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Low stoichiometry operation of fuel cells induces nonuniformities in the current generation and electrode potentials across the active electrode area. In this study, current and potential distributions are measured simultaneously in a fuel cell operating under reactant (fuel/air)-starvation conditions. During the galvanostatic operation under local reactant starvation, the localized increase of current density is observed closer to the inlet. Here under air starvation, cathode potentials dropped uniformly across the electrode area. However, during fuel starvation, a nonuniform cathode potential profile is observed. During the potentiostatic mode of operation under air-starvation condition, cathode potentials remained uniform and constant across the electrode area. However, under fuel starvation, the cathode potential profile is influenced by the anode potential profile. Electrode–electrode interaction especially during fuel starvation is captured by simultaneous measurements of current and potential distribution.

Binary Pt–Sn/SnO2–C electro-catalysts comprising Pt and Sn in varying weight ratio, namely 31 : 9, 33 : 7 and 35 : 5, were synthesized by an alcohol-reduction process using ethylene glycol as solvent and reducing agent. The electro-catalysts were characterized by XRD, XPS, TEM, SEM-EDAX, ICP-OES, Cyclic Voltammetry (CV), chronoamperometry and CO stripping techniques. XRD spectra reveal shifting of Pt diffraction peaks to lower angles with the addition of Sn compared with Pt–C and also the presence of SnO2. XPS results also confirm the presence of Sn in the form of PtSn alloy and in the form of SnO2 phase in the catalyst. The effect of composition towards electro-oxidation of ethanol has been studied by the CV technique. The direct ethanol fuel cells (DEFCs) with Pt–Sn/SnO2–C anode catalyst with reduced Pt loading exhibits an enhanced peak power density of 27.0 mW cm−2 while a peak power-density of only 2.2 mW cm−2 is obtained for the DEFC employing Pt–C at 90 °C.

Porous titanium oxide-carbon hybrid nanostructure (TiO2-C) with a specific surface area of 350 m(2)/g and an average pore-radius of 21 center dot 8 is synthesized via supramolecular self-assembly with an in situ crystallization process. Subsequently, TiO2-C supported Pt-Ru electro-catalyst (Pt-Ru/TiO2-C) is obtained and investigated as an anode catalyst for direct methanol fuel cells (DMFCs). X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM) have been employed to evaluate the crystalline nature and the structural properties of TiO2-C. TEM images reveal uniform distribution of Pt-Ru nanoparticles (d (Pt -aEuro parts per thousand Ru) = 1 center dot 5-3 center dot 5 nm) on TiO2-C. Methanol oxidation and accelerated durability studies on Pt-Ru/TiO2-C exhibit enhanced catalytic activity and durability compared to carbon-supported Pt-Ru. DMFC employing Pt-Ru/TiO2-C as an anode catalyst delivers a peak-power density of 91 mW/cm(2) at 65 A degrees C as compared to the peak-power density of 60 mW/cm(2) obtained for the DMFC with carbon-supported Pt-Ru anode catalyst operating under similar conditions.

TiO2 on carbon was prepared by sol–gel method. Pd supported on TiO2–C comprising Pd and Ti in varying atomic ratios namely, 1:1, 2:1 and 3:1 was prepared and characterized by X-ray diffraction and Transmission electron microscopy techniques. The electrocatalytic activity for oxygen reduction reaction in aqueous 0.1 M KOH solution containing methanol was characterized by rotating disk electrode. Catalytic activity of Pd–TiO2(3:1)/C for ORR and methanol tolerance was found to be superior in relation to Pd/C. Keywords: Electro-catalyst, Methanol-tolerant catalyst, Alkaline medium, Pd–TiO2/C

A novel nanocomposite comprising MWNTs and mixed-conducting polymeric components (electronic and ionic) is prepared, characterized and investigated as a support for platinum (Pt). Nanocomposite of MWNTs and poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT–PSS) is prepared by in situ polymerization and characterized using Fourier–Transform infrared spectroscopy (FT–IR), thermogravimetric analysis (TGA) in conjunction with scanning electron microscopy (SEM). Atomic force microscopy (AFM) studies are also carried out to characterize the surface topography of MWNTs/PEDOT–PSS nanocomposite. X-ray diffraction (XRD) studies reveal that MWNTs/PEDOT–PSS nanocomposite provides better backbone for the improved dispersion of Pt as evidenced by the reduced Pt crystallite size over MWNTs/PEDOT–PSS nanocomposite compared to MWNTs. Electrochemical characterization studies performed with Pt/nanocomposite and Pt/MWNTs demonstrate the superior catalytic activity of Pt/nanocomposite under reduced Nafion loadings in relation to Pt/MWNTs. It is observed that mixed conducting nanoporous network of MWNTs/PEDOT–PSS composite structure promotes the catalytic activity of Pt by enhancing catalyst utilization.

