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Scanning electrochemical potential microscopy (SECPM) is a type of probe microscopy, in which a sharp tip similar to those employed in electrochemical tunnelling microscopy is connected to a high impedance amplifier, but the tip potential instead of tip current is used as the signal in the feedback loop. SECPM has been found to provide much higher spatial resolution than would be expected on the basis of a mechanism in which the tip responds to the local electrochemical potential of the solution; in fact, it can obtain atomic resolution similar to STM, but is a superior technique for imaging electronically insulating objects such as proteins on a metal surface. We suggest a mechanism for these high-resolution images based on electron exchange between tip and substrate coupled to faradaic processes at the tip/solution interface. This mechanism operates alongside the conventional mechanism in which the tip responds to the local potential in the diffuse layer of the substrate and allows a simple description of the sigmoidal tip potential−distance curves that have been reported.

The presence of water in room temperature ionic liquids (RTILs) can have a strong effect on their properties. In particular, water adsorption at electrodes can reduce the electrochemical potential window of the system. It is thus important to understand where water will be present depending on the electrode potential, the type of ionic liquid and the electrode material. We investigate the influence of water on RTILs by measuring the potential dependent double layer capacitance of various water-RTIL mixtures. The resulting capacitance versus potential curves are reproduced employing mean-field theory calculations. From the parameters used to obtain the best agreement between experimental and theoretical curves some properties of the RTILs can be deducted, such as a stronger interaction of water with RTIL anions than cations and an agglomeration of water at potentials positive or negative of the potential of zero charge.

BaZr0.9Y0.1O3-δ has been synthesised by three different methods: the solid-state reaction, the spray pyrolysis and the spray drying. Significantly different apparent lattice parameters (between 0.4192 nm for the sample prepared by the solid-state reaction method and sintered at 1,500 °C and 0.4206 nm for the sample prepared by the solid-state reaction method and sintered at 1,720 °C) are observed after calcination and sintering, depending on the synthesis method and the sintering temperature. The bulk conductivity values also vary over several orders of magnitude (–7.2< log σb

In order to develop catalysts it is important to characterize the system in terms of particle size and size distribution. TEM or STEM are used as the state-of-the-art methods. In this study monodispersed Pt3Co alloy nanoparticles supported on carbon black (CB) prepared by the nanocapsule method are investigated and the results are compared with a commercially available Pt3Co/C catalyst system. To avoid the obstacles of conventional bright-field TEM or STEM regarding the image analysis, an advanced computerized image processing procedure is introduced. The so-called local adaptive threshold (LAT) is a method for a precise determination of particle diameter and size distribution in the subnanometer scale. The results demonstrate the advantage of a completely computerized particle evaluation as compared to a conventional particle analysis.

The fuel cell differential electrochemical mass spectrometry (FC-DEMS) measurements were performed for studying the ethanol oxidation reaction (EOR), using alkaline membrane electrode assemblies (MEAs) made up of nanoparticle Pt catalyst and alkaline polymeric membranes. The obtained results indicate that in an alkaline medium, ethanol undergoes significantly more complete electro-oxidation to CO2 than in an acidic MEA using the same Pt anode. The CO2 current efficiency (CCE) can be compared for acidic and alkaline MEA with similar electrochemical active area on the anode side. The CCE estimated, in case of alkaline MEA with Pt anode, is around 55% at 0.8 V/RHE, 60 °C and 0.1 M ethanol. In comparison, under similar conditions, acidic MEAs using the same anode catalyst show only 2% CCE. This might indicate that the C–C bond scission rates are much higher in alkaline media. However, the mechanism of ethanol oxidation in alkaline media is not exactly known. CO2 produced in electrochemical reaction forms soluble carbonates in the presence of aqueous alkaline electrolyte. This makes it difficult to study ethanol oxidation in alkaline media using FTIR or model DEMS systems. The alkaline polymer electrolyte membranes as used in this study for making alkaline MEAs provide an important opportunity to observe CO2 produced during EOR using FC-DEMS system.

