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Direct methanol fuel cells (DMFCs) have been actively investigated from both fundamental and applied points of view due to their interesting perspectives for the application in the fields of auxiliary power supply and portable power sources. However, research efforts are still needed to solve the drawbacks presently affecting these devices, such as methanol cross-over constraints, high costs of materials, etc. The present paper addresses these issues by using a new FUMATECH proton exchange membrane (fumapem ® F-1850), characterized by a nominal equivalent weight of 1800, as the electrolyte, and low electrode noble metal loadings compared to the state of the art. A membrane-electrode assembly (MEA) based on this membrane was investigated in a small area (5 cm 2 ) direct methanol fuel cell at 60 °C and compared to a benchmark Nafion ® 115 membrane in terms of performance and methanol cross-over. The F-1850 membrane showed a lower methanol cross-over rate than Nafion ® 115, despite a lower thickness of the fumapem ® membrane. This allowed to obtain a higher performance (74 vs. 64 mW cm −2 ) for the F-1850 membrane compared to Nafion ® at ambient pressure. To study the scalability of the DMFC device and related components, the new membrane was integrated in large-area MEAs (100 cm 2 ) and investigated in a 5-cell and 10-cell pressurized stack based on a bipolar design. The stack was tested at 75 °C, 5 M methanol solution at the anode and pressurized oxygen (2 atm. rel.) at the cathode, giving a normalized power density per cell of about 130 mW cm −2 . The results obtained with the 10-cell stack showed a good agreement with the performance recorded with the 5-cell stack, confirming the scalability of the DMFC device. [ABSTRACT FROM AUTHOR]

A composite anode was developed to increase the performance of a direct methanol fuel cell (DMFC). High surface area IrO2 nanopowder was synthesized by a sulfite complex method and added to a 50% PtRu/C catalyst prepared by the same procedure. A catalytic ink, composed of PtRu/C catalyst, IrO2 and Nafion ionomer, was deposited on a carbon-cloth-based backing layer and used as composite anode in a DMFC. A significantly higher performance was recorded for the composite electrode-based MEA compared to a bare one, at 60°C and 90°C, confirming that the electrocatalytic activity is related to the characteristics of water displacement of IrO2 additive, which acts as a co-catalyst for this reaction. The improvement was significantly higher by using 5M methanol solution as the fuel. These results evidence that a multifunctional catalyst can operate better than PtRu for methanol oxidation since this multi-step process requires different functionalities to speed up the reaction rate. [ABSTRACT FROM AUTHOR]

Abstract: Composite membranes based on recast Nafion with the inclusion of chabazite and clinoptilolite as fillers were used to increase the operation temperature of direct methanol fuel cells (DMFCs). Membranes containing different amounts (3 and 6vol%) of these zeolites were prepared. The electrochemical behaviour of the composite membranes was investigated at different temperatures (from 90 up to 140°C). Similar performances (around 350–370mWcm−2 under oxygen feed, 200–210mWcm−2 under air feed, at 140°C) were recorded for the cells based on the composite membranes with 3 and 6vol% of zeolite filler. Cell resistance measurements showed an improvement of the water retention properties at high temperature for the composite membranes compared to bare Nafion. [Copyright &y& Elsevier]

Methanol oxidation behaviour at three Pt–Ru catalysts varying by the concentration of active phase on the carbon support has been investigated in a wide temperature range (80–130 °C). An increase of the adsorbed methanolic residue stripping charge is observed with the increase of catalyst dispersion. As the temperature is increased, the stripping peak potential shifts more negatively accounting for a lower activation barrier for the reaction. An increase of temperature above 90 °C also produces a strong decrease in the coverage of adsorbed methanolic residues. The fuel cell performance is significantly enhanced by catalysts with intrinsically high catalytic activity, whereas the methanol reaction rate appears to be less influenced by an increase in coverage of active species. Catalysts characterized by a higher degree of alloying and metallic behaviour on the surface appear to be more active towards methanol oxidation. However, the physico-chemical properties of the catalysts have less influence on the anode electrochemical behaviour at high temperature since CO poisoning is alleviated under such conditions. The decrease of CO-like species coverage with temperature and the methanol tolerance characteristics of a Pt/C cathode are also discussed in relation to the crossover drawback of direct methanol fuel cells. [Copyright &y& Elsevier]

Simple and functional stack designs were developed for direct methanol fuel cells (DMFCs) with the aim of reducing capital costs. A simplified planar and monopolar ministack, with a reduced number of components, was designed for portable applications. This planar design facilitated the manufacturing of a compact passive mode operation ministack. The ministack provided an output power of 1.30 W under air breathing mode operation, at room pressure and temperature without any auxiliary. For application in auxiliary power units (APU), a self-heating and modular bipolar stack, operating up to 90 °C without internal cooling, was designed. Bipolar stacks consisted of 5–10 cells (100 cm 2 active area), providing an output power of 90–180 W. The recirculated methanol solution was used as thermostating fluid. The stacks achieved a normalised power density per cell of 180 mW cm −2 . Whereas, for the passive mode operation, ministack approached 30 mW cm −2 with 5 M methanol feed. These results favourably compare with the best performance reported in the literature for DMFCs operating under similar conditions. [ABSTRACT FROM AUTHOR]