The effect of the anode and cathode flow field depths on the performance of a single cell Direct methanol fuel cell (DMFC) of 45 cm2 active area were experimentally investigated. Double serpentine flow fields (DSFFs) with varying channel depth namely, 0.2, 0.4, 0.6, 0.8, and 1 mm but with fixed channel and rib width each of 1 mm on both anode and cathode were designed, fabricated, and tested. The experimental study involved measurement of pressure drops across anode and cathode flow field plates, polarization, and carbon dioxide concentration measurements at various current densities. The mass transport at both anode and cathode were found to increase with increase in pressure drop across the flow field on account of reduced channel depth from 1.0 to 0.4 mm at all current densities. However, further decrease to a channel depth of 0.2 mm was found to be counter-productive with different phenomena operating on either side viz., increased CO2 slug length on the anode flow channel and increased methanol crossover on the cathode side. Hence, the maximum performance for DMFCs was observed for a channel depth of 0.4 mm on anode and cathode flow fields. A decrease in flow field channel depth at cathode was found to increase the methanol crossover due to convective mass transfer effect.

PEFCs employing Nafion-silica (Nafion-SiO2) and Nafion-mesoporous zirconium phosphate (Nafion-MZP) composite membranes are subjected to accelerated-durability test at 100 degrees C and 15% relative humidity (RH) at open-circuit voltage (OCV) for 50 h and performance compared with the PEFC employing pristine Nafion-1135 membrane. PEFCs with composite membranes sustain the operating voltage better with fluoride-ion-emission rate at least an order of magnitude lower than PEFC with pristine Nafion-1135 membrane. Reduced gas-crossover, fast fuel-cell-reaction kinetics and superior performance of the PEFCs with Nafion-SiO2 and Nafion-MZP composite membranes in relation to the PEFC with pristine Nafion-1135 membrane support the long-term operational usage of the former in PEFCs. An 8-cell PEFC stack employing Nafion-SiO2 composite membrane is also assembled and successfully operated at 60 degrees C without external humidification.

Dynamic spillover of metal oxide aided by yttrium hydroxide through its altervalent nature is utilized to develop a new carbon supported Pt–Y(OH)3 hybrid catalyst with varying Pt:Y atomic ratio of 1:1, 2:1 and 3:1 and characterized by X-Ray diffraction and Transmission electron microscopy techniques. Pt–Y/C catalysts exhibit significant improvement in oxygen reduction reaction (ORR) over commercial Pt/C. The effects of composition toward ORR with and without methanol have been studied. Among the various Pt–Y(OH)3/C catalysts, the one with Pt to Y in 3:1 atomic ratio shows the highest activity for ORR in aqueous HClO4 solution without methanol while the one with Pt to Y in 2:1 atomic ratio shows the maximum activity for ORR in presence of methanol. A direct methanol fuel cell (DMFC) employing carbon-supported Pt–Y(OH)3 as the cathode catalyst delivers a peak-power density of 105 mW/cm2 at 70 °C as compared to a peak-power density of 64 mW/cm2 obtained with the DMFC employing carbon-supported Pt catalyst operating under similar conditions. Keywords: DMFCs, Electro-catalysis, ORR catalyst, Methanol-tolerant catalyst, Pt–Y(OH)3

