Energy Barrier Of Proton Transfer In 3d Transition Metal-Doped Boehmite

The crystal structure of boehmite contains a large number of hydrogen-bond chains, which are deemed proton-transfer channels that are essential for proton-exchange-membrane materials. The efficiency of proton transfer along these chains is expected to change with the nearby chemical environment, whereas the dependency remains largely unknown. In this study we calculate energy barriers of proton transfer along hydrogen-bond chains of 3d transition metal-doped boehmite, using the nudged elastic band method based on density functional theory. Eight 3d transition metals from Sc to Ni are considered with variable doping concentrations from 1/12 to 1/4. Our results show that the energy barriers vary largely with dopant types and concentrations. Ti dopant consistently reduces the energy barrier by up to 2.5 kJ mol(-1) compared to pure boehmite. It is found that short hydrogen-bond lengths are generally associated with low energy barriers, and this enables us to search for potential proton conductors in materials of similar structures.