Fe-Doping Strategy Enhances Reversible Hydrogen Capacity and Cycle Stability of V-Ti-Cr Solid Solution Alloy

The vanadium-based solid solution alloy that features high volumetric hydrogen density is a competitive solution for hydrogen storage system. However, the strong V-H bonding fundamentally limits its reversible hydrogen storage capacity (C_re) and cycling performance. Herein, we design a series of Fe-doped BCC single-phase alloys, V₈₀Ti_6.67Cr_13.3.3-xFe_x (x=0,1,2,3), to systematically investigate the Fe doping effect. DFT calculations reveal that in the alloys and hydrides phases, vanadium atoms donate electrons to iron through charge transfer, reducing both the electron density of states near hydrogen sites and the V-H bond strength. This electronic modulation leads to a measurable increase in V-H bond length from 1.76 Å of V₈₀Ti_6.67Cr_13.33 hydride to 1.80 Å of V₈₀Ti_6.67Cr_12.33Fe₁ hydride. PCT measurements demonstrate a non-monotonic trend in reversible capacity with Fe content, peaking at 2.34 wt.% for the 1% Fe-doped alloy. Notably, under experimental conditions (273 K absorption/343 K desorption), V₈₀Ti_6.67Cr_12.33Fe₁ alloy achieves a C_re of 2.58 wt.%. Moreover, the V₈₀Ti_6.67Cr_12.33Fe₁ alloy exhibits exceptional cycling stability with 93.6% capacity retention after 500 cycles at 298 K, demonstrating the critical role of Fe in enhancing cycling performance. This achievement opens new insight into bonding structure engineering for developing advanced alloys with enhanced hydrogen storage capability.