Genwen Zheng

Chitosan/silica coated carbon nanotubes composite proton exchange membranes for fuel cell applications

Silica-coated carbon nanotubes (SCNTs), which were obtained by a simple sol-gel method, were utilized in preparation of chitosan/SCNTs (CS/SCNTs) composite membranes. The thermal and oxidative stability, morphology, mechanical properties, water uptake and proton conductivity of CS/SCNTs composite membranes were investigated. The insulated and hydrophilic silica layer coated on CNTs eliminates the risk of electronic short-circuiting and enhances the interaction between SCNTs and chitosan to ensure the homogenous dispersion of SCNTs, although the water uptake of CS/SCNTs membranes is reduced owing to the decrease of the effective number of the amino functional groups of chitosan. The CS/SCNTs composite membranes are superior to the pure CS membrane in thermal and oxidative stability, mechanical properties and proton conductivity. The results of this study suggest that CS/SCNTs composite membranes exhibit promising potential for practical application in proton exchange membranes.

Density functional studies of zirconia with different crystal phases for oxygen reduction reaction

To understand the origin of its catalytic activity, the oxygen reduction reaction (ORR) on zirconia with different phases is investigated by the first principles method. The free energy diagrams for an associative mechanism are firstly given to identify the rate-determining step for the ORR on the (111) surface of monoclinic, tetragonal and cubic phase zirconia. The calculation results show that the first electron transfer is the rate-determining step for the ORR on monoclinic and cubic phase zirconia, whereas the last electron transfer is the rate-limiting step for the ORR on tetragonal phase zirconia. The d-electron partial density of states for the active zirconium atoms is calculated to explore the relationship between the ORR catalytic activity of zirconia with different phases and their electronic properties. The calculated results show that the catalytic activity of zirconia for ORR is strongly dependent on the d-orbital occupation of the active zirconium atoms.