Ti/Cr regulated and strategic Ce doped V-Ti-Cr-Mn-Fe high-entropy alloys with extraordinary reversible hydrogen storage properties at ambient temperature

Abstract

High-entropy alloys (HEAs) are garnering widespread interest due to their exceptional hydrogen storage capabilities at ambient temperatures. Herein, a series of HEAs composed of V-Ti-Cr-Mn-Fe with varying Ti/Cr ratios has been synthesized via arc melting to serve as carrier materials for room-temperature hydrogen storage. Thanks to the composition of a large amount of body centered cubic (BCC) phase V32TixCr58-xMn5Fe5 exhibits excellent hydrogen storage performance, and the hydrogen absorption capacity of these HEAs escalates while the desorption capacity initially rises followed by a decline with an increase in the Ti/Cr ratio. Notably, the HEA with a Ti/Cr ratio of 1.0, namely V32Ti29Cr29Mn5Fe5, demonstrates exceptional performance by absorbing 3.55 wt% H2 within 60 min and rapidly releasing 2.16 wt% H2 within 5 min at 303 K. Further enhancement is achieved with the strategic doping of Ce in the V32Ti29Cr29Mn5Fe5, which leads to the removal of the Ti-rich phase and the incorporation of CeO2, significantly improves the activation performance, allowing the Ce-doped HEA to reach saturation in the 3rd hydrogen absorption cycle. Consequently, the hydrogen ab-/desorption capacities at ambient temperature are further augmented to 3.73 wt% and 2.26 wt%, respectively, and the enthalpies of hydrogen ab-/desorption are significantly reduced to −25.0 and 23.4 kJ/mol H2, marking a new benchmark for V-based HEAs. Dramatically, DFT calculations suggestes that the incorporation of Ce diminishes the structure energy of BCC phase structure for V32Ti29Cr29Mn5Fe4Ce1 as well as elongates the average distance of M−H from 1.955 Å to 1.969 Å, which corroborate the experimental results, offering profound insights into the underlying mechanisms of hydrogen storage within BCC-phase HEAs at ambient temperature.