Direct methanol fuel cell

A methanol concentration sensor based on twin Nafion membrane electrode assemblies (MEAs) was constructed and characterized by electrochemical methods. Pulsed amperometric detection (PAD) method, using a low frequency (67 mHz) potential waveform of E red (cathodic activation potential) = −0.2 V, E pre-oxd (anodic pre-oxidation potential) = +0.60 V and E det (detection potential) = +0.80 V versus DHE with the same pulse width of 5 s was applied to the sensor to enhance its performance. The response in pulsed mode had better linearity over a wider concentration range than that in potentiostatic mode. Furthermore, using this PAD method, the stability of the sensor was enhanced significantly with a slightly linear degradation rate of 2.9 mA h −1 during long-time test. The performances of the sensor in terms of linearity, low anodic saturation and high stability show its potential application for direct methanol fuel cells.

. Ž . Ž . Serpentine SFF and interdigitated IFF flow fields were investigated with regard to their use in a direct methanol fuel cell DMFC . The DMFC equipped with SFFs showed lower methanol cross-over, higher fuel utilisation and slightly larger voltage efficiency at low current densities. IFFs enhanced mass transport and membrane humidification allowing to achieve high power densities of 450 and 290 mW cm y2 in the presence of oxygen and air feed, respectively, at 1308C. A fuel efficiency of 90% was obtained with the IFFs in the presence of 1 M methanol feed at 1308C and a current load of 500 mA cm y2 . q 2000 Elsevier Science S.A. All rights reserved.

A novel sulfonated diamine monomer, 1,4-bis(4-aminophenoxy)-naphthyl-2,7-disulfonic acid (BAPNDS), was synthesized. A series of sulfonated polyimide copolymers were prepared from BAPNDS, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and nonsulfonated diamine 4,4′-diaminodiphenyl ether (ODA). Flexible, transparent, and mechanically strong membranes were obtained. The membranes displayed slightly anisotropic membrane swelling. The dimensional change in thickness direction was larger than that in planar. The novel SPI membranes showed higher conductivity, which was comparable or even higher than Nafion 117. Membranes exhibited methanol permeability from 0.24 × 10−6 to 0.80 × 10−6 cm2/s at room temperature, which was much lower than that of Nafion (2 × 10−6 cm2/s). The copolymers were thermally stable up to 340 °C. These preliminary results have proved its potential availability as proton-exchange membrane for PEMFCs or DMFCs.

In order to observe the performance of the anode and cathode during actual direct methanol fuel cell (DMFC) operating conditions and to minimize the polarization of the reference electrode, we used a reversible hydrogen reference electrode (RHE) with its instability minimized. For analysis of the I-V polarization curve of each electrode, Tafel plots were used as the diagnostic tool. According to the slopes in the Tafel plot, the I-V polarization curves of each electrode were divided into the several regions. The effects of operating parameters on the performance of each electrode were interpreted in terms of mass transfer and electrode activation. The methanol and oxygen crossover through the membrane significantly affected the performance of the cell.

This paper describes an anode model for the direct methanol fuel cell (DMFC). It is a steady state, isothermal model, in which electrochemical reaction rates are governed by the Tafel kinetics. Mass transfer and diffusion are considered in the transport equations. The main purpose of the model is to calculate the anode potential loss and methanol crossover current density using cell current density, concentration and flow rate of methanol as inputs. The model also calculates the flux of methanol at the exit of the anode, as well as methanol concentration at the anode catalyst layer and at the membrane-catalyst interface.

A unified treatment of the mechanism of electrocatalysis of methanol oxidation on platinum and platinum-containing alloys is put forward. The effect of various alloys is shown to be interpretable within this overall model, and methods for the systematic improvement of the rate of electro-oxidation of methanol are described. Finally, some recent results for model direct methanol fuel cells are given, showing that critical performance parameters for commercial exploitation are now achievable with modem catalytic formulations and cell designs. 0 1997 Elsevier Science B.V.

Homogeneuosly sulfonated poly(styrene) (SPS) was prepared with various concentration of sulfonic acid groups in the base polymer. Membranes cast from these materials were investigated in relation to proton conductivity and methanol permeability in the temperature range from 20 • C to 60 • C. It was found that both these properties increase as the polymer is increasingly sulfonated, with abrupt jumps occurring at a concentration of sulfonic acid groups of about 15 mol%. The most extensively sulfonated membrane exhibited conductivity equal to that of Nafion. As a consequence, this membrane material is potentially an appealing alternative to the very expensive Nafion, for a number of electrochemical applications. For the membrane with the highest degree of sulfonation we measured a methanol permeability about 70% smaller than for Nafion. This characteristic is especially desirable in applications related to the direct methanol fuel cell (DMFC).

