Optimized Sustainable Hydrogen Generation from Liquid Metal Activated Aluminum-Water Reactions

Abstract

This study presents a sustainable and cost-effective method for hydrogen generation using aluminum waste, addressing both energy and environmental challenges. Activated aluminum reacts with water to produce hydrogen, heat, and aluminum oxyhydroxide (boehmite), a commercially valuable byproduct. As a safe, efficient, and cost-effective energy carrier with an energy density exceeding 20 kWh/L (8 kWh/kg), aluminum enables on-demand hydrogen production for diverse applications, including maritime transport and off-grid power systems. This research optimizes reaction kinetics to enhance hydrogen yield and rate while minimizing costs and carbon emissions.

Activation involves coating aluminum with a gallium-indium eutectic (eGaIn) liquid metal, which disrupts the oxide layer and enables spontaneous reaction in aqueous environments. The study investigates seawater as an ionic medium for eGaIn eutectic agglomeration and reuse. However, chlorine binding slows the reaction, which was countered using high-temperature operation and catalytic enhancement. Adding 0.02 M imidazole accelerated the reaction 60-fold, enabled 92% eutectic recovery, and achieved 99% of the theoretical hydrogen yield.

Environmental conditions significantly influence reaction efficiency. Increasing seawater temperature from 20°C to 90°C enhanced reaction rates 44-fold, aligning with Arrhenius Law. Isochoric reactions at high pressure were tested to simulate deep-sea vehicle environments using onboard hydrogen reactors fueled by aluminum and surrounding seawater. Results showed a 33% yield increase at 6 MPa (586 m depth) compared to atmospheric pressure, primarily due to surface tension effects that reduce hydrogen bubble size, improving aluminum-water contact at higher pressures.

A life cycle and cost analysis identified an optimized production scenario with a carbon footprint of 1.45 kgCO2eq/kg H2, meeting green hydrogen standards. Major contributors include recycled aluminum use and processing, and the eGaIn alloy; but eutectic recovery and thermal energy reuse further reduce emissions. Using scrap aluminum and recovering byproducts, hydrogen production costs are estimated at $9.2/kg. Additionally, reselling boehmite (market price $2.5/kg) could generate revenue 5.6 times greater than input costs, significantly improving economic viability.

To demonstrate scalability, a modular hydrogen reactor was developed and directly integrated with a commercial generator, reliably producing 400W of power from on-demand, 99% purity lab-tested hydrogen. The envisioned application is a fully integrated aluminum recycling system that utilizes aluminum waste and seawater to generate hydrogen, thermal energy, and boehmite. This approach advances clean energy technology by providing a scalable and economically viable hydrogen production pathway.

Beyond its direct application in underwater technologies, this optimized reaction can support energy-intensive operations such as heating, desalination, transportation, industrial hydrogen production for refining and fertilizer synthesis, stationary energy systems for off-grid power, and renewable energy storage. Its versatility strengthens energy security and decarbonization efforts while offering a cost-competitive alternative to conventional fuels, positioning it as a key enabler of a sustainable energy future.