Showing papers on "Direct methanol fuel cell published in 2013"

Fluorine-Doped Carbon Blacks: Highly Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction

Abstract: For the goal of practical industrial development of fuel cells, inexpensive, sustainable, and high performance electrocatalysts for oxygen reduction reactions (ORR) are highly desirable alternatives to platinum (Pt) and other rare materials. In this work, sustainable fluorine (F)-doped carbon blacks (CB-F) as metal-free, low-cost, and high-performance electrocatalysts for ORR were synthesized for the first time. The performance (electrocatalytic activity, long-term operation stability, and tolerance to poisons) of the best one (BP-18F, based on Black Pearls 2000 (BP)) is on the same level as Pt-based or other best non-Pt-based catalysts in alkaline medium. The maximum power density of alkaline direct methanol fuel cell with BP-18F as the cathode (3 mg/cm2) is ∼15.56 mW/cm2 at 60 °C, compared with a maximum of 9.44 mW/cm2 for commercial Pt/C (3 mgPt/cm2). All these results unambiguously demonstrate that these sustainable CB-F catalysts are the most promising alternatives to Pt in an alkaline fuel cell. Sin...

Nitrogen: unraveling the secret to stable carbon-supported Pt-alloy electrocatalysts

Abstract: Nitrogen functionalities significantly improve performance for metal-based carbon-supported catalysts, yet their specific role is not well understood. In this work, a direct observation of the nanoscale spatial relationship between surface nitrogen and metal catalyst nanoparticles on a carbon support is established through principal component analysis (PCA) of electron energy loss spectral (EELS) imaging datasets acquired on an aberration-corrected scanning transmission electron microscope (STEM). Improved catalyst–support interactions correlated to high substrate nitrogen content in immediate proximity to stabilized nanoparticles are first demonstrated using model substrates. These insights are applied in direct methanol fuel cell prototypes to achieve substantial improvements in performance and long-term stability using both in-house and commercial catalysts doped with nitrogen. These results have immediate impact in advanced design and optimization of next generation high performance catalyst materials.

An overview of fuel management in direct methanol fuel cells

Abstract: Fuel cells were an important technology that could be used for a variety of power applications. The direct methanol fuel cell (DMFC) was a promising candidate for powering portable electronic devices such as laptops, digital cameras and cell phones. Compared with conventional batteries, DMFCs could provide a higher power density with a longer lifetime and almost instant recharging. However, many issues related to the design, fabrication and operation of miniaturised DMFC power systems remain unsolved. Fuel delivery was a key issue in determining the performance of a DMFC. To achieve the desired performance, an efficient fuel delivery system was required to provide an adequate amount of fuel for consumption and to remove the carbon dioxide generated in the fuel-cell devices. This paper presented a detailed description of various fuel flow-field designs for DMFCs and their respective advantages. This paper also discussed the current approaches and challenges in existing fuel delivery and fuel storage systems, including active and passive DMFCs and micro-fluidic systems. The commercialisation of DMFCs with storage was presented.

Design and synthesis of Pd-MnO2 nanolamella-graphene composite as a high-performance multifunctional electrocatalyst towards formic acid and methanol oxidation.

Abstract: One great challenge in the development of portable fuel cell systems is to explore novel electrocatalysts with better performance and lower costs. Here we report a facile strategy to fabricate a ternary nanocomposite based on Pd/MnO2 nanolamella–graphene sheets (Pd/MNL/GS) and demonstrate its application as a multifunctional catalyst for both the direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC). The developed route rationally utilizes graphene as both a green reducing agent in the synthesis of MnO2 nanolamella and a superior supporting material for growing and supporting Pd nanoparticles (NPs). Whether for formic acid oxidation or methanol oxidation, the as-prepared Pd/MNL/GS hybrid has extremely large electrochemically active surface area (ECSA) values and exhibits significantly high forward peak current densities, both of which are nearly 3 times greater than those of the Pd/GS catalyst and 6 times the Pd/Vulcan XC-72 catalyst, revealing that metal Pd can be effectively utilized in the presence of promoter components (MNL and GS). Therefore, such a ternary composite with a sophisticated 2D configuration may bring new design opportunities of high-performance energy conversion devices in the future.

