Hydrogen trapping in vanadium carbide alloyed with transition metals

Abstract

The mechanism of hydrogen trapping in carbides via transition metal alloying is essential for material design of hydrogen barrier coatings in hydrogen energy applications, which however, is still elusive. Herein we have investigated the effect of transition metal solutes (Ti, Cr, Zr, Nb, and Mo) doping on multiple hydrogen trapping in vanadium carbide using density functional theory calculations. The hydrogen binding energetics with alloying elements depends on the local atomic environment of neighboring interstitial sites. The hydrogen trapping ability is ordered by Cr > Zr > Nb > Ti > Mo. Cr dopant has a distinctive performance, because its first-nearest-neighbor trigonal interstitial sites are more stable, and up to six hydrogen atoms can be trapped, surpassing other elements. This distinction is partially attributed to less lattice contractive distortion and lower loss of charge. Charge transfer and electronic analysis indicate that CH interactions play a critical role in hydrogen binding energies. The stability of multiple hydrogen could be measured by the length and strength of the CH bond.

Keywords

• Hydrogen barrier coating
• Vanadium carbide
• First-principles calculations
• Transition-metal alloying