Surface configuration and wettability of nickel(oxy)hydroxides: a first-principles investigation

This article explores the wetting behavior of beta-type nickel hydroxide, beta-Ni(OH)(2), and nickel oxyhydroxide, beta-NiOOH, by means of first-principles calculations. Water is found to interact weakly with beta-Ni(OH)(2)(001), but strongly with beta-NiOOH(001). As unveiled with the use of ab initio molecular dynamics simulations, surface water layers at beta-NiOOH(001) show a high degree of ordering correlated with a large surface polarization effect. In comparison, interfacial water at beta-Ni(OH)(2)(001) exhibits enhanced disorder and higher mobility. The weak interaction of water with beta-Ni(OH)(2)(001) is consistent with the small dipole moment of this surface. On the surface of beta-NiOOH(001), in addition to the significantly increased surface dipole moment, unsaturated O atoms increase the number of hydrogen bonds between water molecules and the surface, resulting in strong water binding. The wettability trends found in this simulation study are consistent with experimental observations. Another theoretical observation is the increased work function of beta-NiOOH(001) relative to beta-Ni(OH)(2)(001) that agrees with experimental results reported in the literature.