DMFC Electrodes Research Articles

The Role of Solvated Electrons in Direct Methanol Fuel Cells

AbstractDirect methanol fuel cells, DMFCs, have for long been considered as a superior alternative to rechargeable batteries for various portable applications with respect to significantly higher theoretical power densities and faster recharging by simply filling up with new liquid fuel. In reality, however, DMFCs so far have much low power densities, suffer from high fuel losses, and require extremely expensive catalysts at high loadings. Here we show that an until now not considered process at the DMFC electrodes may cause these severe losses in performance. The process is that electrons generated at nano‐structured catalyst loaded electrodes become solvated into the surrounding electrolyte. Taking this new process and resulting reaction mechanism(s) fully into account, material and catalyst/electrode design should be reconsidered to realize the true potential of DMFCs.

Parametric Investigations of Direct Methanol Fuel Cell Electrodes Manufactured by Spraying

Key processing steps in the thin-film process of manufacturing catalyst layers for direct methanol fuel cells are catalyst ink formulation and its application. The catalyst ink is typically composed of supported or unsupported catalysts, binder (ionomer), solvents, and additives. Rheological properties of the ink, amount of binder, and choice of solvents are tuned to match the particular ink application process used to fabricate the electrode, as each coating process has its own unique requirements. Besides affecting the coating process, the choice and ratios of these components can significantly affect the electrochemical performance of the electrode. In this study, catalyst inks are designed and investigated for the spraying process, for utilization in the continuous fabrication of DMFC electrodes. For this purpose, the effect of the binder (ionomer) content on the performance of the electrodes is studied in detail. Decal-transfer electrodes are fabricated on a custom-built automated spraying apparatus with individually specified anode and cathode binder contents, and assembled to form a catalyst coated membrane (CCM) type membrane electrode assembly (MEA). These electrodes are rigorously tested to specifically identify their electrochemical performance, catalyst utilization and electrode morphology.

Preparation and Characterization of DMFC Electrodes and MEAs

A stencil method, that utilizes a dried powder made of the catalyst and the Nafion ionomer phase, is used to make catalyst layers and membrane electrode assemblies (MEAs). The influence of different hot-pressing conditions on the DMFC performance and various properties of the MEAs, in particularly on the properties of the anode, are investigated and compared to MEAs made by the conventional spray method. The highest DMFC performance is achieved using MEAs made by stenciling. It is also found that the membrane resistance (Rm), the resistance to proton transport within the catalyst layer (Rp) and the charge transfer resistance (Rct) towards the CH3OH oxidation reaction are lower for stenciled vs. sprayed anodes.

Complex Capacitance Analysis of Ionic Resistance and Interfacial Capacitance within Cathode Layers of PEMFC and DMFC Electrodes

For PEMFC and DMFC catalyst layers, a complex capacitance analysis of impedance data was developed to evaluate the catalyst/ionomer interfacial capacitance and ionic resistance of ionomer networks, without non-linear data fitting. Assuming no Faradaic reactions, equivalent circuits for the catalyst layers were suggested, and it was confirmed that the plots of the real and imaginary parts as a function of ac frequency are determined by the catalyst/ionomer interfacial capacitances and RC time constants, which are important characteristics for high fuel cell performances. By performing a complex capacitance analysis, the interfacial capacitances and ionic resistances of PEMFC MEAs can be experimentally obtained at various relative humidities, proving that the catalytic activity in fuel cell operation depends on ionic resistances as well as on the catalyst/ionomer interfacial area. In addition, the effects of various MEA preparation methods on the ionomer distributions and DMFC performances were analyzed by a complex capacitance analysis.

Accelerated durability test of DMFC electrodes by electrochemical potential cycling

Durability of direct methanol fuel cell electrodes was evaluated by electrochemical potential cycling and we observed the degradation phenomena during the performance decay. An individual potential measurement of anode and cathode with built-in reversible hydrogen electrode revealed that the anode and cathode performance contributions are almost of the same order of magnitude to the entire performance loss, although the anode degradation is relatively bigger, due to the dominating effect of ruthenium dissolution, corresponding loss of electrocatalytic activity. On the contrary, it was apparent that the electrochemical active surface area of Pt cathode decreased significantly with potential cycling under methanol crossover condition, which is not clearly reflected on the performance loss due to the initial decrease of interfacial resistance between membrane and cathode catalyst layer. Impedance studies could reinforce the current–voltage polarization by more comprehensive information.

