Alkaline Direct Methanol Fuel Cells Research Articles

Permeant transport properties and cell performance of potassium hydroxide doped poly(vinyl alcohol)/fumed silica nanocomposites

Polyvinyl alcohol/fumed silica (PVA/FS) nano-composites were prepared through a solution casting method. The water diffusivity increased as FS was incorporated into the PVA matrix. The ionic conductivity of the KOH-doped PVA composites increased with the FS concentration. Meanwhile, the methanol permeability in the resulting composites decreased with FS addition due to suppressed methanol solubility and diffusivity. The PVA/KOH and PVA/FS/KOH electrolytes were employed in direct methanol alkaline fuel cells (DMAFCs). The effects of methanol and KOH concentrations, oxygen humidification, oxygen flow rate and the operating temperature on cell performance were investigated from the standpoints of kinetics and material characteristics. Oxygen humidification was necessary and a higher oxygen flow rate improved the cell performance. The open-circuit voltage and maximum power density of the PVA/(20%)FS/KOH electrolyte increased with increasing FS concentrations and operating temperatures. Among the tested methanol and KOH concentrations, the maximum power density of 15.3 mW cm −2 was achieved for a DMAFC consisting of a PVA/(20%)FS/KOH electrolyte with 2 M methanol and 2 M KOH as the anode feed. This inexpensive electrolyte is promising for DMAFC applications.

Enhanced performance of a direct methanol alkaline fuel cell (DMAFC) using a polyvinyl alcohol/fumed silica/KOH electrolyte

A novel polymer–inorganic composite electrolyte for direct methanol alkaline fuel cells (DMAFCs) is prepared by physically blending fumed silica (FS) with polyvinyl alcohol (PVA) to suppress the methanol permeability of the resulting nano-composites. Methanol permeability is suppressed in the PVA/FS composite when comparing with the pristine PVA membrane. The PVA membrane and the PVA/FS composite are immersed in KOH solutions to prepare the hydroxide-conducting electrolytes. The ionic conductivity, cell voltage and power density are studied as a function of temperature, FS content, KOH concentration and methanol concentration. The PVA/FS/KOH electrolyte exhibits higher ionic conductivity and higher peak power density than the PVA/KOH electrolyte. In addition, the concentration of KOH in the PVA/FS/KOH electrolytes plays a major role in achieving higher ionic conductivity and improves fuel cell performance. An open-circuit voltage of 1.0 V and a maximum power density of 39 mW cm −2 are achieved using the PVA/(20%)FS/KOH electrolyte at 60 °C with 2 M methanol and 6 M KOH as the anode fuel feed and with humidified oxygen at the cathode. The resulting maximum power density is higher than the literature data reported for DMAFCs prepared with hydroxide-conducting electrolytes and anion-exchange membranes. The long-term cell performance is sustained during a 100-h continuous operation.

Organic-inorganic hybrid alkaline membranes by epoxide ring opening for direct methanol fuel cell applications

Recently, alkaline or anion-exchange membranes (AEMs) have attracted remarkable interest for direct methanol fuel cells (DMFCs) application, operated at intermediate temperature (100–200 °C). In this manuscript, we report synthesis of organic–inorganic hybrid anion-exchange silica precursor (AESP) with ammonium functionality by ring opening of glycidoxypropyltrimethylammonium chloride under mild heating condition. A simple and ecofriendly procedure based on sol–gel method was used for the preparation of hydroxide conductive organic–inorganic AESP–poly(vinyl alcohol) (PVA) cross-linked AEM in aqueous media. Developed AEMs were extensively characterized for their physicochemical and electrochemical properties under DMFC operating conditions. These membranes were designed to possess all the required properties of highly ion conductive membrane, namely reasonable swelling, dimensional and oxidative strength, flexibility, low methanol permeability along with reasonable hydroxyl ion conductivity (7.57 × 10 −2 S cm −1) due to quaternary ammonium group functionality. Reported AEM-100 showed 7.57 × 10 −2 S cm −1 membrane conductivity much higher than reported values (0.30–3.40 × 10 −2 S cm −1) for other AEMs in the literature. Moreover, from the selectivity parameter among all developed membranes, AEM-100 (100 wt% to PVA of AESP in the membrane matrix), exhibited best result for alkaline DMFC applications.