Carbon-supported Pt–Au (Pt–Au/C) catalyst is prepared separately by impregnation, colloidal and micro-emulsion methods, and characterized by physical and electrochemical methods. Highest catalytic activity towards oxygen-reduction reaction (ORR) is exhibited by Pt–Au/C catalyst prepared by colloidal method. The optimum atomic ratio of Pt to Au in Pt–Au/C catalyst prepared by colloidal method is determined using linear-sweep and cyclic voltammetry in conjunction with cell-polarization studies. Among 3:1, 2:1 and 1:1 Pt–Au/C catalysts, (3:1) Pt–Au/C exhibits maximum electrochemical activity towards ORR. Powder X-ray diffraction pattern and transmission electron micrograph suggest Pt–Au alloy nanoparticles to be well dispersed onto the carbon-support. Energy dispersive X-ray analysis and inductively coupled plasma-optical emission spectroscopy data suggest that the atomic ratios of the alloying elements match well with the expected values. A polymer electrolyte fuel cell (PEFC) operating at 0·6 V with (3:1) Pt–Au/C cathode delivers a maximum power-density of 0·65 W/cm 2 in relation to 0·53 W/cm 2 delivered by the PEFC with pristine carbon-supported Pt cathode.

The influence of surface characteristics of multi-walled carbon nanotubes (MWNTs) support on the catalytic performance of PEFC electrodes is investigated by using oxidized and non-oxidized MWNTs as the supports for platinum. The defect-free morphology, high electrical conductivity and favorable pore-size distribution of non-oxidized MWNTs ameliorate catalytic activity and electrochemical stability of platinum. Physico-chemical properties of oxidized and non-oxidized MWNTs and the respective catalysts are studied by BET surface-area, XRD, XPS and TEM measurements. Electrochemical stability of MWNTs-supported platinum as PEFC electrodes is assessed using potential cycling and potentiostatic techniques. Owing to the higher corrosion-resistance, platinum on non-oxidized MWNTs show lower loss in electrochemical surface area (ESA) and also exhibit 22% lower corrosion current than oxidized MWNTs.

Nano-sized Pt-Ru supported onto a mixed-conducting polymer composite comprising poly(3,4-ethylenedioxythiophene)-polystyrene sulphonic acid (PEDOT-PSSA) is employed as anode in a solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFC) and its performance compared with the SPE-DMFC employing conventional Vulcan XC-72R carbon supported Pt-Ru anode. Physical characterization of the catalyst is conducted by Fourier-transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray analysis (EDAX) in conjunction with cyclic voltammetry and chronoamperometry. The study suggests that PEDOT-PSSA to be a promising alternative catalyst-support-material for SPE-DMFCs.

Poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (styrene sulphonic acid) (PSSA) supported platinum (Pt) electrodes for application in polymer electrolyte fuel cells (PEFCs) are reported. PEDOT-PSSA support helps Pt particles to be uniformly distributed on to the electrodes, and facilitates mixed electronic and ionic (H+-ion) conduction within the catalyst, ameliorating Pt utilization. The inherent proton conductivity of PEDOT-PSSA composite also helps reducing Nafion content in PEFC electrodes. During prolonged operation of PEFCs, Pt electrodes supported onto PEDOT-PSSA composite exhibit lower corrosion in relation to Pt electrodes supported onto commercially available Vulcan XC-72R carbon. Physical properties of PEDOT- PSSA composite have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. PEFCs with PEDOT-PSSA-supported Pt catalyst electrodes offer a peak power-density of 810 mW cm−2 at a load current-density of 1800 mA cm−2 with Nafion content as low as 5 wt.% in the catalyst layer. Accordingly, the present study provides a novel alternative support for platinized PEFC electrodes.

Organic-inorganic composite membranes comprising Nafion with inorganic materials such as silica, mesoporous zirconium phosphate (MZP) and mesoporous titanium phosphate (MTP) are fabricated and evaluated as proton-exchange-membrane electrolytes for direct methanol fuel cells (DMFCs). For Nafion-silica composite membrane, silica is impregnated into Nafion matrix as a sol by a novel water hydrolysis process precluding the external use of an acid. Instead, the acidic nature of Nafion facilitates in situ polymerization reaction with Nafion leading to a uniform composite membrane. The rapid hydrolysis and polymerization reaction while preparing zirconia and titania sols leads to uncontrolled thickness and volume reduction in the composite membranes, and hence is not conducive for casting membranes. Nafion-MZP and Nafion-MTP composite membranes are prepared by mixing pre-formed porous MZP and MTP with Nafion matrix. MZP and MTP are synthesised by co-assembly of a tri-block co-polymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide/titanium isopropoxide and phosphorous trichloride as inorganic precursors. Methanol release kinetics is studied by volume-localized NMR spectroscopy (employing "point resolved spectroscopy", PRESS), the results clearly demonstrating that the incorporation of inorganic fillers in Nafion retards the methanol release kinetics under osmotic drag. Appreciable proton conductivity with reduced methanol permeability across the composite membranes leads to improved performance of DMFCs in relation to commercially available Nafion-117 membrane. � 2009 Elsevier B.V. All rights reserved.

