Tuning atomic mismatch with trace Al for enhanced long-term hydrogen storage performance of TiCrMo alloy

Abstract

The BCC-type hydrogen storage alloy exhibits a theoretical capacity of 3.8 wt% at ambient temperature, yet faces challenges of high V-metal cost and limited cycling stability. In this work, trace Al substitution strategically tunes atomic mismatch in V-free Ti–Cr–Mo-based BCC alloys, enabling cost-effective hydrogen storage with enhanced long-term performance. A stable and uniform BCC matrix was formed through the partial substitution of Cr with Al, which adjusted atomic mismatch and lattice parameters while effectively inhibiting the precipitation of Ti-rich phases. The optimized Ti₄₂Cr₅₁Mo₅Al₂ alloy achieves a remarkable 3.65 wt% hydrogen capacity at 5 °C, with 2.54 wt% effective desorption at 85 °C. Kinetic analysis attributes the accelerated hydrogen desorption (E_a reduced from 47.0 to 37.5 kJ mol⁻¹) to an interface-controlled reaction mechanism, while thermodynamic evaluation yields a moderate desorption enthalpy (ΔH reduced from 49.96 to 39.84 kJ mol⁻¹). Critically, Al substitution enhances cycling durability, retaining 91% capacity after 500 cycles. This atomic-scale tuning strategy provides a scalable approach to develop low-cost, high-performance hydrogen storage materials for practical application.