Supporting Information for the following article: "Hydrogen Generation and Serpentinization of Olivine under Flow Conditions"

Serpentinization of olivine is often studied in the laboratory under batch conditions. Olivine conversion in situ with enhanced natural hydrogen production will likely be implemented via injection of aqueous solutions. Hence, transport is relevant to the extent of olivine reaction and, potentially, the morphology of precipitates formed. To test conditions for optimal H2 generation and outcomes, serpentinization was induced by injecting pH = 12.5 brine at 0.015 cm3/min (0.5 pore volumes per day) into an olivine sand pack (250 to < 355 µm grain size) at 245°C generating, at minimum 76 and 89 mol% H2 at 35 and 57 d, respectively. Grain-coating serpentine with radiating needles cemented the reacted sand grains. Importantly, pore space was maintained between the dissolving grains and the serpentine precipitates. Hence, reactivity continued as a result of fluid access to mineral surfaces, the large grain size, and the continuous injection of undersaturated alkaline fluids.