Composite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)-polystyrene sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging) and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that the dispersion of mordenite in PVA-PSSA retards the methanol release kinetics considerably. A peak power-density of 74 mW/cm2 is achieved for the DMFC using a PVA-PSSA membrane electrolyte with 50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low as 7.5 mA/cm2 with 2 M methanol feed at the DMFC anode is observed while using the optimized composite membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and PVA-PSSA membranes, respectively, when tested under identical conditions. � 2009 Elsevier B.V. All rights reserved.

A direct borohydride fuel cell (DBFC) employing a poly (vinyl alcohol) hydrogel membrane electrolyte (PHME) is reported. The DBFC employs an AB5 Misch metal alloy as anode and a goldplated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. Room temperature performances of the PHME-based DBFC in respect of peak power outputs; ex-situ cross-over of oxidant, fuel, anolyte and catholyte across the membrane electrolytes; utilization efficiencies of fuel and oxidant, as also cell performance durability are compared with a similar DBFC employing a Nafion®-117 membrane electrolyte (NME). Peak power densities of ∼30 and ∼40 mW cm−2 are observed for the DBFCs with PHME and NME, respectively. The crossover of NaBH4 across both the membranes has been found to be very low. The utilization efficiencies of NaBH4 and H2O2 are found to be ∼24 and ∼59%, respectively for the PHME-based DBFC; ∼18 and ∼62%, respectively for the NME-based DBFC. The PHME and NME-based DBFCs exhibit operational cell potentials of ∼1·2 and ∼1·4 V, respectively at a load current density of 10 mA cm−2 for ∼100 h.

Poly(styrene sulfonic acid) (PSSA) content in poly(vinyl alcohol) (PVA) and PSSA blend membrane is varied and its effect on proton conductivity is studied at varying relative humidity (RH) values. The maximum proton conductivity is observed for the PVA-PSSA membrane with about 35 wt. % PSSA at all humidity values. At 30% RH value, the conductivity of PVA-PSSA blend membrane is 1.20 � 10-3 S/cm, which is about two orders of magnitude higher than the conductivity value of 2.27 � 10-5 S/cm observed for pristine PVA membrane. Water self-diffusion coefficients and water release kinetics of these materials have been characterized by nuclear magnetic resonance (NMR) imaging technique, which validate the use of this membrane in polymer electrolyte fuel cells (PEFCs). A peak power density of 210 mW/cm2 at a load current-density of 500 mA/cm2 is achieved for the PEFC with the optimized PVA-PSSA membrane as electrolyte compared to a peak power density of only 38 mW/cm2 observed at a load current-density of 80 mA/cm2 for the PEFC with pristine PVA membrane as electrolyte while operating at 75 �C with H2 and O2 feeds to the fuel cell maintained at atmospheric pressure. � 2008 Elsevier B.V. All rights reserved.

A direct borohydride-hydrogen peroxide fuel cell employing carbon-supported Prussian Blue (PB) as mediated electron-transfer cathode catalyst is reported. While operating at 30 °C, the direct borohydride-hydrogen peroxide fuel cell employing carbon-supported PB cathode catalyst shows superior performance with the maximum output power density of 68 mW cm−2 at an operating voltage of 1.1 V compared to direct borohydride-hydrogen peroxide fuel cell employing the conventional gold-based cathode with the maximum output power density of 47 mW cm−2 at an operating voltage of 0.7 V. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDAX) suggest that anchoring of Cetyl-Trimethyl Ammonium Bromide (CTAB) as a surfactant moiety on carbon-supported PB affects the catalyst morphology. Polarization studies on direct borohydride-hydrogen peroxide fuel cell with carbon-supported CTAB-anchored PB cathode exhibit better performance with the maximum output power density of 50 mW cm−2 at an operating voltage of 1 V than the direct borohydride-hydrogen peroxide fuel cell with carbon-supported Prussian Blue without CTAB with the maximum output power density of 29 mW cm−2 at an operating voltage of 1 V.

