Leveraging Grain Size Effects on Hydrogen Generated via Doped Aluminum–Water Reactions Enabled by a Liquid Metal

Through the aluminum–water reaction, hydrogen is densely stored and generated on-demand. To enable the reaction, we harness eutectic gallium–indium which permeates through aluminum's grain boundaries, disrupting aluminum's oxide layer and inhibiting further passivation of the aluminum grain surfaces. We find that, in addition to doping, grain refining and grain coarsening offer a latitude in engineering aluminum microstructures to tune hydrogen generation rates and reaction efficiency. In Mg-doped, Mg2Si-doped, and pure aluminum, reducing the grain size from an as-cast structure to around 30 μm increases the rate of hydrogen flux by an order of magnitude. Mild silicon doping at 0.6 wt % significantly increases the reaction rate in which the same grain size reduction increases hydrogen flux rates by two orders of magnitude. Additionally, the byproduct of the aluminum–water reaction varies with both doping and grain size. Results of combined grain size and doping effects on hydrogen evolution rates allow for further exploration into the underlying reaction mechanism in the presence of a liquid metal.