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Abstract: A Pt-Nafion/C catalyst is synthesized through a modified ion-exchange method, in which [Pt(NH3)2]2+ cations exchange with H+ ions of Nafion/C composites and are reduced by H2. Based on the results from transmission electron microscopy and inductively coupled plasma atomic emission spectrometry, it is found that the average size of Pt particles is around 2.3 nm and the Pt loading is about 1.8 wt% in the Pt-Nafion/C catalyst. Although the Pt mass activities (MAs) toward oxygen reduction reaction tested in half cells are similar, when used as cathode catalyst for a direct methanol fuel cell, the Pt MA as high as 4.36 A mgPt −1 are achieved for the Pt-Nafion/C catalyst at 825 mV, which is 6 times higher than that of the Pt/C catalyst. The enhanced Pt utilization could be attributed to the defined location of Pt nanoparticles in the triple phase zones in electrode. [Copyright &y& Elsevier]

Abstract: The effect of hydrous RuO2 (RuO2·xH2O) in anode on the performance of direct methanol fuel cells (DMFCs) was examined by voltammetry, methanol stripping analysis, electrochemical impedance spectroscopy, polarization measurement and chronopotentiometry. The results showed that, compared with the DMFC with conventional structures, the dynamic response and quasi-steady state performance of the RuO2·xH2O-introduced DMFCs were significantly improved. The DMFC with RuO2·xH2O layer (ROL) sandwiched between anode catalyst layer and gas diffusion layer exhibited better quasi-steady state performance than those either with ROL sandwiched between anode catalyst layer and electrolyte membrane or with RuO2·xH2O uniformly distributed in anode catalyst layer. The maximum power density of the DMFC with this novel structure was 16% higher than the DMFC with the conventional structure. Moreover, the dynamic response of this RuO2·xH2O-introduced cell was more stable during 250-hour of operation when compared with that of the conventional cell. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Nafion® ionomer aggregation in solution on the structure of the cathode catalyst layer of a direct methanol fuel cell (DMFC) was investigated by dynamic light scattering (DLS), laser particle sizer, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The results showed that large aggregation particles were suppressed by the addition of NaOH to aqueous solutions of Nafion®, which led to a smaller agglomerate particle size distribution in the catalyst ink. The cathode catalyst layer made from the catalyst ink with NaOH addition showed a more uniform distribution of sulfur and Pt elements, a higher electrochemical active surface area (48% increase) and achieved a better performance in the DMFC than one made from the catalyst ink without NaOH addition. [Copyright &y& Elsevier]

Abstract: A five-layer catalyst coated membrane (CCM) based upon Nafion 115 membrane for direct methanol fuel cell (DMFC) was designed and fabricated by introducing a modified Nafion layer between the membrane and the catalyst layer. The properties of the CCM were determined by SEM, cyclic voltammetry, impedance spectroscopy, ruinous test and I–V curves. The characterizations show that the modified Nafion layers provide increased interface contact area and enhanced interaction between the membrane and the catalyst layer. As a result, higher Pt utilization, lower contact resistance and superior durability of membrane electrode assembly was achieved. A 75% Pt utilization efficiency was obtained by using the novel CCM structure, whereas the conventional structure gave 60% efficiency. All these features greatly contribute to the increase in DMFC performance. The DMFC with new CCM structure presented a maximum power density of 260mWcm−2, but the DMFC with conventional structure gave only 200mWcm−2 under the same operation condition. [Copyright &y& Elsevier]

Abstract: In this paper, the reversible and the irreversible loss in performance of direct methanol fuel cell (DMFC) single cells induced by freeze/thaw cycling are determined and discussed. The reversible loss in performance is attributed to the decreased activity of electrocatalysts due to the strong adsorption of the intermediates from methanol electro-oxidation at subzero temperatures, while the irreversible loss in performance is due to the damage of membrane electrode assembly (MEA) structure. It is found that the reversible degradation of performance is dominant when the cell operated at low current densities with O2; the irreversible degradation is more obvious when the cell discharged at high current densities or operated with air. A method, applying a reverse current on the single cell, is put forward to recover the reversible loss in performance. By this method, the voltage of the single cell operated with O2 at 100 mA cm−2 drops only about 16 mV after experiencing 100 freeze/thaw cycles between−10 and 60 °C. [Copyright &y& Elsevier]

Abstract: A graphitic mesoporous carbon (denoted as GMC) was synthesized using resorcinol and formaldehyde as carbon precursors and iron nitrate as a graphitization catalyst. The GMC was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and nitrogen adsorption. The results show that the GMC has a mesoporous structure and a high surface area of 403 m2 g−1, and particularly, a well-defined graphitic framework. Using the GMC as the support, a PtRu/GMC was synthesized to act as an electrocatalyst for the methanol oxidation reaction (MOR). A counterpart with Vulcan® XC-72 (denoted as XC) as the support was prepared for comparison. TEM images show that PtRu nanoparticles are distributed uniformly on the carbon supports for both electrocatalysts. The electrochemical activity of the PtRu/GMC toward the MOR is slightly higher than that of the PtRu/XC in both half cell and single cell measurements. The 1500h stability test of a single cell suggests that the PtRu/GMC is excellent stable. [Copyright &y& Elsevier]

