bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial distribution of the source-receptor relationship of sulfur in Northeast Asia
Authors: Kajino M. , Ueda H. , Sato K. , Sakurai T.
Published: December 2010

Abstract. The spatial distribution of the source–receptor relationship (SRR) of sulfur over Northeast Asia was examined using an off-line coupled meteorological/chemical transport model (MM5/RAQM). The simulation was conducted for the entire year of 2002. The results were evaluated using monitoring data for six remote stations of the Acid Deposition Monitoring Network in East Asia (EANET). The modeled SO2 and O3 concentrations agreed well with the observations quantitatively. The modeled aerosol and wet deposition fluxes of SO42− were underestimated by 30% and 50%, respectively, whereas the modeled precipitation was overestimated by 1.6 to 1.9 times. The domain was divided into 5 source–receptor regions: I, North China; II, Central China; III, South China; IV, South Korea; and V, Japan. The sulfur deposition in each receptor region amounted to about 50–75% of the emissions from the same region. The largest contribution to the deposition in each region was the domestic origin, accounting for 53–84%. The second largest contribution after the domestic origin was due to region II, supplying 14–43%, outside region II itself. The spatial distributions of the SRRs revealed that subregional values varied by about two times more than regional averages due to nonuniformity across the deposition fields. Examining the spatial distributions of the deposition fields was important for identifying subregional areas where the deposition was highest within a receptor region. The horizontal distribution changed substantially according to season.
Vertical profiles of nitrous acid in the nocturnal urban atmosphere of Houston, TX
Authors: Wong K. W. , Oh H.-J. , Lefer B. , Rappenglück B. , Stutz J.
Published: December 2010

Abstract. Nitrous acid (HONO) often plays an important role in tropospheric photochemistry as a major precursor of the hydroxyl radical (OH) in early morning hours and potentially during the day. However, the processes leading to formation of HONO and its vertical distribution at night, which can have a considerable impact on daytime ozone formation, are currently poorly characterized by observations and models. Long-path differential optical absorption spectroscopy (LP-DOAS) measurements of HONO during the 2006 TexAQS II Radical and Aerosol Measurement Project (TRAMP), near downtown Houston, TX, show nocturnal vertical profiles of HONO, with mixing ratios of up to 2.2 ppb near the surface and below 100 ppt aloft. Three nighttime periods of HONO, NO2 and O3 observations during TRAMP were used to perform model simulations of vertical mixing ratio profiles. By adjusting vertical mixing and NOx emissions the modeled NO2 and O3 mixing ratios showed very good agreement with the observations. Using a simple conversion of NO2 to HONO on the ground, direct HONO emissions, as well as HONO loss at the ground and on aerosol, the observed HONO profiles were reproduced well by the model. The unobserved increase of HONO to NO2 ratio (HONO/NO2) with altitude that was simulated by the initial model runs was found to be due to HONO uptake being too small on aerosol and too large on the ground. Refined model runs, with adjusted HONO uptake coefficients, showed much better agreement of HONO and HONO/NO2 for two typical nights, except during morning rush hour, when other HONO formation pathways are most likely active. One of the nights analyzed showed increase of HONO mixing ratios together with decreasing NO2 mixing ratios that the model was unable to reproduce, most likely due to the impact of weak precipitation during this night. HONO formation and removal rates averaged over the lowest 300 m of the atmosphere showed that NO2 to HONO conversion on the ground was the dominant source of HONO, followed by traffic emission. Aerosol did not play an important role in HONO formation. Although ground deposition was also a major removal pathway of HONO, net HONO production at the ground was the main source of HONO in our model studies. Sensitivity studies showed that in the stable NBL, net HONO production at the ground tends to increase with faster vertical mixing and stronger emission. Vertical transport was found to be the dominant source of HONO aloft.
Geomagnetic activity related NOx enhancements and polar surface air temperature variability in a chemistry climate model: modulation of the NAM index
Authors: Baumgaertner A. J. G. , Seppälä A. , Jöckel P. , Clilverd M. A.
Published: December 2010

