Hy-Eval

NHSG has developed an innovative approach, Hy-Eval®, to evaluate and quantify hydrogen yield that could be generated through the process of serpentinisation from variable protolith compositions. Our Hy-Eval approach, which uses open source software, has been validated through comparison with publications by experts in the field, 

The procedure adopts a similar approach to that detailed by McCollom & Bach (2009), Klein et al. (2013) & McCollom et al. (2022) and uses as input a quantitative mineralogy that can be derived from whole-rock chemistry or quantitative petrographic analysis. Potential hydrogen production is evaluated at temperatures from 25-400°C. At higher temperatures, serpentine minerals are not stable and hydrogen production by fluid rock interaction is effectively negligible.

The yields calculated using the procedures outline here represent the potential yields at various temperatures, as if water-rock reaction happened at that temperature and reached equilibrium. The base case yields, expressed in the graph in tonnes H2 per km3 with Fo90 olivine as reference, are calculated at a water:rock ratio of 1:1.

These calculations do not reflect the maximum potential yield which would result from the oxidation of all Fe2+ in the protolith to Fe3+ but rather reflect what would occur in nature by taking into account how the mineralogy changes as a function of temperature.

The calculated yields can be used to quantify the potential of different rock types (protoliths) to generate hydrogen under given sub-surface temperature regimes, and provide a useful means for comparing various rock types as potential sources of hydrogen formed by water-rock reaction.

Klein, F., Bach, T. & McCollom, T. M., 2013. Compositional controls on hydrogen generation during serpentinization of ultramafic rocks. Lithos, 178, 55-69, http://dx.doi.org/10.1016/j.lithos.2013.03.008 

McCollom,  T. M. & Bach, W. , 2009. Thermodynamic constraints on hydrogen generation during serpentinization of ultramafic rocks. Geochimica Cosmochimica Acta, 73, 856-875. doi:10.1016/j.gca.2008.10.032

McCollom, T. M., Klein, F., & Ramba, M., 2022. Hydrogen generation from serpentinization of iron-rich olivine on Mars, icy moons, and other planetary bodies. Icarus, 372, https://doi.org/10.1016/j.icarus.2021.114754