Complex Capacitance Analysis of Ionic Conductivity and Interfacial Capacitance within Cathode Layers of PEMFC and DMFC Electrodes

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Preparation and Characterization of DMFC Electrodes and MEAs

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Application of low-voltage electrophoretic deposition to fabrication of direct methanol fuel cell electrode composite catalyst layer

In this study, the application of a low-voltage electrophoretic deposition (EPD) approach to the fabrication of DMFC electrode composite (i.e., catalyst/ionomer) catalyst layers using a CNT-supported PtRu (PtRu/CNT) anode nanocatalyst was investigated. In the operation of EPD, the PtRu/CNT electrocatalyst was first well mixed with a suitable amount of Nafion ® solution (ionomer dispersion) with or without the addition of HClO 4 as a supporting electrolyte and then electrophoretically deposited onto a non-catalyzed electrode base at a low applied DC voltage range of 0–5 V for 0–60 min. The resultant composite catalyst layer appeared to be thin and quite smooth exhibiting a lustrous texture particularly when the supporting electrolyte was employed in the suspension. Electrochemical impedance spectroscopy (EIS), however, showed that the coated composite catalyst layer exhibited a fairly high resistance indicating an excessive amount of ionomer was preferably deposited. Application of the fabricated electrode to a DMFC resulted in a cell performance with low but reasonable power density. These test results suggested that the low-voltage EPD could be a feasible approach to effective fabrication of DMFC electrode composite catalyst layers incorporated with CNT-supported electrocatalysts, although significant improvements are deemed to be necessary.

Dispersion of Pt/Ru catalyst onto arc-soot and its performance evaluation as DMFC electrode

Abstract The arc-soot (AS) nano-carbon was synthesized by using arc discharge apparatuses which were the conventional arc apparatus and the new twin-torch-arc apparatus. AS synthesized with the conventional arc apparatus contained cocoon-like carbon nano-horn (CNH), dahlia-like CNH, and graphite ball. On the other hand, AS which was synthesized using the new twin-torch-arc apparatus contained mainly cocoon-like CNH and dahlia-like CNH, and contained a little graphite ball. The quality of dispersion was characterized and evaluated by the index of dispersion which was based on a diameter and a number density of catalyst particles. The electrocatalystic activity of the Pt/Ru catalysts was evaluated by the methanol-impregnated paper burning method. If the index of dispersion of the AS was high, then the AS burned violently. In the dispersion process, the optimum dispersion temperature obtained was 150 °C. Some MEAs of DMFC cell consisted of each Pt/Ru–AS catalyst which had different characteristics. It was observed that the power density increased with the index of dispersion. It was suggested that the power density of DMFC increased by 500% with a 350% increase in the index of dispersion. Pt/Ru–AS catalyst used AS, which was synthesized using the new twin-torch-arc apparatus, was better than Pt/Ru–AS catalysts using AS which were synthesized with the conventional arc apparatus to apply for the catalyst of DMFC.

Solid - Phase Synthesis of Carbon Nanoparticles and their Application to Direct Methanol Fuel Cell

Carbon nanoparticles were prepared by simple method. TEM image shows that the particle size is several nanometers. Furthermore, the specific surface area of the material is reached for 425.8 m2/g. It is much larger than that of carbonVulcan-XC72, which they is widely used as catalyst supports for DMFC electrodes. Carbon nanoparticles is a kind of promising material used for catalyst support in DMFC.

DMFC Electrode Fabrication, Structure and Fuel Cell Performance

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High performance of cup-stacked-type carbon nanotubes as a Pt–Ru catalyst support for fuel cell applications

The potential of cup-stacked-type carbon nanotubes (CSCNTs) as a catalyst support for the direct methanol fuel cells has been investigated by the electrochemical oxidation of methanol at various temperatures. The CSCNT-supported platinum–ruthenium (Pt–Ru) bimetallic catalyst exhibited twice as high a power density as the Pt–Ru catalyst supported on Vulcan XC-72 carbon, which is widely used as a catalyst support for the DMFC electrodes. The microscopic analysis of the CSCNT-supported Pt–Ru catalysts revealed that the bimetallic electrocatalysts were well dispersed on the CSCNT supports, and the particle size of the electrocatalysts was ca.5nm . The results of this work indicate that the performance of the carbon support materials is largely influenced by their electrical properties, morphology and crystallographic structures.

DMFC electrode treatment

DMFC electrode treatment