Effect of Niobium doping on the crystal structure and hydrogen sorption properties of TiFe: combined X-ray diffraction and absorption study

TiFe alloys have attractive attention as solid-state stationary hydrogen storage compounds. They can absorb hydrogen gas reversibly at near ambient temperatures and practical pressures with high volumetric capacities surpassing that of cryogenically liquified H 2 . The main drawback of TiFe is a costly activation procedure. Doping the alloy with various additives is known to improve hydrogen diffusion softening the conditions of the activation. Little attention has been dedicated to the fundamental understanding of the effects of hydrogen sorption on the alloys’ structure. The latter, however, is an important information in the knowledge-guided design of novel materials. In this work, we investigate effects of Nb-doping on crystallographic structure of TiFe and its hydrogen sorption properties. TiFe samples with two different Nb stoichiometries were synthesized using arc-melting (AM) and characterised with synchrotron powder X-ray diffraction (SR-PXRD) and extended X-ray absorption fine structure (EXAFS) analysis. Overall, H 2 absorption measurements (at 50 ± 2 °C and 40 ± 2 bar), have shown that doping of TiFe with Nb can improve matrix activation and kinetics of hydrogen sorption without compromising the overall storage capacities. Refinement of SR-PXRD and EXAFS data showed significant Nb occupancy in secondary Ti phases, which improved the hydrogenation properties of the alloys.