Hydrogen adsorption and dissociation on nickel-adsorbed and -substituted Mg17Al12 (100) surface

Advancement of hydrogen storage materials is detrimental to the improvement of hydrogen fuel cell technology. Magnesium-aluminum alloys are typical hydrogen storage materials with great potential for use in hydrogen fuel cells. To this end, much has been done in a bid to comprehend the hydrogen storage mechanism of such magnesium-based hydrides. Various attempts have also been made to try and promote their hydrogen adsorbing/desorbing characteristics. Ideally, this can be achieved via ball-milling and/or adding small amounts of other metal elements or catalysts. Through Calculations, it has been seen that metal dopants do provide a catalytic effect on hydrogen desorption.

 A team of researchers led by Professor Hua Ning at Guangxi University in China investigated the catalytic effects and role of nickel on the hydrogenation properties of Magnesium-aluminum alloys. The researchers hoped to cross-examine the adsorption and dissociation behaviors of hydrogen on nickel-containing Mg₁₇Al₁₂(100) surfaces, including the nickel adsorbed and -doped surfaces. Their work is published in the research journal, International journal of hydrogen energy.

The research techniques employed involved performing calculations using the Vienna ab initio simulation package based on the density functional theory with the projector-augmented wave method. The research team evaluated the exchange correlation energies with the Perdew-Burke-Ernzerhof form of the generalized gradient approximation. Next, they employed the Monkhorst-Pack k-point mesh to sample the whole Brillouin’s zone in different (100) surfaces. Atomic and molecular hydrogen as well as nickel atoms were adsorbed on the one side of the target slabs. This was periodically repeated and the slabs were separated by a 15 Å vacuum so as to avoid the interference between neighboring slabs. Eventually, vdW density functional was considered so as to obtain the correct interfacial properties.

The authors observed that the nickel atoms had a higher preference to the magnesium atoms and absorbed better on Mg-Mg bridge sites of the Mg₁₇Al₁₂ (100) surface. In addition, it was noted that both atomic and molecular hydrogen absorbed more easily on the nickel containing surfaces than on the Mg₁₇Al₁₂ (100) surfaces. Moreover, the dissociative energy of hydrogen gas on the Mg₁₇Al₁₂ (100) surface was recorded to have been improved due to the addition of nickel.

Hua Ning and her colleagues study successfully utilized density functional theory to cross-examine hydrogen adsorption and dissociation on Mg₁₇Al₁₂ (100) surfaces with the addition of nickel element. In this work, two distinct types of nickel containing surfaces have been considered. The nickel has been seen to exhibit excellent catalytic properties of hydrogen adsorption and dissociation. Altogether, the density functional theory results have been satisfied with the experiments very well.