The gas-diffusion layer (GDL) influences the performance of electrodes employed with polymer electrolyte fuel cells (PEFCs). A simple and effective method for incorporating a porous structure in the electrode GDL using sucrose as the pore former is reported. Optimal (50 w/o) incorporation of a pore former in the electrode GDL facilitates the access of the gaseous reactants to the catalyst sites and improves the fuel cell performance. Data obtained from permeability and porosity measurements, single-cell performance, and impedance spectroscopy suggest that an optimal porosity helps mitigating mass-polarization losses in the fuel cell resulting in a substantially enhanced performance.

Incorporation of silica particles through a sol-gel process into the anode-catalyst layer with a sol-gel modified Nafion-silica composite membrane renders easy retention of back-diffused water from the cathode to anode through the composite membrane electrolyte, increases the catalyst-layer wettability and improves the performance of the Polymer Electrolyte Fuel Cell (PEFC) while operating under relative humidity (RH) values ranging between 18% and 100% with gaseous hydrogen and oxygen reactants at atmospheric pressure. A peak power density of 300 mW cm−2 is achieved at a load current-density value of 1200 mA cm−2 for the PEFC employing a sol-gel modified Nafion-silica composite membrane and operating at 18% RH. Under similar operating conditions, the PEFC with a Membrane Electrode Assembly (MEA) comprising Nafion-silica composite membrane with silica in the anode-catalyst layer delivers a peak power density of 375 mW cm−2. By comparison, the PEFC employing commercial Nafion membrane fails to deliver satisfactory performance at 18% RH due to the limited availability of water at its anode, acerbated electro-osmotic drag of water from anode to cathode and insufficient water back diffusion from cathode to anode causing the MEA to dehydrate.

Zirconium-substituted TiMn 2 -based hydrogen storage alloy electrodes were prepared and their electrochemical characteristics have been evaluated in 6 M aqueous KOH solution. The electrode characteristics of Ti 1− x Zr x Mn 1.6 Ni 0.4 ( x =0.1 and 0.2) alloys such as discharge capacity, high rate capability and cycle life were evaluated. The alloy Ti 0.9 Zr 0.1 Mn 1.6 Ni 0.4 was found to have higher capacity than Ti 0.8 Zr 0.2 Mn 1.6 Ni 0.4 alloy. The exchange current density was also higher for Ti 0.9 Zr 0.1 Mn 1.6 Ni 0.4 alloy.

Effect of nickel substitution on the electrochemical hydriding and dehydriding behavior of TiMn2 type hydrogen storage alloys in 6 M aqueous KOH solution was investigated. The electrode characteristics of TiMn2−xNix (x=0.0–0.5), such as discharge capacity, high rate dischargeability and cycle life, indicate that addition of nickel in the alloy increases the discharge capacity and cycle life characteristics of the alloy. The electrochemical kinetics was evaluated using dc polarization and ac impedance analysis techniques, and it was found that both diffusion and charge transfer of hydrogen play a role in electrolytic absorption of hydrogen. The hydrogen diffusivity in the alloys was estimated by an electrochemical method for fully charged alloy electrodes and was found to increase with increase in nickel content in the alloy.

The characteristic features of the electrochemical behaviour of the treated hydrogen-storage alloy TiMn 1.6 Ni 0.4 in an etching solution containing hydrogen fluoride and untreated alloy in alkaline media are investigated. Alloy characteristics such as discharge capacity, high-rate dischargebility and cycle-life are examined. The exchange current density, polarisation resistance and diffusion coefficients are also determined as functions of state-of-charge of the electrodes. The diffusion coefficient is found to be of the same order for the treated and the untreated alloy.

Retention of the water content of the membrane in the polymer electrolyte membrane fuel cell is critical for obtaining the maximum power density. Humidification of the reactants is a must to keep the membrane in a wet condition. The present paper identifies the parameters to achieve the maximum humidification of the reactants. Optimization of humidification is also discussed with respect to the pressure drop of the reactants while trying to achieve the theoretical relative humidity (RH), especially for the requirements of a multi-kilowatt stack.

Two methods of humidifying the anode gas, namely, external and membrane humidification, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insufficient external humidification. In a membrane-based humidification, an optimum set of parameters, such as gas flow rate, area and type of the membrane, must be chosen to achieve effective humidification. The present study examines the dependence of water pick-up by hydrogen on the temperature, area and thickness of the membrane in membrane humidification. Since the performance of the fuel cell is dependent more on hydrogen humidification than on oxygen humidification, the scope of the work is restricted to the humidification of hydrogen using Nafion® membrane. An examination is made on the dependence of water pick-up by hydrogen in membrane humidification on the temperature, area and thickness of the membrane. The dependence of fuel cell performance on membrane humidification and external humidification in the anode gas is also considered.