Abstract: In this study, Nafion ionomer, as a kind of hyperdispersant, was added to polytetrafluoroethylene (PTFE) water dispersion system to suppress the size of PTFE particles in the ink of microporous layer (MPL). The agglomeration behavior of PTFE in ethanol and MPL were investigated by laser diffraction, dynamic light scattering (DLS) and metallurgical microscopes. The electronic resistance, pore size distribution, gas permeability and surface hydrophobic/hydrophilic properties were also characterized for prepared gas diffusion layers (GDLs). It was shown that PTFE water dispersion system suffered flocculating when dispersed in ethanol and this agglomeration behavior was reduced by employing Nafion ionomer. With the increase in the Nafion ionomer adopted in the MPL, not only the decreased hydrophobic property was shown in the MPL, but the decreased PTFE particle size was also achieved, which results in improved crosslink of carbon and pores themselves as well as the volume loss of pores in micron scale. The increased gas permeability and electronic conductivity of the GDL made the one employing the PTFE dispersion system with 1% Nafion content own its advantages as the cathode diffusion layer for a direct methanol fuel cell (DMFC) under near-ambient conditions. [Copyright &y& Elsevier]

Abstract: In this work, an integrated catalyst-coated membrane (CCM) is prepared by successively spray deposit Pt/C nano-suspension, Nafion solution and Pt–Ru/C nano-suspension on a cathode gas diffusion layer using electrohydrodynamic atomization (EHDA) Layer-by-Layer (LbL) deposition. Porous cathode and anode catalyst layers and dense Nafion membrane are deposited using the EHDA LbL deposition technique. It is also found that the EHDA LbL deposited CCM presents close packed structure. An 85 h life test shows that the EHDA LbL deposited cathode electrode side of the integrated CCM still presents well compact feature. Whereas, the delamination of the anode electrode side formed by direct pressing method is evident. The performance of the cell with different methanol concentrations is also examined. It is found that the 3 M methanol concentration gives the highest cell performance. Moreover, the polarization behaviour, methanol crossover and impedance response of the cell at different working temperatures are analysed. The cell performance demonstrates faster increase between 20 °C and 50 °C than between 50 °C and 70 °C. The methanol crossover test shows that the cell presents higher increase level of methanol crossover between 40 °C and 50 °C than other 10 °C temperature increase steps. [Copyright &y& Elsevier]

Abstract: Vulcan XC-72R, Ketjen Black EC 300J and Black Pearls 2000 carbon blacks were used as the additive in Pt black cathode catalyst layer to investigate the effect on direct methanol fuel cell (DMFC) performance. The carbon blacks, Pt black catalyst and catalyst inks were characterized by N2 adsorption and scanning transmission electron microscopy (STEM) with Energy dispersive X-ray (EDX) spectroscopy. The cathode catalyst layers without and with carbon black additive were characterized by scanning electron microscopy, EDX, cyclic voltammetry and current-voltage curve measurements. Compared with Vulcan XC-72R and Black Pearls 2000, Ketjen Black EC 300J was more beneficial to increase the electrochemical surface area and DMFC performance of the cathode catalyst layer. The cathode catalyst layer with Ketjen Black EC 300J additive was kept intimately binding with the Nafion membrane after 360 h stability test of air-breathing DMFC. [ABSTRACT FROM AUTHOR]

Abstract: In present work, a 600h durability test and in situ measurements of water transport were carried out on a single direct methanol fuel cell (DMFC) at atmospheric pressure and 80°C. Effect of water transport on the single cell performance was investigated in detail, which indicated that the accumulated water in the hydrophobic micropores of the cathode gas diffusion layer (GDL) aggravated the cathode flooding, and consequently led to a temporary and reversible degradation of the cell performance. Further investigation revealed that cathode flooding could be alleviated by blowing the cathode with dry air for 150h at open circuit condition and the partially recovered cell performance within the durability could be obtained in consequence. Water analysis combined with the scanning electron microscopy (SEM), contact angle measurement and energy dispersive X-ray (EDX) was used to explore the characteristics of cathode GDL before and after the durability test. Results showed that the variation of the microstructure and hydrophobic properties for both sides of the cathode GDL is probably one of the inherent reasons for the irreversible degradation of the cell performance besides the electro-catalysts deterioration. [Copyright &y& Elsevier]

Abstract: The transport of methanol through Nafion® membrane in diffusion cell is investigated using the open circuit potential method at different initial methanol concentration solutions. A simple mathematical model based on quasi-steady-state diffusion for the transport of methanol across the membrane in a diffusion cell is developed to simulate the experimental data in order to measure the methanol permeability. The influence of the diffusion cell parameters and thickness of the membrane on the methanol permeability measurement has been evaluated and analyzed. By means of Maclaurin expansion technique, this model can be used to predict the deviation of methanol permeability determined by steady-state diffusion model. [Copyright &y& Elsevier]

Abstract: Ketjen Black EC 300J with an extremely high mesoporous area and electrical conductivity, was used as an additive in the cathode catalyst layer to improve the DMFC (direct methanol fuel cell) performance. Ketjen Black EC 300J and the catalyst ink were characterized by TEM. The cathode catalyst layers were characterized by SEM, in situ cyclic voltammetry and I–V curve measurements. Ketjen Black EC 300J additive increased the dispersion extent of Pt black particles and improved the Pt utilization. In addition, the pore size and porosity was increased when Ketjen Black EC 300J was added into the cathode catalyst layer. The cathode catalyst layer with Ketjen Black EC 300J additive showed a greater single cell performance than the cathode catalyst layer without any additive, especially in the air-breathing mode. These results suggested that the performance improvement was attributed to the increased Pt utilization, oxygen diffusion and water removal capability when Ketjen Black EC 300J was added into the cathode catalyst layer. [Copyright &y& Elsevier]