Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel

Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is ~520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt.

Contribution of direct electron transfer mechanisms to overall electron transfer in microbial fuel cells utilising Shewanella oneidensis as biocatalyst

Objectives To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode. Results A maximum power output of 114 ± 6 mWm−2 was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm−2. The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels. Conclusion S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer.

Electrochemical analysis of the performance of carbon supported Pd nanoparticles for direct formic acid fuel cells: from gold supported electrodes to catalyst-coated membranes

In this work carbon supported Pd nanoparticles were prepared and used as electrocatalysts for formic acid electrooxidation fuel cells. The influence of some relevant parameters such as the nominal Pt loading, the Nafion/total solids ratio as well as the Pd loading towards formic acid electrooxidation was evaluated using gold supported catalytic layer electrodes which were prepared using a similar methodology to that employed in the preparation of conventional catalyst coated membranes (CCM). The results obtained show that, for constant Pd loading, the nominal Pd loading and the Nafion percentage on the catalytic layer do not play an important role on the resulting electrocatalytic properties. The main parameter affecting the electrocatalytic activity of the electrodes seems to be the Pd loading, although the resulting activity is not directly proportional to the increased Pd loading. Thus, whereas the Pd loading is multiplied by a factor of 10, the activity is only twice which evidences an important decrease in the Pd utilization. In fact, the results obtained suggest the active layer is the outer one being clearly independent of the catalytic layer thickness. Finally, catalyst coated membranes with Pd catalyst loadings of 0.1, 0.5 and 1.2 mg cm-2 were also tested in a breathing direct formic acid fuel cell.

Direct spun aligned carbon nanotube web-reinforced proton exchange membranes for fuel cells

A new method combining electrospinning of SPEEK and direct spinning of CNT forests has been used to prepare sulfonated poly(ether ether ketone) (SPEEK)/directly spinnable carbon nanotube (dsCNT) composite proton exchange membranes. The SPEEK/dsCNT membrane is more robust than SPEEK alone, and in a fuel cell significantly outperforms both SPEEK and the commercial Nafion 212 membranes.

Two-Phase Flow In Fuel Cells In Short-Term Microgravity Condition

A visual observation of liquid-gas two-phase flow in anode channels of a direct methanol proton exchange membrane fuel cells in microgravity has been carried out in a drop tower. The anode flow bed consisted of 2 manifolds and 11 parallel straight channels. The length, width and depth of single channel with rectangular cross section was 48.0 mm, 2.5 mm and 2.0 mm, respectively. The experimental results indicated that the size of bubbles in microgravity condition is bigger than that in normal gravity. The longer the time, the bigger the bubbles. The velocity of bubbles rising is slower than that in normal gravity because buoyancy lift is very weak in microgravity. The flow pattern in anode channels could change from bubbly flow in normal gravity to slug flow in microgravity. The gas slugs blocked supply of reactants from channels to anode catalyst layer through gas diffusion layer. When the weakened mass transfer causes concentration polarization, the output performance of fuel cells declines.

Two-phase Flow in Fuel Cells in Short-term Microgravity Condition

A visual observation of liquid-gas two-phase flow in anode channels of a direct methanol proton exchange membrane fuel cells in microgravity has been carried out in a drop tower. The anode flow bed consisted of 2 manifolds and 11 parallel straight channels. The length, width and depth of single channel with rectangular cross section was 48.0 mm, 2.5 mm and 2.0 mm, respectively. The experimental results indicated that the size of bubbles in microgravity condition is bigger than that in normal gravity. The longer the time, the bigger the bubbles. The velocity of bubbles rising is slower than that in normal gravity because buoyancy lift is very weak in microgravity. The flow pattern in anode channels could change from bubbly flow in normal gravity to slug flow in microgravity. The gas slugs blocked supply of reactants from channels to anode catalyst layer through gas diffusion layer. When the weakened mass transfer causes concentration polarization, the output performance of fuel cells declines.