In this work, we report the direct methanol fuel cell (DMFC) performance of micro-patterned (p) Nafion ® 117 (N117) membranes prepared by hot embossing and compare them with that of normal N117 and heat and pressure treated (hp) N117 non-patterned (smooth) membranes.

This paper reports on the fabrication and characterization of a passive silicon microfabricated direct methanol fuel cell (lDMFC). The main characteristics of the device are its capability to work without complex pumping systems, only by capillary pressure, and the fact that its performance is not affected by the device orientation. A simple fabrication process based in deep reactive ion etching (DRIE), allows obtaining a reliable and lowcost final device. The device consists of two silicon microfabricated plates mounted together with a commercial membrane electrode assembly (MEA). The impact of current collector design on microfuel cell performance is explored and current-voltage (I-V) and current-power (I-P) curves of the device at different methanol concentration and orientation are presented. Optimal performance was obtained for methanol concentrations between 3 and 5 M, achieving a maximum power density of 12 mW/cm 2 . The results obtained in this work demonstrate the feasibility of the device and give a guideline for design and conditions optimization.

Methodologies for generating carbon materials from unusual natural sources like Limonea acidissima and Calotropis gigantea are reported. The carbon materials thus obtained have been characterized using a variety of tools. The possibility of modulating the textural properties of these materials has been examined. The carbon materials synthesized have been exploited for specific applications, such as support for noble metals for use in Direct Methanol Fuel Cells and as support for heteropoly acid for the production of gasoline additive. In addition, the utility of some of the activated carbon materials (from commercial sources) for the removal of sulphur from crude petroleum sources is also examined.

Due to the increasing demand for electricity, clean, renewable energy resources must be developed. Thus, the objective of the present study was to develop a passive direct methanol fuel cell (DMFC) for portable electronic devices. The power output of six dual DMFCs connected in series with an active area of 4 cm 2 was approximately 600 mW, and the power density of the DMFCs was 25 mW cm À2 . The DMFCs were evaluated as a power source for mobile phone chargers and media players. The results indicated that the open circuit voltage of the DMFC was between 6.0 V and 6.5 V, and the voltage under operating conditions was 4.0 V. The fuel cell was tested on a variety of cell phone chargers, media players and PDAs. The cost of energy consumption by the proposed DMFC was estimated to be USD 20 W À1 , and the cost of methanol is USD 4 kW h. Alternatively, the local conventional electricity tariff is USD 2 kW h. However, for the large-scale production of electronic devices, the cost of methanol will be significantly lower. Moreover, the electricity tariff is expected to increase due to the constraints of fossil fuel resources and pollution. As a result, DMFCs will become competitive with conventional power sources.

We have prepared multiwalled carbon nanotube (MWCNT)/In 2 O 3 composites using a simple impregnation method. The precursor compound indium(III) chloride (InCl 3 ) was used to cover the surface of MWCNTs and distilled water was used as solvent. The applied mass ratio was 4:1 (In 2 O 3 /MWCNT), and during the calcination process different temperatures (300, 350 and 400°C) were investigated. The produced materials were characterized by Xray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, and a thermogravimetric analysis was executed also. The average thickness of the produced surface layer and the average sizes of the In 2 O 3 particles were calculated with the Scherrer formula and the ImageJ-program. The results show that the heat treatment temperature affected the characteristic morphology and the crystal structure of the as-prepared composite.

A cobalt-polymer-MWCNT composite has been developed as an electrocatalyst for the oxygen reduction reaction (ORR) in PEMFC. The suitability of this electrocatalyst for the ORR in direct methanol fuel cells and direct ethanol fuel cells has been examined by taking Pt-Ru/ MWCNT and Pt-Sn/MWCNT, respectively as an anode electrocatalysts. The study results in improved power densities for hydrogen, methanol and ethanol based fuel cells compared to the previously reported non Pt based electrocatalysts, highlighting the use of this cobalt-polymer-MWCNT composite as a potential candidate for ORR in fuel cells.