Performance Enhancement of Alkaline Direct Methanol Fuel Cells by Ni/Al Layered Double Hydroxides

This paper reports the results of fuel cell performance tests detailing the effects of Ni/Al layered double hydroxide (Ni-LDH) on the performance of alkaline direct methanol fuel cells (DMFCs). It is desirable to enhance the maximum rate of methanol consumption at a fuel cell’s anode so that expensive bimetallic catalysts (such as Pt-Ru) would not be as essential to remedy the well-known sluggish kinetics and Pt catalyst deactivation tendencies of DMFCs. The test cells were constructed using partially hydrolyzed polyvinyl alcohol film membranes impregnated with a 10 M potassium hydroxide electrolyte. The cells were tested at a constant temperature of 40°C, and the effect of the addition of Ni-LDH to the membrane surface was studied by comparison of fuel cell polarization and power production curves of cells with Pt or Pt-Ru anodes paired with Pt cathodes. The benefits of Ni-LDH addition to DMFCs are clearly shown vis-à-vis the extended operating current densities and associated increases in power density for each catalyst type. The enhancement effect of Ni-LDH appears largely as enhancement of cell mass transport. Cells constructed with Pt anodes and membrane surfaces modified by Ni-LDH perform very nearly as well as Ni-LDH-free cells using bimetallic Pt-Ru anodes.

Design of Direct Methanol Alkaline Fuel Cell with Anion Conductive Membrane Prepared by Plasma Polymerization

Direct methanol alkaline fuel cells has been tested to suppress methanol crossover and to improve anodic activity in alkaline media. Plasma-polymerization with 4-vinylpridine and hexafluoropropene followed by quarternization using 1-bromopropane was conducted to prepare anion conductive ionomer in the catalyst layer and anion conductive membrane using porous film. The performance of direct methanol alkaline fuel cell with anion-conductive ionomer and membrane was compared with direct methanol fuel cell with proton exchange membrane at 60 {degree sign}C. The open circuit voltage using anion-conductive membrane was higher than using proton exchange membrane. Anion-conductive ionomer in catalyst layer improved cell performance. The water vapor in the cathode was starved by transport of electro-osmotic water with hydroxide anion. Plasma-polymerized membranes on various porous films were characterized by means of water uptake, ion conductivity and methanol permeability.

Quaternized poly(vinyl alcohol)/alumina composite polymer membranes for alkaline direct methanol fuel cells

The quaternized poly(vinyl alcohol)/alumina (designated as QPVA/Al 2O 3) nanocomposite polymer membrane was prepared by a solution casting method. The characteristic properties of the QPVA/Al 2O 3 nanocomposite polymer membranes were investigated using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cell (ADMFC) comprised of the QPVA/Al 2O 3 nanocomposite polymer membrane were assembled and examined. Experimental results indicate that the DMFC employing a cheap non-perfluorinated (QPVA/Al 2O 3) nanocomposite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC with 4 M KOH + 1 M CH 3OH, 2 M CH 3OH, and 4 M CH 3OH solutions are 28.33, 32.40, and 36.15 mW cm −2, respectively, at room temperature and in ambient air. The QPVA/Al 2O 3 nanocomposite polymer membranes constitute a viable candidate for applications on alkaline DMFC.

Design of Direct Methanol Alkaline Fuel Cell with Anion Conductive Membrane Prepared by Plasma Polymerization

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Cell performance of Pd–Sn catalyst in passive direct methanol alkaline fuel cell using anion exchange membrane

Direct methanol alkaline fuel cell (DMAFC) using anion exchange membrane (AEM) was operated in passive condition. Cell with AEM exhibits a higher open circuit voltage (OCV) and superior cell performance than those in cell using Nafion. From the concentration dependences of methanol, KOH in fuel and ionomer in anode catalyst layer, it is found that the key factors are to improve the ionic conductivity at the anode and to form a favorable ion conductive path in catalyst layer in order to enhance the cell performance. In addition, by using home-made Pd–Sn/C catalyst as a cathode catalyst on DMAFC, the membrane electrode assembly (MEA) using Pd–Sn/C catalyst as cathode exhibits the higher performance than the usual commercially available Pt/C catalyst in high methanol concentration. Therefore, the Pd–Sn/C catalyst with high tolerance for methanol is expected as the promising oxygen reduction reaction (ORR) catalyst in DMAFC.

Alkali doped polybenzimidazole membrane for alkaline direct methanol fuel cell

An anion exchange membrane for alkaline direct methanol fuel cell (ADMFC) was prepared by doping polybenzimidazole(PBI) membrane with KOH. The obtained membrane was characterized by means of XRD, TGA–DTA, AC and so on. The results suggested that it possessed satisfying thermal stability and comparable mechanical strength with acid doped PBI. At room temperature, methanol permeability through this membrane was one order of magnitude lower than that of Nafion ® membrane, while its ionic conductivity was comparable with that of other anion exchange membranes in literatures. For ADMFC at 90 °C based on this PBI/KOH membrane electrolyte, the peak power density was about 31 mW/cm 2, which was significantly improved mainly due to this membrane's high thermal stability, fast kinetics of electrochemical reactions and lower methanol permeability.

