCl accelerates the reaction between the aluminum composite and water. This high water reaction rate makes the composite a promising candidate for use as a mobile hydrogen source. To investigate the catalytic mechanism in depth, we also fabricated other aluminum-based composites containing only graphite fluoride or NaCl. Using scanning electron microscopy (SEM) and X-ray diffraction (XRD), we carefully characterized the microstructure and crystallographic features of each active aluminum composite. Additionally, we thoroughly examined the hydrolysis reaction properties of these composites under ambient conditions and in 0 °C ice-water mixtures. The results demonstrate that the hydrolysis rate of the composites is significantly increased by the simultaneous introduction of Bi, graphite fluoride, and NaCl into the aluminum matrix, owing to their synergistic catalytic effect. Experimental data indicate that the Al-Bi-NaCl-GF composite achieves a remarkable peak hydrogen production rate of 9480 mL g⁻1 min⁻1 at 40 °C, and even at a low temperature of 0 °C, it maintains a high production efficiency of 2700 mL g⁻1 min⁻1. These findings highlight the potential of the Al-Bi-NaCl-GF composite as an efficient and practical method for hydrogen generation, particularly in portable and low-temperature applications.