Abstract Understanding the fundamental steps of adsorption and controlled release of hydrogen in two-dimensional (2D) materials is of relevance for applications in nanoelectronics requiring tuning the physical properties or functionalization of the material, hydrogen storage and environmental sensors. Most applications demand that hydrogen adsorption and desorption can be controlled at room temperature. Here we report an element-specific study on the hydrogenation and dehydrogenation, in a low coverage regime, of a quasi-free standing 2D heterostructure (h-BNG) in the form of coexisting lateral domains of isostructural hexagonal boron nitride (h-BN) and graphene (Gr) on Pt(111). At very low hydrogen coverage a selective and partial hydrogenation of the Gr domains is observed in h-BNG. At the same time no changes are detected in the h-BN domains, indicating a preferential hydrogenation of Gr rather than h-BN domains. At higher coverage, hydrogenation of both Gr and h-BN domains is detected. A thermally facile hydrogen release from h-BN domains near room temperature is observed. Furthermore, the hybrid h-BNG 2D heterostructure enables also a much easier H₂ thermal release from Gr domains when compared with a full Gr monolayer grown on the same Pt(111) substrate. These results suggest that the presence of coexisting hydrogenated h-BN domains could destabilize C–H bonds in Gr.