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A three‐dimensional, nonisothermal, and multiphase model of high temperature proton exchange membrane fuel cells is built to investigate water and phosphoric acid transportation, in which a spherical agglomerate model considering catalyst layer structure and liquid saturation is applied to determine the electrochemical kinetics in the cathode catalyst layer. Experimental polarization curve, water proportion in the anode outlet gas, and phosphoric acid distribution are selected for validation. It is found that the simulated results can represent the experimental data with reasonable accuracy. Based on the model, the effects of current density and stoichiometry on the variable distributions are analyzed. The results show that water in anode is mainly from cathode by concentration diffusion of liquid water, and the proportion of anode outlet water to the total produced water decreases slightly with the increase of current density. A higher current density leads to a greater electromigration of phosphoric acid from cathode to anode and a higher liquid phase fraction in anode, while a lower phosphoric acid concentration in the fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: The stability of a carbon support is especially essential for oxygen reduction reaction (ORR) electrocatalysts in fuel cells. The state‐of‐the‐art support, generally active carbons, usually have poor corrosion resistance and weak interaction with noble metals, leading to degradation of electrocatalyst performance. Herein, a composite electrocatalyst support denoted CeO2/MWNT, combining high corrosion resistance and strong interaction with platinum, was fabricated through ceria deposited on multiwall carbon nanotubes (MWNTs). On the one hand, high electronic conductivity, medium surface area, and abandoned surface functional groups of MWNTs guarantee fine dispersion and performance of platinum. On the other hand, high corrosion resistive MWNTs and strong interactions between platinum and CeO2 prevent the platinum from degrading. The durability of the electrocatalyst and support are evaluated, referring to the NREL standard. After accelerated testing, the mean particle size of Pt‐CeO2/MWNT increases from 3.1 to 3.5 nm, whereas the loss of electrochemical surface area and specific activity are 14.7 and 9.2 %, respectively, which are much lower than those of commercial Pt/C, which uses activated carbon as the support. [ABSTRACT FROM AUTHOR]

Abstract: Here, we develop a facile electrochemical polymerization method for the synthesis of polypyrrole (PPy) nanowires on Pd modified Nafion® membranes. Interestingly, with altering the deposition potential and temperature, we can easily tune the PPy nanowires from disordered nanostructures to well ordered vertically aligned nanowires. The various PPy nanowires show similar electronic conductivity but diverse hydrophobicity/hydrophilicity. The ordered PPy nanowires can significantly facilitate the mass transport and enhance the catalyst utilization. These two factors together make an obvious performance improvement of fuel cells. [Copyright &y& Elsevier]

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: A new anion exchange membrane was synthesized by a green and facile route---chemically grafting polybenzimidazole (PBI) membrane with BrCH2CH3. The obtained membrane was characterized by means of ex-situ and in-situ tests (EDX, FTIR, AC impedance, single cell test and so on). The results suggested that the group of –CH2CH3 was successfully grafted onto N atom within PBI backbone, while with Br− as counter ion. The corresponding ionic conductivity and ethanol permeability were about 0.022 Scm−1 and 5.24 × 10−8 cm2s−1, respectively. Finally, single cell test suggested that air-breathing alkaline direct ethanol fuel cell with quaternized PBI membrane can deliver a peak power density of about 11 mWcm−2 even at ambient temperature of 13 °C, which was better than those of air-breathing alkaline direct methanol fuel cell in literatures. In addition, a possible reaction mechanism was also proposed and discussed. [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]

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion® membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at 1 M CH3OH, 2 atm oxygen and 90 °C yields a current density of 100 mA/cm2 at 0.53 V cell voltage. The peak power density is 120 mW/cm2. The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed. [Copyright &y& Elsevier]

