Over the past years the interest in geochemical reactions forming or oxidizing molecular hydrogen has soared: In addition to the long-standing issue of possible hydrogen production in high-level nuclear waste repositories due to corrosion of canisters or radiolysis of water, the energy transition considering molecular hydrogen as energy carrier calls for a thorough understanding of possible reactions during subsurface storage of hydrogen. Recent findings of unusually hydrogen-rich soil gases have underlined the importance of elucidating the natural hydrogen cycle before advancing the large-scale usage of hydrogen as energy carrier. This session will combine contributions investigating the reactions, processes and kinetics of formation or oxidation of hydrogen e.g. on mineral surfaces or by microorganisms - from both experimentalists and modelers to foster the exchange. Additionally, it will integrate research on controls of hydrogen migration – as loss from subsurface storage, possible pressure-release mechanism during the long-term storage of high-level nuclear waste or in the context of natural hydrogen fluxes in marine (e.g. hydrothermal) and continental settings, prerequisite for possible accumulations of hydrogen in the geosphere.