Experimental results of tests using a micro-structured steam reformer for hydrogen generation from methane in fuel cell systems are reported. A distinctive feature of this work is the integration of a catalytic combustor into the reactor to deliver the necessary heat to the endothermic steam reforming reaction. The tests are performed under static and dynamic load conditions. The reactor is operated autonomously without external heat supply. The best results are obtained by firing the integrated combustor with a mixture of hydrogen and methane in co-flow with the reforming reaction. Providing carbon dioxide to the combustor feed in order to simulate the situation of anode off-gas firing has only minor effects on system performance. Under static load conditions up to 2 / min–1 of hydrogen are produced at high methane conversion rates of about 70%. Start-up tests show that a stable product composition is obtained in less than 20 s after admission of methane to the reformer. Furthermore, the product composition shows only minor variations with throughput and load changes if heating adjustments are done simultaneously. Overall, the reactor proves to be very suitable for operation in fuel cell systems.

Different aspects of the improvement of direct methanol fuel cell (DMFC) systems for portable power generation are investigated, in a project funded by the Bavarian state. The materials research focuses on the development of improved catalysts, in particular for the oxygen reduction reaction. Some recent results on supported ruthenium selenium catalysts are reported. In parallel, tests on other fuel cell materials are performed using MEAs made from industrial unsupported catalysts as the reference. These standard MEAs have catalyst loadings of about 11 mg cm–2 and, at high air flux, can deliver current densities of about 500 mA cm–2 and 100 mA cm–2 at 110 °C and 50 °C, respectively. At low air flux and 50 °C, current densities between 60 and 80 mA cm–2 are possible @ 500 mV. Using these MEAs, different commercial gas diffusion materials are tested as the cathode backing. Thus, it is found that the Sigracet materials by SGL Carbon are the most suitable for operation at a low air flux. Finally, a demonstration stack, comprised of up to ten cells, is developed using graphite PVDF compound bipolar plates by SGL Carbon. As will be reported, this stack shows a high homogeneity of cell voltages and stable operation under relevant conditions, using standard MEAs.

Hydrous ruthenium oxides have been investigated as novel support materials for fuel cell electrocatalysts for use in DMFC applications. These oxides were chosen in particular due to their potential intrinsic proton conductivity. Pt nanoparticles have been deposited onto the new support, and the resulting catalysts characterized both structurally and electrochemically. The Pt nanoparticles are sized between 3–4 nm and are highly dispersed on the support. Transmission electron micrographs show that the individual Pt nanoparticles are covered by an amorphous coating layer – probably hydrous ruthenium oxide, in good agreement with the XPS data. Electrochemical measurements on model electrodes indicate that proton conductivity of the supporting material is strongly affected by interdiffusion of methanol. Nevertheless, initial tests on membrane electrode assemblies (MEAs) showed improved performance, particularly with respect to internal resistance, when compared to Pt-Ru black. The catalyst showed very high activity in CO stripping experiments performed on a full MEA, suggesting high catalyst utilization, despite the comparatively low Nafion® content used in the electrode layer.

The electrode performances of the alternative oxides: La0.05Ca0.95Cr0.05Ti0.95O3-δ-8YSZ and Ce0.8TM0.2O2-δ(TM=Mn, Co) for the direct electrochemical oxidation of methane are investigated to assess their potential as anode materials for efficient methane conversion in a SOFC. The electrochemical oxidation of hydrogen was also studied, for comparison. The oxides are characterised electrochemically with impedance spectroscopy in the frequency range from 10 mHz to 1MHz, using a three-electrode geometry. They are compared to a standard Ni/8YSZ anode for the electrochemical oxidation of hydrogen. It is found that La0.05Ca0.95Cr0.05Ti0.95O3-δ-8YSZ demonstrates a poor electrochemical activity in both hydrogen and methane. However, the electrochemical activity of Ce0.8Mn0.2O2-δ is promising, but the electronic conductivity needs to be increased, e.g., by adding a conducting oxide, before it can be used as an anode material in a SOFC.