The present paper highlights on the need to understand the correlation of the characteristics of the catalyst layer with the performance of the polymer electrolyte membrane fuel cell (PEMFC). This paper deals with the correlation of the platinum loading in the catalyst layer and the performance of the polymer electrolyte membrane fuel cell and also the correlation of the required hydrophilicity/hydrophobicity in the catalyst layer to get the optimum performance under given operating conditions.

A self-supported 40W Direct Methanol Fuel Cell (DMFC) system has been developed and performance tested. The auxiliaries in the DMFC system comprise a methanol sensor, a liquid-level indicator, and fuel and air pumps that consume a total power of about 5 W. The system has a 15-cell DMFC stack with active electrode-area of 45 cm2. The self-supported DMFC system addresses issues related to water recovery from the cathode exhaust, and maintains a constant methanol-feed concentration with thermal management in the system. Pure methanol and water from cathode exhaust are pumped to the methanol-mixing tank where the liquid level is monitored and controlled with the help of a liquid-level indicator. During the operation, methanol concentration in the feed solution at the stack outlet is monitored using a methanol sensor, and pure methanol is added to restore the desired methanol concentration in the feed tank by adding the product water from the cathode exhaust. The feed-rate requirements of fuel and oxidant are designed for the stack capacity of 40 W. The self-supported DMFC system is ideally suited for various defense and civil applications and, in particular, for charging the storage batteries.

During the anodic dead-end mode operation of fuel cells, the inert gases (nitrogen and water) present in the cathode side gas channel permeate to the anode side and accumulate in the anode gas channel. The inert gas accumulation in the anode decreases the fuel cell performance by impeding the access of hydrogen to the catalyst. The performance of fuel cell under potentiostatic dead-end mode operation is shown to have three distinct regions viz. time lag region, transient current region and a steady state current region. A current distribution measurement setup is used to capture the evolution of the current distribution as a function of time and space. Co- and counter-flow operations of dead-end mode confirm the propagation of inert gas from the dead-end of anode channel to the inlet of anode. Experiments with different oxidants, oxygen and air, under dead-end mode confirm that nitrogen which permeates from cathode to anode causes the performance drop of the fuel cell. For different starting current densities of 0.15 A cm-2, 0.3 A cm-2 and 0.6 A cm-2 the inert gas occupies 35%, 45% and 57%, respectively of anode channel volume at the end of 60 min of dead-end mode operation. � 2011 Elsevier B.V. All rights reserved.

Stabilized forms of heteropolyacids (HPAs), namely phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA), are incorporated into poly (vinyl alcohol) (PVA) cross-linked with sulfosuccinic acid (SSA) to form mixed-matrix membranes for application in direct methanol fuel cells (DMFCs). Bridging SSA between PVA molecules not only strengthens the network but also facilitates proton conduction in HPAs. The mixed-matrix membranes are characterized for their mechanical stability, sorption capability, ion-exchange capacity, and wetting in conjunction with their proton conductivity, methanol permeability, and DMFC performance. Methanol-release kinetics is studied ex situ by volume-localized NMR spectroscopy (employing point-resolved spectroscopy'') with the results clearly demonstrating that the incorporation of certain inorganic fillers in PVA-SSA viz., STA and PTA, retards the methanol-release kinetics under osmotic drag compared to Nafion, although PVA-SSA itself exhibits a still lower methanol permeability. The methanol crossover rate for PVA-SSA-HPA-bridged-mixed-matrix membranes decreases dramatically with increasing current density rendering higher DMFC performance in relation to a DMFC using a pristine PVA-SSA membrane. A peak power density of 150 mW/cm(2) at a load current density of 500 mA/cm(2) is achieved for the DMFC using a PVA-SSA-STA-bridged-mixed-matrix-membrane electrolyte. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3465653] All rights reserved.

Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits and demerits with efforts on modified-Nafion membranes.