Interests in the feasibility of micro-direct methanol fuel cells (DMFC) for commercialization, especially in the portable applications area, have encouraged the R&D sections in companies and institutions to create a better, simpler and more economical prototype. Despite the increase in knowledge on how to handle this type of cells, many challenges still remain to be conquered. There is also the question of individuality for each prototype created, which is similar to what is faced in MEMS with its lack of a single driving market, and until one dominant application can be established, fuel cell designs will continue to evolve and bringing with each of them a host of pros and cons. This paper will draw out the current challenges and development of micro-DMFC. Besides that, this paper will also show some marketing prediction in term of economics view.

Direct methanol fuel cell CNT Nano material a b s t r a c t Nanotechnology has recently been applied to direct methanol fuel cells (DMFC), one of the most suitable and promising options for portable devices. With characteristics such as low working temperature, high energy-conversion efficiency and low emission of pollutants, DMFCs may help solve the future energy crisis. However, a significant limitation to DMFC includes slow reaction kinetics, which reduces performance and power output. Recently, research has focused on increasing the performance and activity of catalysts. Catalysts composed of small, metallic particles, such as platinum and ruthenium, supported on nanocarbons or metal oxides are widely used in DMFC. Thus, this paper presents an overview of the development of nanocatalysts for DMFC. Particularly, this review focuses on nanocatalyst structure, catalyst support, and challenges in the synthesis of nanocatalyst. This paper also presents computational approaches for theoretical modeling of nanomaterials such as carbon nanotubes (CNT) through molecular dynamic techniques. (S.K. Kamarudin).

. This paper describes recent advances in the science and technology of direct methanol fuel cells DMFCs made at Los Alamos Ž . National Laboratory LANL . The effort on DMFCs at LANL includes work devoted to portable power applications, funded by the Ž . Defense Advanced Research Project Agency DARPA , and work devoted to potential transport applications, funded by the US DOE. We describe recent results with a new type of DMFC stack hardware that allows to lower the pitch per cell to 2 mm while allowing low air flow and air pressure drops. Such stack technology lends itself to both portable power and potential transport applications. Power densities of 300 Wrl and 1 kWrl seem achievable under conditions applicable to portable power and transport applications, respectively. Ž DMFC power system analysis based on the performance of this stack, under conditions applying to transport applications joint effort . with U.C. Davis , has shown that, in terms of overall system efficiency and system packaging requirements, a power source for a passenger vehicle based on a DMFC could compete favorably with a hydrogen-fueled fuel cell system, as well as with fuel cell systems based on fuel processing on board. As part of more fundamental studies performed, we describe optimization of anode catalyst layers in terms of PtRu catalyst nature, loading and catalyst layer composition and structure. We specifically show that, optimized content of recast ionic conductor added to the catalyst layer is a sensitive function of the nature of the catalyst. Other elements of membranerelectrode Ž . assembly MEA optimization efforts are also described, highlighting our ability to resolve, to a large degree, a well-documented problem of polymer electrolyte DMFCs, namely ''methanol crossover''. This was achieved by appropriate cell design, enabling fuel utilization as high as 90% in highly performing DMFCs. q 2000 Elsevier Science S.A. All rights reserved.

Rare earth-based materials can play different roles in fuel cell systems. These compounds can be used as catalysts, co-catalysts and electrolytes additives in different types of fuels cells. In particular, a promising acid direct methanol fuel cell can be obtained using rare earth-based materials as both anode and cathode co-catalysts and proton exchange membrane additive. In this work an overview of the use of rare earth-based materials in low-temperature fuel cells is presented.

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.

Direct methanol fuel cell a b s t r a c t In the present work, a detailed characterization of the electrochemical behavior of carbon supported PdePt electrocatalysts toward CO and methanol electrooxidation in direct methanol fuel cells is reported. Technical electrodes containing an ionomer in their catalyst layer were prepared for this purpose. CO and methanol electrooxidation reactions were used as test reactions to compare the electrocatalytic behavior of bimetallic supported nanoparticles in acidic liquid electrolyte and in solid polymer electrolyte (real fuel cell operating conditions). Experimental results in both environments are consistent and show that the electrochemical behavior of carbon supported PdePt depends on their composition, giving the best performance in direct methanol single fuel cell with a Pd:Pt atomic ratio of 25:75 in the catalyst.

Electrocatalyst Oxygen reduction Platinum a b s t r a c t 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.