Abstract. The atmospheric chemistry general circulation model ECHAM5/MESSy is used to simulate polar surface air temperature effects of geomagnetic activity variations. A transient model simulation was performed for the years 1960–2004 and is shown to develop polar surface air temperature patterns that depend on geomagnetic activity strength, similar to previous studies. In order to eliminate influencing factors such as sea surface temperatures (SST) or UV variations, two nine-year long simulations were carried out, with strong and weak geomagnetic activity, respectively, while all other boundary conditions were held to year 2000 levels. Statistically significant temperature effects that were observed in previous reanalysis and model results are also obtained from this set of simulations, suggesting that such patterns are indeed related to geomagnetic activity. In the model, strong geomagnetic activity and the associated NOx enhancements lead to polar stratospheric ozone loss. Compared with the simulation with weak geomagnetic activity, the ozone loss causes a decrease in ozone radiative cooling and thus a temperature increase in the polar winter mesosphere. Similar to previous studies, a cooling is found below the stratopause, which other authors have attributed to a decrease in the mean meridional circulation. In the polar stratosphere this leads to a more stable vortex. A strong (weak) Northern Hemisphere vortex is known to be associated with a positive (negative) Northern Annular Mode (NAM) index; our simulations exhibit a positive NAM index for strong geomagnetic activity, and a negative NAM for weak geomagnetic activity. Such NAM anomalies have been shown to propagate to the surface, and this is also seen in the model simulations. NAM anomalies are known to lead to specific surface temperature anomalies: a positive NAM is associated with warmer than average northern Eurasia and colder than average eastern North Atlantic. This is also the case in our simulation. Our simulations suggest a link between geomagnetic activity, ozone loss, stratospheric cooling, the NAM, and surface temperature variability.
Modeling organic aerosols in a megacity: comparison of simple and complex representations of the volatility basis set approach
Authors: Shrivastava M. , Fast J. , Easter R. , Gustafson W. I. , Zaveri R. A. , Jimenez J. L. , Saide P. , Hodzic A.
Published: December 2010

Abstract. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to include a volatility basis set (VBS) treatment of secondary organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase chemistry mechanism, is used to model gas-particle partitioning and multiple generations of gas-phase oxidation of organic vapors. In addition to the detailed 9-species VBS, a simplified mechanism using 2 volatility species (2-species VBS) is developed and tested for similarity to the 9-species VBS in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the atmosphere. WRF-Chem results are evaluated against field measurements of organic aerosols collected during the MILAGRO 2006 campaign in the vicinity of Mexico City. The simplified 2-species mechanism reduces the computational cost by a factor of 2 as compared to 9-species VBS. Both ground site and aircraft measurements suggest that the 9-species and 2-species VBS predictions of total organic aerosol mass as well as individual organic aerosol components including primary, secondary, and biomass burning are comparable in magnitude. In addition, oxygen-to-carbon ratio predictions from both approaches agree within 25%, providing evidence that the 2-species VBS is well suited to represent the complex evolution of organic aerosols. Model sensitivity to amount of anthropogenic semi-volatile and intermediate volatility (S/IVOC) precursor emissions is also examined by doubling the default emissions. Both the emission cases significantly under-predict primary organic aerosols in the city center and along aircraft flight transects. Secondary organic aerosols are predicted reasonably well along flight tracks surrounding the city, but are consistently over-predicted downwind of the city. Also, oxygen-to-carbon ratio predictions are significantly improved compared to prior studies by adding 15% oxygen mass per generation of oxidation; however, all modeling cases still under-predict these ratios downwind as compared to measurements, suggesting a need to further improve chemistry parameterizations of secondary organic aerosol formation.
Amplification and dampening of soil respiration by changes in temperature variability
Authors: Sierra C. A. , Harmon M. E. , Thomann E. , Perakis S. S. , Loescher H. W.
Published: December 2010

