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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 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: 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 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: Using resorcinol and formaldehyde as carbon precursors, graphitic mesoporous carbons (GMC) with different surface areas were synthesized by adjusting the amount of iron nitrate used as a graphitization catalyst. The BET surface area of the GMC decreases with increasing pore diameter and the material becomes more graphitic with increasing amount of catalyst. Using the GMC as the support, a series of PtRu electrocatalysts (PtRu-GMC) were synthesized. The electrocatalytic activities of the PtRu-GMC toward the methanol oxidation reaction were investigated in both half cells and single cells. The results indicate that the pore size of the GMC is especially important in determining the performance of direct methanol fuel cells. [Copyright &y& Elsevier]