Changwei Xu

Nafion membranes with ordered mesoporous structure and high water retention properties for fuel cell applications

Ordered mesoporous structures were successfully introduced into Nafion membranesvia a soft micelle templating method, using a non-ionic block copolymer surfactant, PEO127–PPO48–PEO127 (Pluronic F108). Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) analysis show the typical features of the formation of ordered mesopores in the as-prepared Nafion membranes. TGA and FTIR results show that the mesoporous Nafion (meso-Nafion) has a much higher water retention capability as compared to conventional Nafion membranes. The proton conductivities of meso-Nafion are much higher than those of Nafion 115 membranes especially at reduced relative humidity (RH) and elevated temperatures. The results show that the conductivity and water retention ability are sensitive to the surfactant loading. At 80 °C and 40%RH, the conductivity of the best meso-Nafion membrane is 0.07 S cm−1, 5 times better than 0.013 S cm−1 obtained on Nafion 115. At 60%RH and 80 °C, the cell with meso-Nafion reached a stable power output of 0.63 W cm−2, more than 2 times higher than the cell with pristine Nafion 115 under identical experimental conditions. When the RH reduced to 20%, the power output of meso-Nafion membranes is 5.6 times higher than that of Nafion 115. The cells with meso-Nafion membranes also demonstrate much better power output at elevated temperature of 120 °C and reduced humidity.

Au-NiCo2O4 supported on three-dimensional hierarchical porous graphene-like material for highly effective oxygen evolution reaction

A three-dimensional hierarchical porous graphene-like (3D HPG) material was synthesized by a one-step ion-exchange/activation combination method using a cheap metal ion exchanged resin as carbon precursor. The 3D HPG material as support for Au-NiCo2O4 gives good activity and stability for oxygen evolution reaction (OER). The 3D HPG material is induced into NiCo2O4 as conductive support to increase the specific area and improve the poor conductivity of NiCo2O4. The activity of and stability of NiCo2O4 significantly are enhanced by a small amount of Au for OER. Au is a highly electronegative metal and acts as an electron adsorbate, which is believed to facilitate to generate and stabilize Co4+ and Ni3+ cations as the active centres for the OER.

Facile synthesis of Pd–Mn3O4/C as high-efficient electrocatalyst for oxygen evolution reaction

Herein, we report the use of carbon black as conducting scaffold to support highly-active Pd and Mn3O4 nanoparticles, and demonstrate their enhanced electroactivity for oxygen evolution reaction (OER). Benefiting from the synergistic effect, the as-prepared Pd–Mn3O4/carbon black catalyst showed substantially higher OER activity and stability than the Pd–Mn3O4 and Pd/C catalysts.

Manganese oxides supported on hydrogenated TiO2 nanowire array catalysts for the electrochemical oxygen evolution reaction in water electrolysis

Hydrogenated TiO2/MnOx nanowires (NWs) with a diameter of 50–80 nm and a length of 0.5–0.8 μm supported on carbon cloth have been successfully prepared. The entire surface of the H–TiO2 NWs is covered uniformly by amorphous MnOx with an average thickness of 7.0 nm. The H–TiO2 NWs are poorly active for the oxygen evolution reaction (OER) and the MnOx as a major potential feasible electrocatalyst shows a considerable activity. The onset potential shifts negatively and the current density improves not only by the enlarged surface area of the MnOx support on the H–TiO2 NWs, but also by a synergistic effect between TiO2 and MnOx. The presence of three manganese oxides with different valences such as MnO, Mn2O3 and MnO2 in the H–TiO2/MnOx NWs is apt to effect the OER due to electron transfer. The percentage of Mn2+ increases and the percentages of Mn3+ and Mn4+ decrease after the test, which proves the assumption that Mn4+ is first reduced to Mn3+ by electron injection from H2O, and then Mn3+ is further reduced to Mn2+ when the O2 evolution occurs during the OER in alkaline media at pH ≥ 9.

Three-dimensional ordered mesoporous Co 3 O 4 enhanced by Pd for oxygen evolution reaction

Considerable efforts have been devoted recently to design and fabrication of high performance and low cost electrocatalysts for oxygen evolution reaction (OER). However, catalytic activity of current electrocatalysts is usually restricted by high onset potential and limited active sites. Herein, we fabricated three-dimensional (3D) highly ordered mesoporous Pd-Co3O4 composite materials as excellent electrocatalysts for OER in alkaline solution with high activity and stability. Three-dimensional highly ordered mesoporous Co3O4 material was firstly synthesized using mesoporous silica KIT-6 as hard template. Then, Pd-Co3O4 nanomaterials were prepared by a simple reduction method. The as-prepared 3D mesoporous Pd-Co3O4 catalysts have ordered mesoporous structure with a high surface area of 81.0 m2 g−1. Three-dimensional highly ordered mesoporous structure can facilitate diffusion and penetration of electrolyte and oxygen. Moreover, the catalysts can also keep catalyst particles in a well dispersed condition with more catalytic active sites. Electrochemical measurements reveal that the 3D mesoporous Pd-Co3O4 catalysts exhibit superior performance in alkaline solution with low onset potential (0.415 V vs. SCE) and excellent long-duration cycling stability.

Determination of Diffusion Coefficient of Isopropanol in Alkaline Medium using Electrochemical Methods on Pd Electrode~!2009-12-09~!2010-02-20~!2010-06-09~!

The diffusion coefficient of isopropanol in alkaline medium using electrochemical methods on Pd electrode has been studied by linear sweep voltammetry (LSV) with different sweep rate and chronoamperometry in 1.0 M KOH solution containing 1.0 M isopropanol. Isopropanol oxidation on the Pd electrode is an irreversible charge-transport process and controlled by a diffusion process. The diffusion coefficient of isopropanol on the Pd electrode is obtained as 1.01 10 -6 cm 2 s -1 using the LSV method and 1.06 10 -6 cm 2 s -1 using the chronoamperometry method. The average diffusion coefficient of isopropanol is 1.04 10 -6 cm 2 s -1 .