Development of Anion Exchange Membranes for Direct Methanol Alkaline Fuel Cells

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Synthesis and Characterizations of Quaternized Polysulfone Anion Exchange Membrane for Direct Methanol Alkaline Fuel Cell

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Improving anion exchange membranes for DMAFCs by inter-crosslinking CPPO/BPPO blends

New anion exchange membranes are prepared by heat-treating the blend base membranes of chloroacetylated poly(2,6-dimethyl-1,4-phenyleneoxide)(CPPO)/bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO). A partially inter-crosslinked structure can be formed therein via a Friedel–Crafts reaction without adding any crosslinking reagent or catalyst. FT-IR and NMR analyses are used to confirm this inter-crosslinking structure and quantify the crosslinking distribution. Physical properties, such as toughness and thermal stability, are enhanced remarkably due to this heat treatment. Furthermore, the final membranes exhibit a high hydroxyl conductivity (up to 0.032 S cm −1 at 25 °C) and extremely low methanol permeability (1.26–1.04 × 10 −7 cm 2 s −1), which match the requirements for application in low temperature direct methanol alkaline fuel cells (DMAFCs).

Development of alkaline direct methanol fuel cells based on crosslinked PVA polymer membranes

A novel crosslinked PVA/SSA (10 wt.% sulfosuccinic acid) solid polymer membrane was obtained by a solution casting technique. An alkaline direct methanol fuel cell (DMFC) is composed of an air cathode with a mixture of MnO 2/BP2000 + CNT binary carbon inks, a Ti-based anode electrode with PtRu black inks (varied from 0.25 to 4.50 mg cm −2) and an alkaline crosslinked PVA/SSA solid polymer membrane. The electrochemical characteristics of the anode and cathode electrodes were investigated by the linear polarization method, cyclic voltammetry (CV) analysis, potentiostatic method and AC impedance spectroscopy. A Ti-mesh (Delker) with a thickness of 0.1 mm was used as a current collector on the anode electrode without a diffusion layer, which greatly reduced the mass transfer resistance for the electrode reaction. It was demonstrated that the alkaline DMFC using this novel crosslinked PVA/SSA solid polymer membrane showed excellent electrochemical performance at ambient temperature and pressure. The maximum peak current density of the DMFC was about 4.13 mW cm −2 at 60 °C and 1 atm in 2 M KOH + 2 M CH 3OH solution.

Application of sodium conducting membranes in direct methanol alkaline fuel cells

A study of a direct methanol alkaline fuel cell (DMAFC) operating with sodium conducting membranes is reported. Evaluation of the fuel cell was performed using membrane electrode assemblies incorporating carbon supported platinum catalysts and Nafion® 117 and 112 membranes. A membrane electrode assembly was also prepared by the direct chemical deposition of platinum into the surface region of the membrane. Evaluation of the chemically deposited assembly showed it to be less active than those based on carbon supported catalysts. SEM & TEM analysis indicate that this behaviour is due to the low surface area of the chemically deposited catalyst layer. The fuel cell performance with Nafion membranes is reported and is not as good as achieved with hydroxide ion conducting membranes suggesting that Nafion may not be suitable for DMAFC operation.

Development of direct methanol alkaline fuel cells using anion exchange membranes

Research into the development of direct methanol alkaline fuel cell (DMAFC) using an anion exchange polymer electrolyte membrane is described. The commercial membrane used had a higher electric resistance, but a lower methanol diffusion coefficient than Nafion® membranes. Fuel cell tests were performed using carbon supported Pt catalyst, and the effect of temperature, methanol concentration, methanol flow rate, air pressure and Pt loading were investigated. It was found that the cell performance improved drastically with a membrane assembly electrode (MEA) which did not include the gas diffusion layer on the anode, because of lower reactant mass transfer resistance. To give suitable cathode performance, humidification of the air and a subtle balance between the air pressure and water transport is required.

Preparation of annular hollow fibre membranes : Wang, Dongliang, Li, K., Teo, W.K., National University of Singapore, Singapore in journal of membrane science, vol 166 issue 1, 2000

In this study, we designed a method for the preparation of chitosan nanoparticles incorporated into a quaternized poly(vinyl alcohol) (QPVA) matrix for direct methanol alkaline fuel cells (DMAFCs). The structural and morphological properties of the prepared nanocomposites were studied using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM) and dynamic laser-light scattering (DLS). The crystallinity of the nanocomposite solid electrolytes containing 0 and 10% chitosan nanoparticles were investigated using differential scanning calorimetry (DSC). The electrochemical measurement of resulting nanocomposite membranes were analyzed according to the following parameters: methanol permeability, liquid uptakes, ionic conductivity and cell performances. The composite membranes with 10% chitosan nanoparticles in a QPVA matrix (CQPVA) show suppressed methanol permeability and higher ionic conductivity than pristine QPVA. In addition, the glutaraldehyde cross-linked nanocomposite film exhibited improvement on the methanol barrier property at 80 °C. The peak power density of the DMAFCs reached 67 mW cm−2 when fed into 1 M of methanol in 6 M of KOH.