Local initiative hydrogen production by utilization of aluminum waste materials and natural acidic hot-spring water

Hydrogen is gaining attention as an energy source, but its production through fossil-fuel use is not environmentally friendly. A more sustainable source could be the hydrothermal reaction involving aluminum and water reaction, which owns technical issues on aluminum passivation and material sources for the upscale application. This study analyzes the aluminum-water hydrothermal reaction at laboratory and field scales and includes an environmental assessment of H₂ fuel production involving hot-spring water with extremely low pH (~1) and boiling temperature (~373 K). Acidic hot-spring alternates water sources, and its unique feature activates aluminum surface by attacking oxide layer, hence enables H₂ generation. Aluminum waste sources include dross and cutting chips, which could replace primary aluminum metal. The highest H₂ yield could be obtained of about ~55 mmol H₂ g_Al⁻¹ for the chip (almost reached theoretical yield) and a smaller amount of ~20 mmol H₂ g_Al⁻¹ for dross. The environmental assessment comprises carbon dioxide emissions and energy consumption from the overall H₂ fuel system resulting in a reduced environmental impact. The proposed hydrogen production method encourages hydrogen energy development from the local scale. In addition, the use of aluminum waste materials is a new and useful waste management strategy than direct disposal, and hot-springs use advances its direct utilization.