Hydrogen (deuterium) retention and desorption from boron: Efficient dissociation of molecular hydrogen and absence of diborane desorption

Understanding hydrogen isotope retention in plasma-facing materials is essential for the safe and efficient operation of fusion reactors. This study investigates hydrogen and deuterium interactions with polycrystalline β -phase boron with surface carbon contamination. Using a combination of X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM)/Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and Temperature Programmed Desorption (TPD), we characterize materials and evaluate the retention, desorption, and possible reaction pathways of hydrogen isotopes. Our experiments demonstrate efficient molecular hydrogen dissociation on boron surfaces and significant isotope retention, even after neutral molecular exposure at room temperature. Importantly, diborane (B 2 H 6 ) production was found to be negligible under available experimental conditions. TPD spectra reveal two distinct desorption features: a low-temperature desorption peak consistent with previous literature and a previously unreported high-temperature desorption peak above 1000 K. We show that repeated thermal cycling enhances boron chemical activity, likely due to boron sublimation and the formation of new active sites. Preliminary experiments suggest that both low-energy and high-energy trapping sites may be accessed through molecular isotope exposure, but without clear evidence of isotope exchange between these sites, and without significantly reducing the population of the initially present isotope. These findings highlight the critical role of boron surface chemistry in hydrogen isotope retention, with potential challenges for tritium management in future fusion devices. • Efficient dissociation of molecular hydrogen on β -boron surfaces at room temperature. • Negligible production of diborane during hydrogen isotope desorption up to 1350 K. • Observation of a previously unreported high-temperature desorption peak above 1000 K. • Evidence of increased chemical activity and isotope retention after repeated thermal cycling.