Blend membranes are fabricated from sulfonated poly(ether ether ketone) (SPEEK) and poly[bis(phenoxy)phosphazene] (POP). The effect of POP content on the distribution of ionic channels is investigated by atomic force microscopy (AFM). The water uptake and methanol permeability for the blend membranes are also investigated. The blend membranes are characterized in terms of their thermal and mechanical properties in conjunction with their ionic conductivity. The proton conductivity of the blend membranes slightly decreased with increasing POP content in comparison with the pristine SPEEK membrane. The hydrophobic nature of POP blocks the ionic channels in the SPEEK matrix, subsequently decreasing its water uptake and methanol permeability. The blend membranes showed higher power density compared to a pristine SPEEK membrane in direct methanol fuel cells (DMFCs).

Direct Methanol Fuel Cells (DMFCs) are attractive for portable power applications owing to the easy transportation, storage and refueling of methanol in conjunction with the reduced system-weight, size, highenergy-efficiency and low-temperature operation (1). However, to improve the commercial viability of DMFCs, there are several scientific issues, such as methanol crossover, sluggish electrode kinetics and durability that need to be addressed with concomitant improvements in performance characteristics. One of the problems with the DMFCs is the limited activities of the pure platinum anode catalysts as pure platinum is easily poisoned by carboxylic reaction-intermediates produced during the methanol oxidation reaction (MOR). The use of alloy catalysts such as Pt:Ru has helped mitigating the aforesaid problem substantially. But the CO tolerance of PtRu alloy catalyst is still unsatisfactory for practical DMFC applications (2). Accordingly, it is imperative to further the catalytic activity of Pt-Ru alloy catalyst. It has been reported that the addition of transition metal oxides, such as, CeO2, TiO2, WO3, MoO3, etc., to PtRu alloy catalyst can improve its CO tolerance and activity towards MOR due to the “spillover” effect. Among these metal oxides, TiO2 seems most promising due to its natural abundance, cost and stability in acidic environment. Homogeneously-dispersed composite of PtRu alloy catalyst with TiO2 could be realized by (a) intimate mixing of Pt, Ru, and TiO2 precursor solutions, (b) impregnation and colloidal methods using Pt-Ru/C or TiO2 particles, and (c) physical mixing of PtRu/C with TiO2 particles. Among these colloidal methods and solgel routes are more effective to achieve homogenous nanoscale mixing of the metal and metal oxide phases. However, these methods need pyrolysis at high temperatures that affects the performance of the catalyst. Accordingly, it is desirable to develop an effective synthetic route to realize a homogenous nanocomposite catalyst devoid of any post-heat treatment. In the present study, a porous titanium oxide-carbon hybrid nanocomposite is directly synthesized using a supramolecular self-assembly concept with in situ crystallization process. The microstructure of the catalyst including surface area, morphology and crystallinity are characterized by Brunauer–Emmett–Teller (BET), Transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Pt-Ru on titanium oxide-carbon composite is prepared by treating with chloroplatinic acid and ruthenium chloride followed by reduction with NaBH4. The crystalline nature and alloy formation are confirmed by XRD studies, and the morphology and particle-size distribution are studied by TEM. Methanol electro-oxidation and Accelerated Durability Test (ADT) are performed using Cyclic Voltammetry (CV). The catalysts have also been performance tested in DMFCs at 65C using methanol and oxygen. Fig. 1 shows electro-catalytic activities for PtRu/C and Pt-Ru decorated Titanium oxide-carbon towards methanol oxidation reaction. It is clear that titanium oxide-carbon composite supported electrocatalyst exhibit enhanced catalytic activity in relation to Pt-Ru/C. Besides the peak potentials for methanol oxidation are 0.52V and 0.56V for Pt-Ru supported on titanium oxide-carbon composite and Pt-Ru/C, respectively, suggesting that methanol oxidation occurs at a lower potential on titanium oxide-carbon composite supported catalyst in relation to carbon supported catalyst.

A new class of bio-composite polymer electrolyte membranes comprising chitosan (CS) and certain biomolecules in particular, plant hormones such as 3-indole acetic acid (IAA), 4-chlorophenoxy acetic acid (CAA) and 1-naphthalene acetic acid (NAA) are explored to realize proton-conducting bio-composite membranes for application in direct methanol fuel cells (DMFCs). The sorption capability, proton conductivity and ion-exchange capacity of the membranes are characterized in conjunction with their thermal and mechanical behaviour. A novel approach to measure the permeability of the membranes to both water and methanol is also reported, employing NMR imaging and volume localized NMR spectroscopy, using a two compartment permeability cell. A DMFC using CS-IAA composite membrane, operating with 2M aqueous methanol and air at 70 degrees C delivers a peak power density of 25 mW/cm(2) at a load current density of 150 mA/cm(2). The study opens up the use of bio-compatible membranes in polymer-electrolyte-membrane fuel cells. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.030111jes] All rights reserved.