The temperature dependence of the oxygen reduction kinetics on carbon-supported RuxSey catalysts is studied using a rotating disc electrode in 0.5 M H2SO4 in the temperature interval from 25 °C to 65 °C. When the absolute value of the overpotential is below ca. 0.65 V, the reaction is limited by a one-electron charge transfer step, where the transfer coefficient is independent of the temperature and equal to 0.44. The apparent activation enthalpy at zero overpotential is 0.49 eV and the pre-exponential factor is independent of the temperature.

SOFC systems, working at high temperatures of about 800 °C, have recently attracted significant interest for application as automotive and stationary power supply systems, based on gasoline or diesel heating. For periodically changing operation, the thermal management of the system, including start-up and load following capability, is considered a crucial point. In this work, the thermal behaviour during start-up, operation, shut down, and restart of a simple SOFC system for mobile applications is studied. Different operating strategies, such as keeping the system at operating temperature and thermal cycling, are investigated and compared with respect to heat management, energy consumption, and start-up performance. The characteristics depend on the system size and weight. For a 50 kWel system, with suitable insulation, immediate restart of the vehicle should be achievable for up to three days, hence no external heat is needed within that period of time. Smaller systems, e.g., Auxiliary Power supply Units (APU), replacing the conventional alternator in vehicles, cool down more rapidly. If an immediate restart is desirable ‘keeping the system at temperature’ would be the more favourable strategy.

A simulation model of a car driven by a gasoline based fuel cell system was generated with Matlab/SIMULINK. The model of the vehicle represents a common compact class passenger car equipped with an electric power train, fuel cell system and with and without an additional battery. For the fuel cell system two variants have been implemented, a PEMFC and a high temperature SOFC system. Both models consist of an on-board gasoline reformer, stack and auxiliary components such as evaporator, catalytic burner, fuel pump, fans and control unit with additional FC-type specific components such as air preheater or CO-shifter. The simulation model allows the comparison of the two FC systems in different automotive traction concepts (fuel cell vehicle, hybrid car) varying all important parameters such as driving cycle or fuel cell nominal power. In this paper the simulation model is described and first simulation results are given.

The activity of in house prepared carbon-supported Pt-Ru catalysts for methanol oxidation and carbon-supported RuSe for the oxygen reduction reaction in direct methanol fuel cells (DMFCs) was investigated. The composition of Pt-Ru/C was varied both in terms of weight loading (ratio of total metal content to carbon) as well as the ratio of Pt to Ru. The measurements were carried out in a half cell arrangement in sulphuric acid at various temperatures. The weight loading and ratio of Pt to Ru were varied in order to find out the optimum weight loading of precious metal and the temperature dependence of Pt to Ru ratio on methanol oxidation reaction. It has been found that there exists an optimum in the weight loading at 60 wt.% for carbon-supported Pt-Ru catalyst towards its maximum mass activity. While 1:1 Pt to Ru ratio exhibits a higher activity than 3:2 Pt:Ru above 60 °C, 3:2 ratio exhibits a higher activity at lower temperature. It has been observed that RuSe is inactive towards methanol and it is realised that RuSe is a potential candidate as methanol tolerant oxygen reduction catalyst. The activity of carbon supported RuSe for oxygen reduction reaction (ORR) was tested in sulphuric acid in the presence of methanol. Even though the mass specific activity of the RuSe catalyst is somewhat lower than that of Pt/C, the surface activity of carbon-supported RuSe is superior than that of carbon supported Pt which indicate the unfavourable size distribution of RuSe/C catalyst.

In order to compare the electrochemical performance of Ce 0.9 Gd 0.1 O 2-δ (CGO) in various fuels, impedance spectroscopy measurements were carried out in the atmospheres containing H 2 , CO, CO 2 , CH 4 , N 2 at various compositions, in the temperature range 650 °C to 850 °C. Ohmic loss and polarization resistance were derived from impedance spectroscopy measurements. The stability at different temperatures of the anode was also investigated in 9%H 2 /91%N 2 humidified with 3% H 2 O. The microstructure of the anode before and after degradation test was analysed by SEM. These investigations indicated similarities in the impedance and the activation enthalpies in hydrogen/water, methane/water and CO/CO 2 atmospheres. No indications of methane cracking leading to carbon formation were found.