Blend membranes made of chitosan (CS) and poly(vinyl pyrrolidone) (PVP), were synthesized and characterized for their ion exchange capacity (IEC) and Swelling Index to investigate their applicability in direct methanol fuel cells (DMFC). These membranes were assessed for their intermolecular interactions and thermal stability using FT-IR, X-ray diffraction methods, and TGA. Their methanol permeability and proton conductivity were also estimated and compared to that of Nafion 117. In addition to being effective methanol barriers, the membranes have a high ion exchange capacity (IEC) and possess adequate thermal stability. Crosslinking the polymer blend using glutaraldehyde and sulfuric acid has been particularly effective in producing a reduction of methanol permeability from 9.2 × 10 −8 cm 2 s −1 for CS/PVP blend to 7.3 × 10 −8 cm 2 s −1 for crosslinked CS/PVP blend (GS-CS/PVP) and enhancing the conductivity from 0.019 S cm −1 for CS/PVP blend to 0.024 S cm −1 for GS-CS/PVP, thereby rendering it more suitable for a DMFC. Low methanol permeability, excellent physico-mechanical properties and above all, the cost effectiveness could make their use in DMFC quite attractive.

Ionic groups incorporated into a polymer have a decided effect on its physical properties. A number of ionomers and polyelectrolytes have been widely applied. In particular, sulfonated bisphenol-A polysulfone (SPSF) has been used as a composite or single-component membrane for the desalination of water. In this article, the synthesis and physical characteristics of sulfonated polysulfone are addressed. A detailed synthesis route is provided and methods that yield determinable levels of sulfonation are described. These ion-containing polymers retain an excessive amount of residual salts, which, of course, are impurities to the system. Therefore, before any analyses were made the polymers were subjected to a thorough soxhlet extraction process with boiling water, which appeared to be quite effective. The degree of sulfonation was assessed by several methods such as 1H NMR and FT-IR. A new 1H NMR method was derived because the method cited in the literature proved to be too inconsistent for our work. The new 1H NMR method used a quaternary ammonium counterion [N(CH3)4]. These methyl protons are easily measured and may be ratioed against the isopropylidene protons in the polymer backbone that act as an internal standard. Characterization of the physical properties of SPSF consisted of water uptake, differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and solubility studies. Its physical appearance and mechanical behavior were improved by the solution procedure. Also addressed were the effects of different counterions (Na+ & Mg++) with SPSFs of low levels of sulfonation. The variation in physical properties between the divalent and monovalent counterions is dramatic, especially when observed by TMA in the rubber plateau above the apparent glass temperature.

In this review, we present the synthesis and characterization of Pt, Pd, Pt based bimetallic and multi-metallic nanoparticles with mixture, alloy and core-shell structure for nano-catalysis, energy conversion, and fuel cells. Here, Pt and Pd nanoparticles with modified nanostructures can be controllably synthesized via chemistry and physics for their uses as electro-catalysts. The cheap base metal catalysts can be studied in the relationship of crystal structure, size, morphology, shape, and composition for new catalysts with low cost. Thus, Pt based alloy and core-shell catalysts can be prepared with the thin Pt and Pt-Pd shell, which are proposed in low and high temperature proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs). We also present the survey of the preparation of Pt and Pd based catalysts for the better catalytic activity, high durability, and stability. The structural transformations, quantum-size effects, and characterization of Pt and Pd based catalysts in the size ranges of 30 nm (1-30 nm) are presented in electro-catalysis. In the size range of 10 nm (1-10 nm), the pure Pt catalyst shows very large surface area for electro-catalysis. To achieve homogeneous size distribution, the shaped synthesis of the polyhedral Pt nanoparticles is presented. The new concept of shaping specific shapes and morphologies in the entire nano-scale from nano to micro, such as polyhedral, cube, octahedra, tetrahedra, bar, rod, and others of the nanoparticles is proposed, especially for noble and cheap metals. The uniform Pt based nanosystems of surface structure, internal structure, shape, and morphology in the nanosized ranges are very crucial to next fuel cells. Finally, the modifications of Pt and Pd based catalysts of alloy, core-shell, and mixture structures lead to find high catalytic activity, durability, and stability for nano-catalysis, energy conversion, fuel cells, especially the next large-scale commercialization of next PEMFCs, and DMFCs.

