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Abstract: A co-planar micro Direct Methanol Fuel Cell (μDMFC) configuration was designed, developed and tested. The system geometry consisted of anodic and cathodic micro-channels arranged in the same plane. Firstly, micro-channels for a uniform distribution of oxygen and methanol were designed and realized on a polymeric substrate of polycarbonate. Then, the deposition of the catalytic elements inside the micro-channels by a spray-coating technique was carried out. Micro-channels were then covered by a catalyzed membrane containing separate anode and cathode layers. Different cell configurations were built, tested and evaluated. It was observed that the open circuit voltage varied significantly as a function of the membrane humidification degree and distance between anode and cathode channels in this planar design. In the presence of a large distance between the anode and cathode channel, the OCV reached 0.97 V. This high OCV reflected the absence of methanol cross-over due to the specific planar configuration. Regrettably, the overall cell impedance (ohmic and polarization resistance) limited the performance. A maximum power density of 1.3 mW cm−2 (active area) was achieved at room temperature with the smallest distance between anode and cathode (0.25 mm). [Copyright &y& Elsevier]

Abstract: Small angle X-ray scattering (SAXS) and nuclear magnetic resonance (NMR) investigations of recast composite and bare Nafion membranes have been carried out. The self-diffusion coefficients of water and methanol have been determined over a wide temperature range by PFGSE 1H NMR method. The transport mechanism appears to be influenced by surface properties of inorganic fillers. Acidic silica filler appears to promote proton transport in the membrane with respect to basic alumina. An interaction of the silica surface with methanol molecules is also envisaged from the analysis of proton self diffusion coefficients of methanol. The SAXS analysis revealed a modification of the polymer structure immersed in pure methanol or methanol solution with respect to water. A significant increase of the average ion clusters dimension is observed for the composite SiO2 membrane. [Copyright &y& Elsevier]

Abstract: The status of research and development of polymer electrolyte membranes (PEMs) for direct methanol fuel cells (DMFCs) is described. Perfluorosulfonic acid membranes, e.g. Nafion, are widely used in fuel cell technology; but, despite their success, they show some drawbacks such as high cost, limited operating temperature range and high methanol crossover. These limit their widespread commercial application in DMFCs. Such disadvantages are inspiring worldwide research activities for developing new PEM materials based on non-perfluorinated polymers as alternative to Nafion for DMFCs. A review of membrane properties is carried out on the basis of thermal stability, methanol crossover and proton conductivity. The analysis of DMFC performance covers perfluorosulfonic acid membranes (PFSA), sulfonated aromatic polymers (SAPs) and composite membranes. PFSA membranes are suitable materials in terms of power density, SAPs are more advantageous regarding the low methanol permeability and cost, whereas composite membranes are more appropriate for operation above 100 °C. DMFC power density values reported in literature show that, although there are remarkable research efforts on this subject, the achieved results are not yet satisfying. Further work is especially necessary on non-perfluorinated polymers to improve performance and durability for an effective application in practical DMFC devices. [Copyright &y& Elsevier]

Abstract: Composite membranes based on sulfonated polysulfone and acidic silica filler were prepared and investigated for direct methanol fuel cells. A significant influence of nanosized acidic silica on composite membrane properties was observed. A better distribution of acidic silica than bare silica was found in the membranes as well as a higher ionic conductivity of acidic silica membrane. The composite membranes based on sulfonated polysulfone modified silica (SPSf–SiO2–S) and bare silica (SPSf–SiO2) showed also an increase of DMFC performance compared to bare SPSf. The best electrochemical performance was obtained with the composite SPSf–SiO2–S membrane that showed satisfactory proton conductivity, low methanol crossover and low swelling in comparison to bare SPSf membrane. Methanol crossover currents of 20, 25 and 31mAcm−2 were measured for SPSf–SiO2–S, SPSf–SiO2 and SPSf membranes, respectively. The highest DMFC performance of 60mWcm−2 was obtained with the composite acidic silica-SPSf membrane (SPSf–SiO2–S) at 60°C. [Copyright &y& Elsevier]

Abstract: This paper reports on the development of polymer electrolyte membranes (PEMs) based on sulfonated polysulfone for application in a DMFC mini-stack operating at room temperature in passive mode. The sulfonated polysulfone (SPSf) with two degrees of sulfonation (57 and 66%) was synthesized by a well-known sulfonation process. SPSf membranes with different thicknesses were prepared and investigated. These membranes were characterized in terms of methanol/water uptake, proton conductivity, and fuel cell performance in a DMFC single cell and mini-stack operating at room temperature. The study addressed (a) control of the synthesis of sulfonated polysulfone, (b) optimization of the assembling procedure, (c) a short lifetime investigation and (d) a comparison of DMFC performance in active-mode operation vs. passive-mode operation. The best passive DMFC performance was 220mW (average cell power density of about 19mWcm−2), obtained with a thin SPSf membrane (70μm) at room temperature, whereas the performance of the same membrane-based DMFC in active mode was 38mWcm−2. The conductivity of this membrane, SPSf (IEC=1.34mequiv.g−1) was 2.8×10−2 Scm−1. A preliminary short-term test (200min) showed good stability during chrono-amperometry measurements. [ABSTRACT FROM AUTHOR]