Fuel cells will make a valuable contribution to future power generation facilities. They improve the flexibility and increase the options for many applications, such as distributed power, vehicle propulsion, and portable devices. Their main property is the high electrical efficiency compared to other energy conversion devices. Both the low-temperature and the high-temperature fuel cells have their advantages and disadvantages depending on the application. Sometimes, they can both be implemented in similar applications. The modularity of fuel cells makes them quite flexible as the power needed can easily be attained by changing the number of modules. Twenty years ago, mainly universities and research institutions but only a few companies conducted fuel cell research working on the fundamentals of fuel cells. Nowadays due to the commercial interest innumerable research groups and companies have fuel cell activities ranging from the investigation of catalysts (both improving existing catalyst systems as searching for new catalysts), the development of novel membranes for PEMFCs and DMFCs, to the development of other components for fuel cells. Optimisation of flow field structures, backing layers, and other components of the single cells have intensified. (orig.)

Designing an appropriate methanol steam reformer requires detailed knowledge about the processes within such a reactor. Thus, the axial temperature and concentration gradients and catalyst ageing were investigated. It was found that for a fresh catalyst load, the catalyst located in the reactor entrance was most active during the experiment. The activity of this part of the catalyst bed decreased after some time of operation due to ageing. With further operation, the most active zone moved through the catalyst bed. From the results concerning hydrogen production and catalyst degradation, the necessary amount of catalyst for a mobile PEMFC-system can be estimated.

A novel core–shell heterostructure with multi-walled carbon nanotubes (MWCNTs) as the core and graphene oxide nanoribbons (GONRs) as the shell (MWCNT@GONR) is investigated for the first time as anode material for Na-ion batteries (NIBs) in this study. The MWCNT@GONR material with carboxylic acid groups has been synthesized through unzipping of MWCNTs by a microwave-assisted process. The influence of the amount of carboxylic acid groups on the electrochemistry of MWCNT@GONR is investigated in this work by applying thermal treatment at different temperatures. In this MWCNT@GONR core-shell structure, the MWCNTs between flat GONR sheets prevent the restacking problem of graphene and enable penetration of the electrolyte. MWCNTs provide high electronic conductivity and direct electron transfer path while GONRs provide high surface area and defect sites (carboxylic acid groups, COOH-) that can adsorb more Na ions on the surface thereby increasing capacity. MWCNT@GONR provides high capacity (317 mA h g−1) at a current density of 50 mA h g−1 in the second cycle. A full cell using MWCNT@GONR as anode and P2-NaxMnO2 as cathode is fabricated and it exhibits a high energy density of 99 Wh kg−1 which successfully demonstrates that MWCNT@GONR is a promising anode material for NIB applications.

The impedance of the cell Au/HClO4-5.5 H2O/Au was investigated in the frequency range 1 to 105 Hz between 4.2 and 300 K. The analysis of the data enables an evaluation of important electrolyte properties such as conductivity and dielectric constant in a wide range of temperatures, predominantly in the solid state of the electrolyte HClO4-5.5 H2O (Tf = 228 K). The double layer capacity of the gold electrodes was also determined; it shows a qualitatively similar result compared with previous measurements. In the solid state, the ionic conductivity exhibits two distinct activation energies of 0.37 and 0.54 eV corresponding to the two phases present in HClO4-5.5 H2O above and below 170 K. Below 120 K the activation energy becomes very small and tends to zero around 80 K indicating possible tunneling processes in the rigid H2O structure. At about the same temperature the dielectric constant reaches its low temperature limit with a value ϵ∞ ≈ 11 which is considerably higher than the value of pure ice of ϵ∞ ≈ 3.

