[Paper Review] Effect of Niobium Doping on the Crystal Structure and Hydrogen Sorption Properties of TiFe: Combined Synchrotron X-ray Diffraction and Extended X-ray Absorption Fine Structure Study

Abhishek Banerjee, Stefano Deledda+1 more|arXiv (Cornell University)|Jan 13, 2026

Hydrogen Storage and Materials0 citations

TL;DR

The study investigates Nb-doped TiFe alloys using synchrotron X-ray diffraction and EXAFS to understand structural changes and hydrogen sorption improvements, showing enhanced activation and kinetics without loss of storage capacity, linked to Nb occupancy in secondary Ti-containing phases.

ABSTRACT

TiFe alloys are attractive compounds for solid-state stationary hydrogen storage. They can absorb hydrogen gas reversibly at near ambient temperatures and practical pressures with high volumetric capacities surpassing that of cryogenically liquified H2. The main drawback of TiFe-based storage systems is a costly activation procedure required due to the formation of oxide surface layer, which hinders hydrogen diffusion into the bulk. Doping the alloy with various additives is known to improve hydrogen diffusion softening the conditions of the activation procedure. Hydrogen sorption properties of the modified alloys have been the focus of most studies whereas less 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 investigated effects of Nb-doping on crystallographic structure of TiFe metal-alloy compounds and their 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, H2 absorption measurements (at 50 +/- 2 degrees 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.

Motivation & Objective

• Understand how Nb doping affects the crystallographic structure of TiFe-based alloys.
• Determine the impact of Nb on hydrogen sorption properties and activation behavior.
• Identify structural features (via SR-PXRD and EXAFS) that correlate with improved kinetics and retained storage capacity.

Proposed method

• Synthesize TiFe alloys with two Nb stoichiometries via arc-melting.
• Characterize structure using synchrotron powder X-ray diffraction (SR-PXRD).
• Analyze local structure with extended X-ray absorption fine structure (EXAFS).
• Perform hydrogen absorption measurements at 50 ± 2 °C and 40 ± 2 bar to assess activation and kinetics.
• Refine SR-PXRD and EXAFS data to determine Nb occupancy in secondary Ti phases.

Experimental results

Research questions

• RQ1 Does Nb doping alter the crystal structure of TiFe alloys in a way that affects hydrogen diffusion pathways?
• RQ2 How does Nb incorporation influence activation procedures and hydrogen sorption kinetics?
• RQ3 What is the role of Nb occupancy in secondary Ti phases for the hydrogen storage properties of TiFe?
• RQ4 Can Nb doping maintain or improve storage capacity while enhancing kinetics?

Key findings

• Nb doping improves matrix activation and hydrogen sorption kinetics in TiFe alloys.
• Hydrogen storage capacity is preserved despite Nb addition.
• Refinement indicates significant Nb occupancy in secondary Ti-containing phases, correlating with improved hydrogenation properties.
• Two Nb stoichiometries were studied to elucidate the role of Nb distribution in the structure.
• Activation and kinetics benefits are achieved without compromising overall storage performance.