The enhanced hydrogen storage performance of Zr_0.8Hf_xTi_0.2-xCo (x=0, 0.05, 0.1, 0.15) alloys via Hf doping

Single element doping is considered feasible strategy to boost the hydrogen storage performance of ZrCo based alloy. However, single element doping has limitations. Element composition design and multielement co-doping are considered research trends. In this study, the quaternary alloys of Zr_0.8Hf_xTi_0.2-xCo (x = 0.05, 0.1, 0.15) were designed via Hf doping based Zr–Ti–Co alloy, and the hydriding/dehydriding kinetics and cycling stability were significantly enhanced. The base alloy Zr_0.8Ti_0.2Co exhibits a CsCl-type cubic phase, while the addition of Hf introduces a secondary HfCo phase. The hydriding/dehydriding kinetics is enhanced sharply due to the catalytic effect of HfCo second phase. The cyclic retention rate of Zr_0.8Hf_0.1Ti_0.1Co alloy increases to 76.9 % (compared to Zr_0.8Ti_0.2Co with retention rate 65.9 %), which is attributed to the good anti-disproportionation performance and better structural stability during absorption/desorption process. The design of quaternary alloys is an effective approach to enhance the hydrogen storage properties of ZrCo based alloy and provides elemental alloying design strategies for ZrCo based alloy.