Abstract. Accelerated release of carbon from soils is one of the most important feedbacks related to anthropogenically induced climate change. Studies addressing the mechanisms for soil carbon release through organic matter decomposition have focused on the effect of changes in the average temperature, with little attention to changes in temperature variability. Anthropogenic activities are likely to modify both the average state and the variability of the climatic system; therefore, the effects of future warming on decomposition should not only focus on trends in the average temperature, but also variability expressed as a change of the probability distribution of temperature. Using analytical and numerical analyses we tested common relationships between temperature and respiration and found that the variability of temperature plays an important role determining respiration rates of soil organic matter. Changes in temperature variability, without changes in the average temperature, can affect the amount of carbon released through respiration over the long-term. Furthermore, simultaneous changes in the average and variance of temperature can either amplify or dampen the release of carbon through soil respiration as climate regimes change. These effects depend on the degree of convexity of the relationship between temperature and respiration and the magnitude of the change in temperature variance. A potential consequence of this effect of variability would be higher respiration in regions where both the mean and variance of temperature are expected to increase, such as in some low latitude regions; and lower amounts of respiration where the average temperature is expected to increase and the variance to decrease, such as in northern high latitudes.
Topographic effects on solar radiation distribution in mountainous watersheds and their influence on reference evapotranspiration estimates at watershed scale
Authors: Aguilar C. , Herrero J. , Polo M. J.
Published: December 2010

Abstract. Distributed energy and water balance models require time-series surfaces of the climatological variables involved in hydrological processes. Among them, solar radiation constitutes a key variable to the circulation of water in the atmosphere. Most of the hydrological GIS-based models apply simple interpolation techniques to data measured at few weather stations disregarding topographic effects. Here, a topographic solar radiation algorithm has been included for the generation of detailed time-series solar radiation surfaces using limited data and simple methods in a mountainous watershed in southern Spain. The results show the major role of topography in local values and differences between the topographic approximation and the direct interpolation to measured data (IDW) of up to +42% and −1800% in the estimated daily values. Also, the comparison of the predicted values with experimental data proves the usefulness of the algorithm for the estimation of spatially-distributed radiation values in a complex terrain, with a good fit for daily values (R2 = 0.93) and the best fits under cloudless skies at hourly time steps. Finally, evapotranspiration fields estimated through the ASCE-Penman-Monteith equation using both corrected and non-corrected radiation values address the hydrologic importance of using topographically-corrected solar radiation fields as inputs to the equation over uniform values with mean differences in the watershed of 61 mm/year and 142 mm/year of standard deviation. High speed computations in a 1300 km2 watershed in the south of Spain with up to a one-hour time scale in 30 × 30 m2 cells can be easily carried out on a desktop PC.
Design flood hydrographs from the relationship between flood peak and volume
Authors: Mediero L. , Jiménez-Álvarez A. , Garrote L.
Published: December 2010

Abstract. Hydrological frequency analyses are usually focused on flood peaks. Flood volumes and durations have not been studied as extensively, although there are many practical situations, such as when designing a dam, in which the full hydrograph is of interest. A flood hydrograph may be described by a multivariate function of the peak, volume and duration. Most standard bivariate and trivariate functions do not produce univariate three-parameter functions as marginal distributions, however, three-parameter functions are required to fit highly skewed data, such as flood peak and flood volume series. In this paper, the relationship between flood peak and hydrograph volume is analysed to overcome this problem. A Monte Carlo experiment was conducted to generate an ensemble of hydrographs that maintain the statistical properties of marginal distributions of the peaks, volumes and durations. This ensemble can be applied to determine the Design Flood Hydrograph (DFH) for a reservoir, which is not a unique hydrograph, but rather a curve in the peak-volume space. All hydrographs on that curve have the same return period, which can be understood as the inverse of the probability to exceed a certain water level in the reservoir in any given year. The procedure can also be applied to design the length of the spillway crest in terms of the risk of exceeding a given water level in the reservoir.
Engaging Students with Micro-Businesses
Authors: McConnell Catherine
Published: December 2010

