Studying the Proton Conduction through the Grain Surface of UiO-66-NH2

Previous proton conducting research mainly focused on the proton conducting behavior in the bulk phase. This work studied the proton conduction in the MOF grain surface. We prepared UiO-66-NH2 particles with different sizes and compared their proton conductivities. It is found that protons will selectively transfer from the faster pathway. When the grain surface is the much faster proton conducting pathway, the bulk phase will be bypassed. Further, the particle surface was modified with organic phosphonic acid, and the proton conductivity of the modified particle increases significantly. All these demonstrate that the grain surface can be a significant transport path for the proton and the optimization of the grain surface is an effective method to improve proton conduction.