Unlocking Low-Temperature Hydrogen Release from Ti–Cr–Mo Hydrogen Storage Alloys via Cobalt Substitution

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Abstract Hydrogen release from Ti–Cr–Mo-based BCC alloys suffers from sluggish kinetics and high hydride stability at low temperatures, limiting their use in subambient hydrogen supply. In this work, we systematically investigate the effect of minor Co substitution on the low-temperature desorption behavior of Ti40Cr50Mo10 (TCM) and Ti40Cr49Mo10Co1 (TCMC) alloys prepared by vacuum arc melting and homogenization. Both alloys retain a single BCC phase. While Co substitution barely affects absorption capacity, it significantly accelerates the release of hydrogen and improves the desorption capacity. In particular, at 273 K, TCM released only 0.21 wt % hydrogen, with the hydrogen-release reaction nearly halted, whereas TCMC released 1.14 wt %, sufficient to support the cold start of winter hydrogen storage devices. Kinetic analysis shows that TCMC exhibits consistently higher rate constants than TCM across various temperatures. JMAK analysis reveals a decreased apparent activation energy for reversible hydride decomposition from 45.70 to 42.48 kJ·mol–1 at ambient temperature, indicating a lower energy barrier. TDS results further confirm that TCMC has a lower dehydrogenation temperature and reduced activation energies for all desorption peaks. The improved low-temperature performance arises from synergistic enhancement of hydrogen diffusion and hydride thermodynamics by Co substitution. This work offers a viable strategy for designing V-free BCC alloys with superior low-temperature hydrogen release.