Resumo:
The hydrolysis route of aluminum alloys has been gaining prominence for producing green hydrogen in a clean, simple, and in situ manner, reducing costs associated with transportation and storage. However, this route still requires research aimed at improving the reaction yield. In this context, the addition of various metallic additives to aluminum through high-energy milling has been studied. Although it has theoretical potential, the use of niobium as an additive does not have extensive literature on this topic. With a focus on understanding the role of this additive, this study produced Al-Nb samples with compositions of 80, 85, 90, and 95% aluminum, respectively. The use of niobium as an additive in combination with bismuth was also evaluated, given the widespread use of bismuth in the literature, and for comparative purposes, pure aluminum milled for 7 hours was also assessed. With the exception of pure aluminum, the samples were milled for 15 and 21 hours at 300 rpm with a ball-to-powder mass ratio of 1:30. The morphology of the samples, as well as the distribution of the additives, were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and particle size analysis. The hydrolysis reaction was conducted in an aqueous medium containing 0.5 mol·L⁻¹ NaOH at 30 °C. The incorporation of niobium into aluminum promoted an increase in the reaction yield, with the 95 wt.% Al-5 wt.% Nb mixture achieving 90% yield in the hydrogen production reaction. This effect was attributed to structural defects introduced into the aluminum particles during milling, along with the additive. The hydrogen production rate was also evaluated, reaching a maximum value of 116.8 ml/min in the sample containing bismuth. This result was influenced by particle size, as well as by the anodic activation effect caused by the difference in reduction potential of the additives relative to aluminum. The study demonstrated the potential of niobium and its combined use with bismuth, providing initial data for further research on the topic.
