Recent progress in rhombohedral boron monosulfide and hydrogen boride for hydrogen-related applications.

Hydrogen is a promising energy vector with the potential to become the cornerstone of sustainable energy systems with the support of green production, storage, and utilization technologies. Among the materials explored to advance the hydrogen ecosystem, two-dimensional (2D) boron-based materials have garnered considerable research interest because of their exceptional physicochemical properties, including tunable electronic properties and remarkable chemical stability. While extensive literature on pristine 2D boron nanosheets (borophene) and its hydrogen-related applications exists, comparatively little is known of other emerging members of this material family. This review examines two experimentally realized but underexplored members of this family: rhombohedral boron monosulfide (r-BS) and hydrogen boride (HB). r-BS is assessed as an anodic oxygen evolution reaction (OER) electrocatalyst that supports overall electrochemical hydrogen production by lowering kinetic losses in water oxidation, rather than as a direct hydrogen evolution reaction catalyst. The measured OER response is evaluated in relation to p-type transport, conductive supports, and wettability, whereas the proposed roles of boron vacancies and carbon substitution are identified as theoretical predictions. HB is discussed in the context of a solid-state hydrogen storage material, where its unique H-terminated layered structure not only offers favorable thermodynamic and gravimetric properties, but also enables stimulus-dependent dehydrogenation with thermal, photoinduced, and photothermal release pathways. By linking structure, synthesis, and interfacial chemistry to function, this review defines key challenges in scalable production, defect and layer control, mechanistic validation, recyclable hydrogen release/storage, and system-level assessment. Finally, current research challenges and future opportunities are discussed, offering an outlook on both r-BS and HB for hydrogen technology and related applications.