This paper provides an overview of several operating conditions which can have a significant effect on the durability of polymer electrolyte fuel cells (PEFCs) and direct methanol fuel cells (DMFC), including: low reactant flows, high and low humidification levels, and high and low temperatures. The possible effects of these conditions, along with possible mitigating strategies, are discussed. Data from various tests are presented demonstrating lifetimes from 1000 h to greater than 13,000 h for various conditions and applications.

A laboratory-scale liquid-feed direct methanol fuel cell (DMFC) was operated with di!erent methanol feeding strategies. A proton exchange membrane (PEM) was used as the elecytrolyte. The cell voltage response to dynamic feeding of methanol revealed that a signi"cant voltage increase can be obtained from dynamic changes in methanol feed concentration. The observed fuel cell behaviour was analysed with a mathematical model which consists of anode mass balances, charge balances of both electrodes and electrode kinetic expressions. Anode kinetics were derived from a four-step reaction mechanism with several intermediates bound to the catalyst surface. The model also accounts for the undesired cross-over of methanol, through the PEM, towards the cathode catalyst layer. First, the model is applied to predict steady-state current}voltage characteristics. Then, the cell voltage response to dynamic changes of methanol feed concentration is simulated. The simulated results are in full agreement to experimental observations. It turns out that methanol cross-over can be reduced by periodically pulsed methanol feeding.

Liquid-fed direct methanol fuel cells (DMFCs) are one of the most promising candidates for portable power electronics and automotive applications due to their potentially high-energy density, simple storage, and distribution of the fuel. The concentration of methanol in the fuel circulation loop of a DMFC system is an important operating parameter, because it determines the electrical performance and efficiency of the system. The methanol concentration in the circulating fuel stream is usually measured continuously with a suitable sensor for the purpose of maintaining optimal power and efficiency in the DMFC system. Various methods of sensing methanol concentration have been proposed over the past decade. This paper reviews these methanol concentration sensors for DMFCs, which are generally classified into two groups: electrochemical and physical. The construction and operating principles of each sensor, as well as its advantages and disadvantages, are described. The sensorless methods for controlling the methanol concentration are introduced briefly. Finally, the perspective on the future of methanol concentration sensors is discussed. Crown

Double layer proton exchange membrane Structurally modified chitosan Methanol crossover Direct methanol fuel cell a b s t r a c t A novel double layer proton exchange membrane (PEM) comprising a layer of structurally modified chitosan, as a methanol barrier layer, coated on Nafion Ò 112 was prepared and assessed for direct methanol fuel cell (DMFC) applications. Scanning electron microscope (SEM) micrographs of the designed membrane revealed a tight adherence between layers, which indicate the high affinity of opposite charged polyelectrolyte layers. Proton conductivity and methanol permeability measurements showed improved transport properties of the designed membrane compared to Nafion Ò 117. Moreover, DMFC performance tests revealed a higher open circuit voltage and power density, as well as overall fuel cell efficiency for the double layer membrane in comparison with Nafion Ò 117, especially at elevated methanol solution feed. The obtained results indicate the designed double layer membrane as a promising PEM for high-performance DMFC applications. (M.M. Hasani-Sadrabadi).

Potential-scan tests were conducted to evaluate the stability of a PtRu/C electrocatalyst at anode potentials in a direct methanol fuel cell (DMFC). The results show that, under normal operating conditions, the anode potential in a DMFC is benign for the PtRu/C electrocatalyst. But in the case of deep discharge or short circuit, the anode potential value may exceed 0.6 V versus DHE, which is harmful to the PtRu/C electrocatalyst. The dissolution of catalyst components results in an enhanced ohmic resistance and a lowered catalytic activity for methanol electro-oxidation.

Long-term durability Hydrocarbon membrane Membrane electrode assembly a b s t r a c t A long-term durability test has been conducted for a direct methanol fuel cell (DMFC) using the commercial hydrocarbon membrane and Nafion ionomer bonded electrodes for 500 h.

