Effect of Ni doping on methane removal from hydrogen in ZrMnFe alloy and mechanism analysis

Getter alloy has the advantages of low cost and high hydrogen purity in small and mediumscale hydrogen purification. However, the commonly used ZrMnFe alloy is reactive to various impurities in hydrogen, and requires a temperature above 600 degrees C to remove methane. To improve reactivity with methane and ensure a high hydrogen adsorption platform pressure, partial substitution of Fe with Ni, which has a smaller bonding energy with methane ligand, is beneficial. In this work, we prepared ZrMnFeNi alloys with different Ni stoichiometric ratios by suspension induction melting and investigated their performance in purifying hydrogen containing trace amounts of methane. All alloys maintain C14 Laves phase, and the interplanar spacing of the (103) crystal planes decreases with the replacement of Ni. It is proved that ZrMnFeNi alloys can significantly improve the absorb efficiency of methane in hydrogen and reduce the removal temperature. At 450 degrees C, ZrMnFe0.7Ni0.3 can remove 10 ppm methane to 0.124 ppm. The purification efficiency of hydrogen at 450 degrees C can reach 96.94%, while the purification efficiency of ZrMnFe alloy is only 27.12%. The ZrMnFe0.7Ni0.3 alloy decomposes methane into carbon and hydrogen during purification, and the carbon diffuses into the alloy at high temperature to form a metal carbide with zirconium. The XPS results show that the electron-rich state of Ni is more beneficial for activating the C-H bond breaking of methane.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.