CO adsorption and electro-oxidation on a Pt(111) electrode modified by Ru deposition was studied by IR spectroscopy. The IR spectra in the region of the CO stretching vibration exhibit distinct bands which can be assigned to CO adsorbed on the Pt substrate (CO|Pt) and on Ru islands (CO|Ru). This is in contrast with IR studies of Pt  Ru alloy electrodes where only a single vibrational band of adsorbed CO is observed. The integrated band intensities of the CO|Ru and of CO|Pt bands on the Ru-modified Pt(111) electrode decrease simultaneously at the onset potential of CO oxidation. The results are interpreted within the framework of a bifunctional mechanism of CO electro-oxidation, postulating active Pt sites in close proximity to the Ru islands and a high mobility of the CO|Pt adsorbate layer. The differences in the IR spectra between the Ru|Pt(111) electrode and the Pt  Ru alloys are explained by disparate surface structures (Ru islands versus homogeneous distribution of Pt and Ru atoms).

In this paper, a new proton-conductive compound of (NH4)(2)SnP4O13 was synthesized by a simple solid state method. X-ray diffraction, scanning electronic microscopy and thermal gravimetric analysis investigation were performed on this compound. The conductivity of (NH4)(2)SnP4O13 was measured by impendence spectroscopy with the temperature range of 125-275 degrees C under different atmospheres. Maximum conductivities of 13.8 mS cm-(1) at 275 degrees C under dry H-2 and 35.5 mS cm(-1) at 225 degrees C under wet H-2 respectively were obtained. (C) 2009 Elsevier B.V. All rights reserved.

Hydrates of the alkaline hydroxides LiOH, NaOH, KOH and CsOH in their liquid and solid states were investigated using impedance spectroscopy. KOH · 4H2O was studied using deuteron NMR. From the impedance measurements the electrical conductivity of the hydrate was evaluated. It is an important result of these measurements that the lithium and sodium hydroxide hydrates exhibit a poor conductivity in the solid state; the activation energies of conductivity exceed 3 eV. The potassium and cesium hydroxide hydrates, however, are considerably more conductive in the solid state, especially at low temperatures with activation energies around 0.7 eV. Linewidths and T1 and T2 relaxation times were determined as a function of temperature in the liquid and solid hydrate. The NMR measurements indicate that the protons (deuterons) are the mobile species. The differences in conductivity may be due to a size effect of the cation in that large cations with a single charge favor an extended water network which maybe of clathrate-like structure.

The Fe2+/Fe3+ redox reaction on platinum is investigated in liquid and frozen HClO4 · 5.5 H2O over a temperature range from 130 — 300 K. The exchange current density follows an Arrhenius law in the liquid and in the solid state. Both the energy of activation and the preexponential factor are higher in the solid state; the exchange current density shows a discontinuous rise as one approaches the freezing point from higher temperatures. In the liquid state, mass transport to the electrode occurs through diffusion of the ions; in the solid state mass transfer is much slower is probably due to electron hopping rather than ion transport.

The perfect combination: RuO2⋅x H2O for donating and accepting protons and electrons and carbon nanotubes (CNTs) for compensating the loss of electron conductivity caused by the RuO2 coating, improving the electrode microstructure, and lowering the electrode resistance. The result: superb performance of the title catalyst for direct electrooxidation of methanol.

Department of Physics, Technical University Munich, D-85748 Garching, GermanyA density functional theory database of hydrogen chemisorption energies on close packed surfaces of a number of transition andnoble metals is presented. The bond energies are used to understand the trends in the exchange current for hydrogen evolution. Avolcano curve is obtained when measured exchange currents are plotted as a function of the calculated hydrogen adsorptionenergies and a simple kinetic model is developed to understand the origin of the volcano. The volcano curve is also consistent withPt being the most efficient electrocatalyst for hydrogen evolution.© 2005 The Electrochemical Society. @DOI: 10.1149/1.1856988# All rights reserved.Manuscript submitted May 10, 2004; revised manuscript received August 12, 2004. Available electronically January 24, 2005.