Direct ethanol fuel cell (DEFC) is a promising power source for future use in portable electronic equipments. In general, the power density obtained in DEFC is lower than that of direct methanol fuel cell. In the present study, various losses in DEFC are estimated by performing experiments with the prepared membrane electrode (MEA) to obtain current-voltage characteristics and comparing it with the prediction of mathematical model. MEA for the DEFC is prepared using Pt-Ru (40:20 by wt.%)/C as anode catalyst, Pt-black as cathode catalyst with 1 mg/cm 2 of loadings and cast Nafion ® (SE5112, DuPont) ionomer as proton exchange membrane. The mathematical model for DEFC is developed considering different overpotentials. The activation overpotential term is formulated considering ethanol electrooxidation mechanism proposed in literature and Butler-Volmer equation. The ohmic overpotential is modeled based on proton conductivity of Nafion ® membrane and ohmic losses at the electrodes, current collectors and electrode-current collector interfaces. The concentration overpotential is formulated using Fick's law, modified Butler-Volmer equation and transport process through electrodes and electrocatalyst layers. The experiment data on current-voltage characteristics is predicted by the model with reasonable agreement and the influence of ethanol concentration and temperature on the performance of DEFC is captured by the model.

Kohlenstoff-VulcanXC72 gilt derzeit als Standard-Katalysatorträger in der Niedertemperatur-Brennstoffzelle. Aufgrund seiner relativ niedrigen spezifischen Oberfläche sowie seiner Korrosionsanfälligkeit ist man zurzeit auf der Suche nach Ersatzmaterialien. In diesem Beitrag wird über den Einsatz von Kohlenstoff-Nanoröhren als PtRu-Katalysatorträger in der DMFC-Anode berichtet. Nach chemischer Vorbehandlung der Kohlenstoff-Nanoröhren in Luft bei 300°C bzw. in konzentrierter Salpetersäure wurde eine Zellleistung von 152 bzw.

Technologically advanced human societies require specialized tools and equipment to enable their diverse and mobile activities. Portable electronic devices like laptop, PDA, handphone, etc. are now an essential tool for many people in their daily lives. The rechargeable batteries used to power the portable electronic devices could be improved upon with regards to power density, and there is a crucial need for efficient, renewable and more environmentally friendly power sources. Many researchers have shown that the direct methanol fuel cell (DMFC) is an appropriate alternative to rechargeable battery technology, although many factors must be resolved before it can be commercialized. This paper gives an overview on the possibilities for using the DMFC as portable electronic devices power source along with some views on current and future trends in DMFC development, economic analysis and presents the current problems and solutions by DMFC researchers.

Proton conducting membranes for a direct methanol fuel cell (DMFC) were fabricated from blends of Nafion ® and polybenzimidazole (PBI) by solution casting. Prior to dissolution in the casting solvent, the sulfonic acid groups of the Nafion component of the blend were partially exchanged with sodium ions. The dependence of membrane proton conductivity and methanol permeability on the extent of proton substitution of Nafion during blending and on the PBI content of the final membrane was studied. It was found that membrane selectivity (the ratio of proton conductivity to methanol permeability) was the highest (four times that of Nafion 117) when fully protonated Nafion was used during blending and when the PBI content was 8%. DMFC performance of Nafion-PBI membranes (approximately 60 m in thickness) was found to be superior to that of Nafion 117 at 1.0 and 5.0 M methanol feeds.

Carbon xerogels (CXs) have been prepared by polycondensation of resorcinol and formaldehyde in water by the sol-gel method. Functionalization with diluted and concentrated nitric acid as oxidizing agents was carried out to create surface oxygen groups, acting as anchoring sites for metallic particles. Characterization techniques included nitrogen physisorption, scanning electron microscopy, temperature programmed desorption and temperature programmed oxidation. Functionalized xerogels were used as supports to synthesize Pt and PtRu electrocatalysts by a conventional impregnation method. Catalysts electrochemical activity towards the oxidation of methanol was studied by cyclic voltammetry and chronoamperometry to establish the effect of the surface chemistry on the catalysts synthesis. Carbon monoxide oxidation was also studied to determine the electrochemical active area and the CO tolerance of the as prepared catalysts. Results were compared to those obtained with commercial Pt/C and PtRu/C catalysts supported on Vulcan XC-72R (E-TEK). All electrocatalysts supported on carbon xerogel showed better performances than commercial ones, providing higher current density values for the oxidation of methanol.

Objectives Develop materials and components and optimize operating conditions of the direct methanol fuel cell (DMFC) for maximum power density and fuel conversion efficiency at a minimum cost. In particular: • Design and optimize membrane-electrode assemblies (MEAs) to enhance cell performance. • Advance electrocatalysis of methanol oxidation and oxygen reduction to increase power density and lower total precious metal loading. • Characterize and optimize non-Nafion polymers with reduced crossover and improved performance. • Model, develop and demonstrate practical viability of advanced cell components. Approach • Build, operate and test performance of DMFCs with different anode and cathode catalysts, membranes and MEAs. • Through experimentation, develop thorough understanding of the key factors impacting cell performance and durability. • Maximize efficiency, power and energy density of DMFCs by creative designing of stack components and experimental verification of the hardware ...