Diffusion and chemical reaction in the porous structures of solid oxide fuel cells

The Rolls-Royce Integrated-Planar Solid Oxide Fuel Cell (IP-SOFC) consists of ceramic modules which have electrochemical cells printed on the outer surfaces. The cathodes are the outermost layer of each cell and are supplied with oxygen from air flowing over the outside of the module. The anodes are in direct contact with the ceramic structure and are supplied with fuel from internal gas channels. Natural gas is reformed into hydrogen for use by the fuel cells in a separate reformer module of similar design except that the fuel cells are replaced by a reforming catalyst layer. The performance of the modules is intrinsically linked to the behaviour of the gas flows within their porous structures. Because the porous layers are very thin, a one-dimensional flow model provides a good representation of the flow property variations between fuel channel and fuel cell or reforming catalyst. The multi-component convective-diffusive flows are simulated using a new theory of flow in porous material, the Cylindrical Pore Interpolation Model. The effects of the catalysed methane reforming and water-gas shift chemical reactions are also considered using appropriate kinetic models. It is found that the shift reaction, which is catalysed by the anode material, has certain beneficial effects on the fuel cell module performance. In the reformer module it was found that the flow resistance of the porous support structure makes it difficult to sustain a high methane conversion rate. Although the analysis is based on IP-SOFC geometry, the modelling approach and general conclusions are applicable to other types of SOFC.

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion(R)-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion(R)-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltarnmetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.

Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst for direct methanol fuel cell

Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst shows higher specific activity towards oxygen reduction reaction as compared to Pt/MWNTs when employed as cathodic catalyst in direct methanol fuel cell.

An Electro-osmotic Fuel Pump for Dircet Methanol Fuel Cells

This work reports on the design and performance evaluation of a miniature direct methanol fuel cell(DMFC)integrated with an electro_osmotic(EO)pump for methanol delivery.Electro-osmotic pumps require minimal parasitic power while boasting no moving parts and simple fuel cell integration.Here ,aneletro-osmotic pump is realized from a commercially available porous glass frit.We characterize a custom-fabricated DMFC with a free convection cathode and coupled to an extennal electro-osmotic pump operated at applied potentials of 4.0,7.0,and 10V.Maximum gross power density of our free convection DMFC(operated at 50°)is 55 mW/cm2 using 4.0 mol/L concentration methanol solution supplied by the EO pump.Experimental results show that electro-osmotic pumps can deliver 2.0,4.0 and 8.0mol/L methanol/water mixtures to DMFCs while utilizing ~5.0% of the fuel cell power.Furthermore ,we discuss pertinent design considerations when using electro-osmotic pumps with DMFCs and areas of further study.

Study of ethanol electro-oxidation in acid environment on Pt(3)Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt(3)Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions This material was characterized using X-ray diffraction (XRD). and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt(3)Sn phase. Transmission election microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3 6 nm +/- 1 nm) The polarization curves for a direct ethanol fuel cell using Pt(3)Sn/C as the anode demonstrated Improved performance compared to that of a PtSn/C E-TEK. especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt(3)Sn phase. The maximum power density for the Pt(3)Sn/C electrocatalyst (58 mW cm(-2)) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm(-2)) This behavior is attributed to the presence of a mixed Pt(9)Sn and Pt(3)Sn alloy phase in the commercial catalysts (C) 2009 Elsevier B V All rights reserved

Contribution sharing of a fuel mixture components to the fuel cell potencial of a direct alcohol fuel cell

The increasing worldwide demand for electricity impels to develop clean and renewable energy resources. In the field of portable power devices not only size and weight represent important aspects to take into account, but the fuel and its storage are also critical issues to consider. In this last sense, the direct methanol (MeOH) fuel cells (DMFC) play an important role as they can offer high power and energy density, low emissions, ambient operating conditions and fast and convenient refuelling.

The role of carbon in fuel cells

Carbon possesses unique electrical and structural properties that make it an ideal material for use in fuel cell construction. In alkaline, phosphoric acid and proton-exchange membrane fuel cells (PEMFCs), carbon is used in fabricating the bipolar plate and the gas-diffusion layer. It can also act as a support for the active metal in the catalyst layer. Various forms of carbon - from graphite and carbon blacks to composite materials - have been chosen for fuel-cell components. The development of carbon nanotubes and the emergence of nanotechnology in recent years has therefore opened up new avenues of matenials development for the low-temperature fuel cells, particularly the hydrogen PEMFC and the direct methanol PEMFC. Carbon nanotubes and aerogels are also being investigated for use as catalyst support, and this could lead to the production of more stable, high activity catalysts, with low platinum loadings (< 0.1 Mg cm(-2)) and therefore low cost. Carbon can also be used as a fuel in high-temperature fuel cells based on solid oxide, alkaline or molten carbonate technology. In the direct carbon fuel cell (DCFC), the energy of combustion of carbon is converted to electrical power with a thermodynamic efficiency close to 100%. The DCFC could therefore help to extend the use of fossil fuels for power generation as society moves towards a more sustainable energy future. (c) 2006 Elsevier B.V. All rights reserved.