This paper outlines an action research project developed to investigate the gap in teaching and learning placement materials available to students, academics and practitioners in the art, design and media sector, particularly with respect to micro-businesses. Previous research, funded by the UK's Higher Education Subject Centre for Art Design Media (ADM-HEA) and the Centre for Excellence in Professional Placement Learning (Ceppl) has shown that the creative industries are becoming strongly characterized by ‘portfolio’ employment: sole practitioners, freelancers and the self-employed who have established innovative micro-businesses and small to medium-sized enterprises. Engagement between educators and this industrial sector plays a crucial role in maximizing the placement opportunities available to learners and connecting students with the entrepreneurial options available to them following graduation.
What is (the Point of) an Entrepreneur in Residence?
Authors: George Magnus , Gordon Ian , Hamilton Eleanor
Published: December 2010

The teaching of entrepreneurship as an academic subject, as opposed to the apprenticeship route, is the subject of ongoing debate. The authors suggest that there is a middle road and that, by integrating the business world into teaching in a significant way, the best of both approaches can be achieved. In a similar vein, the credibility of some university interaction with small business has been called into question. The authors discuss how they have used the role of ‘entrepreneur in residence’ (EIR) to integrate and improve research, teaching and academic-business interaction. The paper describes the experiences of the EIR hosted at Lancaster University Management School's Institute for Entrepreneurship and Enterprise Development (IEED) in the UK and examines the outcomes of his work and his perceptions of university life; how his presence challenged internal thinking; and how his fellowship led to service innovation in the host organization. Other formalized EIR activities within and outside the UK are also reviewed; and the authors conclude by proposing how UK HEIs might best make use of similar opportunities, with a challenge to non-management departments. The paper demonstrates one way in which the perceived gulf between entrepreneurship teaching and the business world can be bridged to good effect.
Setting Up the JBrowse Genome Browser
Authors: Skinner Mitchell E. , Holmes Ian H.
Published: December 2010

JBrowse is a Web‐based tool for visualizing genomic data. Unlike most other Web‐base genome browsers, JBrowse exploits the capabilities of the user's Web browser to make scrolling and zooming fast and smooth. It supports the browsers used by almost all Internet users, and is relatively simple to install. JBrowse can utilize multiple types of data in a variety of common genomic data formats, including genomic feature data in bioperl databases, GFF files, BED files, and quantitative data in wiggle files. This unit describes how to obtain the JBrowse software, set it up on a Linux or Mac OS X computer running as a Web server, and incorporate genome annotation data from multiple sources into JBrowse. After completing the protocols described in this unit, the reader will have a Web site that other users can visit to browse the genomic data. Curr. Protoc. Bioinform. 32:9.13.1‐9.13.13. © 2010 by John Wiley & Sons, Inc.
RNA‐Seq Read Alignments with PALMapper
Authors: Jean Géraldine , Kahles André , Sreedharan Vipin T. , Bona Fabio De , Rätsch Gunnar
Published: December 2010

Next‐generation sequencing technologies have revolutionized genome and transcriptome sequencing. RNA‐Seq experiments are able to generate huge amounts of transcriptome sequence reads at a fraction of the cost of Sanger sequencing. Reads produced by these technologies are relatively short and error prone. To utilize such reads for transcriptome reconstruction and gene‐structure identification, one needs to be able to accurately align the sequence reads over intron boundaries. In this unit, we describe PALMapper, a fast and easy‐to‐use tool that is designed to accurately compute both unspliced and spliced alignments for millions of RNA‐Seq reads. It combines the efficient read mapper GenomeMapper with the spliced aligner QPALMA, which exploits read‐quality information and predictions of splice sites to improve the alignment accuracy. The PALMapper package is available as a command‐line tool running on Unix or Mac OS X systems or through a Web interface based on Galaxy tools.Curr. Protoc. Bioinform. 32:11.6.1‐11.6.37. © 2010 by John Wiley & Sons, Inc.
Supported Membrane Formation, Characterization, Functionalization, and Patterning for Application in Biological Science and Technology
Authors: Lin Wan‐Chen , Yu Cheng‐Han , Triffo Sara , Groves Jay T.
Published: December 2010