Nafion/chitosan-wrapped CNT nanocomposite membrane for high-performance direct methanol fuel cells

Abstract: Here we show that the transport properties and electrochemical performance of polyelectrolyte membranes are improved through the dispersion of chitosan-wrapped carbon nanotubes, for direct methanol fuel cell applications. Methanol permeability is reduced via improving the interfacial interactions and the solubilization of CNTs in the Nafion matrix, as well as inducing the formation of long-range oriented conduction pathways in the vicinity of the decorated one-dimensional nanostructure. The improved membrane selectivity results in a considerably enhanced fuel cell efficiency (16% vs. 11%) and a power generation capacity more than two times higher (110 mW cm−2vs. 47 mW cm−2) in a concentrated methanol solution (5 M), in comparison with the commercial Nafion®117 membrane.

Tailoring Chemical Composition To Achieve Enhanced Methanol Oxidation Reaction and Methanol-Tolerant Oxygen Reduction Reaction Performance in Palladium-Based Nanowire Systems

Abstract: In this article, we address two key challenges in the development of electrocatalysts for direct methanol fuel cells by rationally tailoring the morphology and chemical composition of Pd-based nanowires (NWs) for enhanced performance. First, we have examined the morphology and composition-dependent performance of Pt1–xPdx NWs toward the methanol oxidation reaction (MOR). Elemental Pt NWs were found to possess a significant morphology-dependent enhancement of nearly 3-fold in terms of peak MOR-specific activity over that of commercial Pt NP/C. In addition, tailoring the chemical composition in Pt1–xPdx NWs can lead to measurable increases in MOR kinetics, which can be attributed to improved oxidation of formic acid and, potentially, increased selectivity for a direct, CO-free pathway. Second, we have explored the stability of ORR performance in the presence of measurable concentrations of methanol as a function of chemical composition in Pt1–xPdx NWs and Pt-free Pd9Au NWs. In the context of the Pt1–xPdx NW...

Oxygen-Functionalized Highly Mesoporous Carbon Xerogel Based Catalysts for Direct Methanol Fuel Cell Anodes

Abstract: PtRu catalysts were prepared using a highly mesoporous carbon xerogel submitted to different oxygen functionalization treatments: diluted and concentrated nitric acid as well as gas-phase 5% O2–N2 oxidation. Catalysts with 20 wt % loading and equimolar Pt:Ru metallic phase were prepared using an impregnation procedure involving chemical reduction with formic acid. The so-obtained carbon materials, as well as the different catalysts synthesized, were characterized by means of N2 physisorption, temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry and chronoamperometry were performed to study their activity toward carbon monoxide and methanol oxidation. Functionalization of the carbon support was found to play a definitive role in the interaction between carbon material and the active phase, determining metallic dispersion, alloying degree, and reduction extent. The activity of the catalysts in...

1,4-Hydroquinone is a Hydrogen Reservoir for Fuel Cells and Recyclable via Photocatalytic Water Splitting

Abstract: Photocatalytic splitting of water was carried out in a two-phase system. Nanocrystalline titanium dioxide was used as photocatalyst and potassium hexacyanoferrate(III)/(II) as electron transporter. Generated hydrogen was chemically stored by use of a 1,4-benzoquinone/1,4-hydroquinone system, which was used as a recyclable fuel in a commercialised direct methanol fuel cell (DMFC). The electrical output of the cell was about half compared to methanol. The conversion process for water splitting and recombination in a fuel cell was monitored by UV-Vis spectroscopy and compared to a simulated spectrum. Products of side reactions, which lead to a decrease of the overall efficiency, were identified based on UV-Vis investigations. A proof of principle for the use of quinoide systems as a recyclable hydrogen storage system in a photocatalytic water splitting and fuel cell cyclic process was given.