Direct methanol fuel cell performance curves were obtained as a function of three parameters, (1) temperature, (2) fuel flow-rate and concentration. Methanol crossover was measured by gas chromatography as a function of these three parameters at 100 mA/cm 2 in the singlepass fuel delivery mode. The data was used to model a continuous loop mode where pure methanol is injected into a loop that circulates through the flow-field and recovers water from the cathode. The modeled loop composition is identical to the fuel stream used in the singlepass experiments (dilute aqueous methanol). The model results, presented in three-dimensional surfaces, elucidate the impact of parameter variations on the energy and power density of the direct methanol fuel cell (DMFC) and the link between those two figures of merit. In addition, a reasonable estimate of the contribution of mass transport effects due to the carbon fabric current collectors is made along with in situ CO stripping experiments on membrane electrode assembly (MEA) anode surfaces. The analysis shows that, at present, serious compromises are required if reasonable energy and power densities are to be simultaneously maintained in DMFCs using Nafion TM 117 as an electrolyte. #

In this study, a carbon nanotube-supported PtRu electrocatalyst (PtRuCNT) was prepared, characterized and investigated for methanol electro-oxidation by catalytic activity enhancement using an electrochemical treatment. From XPS analyses, the as-prepared catalyst was found to mainly composed of Pt(0)/Pt(II) states for the Pt element and Ru(0)/Ru(IV) states for the Ru element. When the electrocatalyst was subjected to an enhancement treatment, the Ru(IV) state increased substantially from 29.50% to 44.11%. Both CO-stripping experiments and open-circuit cell voltage measurements indicated that the treated PtRuCNT has given rise to an improved performance on methanol electrooxidation caused mainly by the increase of the Ru(IV) state in this particular case. The single-cell test also revealed that a direct methanol fuel cell (DMFC) can be put into its full operation in a short time. A direct application of this finding is to significantly shorten the activation time of a new DMFC stack. However, the electrochemically treated PtRuCNT catalyst still needs a continuous enhancement mechanism to sustain its enhanced activity. A promotional model is proposed to explain the phenomenon observed and a remedial approach is also suggested to solve the problem for practical applications. ß

The effect of side chain architectures on the properties and proton conductivities of graft copolymer membranes for direct methanol fuel cells (DMFCs) are studied. Poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) (PVDF-g-PSSA) copolymers with either linear or arborescent PSSA side chains are prepared and examined. For the copolymers with similar ion exchange values, both graft copolymers show similar water uptakes and bound water contents. Meanwhile, the arborescent samples exhibit higher proton conductivity, lower methanol permeability, and higher selectivity compared to the linear analogues. Incorporation of highly branched side chains effectively increases the properties of the PVDF-g-PSSAbased PEMs for DMFCs because of formation of agglomerate PSSA domains. The PSSA domains promote proton conduction and depress methanol permeation through the PEMs, consequently significantly increase the selectivities (proton conductivity/methanol permeability) of the PEMs.

A series of highly proton conductive electrolyte membranes with improved methanol barrier properties are prepared from polyallylamine hydrochloride (PAH) and polystyrene sulfonic acid (PSS) including salt by Layer-by-Layer (LbL) method. The effects of added salt type (NaCl, MgCl2) and salt concentration (1.0 M, 0.1 M) on proton conductivity (σ) and methanol barrier properties of the LbL self-assembled composite membranes are discussed in terms of controlled layer thickness and charge density. Furthermore, the influences of ion type in the multilayered composite membranes are studied in conjunction with physicochemical and thermal properties.The deposition of the self-assembly of PAH/PSS film on Nafion is followed by UV–Vis spectroscopy and it is observed that the polyelectrolyte layers growth on both sides of Nafion membrane regularly. (PAH/PSS)5–Na+ and (PAH/PSS)5–H+ with 1.0 M NaCl exhibits 49.6 and 27.8% reduction in lower methanol permittivity in comparison with the pristine Nafion®117, respectively, while the proton conductivities are 12.97 and 74.69 mS cm−1. Promisingly, it is found that the membrane selectivity values (Φ) of all multilayered membranes in H+ form are much higher than that of salt form (Na+ and Mg2+) and perfluorosulfonated ionomers reported in the literature. Also, we find out that the use of polyelectrolytes with high charge density causes a further improvement in proton conductivity and methanol barrier properties simultaneously. These encouraging results indicate that upon a suitable choice of LbL deposition conditions, composite membranes exhibiting both high proton conductivity and improved methanol barrier properties can be tailored for fuel cells.

