• CH4 poisons TiFe0.9 alloy via physical coverage without chemical reaction, while CO and CO2 block active sites for H2 dissociation and absorption.
• O2 reacts with the alloy surface to form a passivating layer that prevents hydrogen uptake, highlighting the need for surface protection.
• DFT calculations reveal adsorption energy relationships that explain the experimental poisoning mechanisms, providing a predictive tool for alloy design.
• The findings guide the development of Ti-based high-entropy alloys with enhanced resistance to impurity gas poisoning for practical hydrogen storage.