Abstract: A low-cost fluorine-free proton conducting polymer electrolyte was investigated for application in direct methanol fuel cell (DMFC) mini-stacks. The membrane consisted of a sulfonated polystyrene grafted onto a polyethylene backbone. DMFC operating conditions specifically addressing portable applications, i.e. passive mode, air breathing, high methanol concentration, room temperature, were selected. The device consisted of a passive DMFC monopolar three-cell stack. Two designs for flow-fields/current collectors based on open-flow or grid-like geometry were investigated. An optimization of the mini-stack structure was necessary to improve utilization of the fluorine-free membrane. Titanium-grid current collectors with proper mechanical stiffness allowed a significant increase of the performance by reducing contact resistance even in the case of significant swelling. A single cell maximum power density of about 18mWcm−2 was achieved with the fluorine-free membrane at room temperature under passive mode. As a comparison, the performance obtained with Nafion 117 membrane and Ti grids was 31mWcm−2. Despite the lower performance, the fluorine-free membrane showed good characteristics for application in portable DMFCs especially with regard to the perspectives of significant cost reduction. [Copyright &y& Elsevier]

Abstract: An investigation of properties and operating parameters of a passive DMFC monopolar mini-stack, such as catalyst loading and methanol concentration, was carried out. From this analysis, it was derived that a proper Pt loading is necessary to achieve the best compromise between electrode thickness and number of catalytic sites for the anode and cathode reactions to occur at suitable rates. Methanol concentrations ranging from 1M up to 10M and an air-breathing operation mode were investigated. A maximum power of 225mW was obtained at ambient conditions for a three-cell stack, with an active single cell area of 4cm2, corresponding to a power density of about 20mWcm−2. [Copyright &y& Elsevier]

Abstract: This paper reports the development and characterization of sulfonated polysulfone (SPSf) polymer electrolytes for direct methanol fuel cells. The synthesis of sulfonated polysulfone was performed by a post sulfonation method using trimethyl silyl chlorosulfonate as a mild sulfonating agent. Bare polysulfone membranes were prepared with two different sulfonation levels (60%, SPSf-60 and 70%, SPSf-70), whereas, a composite membrane of SPSf-60 was prepared with 5wt% silica filler. These membranes were investigated in direct methanol fuel cells (DMFCs) operating at low (30–40°C) and high temperatures (100–120°C). DMFC power densities were about 140mWcm−2 at 100°C with the bare SPSf-60 membrane and 180mWcm−2 at 120°C with the SPSf-60-SiO2 composite membrane. The best performance achieved at ambient temperature using a membrane with high degree of sulfonation (70%, SPSf-70) was 20mWcm−2 at atmospheric pressure. This makes the polysulfone-based DMFC suitable for application in portable devices. [Copyright &y& Elsevier]

Abstract: A low temperature preparation procedure, based on a combination of colloidal and incipient wetness methods, was developed to modify the Pt catalyst with transition metals (Fe, Cu and Co). A moderate degree of alloying was obtained with Pt–Fe/C and Pt–Co/C cathode catalysts by using the new low temperature preparation route; whereas, a high degree of alloying was obtained for Pt–Cu/C by using the same procedure. Despite of the high metal concentration (60wt%) on carbon, all catalysts showed small primary metal particle size and a low degree of agglomeration. These catalysts were investigated as cathodes in direct methanol fuel cells (DMFCs) operating at low temperatures (60°C). It appeared that Pt–Fe/C catalysts were superior than Pt/C, Pt–Co/C and Pt–Cu/C catalysts both in terms of catalytic activity and tolerance to methanol. Adsorbed methanolic residues stripping analysis indicated a better methanol tolerance and an enhanced activity towards oxygen reduction in the case of the Pt–Fe system. An improvement of the DMFC single cell performance was also observed in the presence of Pt–Fe catalysts. [Copyright &y& Elsevier]

Abstract: High surface area carbon supported bimetallic Pt–Fe catalysts have been investigated for the oxygen electro-reduction process in low temperature direct methanol fuel cells (30–60°C). The electrocatalysts have been prepared by using a combination of colloidal and incipient wetness methods allowing of synthesis carbon supported bimetallic nanoparticles with a particle size of about 2–3nm. These materials were studied in terms of structure, morphology and composition using XRD, XRF and TEM techniques. Oxygen reduction properties of these bimetallic catalysts were investigated in single cell DMFC polarizations. The electrochemical data were compared with those obtained in the presence of a Pt/C catalyst prepared by the same procedure and characterised by the same concentration of active phase on the carbon support and a similar particle size. An improvement of the DMFC single cell performance was observed in the activation controlled region in the presence of the bimetallic catalysts. Moreover, the influence of the ionomer loading on the performance of the DMFC was investigated. The highest power density was recorded with electrodes containing 25% Nafion loading (87mWcm−2). [Copyright &y& Elsevier]

