UC Davis

Hydrogen fuel can be harnessed to power countless technologies, including hydrogen fuel cell devices and hydrogen-powered cars, buses, boats, aircraft, etc. High-purity hydrogen can be easily, rapidly, and successfully produced from the direct reaction of water with “activated” Al. Al by itself does not significantly react with water, but activated Al is Al that is made to be water-reactive via dissolving it in liquid Ga or liquid “eGIS.” eGIS is eutectic galinstan: 68.5wt%Ga, 21.5wt%In, and 10wt%Sn. | | | | | | | | | | A fairly novel processing technique—amalgamation via a dental amalgamator—was used to fabricate activated Al. This is a single-step technique that is rapid, can be performed at room temperature, and increases the surface-area-to-volume ratio of the activated Al to facilitate faster hydrogen-generation rates, as compared to traditional fabrication technologies. | | | | | | | | | | A very promising result was that the 10wt%eGIS-90wt%Al amalgam was shown to offer a full yield of high-purity hydrogen when it was reacted in water, regardless of variability in water pH and variability in chemical substance contaminants that were present in several tested types of waters—and even in relatively inexpensive and “dirty” tap water. The use of tap water, alkaline water, distilled water, and deionized water all resulted in the successful generation of approximately 100% yield of hydrogen. The 10wt%eGIS-90wt%Al amalgam reacted very rapidly in the 50°C deionized/distilled waters, reaching a 90% yield of hydrogen in as fast as 18 seconds, and reaching ~100% yield shortly thereafter. In 50°C waters, the hydrogen-generation rate of the 10wt%eGIS-90wt%Al amalgam in the deionized water was essentially identical to that in the distilled water and was ~11 times faster than in the alkaline water and ~28 times faster than in the tap water. | | | | | | | | | | Commercially relevant conditions of operational stability and shelf-life stability of the 10wt%eGIS-90wt%Al amalgam were investigated: annealing or aging at high temperature (400°C) for 1 week and at room temperature for 6 months. Remarkably, these conditions did not decrease the amalgam’s hydrogen generation rate or decrease its hydrogen-generation yield from ~100%. | | | | | | | | | | Further analyses explored the roles of Ga and eGIS in Al-Ga/eGIS water-reactivity. Results were consistent with the hypothesis, based on the Al-Ga phase diagram, that Al-Ga amalgams that contain >20wt%Ga give ~100% hydrogen yields but Al-Ga amalgams that contain <20wt%Ga give vastly lower hydrogen yields. However, Al-eGIS amalgams that contain as little as 10wt%eGIS (if not less) were found to be highly water-reactive, rapidly producing ~100% yields of hydrogen. Evidence supported the hypothesis that the high degree of water-reactivity of many compositions of Al-eGIS amalgams, in contrast to some compositions of Al-Ga amalgams, is due to the ability of Ga to remain bonded with In and/or Sn in Al grain boundaries, rather than significantly diffusing into Al grains, thereby allowing Al to readily dissolve into the liquid eGIS-rich phase in the Al grain boundaries to facilitate significantly high amalgam water reactivity. In a separate experiment, numerous different compositions of Al-In-Sn alloys, all Ga-free, displayed <1% yield of hydrogen in the tested water temperature range of ≤50°C. The results suggest that, at least for water bath temperatures of ≤50°C, the addition of Ga is needed for Al-galinstan alloys and amalgams to become activated (water reactive).