Supported membranes, formed as a single continuous lipid bilayer on a solid substrate, such as silica, have been used extensively as a model for protein‐protein and cell‐cell interaction, to study the molecular interactions at interfaces and the heterogeneities of plasma membranes. The advantages of a supported membrane system include the ability to control membrane composition and the compatibility it has with various surface‐sensitive microscopic and spectroscopic techniques. Recent advances in micro‐ and nanotechnology have greatly extended the use of supported membranes to address key questions in cell biology. Although supported membranes can be easily made by vesicle fusion, the samples need careful preparation for this process to be efficient. The protocols in this unit comprehensively describe procedures to prepare, functionalize, and characterize supported membranes. Curr. Protoc. Chem. Biol. 2:235‐269 © 2010 by John Wiley & Sons, Inc.
The electrode–electrolyte interface
Authors: Hamnett A.
Published: December 2010

This chapter describes the structure of the electrochemical double layer formed between an electronically conducting electrode and an ionically conducting electrolyte. The origin of the potential difference across this double layer is explained, and methods for calculating this potential in simple cases are discussed, beginning with the Goüy–Chapman model and incorporating oriented solvent molecules and specifically adsorbed ions at the electrode surface. Some more recent calculational approaches are reviewed in order to shed light on the normal classical models.
Ideal and effective efficiencies of cell reactions and comparison to carnot cycles
Authors: Vielstich W.
Published: December 2010

Data for the ideal efficiency of energy conversion in fuel cells, as calculated from thermodynamics, are listed for several fuel cell reactions. In order to obtain effective efficiency, potential drops at ohmic and kinetic resistances have to be considered. The electric power of a fuel cell is compared with the maximum obtainable work of a heat engine, using the same fuel. Due to Carnot factor limitations of heat engines, fuel cells show advantages over a wide range of power capacities. In addition, conversion efficiencies by using coal as the primary energy source are compared for the final use in fuel cells, secondary batteries or internal combustion engines.
Kinetics of electrochemical reactions
Authors: Hamnett A.
Published: December 2010

This chapter explores the dependence of the
rate
of electrochemical reactions on the potential difference accommodated in the double layer. The concept of overpotential is introduced, and the theory of electron transfer at the electrode–electrolyte interface described. The derivation of the Butler–Volmer equation is shown to depend on the
reorganization
energy of the fundamental electrochemical reaction being large compared to the electrical energy associated with the electron transfer process across the interface. The pre‐exponential expression in the Butler–Volmer equation, the
exchange current
, is shown to depend on the fundamental kinetics of the electrochemical reaction, and some simple examples are given.
High temperature fuel cells
Authors: Divisek J.
Published: December 2010

The principle of energy conservation determines the energy balance equation which can be generally formulated as the sum of single rates of energy input and output, energy production and accumulation. In a fuel cell, the balance takes into account the thermal and the electrical energy. There are three modes of heat transfer process occurring in a fuel cell: conduction, convection and radiation. The fundamentals of these processes are discussed together with the heat transfer occurring with the change of state, such as evaporation, condensation and additional chemical reactions.

The general energy balance equation is analyzed with respect to the heat sources, energy balances for single phases, boundary conditions and parameter definition. Also an approach for the delocalization of reaction entropy in fuel cells is given.

Based on the general heat transfer equations, water and heat management for low temperature fuel cells (hydrogen and direct methanol) is discussed considering the cell structure, current density and temperature distribution.