Proton-exchange membranes, for possible use in H 2 /O 2 and direct methanol fuel cells have been fabricated from poly[bis(3methylphenoxy)phosphazene] by ®rst sulfonating the base polymer with SO 3 and then solution-casting thin ®lms. The ionexchange capacity of the membrane was 1.4 mmol/g. Polymer crosslinking was carried out by dissolving benzophenone photoinitiator in the membrane casting solution and then exposing the resulting ®lms after solvent evaporation to UV light. The crosslinked membranes look particularly promising for possible proton exchange membrane (PEM) fuel cell applications. A sulfonated and crosslinked polyphosphazene membrane swelled less than Na®on 117 in both water and methanol. Proton conductivities in crosslinked and non-crosslinked 200 mm thick water-equilibrated polyphosphazene ®lms at temperatures between 258C and 658C were essentially the same and only 30% lower than those for Na®on 117. Additionally, water and methanol diffusivities in the crosslinked polyphosphazene membrane were very low ( 1.2Â10 À7 cm 2 /s). Sulfonated/ crosslinked polyphosphazene ®lms showed no signs of mechanical failure (softening) up to 1738C and a pressure of 800 kPa and did not degrade chemically when soaked in a hot hydrogen peroxide/ferrous ion solution.

SPEEK PVA DMFC a b s t r a c t The double-layer membranes consisting of sulfonated poly(ether ether ketone) (SPEEK) sub-layer and polyvinyl alcohol (PVA) sub-layer were investigated for direct methanol fuel cell (DMFC). The membranes with different prescriptions were prepared by two-step solvent casting. Swelling behavior in water and 2 M methanol solution, ion exchange capacity (IEC) and methanol permeability of the membranes were studied and discussed. In 2 M methanol solution, SP63 provided the planar swelling ratio of 8.16 % and zero at 80 C and 25 C, respectively. The low swelling behaviors in planar direction are expected to be useful in maintaining the tight contact between electrolyte membrane and catalyst layer. The double-layer membranes were assembled in DMFC, PVA sub-layer adhered to anode to block methanol crossover. Proton conductivities of the double-layer membranes are restricted by the lower conductivity of PVA sub-layer, which would be improved in our further research. The double-layer membranes are suggested to be ideal candidate proton exchange membrane for DMFC application.

This chapter describes a spray-based method to manufacture electrocatalyst powders for fuel cell and related applications. The attributes of this process are compared to traditional solution precipitation/impregnation methods as well as non-powder-based electrocatalyst production methods. The spray-based process described here results in formation of unique spherical, micron-sized aggregates consisting of sub-micron electrocatalyst particles where the nanometer sized active phases (Pt, PtRu, metal alloys, metal oxides, composite and anchored molecular compounds) are highly dispersed on the surface of carbon supports. The advantages of this method to manufacture electrocatalyst powders are described in terms of process economics and performance.

The demand for a solid polymer electrolyte membrane (SPEM) for fuel-cell systems, capable of withstanding temperatures above 130 • C, decreasing the electrode-catalyst loadings and reducing poisoning by carbon monoxide, has prompted this study. A novel, low-cost, highly conductive, nanoporous proton-conducting membrane (NP-PCM) based on a polytetrafluoroethylene (PTFE) backbone has been developed. It comprises non-conductive nano-size ceramic powder, PTFE binder and an aqueous acid. The preparation procedures were studied and the membrane was characterized with the use of: SEM, EDS, pore-size-distribution measurements (PSD), TGA-DTA and electrochemical methods. The ionic conductivity of a membrane doped with 3 M sulfuric acid increases with the ceramic powder content and reaches 0.22 S cm −1 at 50% (v/v) silica. A non-optimized direct-methanol fuel cell (DMFC) with a 250 m thick membrane has been assembled. It demonstrated 50 and 130 mW cm −2 at 80 and 130 • C, respectively. Future study will be directed to improving the membrane-preparation process, getting thinner membranes and using this membrane in a hydrogen-fed fuel cell.