An alloy of aluminium and gallium in pellet form added to water can be used to generate hydrogen. The process also produces alumina, but <answer>the expensive gallium</answer>, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as hydrogen can be produced on-site and does not need to be transported.
What can be reused after the formation?
the expensive gallium