High oxygen transport resistance in the cathode is a main cause of the low performance of high temperature proton exchange membrane fuel cell (HT-PEMFC), and therefore to determine the contribution of different mass transport processes to the oxygen transport resistance is beneficial to the subsequent research work. In this paper, the molecular diffusion resistance (R M) in the cathode was successfully calculated by measuring the limiting currents with using different diluent gases. And the oxygen transport resistance in phosphoric acid (R P A ) was analyzed by changing the humidity and temperature. It was found that the total oxygen transport resistance (R t o t a l ) increased obviously with the increase of the humidify, and the variation of R t o t a l under different conditions was mainly related to the change of R P A . Combined with the phenomenon that the experimental value of R M was less than the calculated value at high humidity, but higher than that at high operation temperature, we speculate that the cause of that R P A increased obviously at high humidity is the occupancy or blockage of gas phase transport channel in catalyst layer (CL) by phosphoric acid due to the water absorption of phosphoric acid in CL and the swelling of membrane. This consequence indicates that it is the change of phosphoric acid distribution that dominate C i s the R t o t a l at high humidity. Image 1 • The separation of molecular diffusion resistance from the total mass transport resistance of HT-PEMFC cathode was realized. • The relationship between the oxygen transport resistance in phosphoric acid and operating conditions was obtained. • The cause of the variation of oxygen transport resistance at different operating conditions was preliminarily analyzing. [ABSTRACT FROM AUTHOR]

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: Novel alkaline anion-exchange membranes (AAEMs) were synthesized by graft copolymerization of vinylbenzyl chloride onto pre-irradiated poly (tetrafluoroethylene-co-perfluoropropyl vinyl ether) film, followed by quaternization and alkalization. Two kinds of radiation modes, continuous radiation and dis-continuous radiation (with 15 min break in each hour''s radiation), were conducted to the PFA films. The structure of the AAEMs was characterized by Fourier transform infrared (FT-IR). The performances of the AAEMs, including ion exchange capacity (IEC), ionic conductivity, water uptake (WU) and methanol permeability, were investigated systematically. The results showed that the degree of grafting of the film prepared by continuous irradiation is higher than the one prepared by discontinuous irradiation, which results in higher IEC, WU and ionic conductivity. The continuously irradiated membrane exhibited a maximum ionic conductivity of 0.05Scm−1 at 60°C. A maximum power density of 16mWcm−2 for a direct methanol single cell was obtained at 60°C with the continuously irradiated membrane as the electrolyte, MnO2/C and PtRu/C as the cathode and anode electrocatalysts, respectively. This result indicates that the direct alcohol alkaline anion-exchange membrane fuel cell is a promising system with further improvement on AAEMs. [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]

A series of 40 wt.% Pt/C electrocatalysts were prepared by a modified polyol process and an improved aqueous impregnation method with different impregnation time. The characterization results of TEM and XRD identically reveal that the size and distribution of Pt nanoparticles on carbon are controllable by modifying impregnation time in both routes. High dispersion of Pt nanoparticles on carbon is achieved by both methods with 15 min impregnation, while aggregation of Pt nanoparticles takes place with prolonging the impregnation time to 36 h, especially in the aqueous impregnation procedure. UV–vis spectroscopy measurements verified that the redox reaction between PtCl62- and formaldehyde could take place at a slow rate under ambient conditions via a two-step reaction path, where PtCl42- serves as an intermediate. On the other hand, PtCl62- anion can be directly reduced to Pt0 above 333 K in the modified polyol process through an autocatalytic pathway. The short-time-impregnated 40 wt.% Pt/C as cathode electrocatalysts in direct methanol fuel cell performs better than that of long-time-impregnated electrocatalysts. Experimental evidence provides clues for fundamental understanding of elementary steps of the redox reactions, which helps guiding the design and preparation of highly dispersed Pt catalyst with high metal loadings for fuel cells. [Copyright &y& Elsevier]

Highlights: [•] The amide-groups are grafted over carbon surface via a simple solvothermal route. [•] Cobalt oxides of 2nm uniformly supporting on the carbon blacks were synthesized. [•] CoO x /XC N shows superior ORR activity than CoO x /XC and CoO x /XC O. [•] The enhanced ORR activity is contributed to the higher content of CoO in composite. [ABSTRACT FROM AUTHOR]

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: 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]