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In situ polymerization of 3,4-ethylenedioxythiophene with sol-gel-derived mesoporous carbon (MC) leading to a new composite and its subsequent impregnation with Pt nanoparticles for application in polymer electrolyte fuel cells (PEFCs) is reported. The composite exhibits good dispersion and utilization of platinum nanoparticles akin to other commonly used microporous carbon materials, such as carbon black. Pt-supported MC-poly(3,4-ethylenedioxythiophene) (PEDOT) composite also exhibits promising electrocatalytic activity toward oxygen reduction reaction, which is central to PEFCs. The PEFC with Pt-loaded MC-PEDOT support exhibits 75% of enhancement in its power density in relation to the PEFC with Pt-loaded pristine MC support while operating under identical conditions. It is conjectured that Pt-supported MC-PEDOT composite ameliorates PEFC performance/durability on repetitive potential cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3486172] All rights reserved.

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Hydrous ruthenium oxide, which exhibits both protonic and electronic conduction, is incorporated in the cathode electrocatalyst layer of the membrane electrode assembly for polymer electrolyte fuel cells (PEFCs). The supercapacitive behavior of ruthenium oxide helps realize a fuel cell–supercapacitor hybrid. Platinum (Pt) nanoparticles are deposited onto carbon-supported hydrous ruthenium oxide and the resulting electrocatalyst is subjected to both physical and electrochemical characterization. Powder X-ray diffraction and transmission electron microscopy reflect the hydrous ruthenium oxide to be amorphous and well-dispersed onto the catalyst. X-ray photoelectron spectroscopy data confirm that the oxidation state of ruthenium in Pt anchored on carbon-supported hydrous ruthenium oxide is Ru4+. Electrochemical studies, namely cyclic voltammetry, cell polarization, intrinsic proton conductivity, and impedance measurements, suggest that the proton-conducting nature of hydrous ruthenium oxide helps extend the three-phase boundary in the catalyst layer, which facilitates improvement in performance of the PEFC. The aforesaid PEFC operating with hydrogen fuel and oxygen as oxidant shows a higher power density (0.62 W/cm2 @ 0.6 V) in relation to the PEFC comprising carbon-supported Pt electrodes (0.4 W/cm2 @ 0.6 V). Potential square-wave voltammetry study corroborates that the supercapacitive behavior of hydrous ruthenium oxide helps ameliorate the pulse-power output of the fuel cell.

Nafion-silica composite membranes are fabricated by embedding silica particles as inorganic fillers in perfluorosulfonic acid ionomer by a novel water hydrolysis process. The process precludes the use of an added acid but exploits the acidic characteristic of Nafion facilitating an in situ polymerization reaction through a sol-gel route. The use of Nafion as acid helps in forming silica/siloxane polymer within the membrane. The inorganic filler materials have high affinity to water and assist proton transport across the electrolyte membrane of the polymer electrolyte fuel cell (PEFC) even under low relative humidity (RH) conditions. In the present study, composite membranes have been tested in hydrogen/oxygen PEFCs at varying RH between 100 and 18% at elevated temperatures. Attenuated total reflectance-Fourier transform infrared spectroscopy and scanning electron microscopy studies suggest an evenly distributed siloxane polymer with Si-OH and Si-O-Si network structures in the composite membrane. At the operational cell voltage of 0.4 V, the PEFC with an optimized silica-Nafion composite membrane delivers a peak power density value five times higher than that achievable with a PEFC with conventional Nafion-1135 membrane electrolyte while operating at a RH of 18% at atmospheric pressures.

Sulphuric acid can be selectively separated from the sulphates of calcium, magnesium, sodium and potassium present in cation exchange regeneration waste by diffusion dialysis. Studies were carried out to determine the optimum flow rate which will result in the maximum recovery of acid with minimum salt concentration. Separation factors between salt and acid for various salts present in the cation exchange regeneration waste are also presented.