Abstract: Noble metal oxides (IrO x , RuO x ) and valve metal oxides (SnO x and VO x ) have been investigated as promoters of Pt electrocatalyst for methanol oxidation in acidic environment. Pt modification was made using low oxide content (5 wt%) in order to evaluate the possibility of using such oxide promoter in a multifunctional catalyst. At this low level of oxide content, IrO x provided a larger promoting effect than RuO x . This occurred in the absence of specific alloying with Pt and also in the presence of lower catalyst dispersion. The electrocatalytic enhancement produced by the valve metal oxides was significantly lower than IrO x and RuO x . These results are interpreted in terms of the different water displacement mechanism for the various oxides. Such evidences seem to indicate that a multifunctional catalyst may represent a valid route to enhance methanol electro-oxidation. [Copyright &y& Elsevier]

Abstract: The electrocatalytic activity towards the methanol oxidation reaction (MOR) of three series of Pt electrocatalysts supported onto the surface of hybrid nanostructures composed of ordered mesoporous carbons (OMCs) and tungsten trioxide (WO3) is investigated. OMC nanostructures are obtained by hard-template method, through the carbonization of sucrose into the mesopores of the SBA-15 silica and subsequent removal of the template. Hybrid OMC–WO3 supports are synthesized by impregnation of phosphotungstic acid (PWA) onto OMCs, followed by thermal decomposition in N2 atmosphere at three different temperatures (400, 500 and 600°C, respectively). Pt/OMC–WO3 electrocatalysts are prepared by the wetness impregnation technique using a solution of chloroplatinic acid hexahydrated in acetone. Hybrid OMC–WO3 supports and Pt/OMC–WO3 electrocatalysts are characterized from the structural–morphological viewpoint by means of X-ray diffraction, X-ray photoelectron spectroscopy with energy-dispersive spectroscopy, scanning and transmission electron microscopies. Cyclic voltammetry, CO stripping and chronoamperometry measurements are used for the electrochemical characterization of the electrocatalysts towards MOR: the electrocatalytic activity is dependent both on the nature of the supporting materials and on the particle size and structure of WO3. Catalysts containing smaller WO3 crystallites, in fact, demonstrate superior mass-specific activity towards MOR, compared to those possessing larger WO3 particles or amorphous WO3. Finally, the electrochemical behaviour of the best performing electrocatalyst, the Pt/OMC–WO3-500, is compared to that of its counterpart with no WO3 (i.e., Pt/OMC) in a single 5cm2 DMFC cell: the obtained slightly enhanced electrocatalytic activity is attributed to the mutual effect of the hybrid support and the metal nanoparticles. The presence of WO3 not only promotes the mass-specific activity of the supported electrocatalysts, but also decreases the ohmic resistance. [Copyright &y& Elsevier]

Abstract: Platinum nanoparticles supported on fishbone carbon nanofibers (CNFs) were synthesized and studied for the oxygen reduction reaction (ORR). The crystalline and textural properties of the CNFs were modified by synthesizing them at different temperatures, allowing the comparison of supports with either improved graphitization degree or improved porosity. A carbon black (Vulcan XC-72R) was used for comparison. Half-cell studies determined that the ORR activity is enhanced when using a CNF with improved graphitization, in contrast with CNFs with better textural properties such as surface area or pore volume. The catalysts were tested at the cathode of a direct methanol fuel cell corroborating the suitability of using highly graphitic CNFs, and a similar behavior was found in comparison with the state of the art carbon black used in this field. [Copyright &y& Elsevier]

For the first time a long-term (500 h) durability study in direct methanol fuel cells (DMFCs) is carried out on a Platinum Group Metal-free (PGM-free) cathodic electro-catalyst commercially available on market. The electro-catalyst is tested for 500 h at a fixed cell voltage (0.3 V), recording the polarization curves during the operation. A drastic decrease in performance is observed after the first 100 h (from 220 to 75 mA cm−2); afterwards, the decrease is flatter, passing from 75 to 25 mA cm−2 (at 500 h). The causes of this performance degradation are investigated by postmortem physicochemical analyzes, such as X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with X-ray energy dispersive analysis (EDX). Possible reasons of degradation are indicated to be PGM-free catalyst aggregation, carbon and nitrogen species decrease, Ruthenium dissolution and migration from the anode to the cathode, poisoning both membrane and cathode catalyst. [ABSTRACT FROM AUTHOR]