Abstract: Methanol electro-oxidation at Pt-decorated unsupported Ru catalysts having a Pt loading of 0.1 mgcm−2 has been investigated in situ in direct methanol fuel cells at high temperatures. The chemistry and morphology of the decorated catalyst has been studied by X-ray techniques and electron microscopy. An analysis of the stripping behaviour of adsorbed CO-like species has been carried out to obtain information on the electrocatalytic activity of the Pt-decorated Ru anode in relation to carbon supported Pt–Ru (1:1) alloy and bare unsupported Ru catalysts. The promoting effect of decorating Pt particles has been investigated by cyclic voltammetric analysis in the presence of a continuous methanol supply. The decorated catalyst has shown lower intrinsic catalytic activity with respect to the Pt–Ru alloy; yet, the decorating particles promote methanol dehydrogenation and adsorption of methanolic residues on the Ru support allowing the reaction to occur at significant rates even in the presence of small Pt amounts. [Copyright &y& Elsevier]

Technological improvements in direct methanol fuel cells (DMFCs) are fuelled by their exciting possibilities in portable, transportation and stationary applications. In this paper, a synopsis of the worldwide efforts resulting in inventions of a plethora of DMFC prototypes with low, medium and high power capacities by a number of Companies, Research Institutions and Universities is presented. The most promising short term application of DMFCs appears to involve the field of portable power sources. Recent advances in the miniaturization technology of DMFCs devices make these systems attractive to replace the current Li-ion batteries. In the field of electrotraction recent demonstration of DMFC stacks with specific power densities and efficiencies approaching those of the combined system methanol reformer-polymer electrolyte fuel cell (PEMFC) have stimulated further investigation on the development of materials with higher performance and lower cost. The most appropriate range of operation temperatures for applications in transportation appears to lie between 100 and 150 °C. These operating conditions may be sustained by using new high temperature electrolyte membranes or composite perfluorosulfonic membranes containing inorganic materials with water retention properties at high temperature. The most challenging problem for the development of DMFCs is the enhancement of methanol oxidation kinetics. At present, there are no practical alternatives to Pt-based catalysts. High noble metal loading on the electrodes and the use of perfluorosulfonic membranes significantly contribute to the cost of these devices. Critical areas include the design of appropriate membrane electrode assemblies for specific DMFC applications and the reduction of methanol cross-over. This latter aspect is strictly related to the use of membrane alternatives to Nafion, but it may also be conveniently addressed by the development of methanol-tolerant oxygen reduction catalysts. [Copyright &y& Elsevier]

The electrochemical behaviour of Pt-decorated unsupported Ru catalysts-based anodes has been investigated in direct methanol fuel cells (DMFCs). A preparation procedure allowing the surface decoration of unsupported Ru catalysts by Pt nanoparticles has been developed. DMFC power densities of 150 mW cm−2 at 130 °C have been achieved with ultra-low Pt loading anodes (0.1 mg cm−2) under air feed operation. Adsorbed methanolic residues stripping voltammetry analysis has been carried out to get information on the electrocatalytic activity of the Pt-decorated anodes in relation to the state-of-art carbon supported Pt–Ru (1:1) alloy and bare unsupported Ru catalysts. [Copyright &y& Elsevier]

Low cost ethylene–tetrafluoroethylene (ETFE)-based grafted membranes have been prepared by a process based on electron beam irradiation, subsequent grafting, cross-linking and sulfonation procedure. Two different grafted membranes varying by their grafting and cross-linking levels have been investigated for applications in direct methanol fuel cells (DMFCs) operating between 90 and 130 °C. DMFC assemblies based on these membranes showed cell resistance and performance values comparable to Nafion 117. Stable electrochemical performance was recorded during 1 month of cycled operation. Tailoring of grafting and cross-linking properties allows a significant reduction of methanol cross-over while maintaining suitable conductivity and performance levels. [Copyright &y& Elsevier]

Various recast Nafion® composite membranes containing ceramic oxide fillers with different surface characteristics (SiO2, SiO2–PWA, Al2O3, ZrO2) have been investigated for application in high temperature direct methanol fuel cells (DMFCs). Cell resistance at 145 °C increases as a function of the pH of slurry of the inorganic filler indicating a strong influence of the acid–base characteristics on the electrolyte conductivity. This effect has been attributed to the different water retention capabilities of the various membranes. Fuel cell performance at 145 °C, expressed as both maximum power density and current density at 0.5 V cell potential, increases almost linearly as the pH of slurry of the oxide materials decreases. Appropriate selection of the surface properties for the inorganic fillers allows to enhance the proton conductivity and extends the operating temperature range of composite membranes. The influence of fuel cell operating pressure on the humidification properties of these electrolytes at high temperature has been also investigated. [Copyright &y& Elsevier]

Abstract: Short-side-chain Hyflon® perfluorinated ionomer based membrane was investigated as electrolyte for high temperature direct methanol fuel cells. A fuel cell performance approaching 300 mW cm–2 was achieved at 140°C in the presence of 1M methanol and air feed. Stable electrochemical performance was achieved indicating suitable perspective for high temperature operation of Hyflon® membrane. [Copyright &y& Elsevier]