Heat transfer in high temperature fuel cells is extremely important for system evaluation. Heat management for high temperature fuel cells (molten carbonate and solid oxide) is analyzed. Heat generation in high temperature fuel cells is strongly influenced by chemical reactions, such as methane/water reforming. Thermodynamic analysis and reaction kinetics of the reforming reaction are presented. A performance analysis of molten carbonate fuel cells, planar and tubular solid oxide fuel cells is made considering the cell geometry, current density and temperature distribution. Finally, heat removal for cogeneration in solid oxide fuel cells is discussed.
Air‐cooled
PEM
fuel cells
Authors: von Helmolt R. , Lehnert W.
Published: December 2010

Proton exchange membrane (PEM) fuel cells operated with hydrogen are usually operated at a voltage of around 0.7 V. This means that power conversion in a PEM fuel cell usually has an efficiency of about 50%. Therefore, a cooling medium has to flow through the bipolar plate and the heat has to be removed by convection of this medium. Most PEM fuel cells are cooled with de‐ionized water. Air cooling can be an option especially for mobile and portable applications. As the complete liquid‐cooling loop is no longer necessary, an air‐cooled system might be much simpler. Advantages and disadvantages of air‐cooled stacks will be discussed in the article. Furthermore some examples of air‐cooled stacks will be presented.
Direct methanol fuel cells (DMFC)
Authors: Hamnett A.
Published: December 2010

The basic principles of operation of the direct methanol fuel cell (DMFC) are described, and ways in which this cell can be realized in practice reviewed. There are several serious problems that currently make it difficult to fabricate practical DMFCs; these include poor performance at both anode and cathode, degradation of the commonly used poly1fluorosulphonic acid membranes and permeation of methanol from anode to cathode cell compartments. Approaches to each of these problems are enumerated, and molecular insights and recent experimental data are brought together to provide an up‐to‐date account of the DMFC and its prospects.
Understanding electrocatalysis: from reaction steps to first‐principles calculations
Authors: Sánchez C. , Leiva E.
Published: December 2010

In this section, the theoretical basis of some calculation methods that have been applied or may be applied to electrocatalytic systems are discussed. Some relevant examples are analyzed.
Catalysis by
UPD
metals
Authors: Sánchez C. , Leiva E.
Published: December 2010

In this Chapter, an overview of the basic aspects of some prototypical fuel cell reactions is given, and the catalytic effects of adatoms and alloys are briefly discussed, in order to provide a framework for the theoretical discussion in Theoretical Aspects of Some Prototypical Fuel Cell Reactions.
Electrode potential and double layer
Authors: Trasatti S.
Published: December 2010

This chapter describes the structure of electrode/solution interfaces and the origin of the electrode potential. Equilibrium conditions are considered. The energy of particles in a phase, the equilibrium between phases and the origin and the physical significance of electrode potentials are discussed. Two main systems are considered: metal/solution and oxide/solution interfaces. Potential of zero charge for the former and point of zero charge for the latter are defined. The structure of the interface and its dependence on a number of parameters such as electrode potential, crystallographic orientation, nature of the solid, etc. are discussed. The fundamental importance of the interaction between the solid and the solvent and its influence on adsorption phenomena is stressed.
Reaction mechanism and rate determining steps
Authors: Trasatti S.
Published: December 2010

The chapter provides the fundamentals on electrochemical kinetics: departure from equilibrium and components of cell potential difference (overpotentials, ohmic drop); additional effects due to the stability and its significance; various types of reaction barriers; description of the parameters of electrode kinetics and how Tafel slopes and reaction mechanisms are interrelated; dependence of Tafel slope on intermediate coverage. The case of multiple Tafel slopes is also discussed.
Theory of electrochemical outer sphere reactions
Authors: Leiva E. , Sánchez C.
Published: December 2010

Different theoretical aspects of electrochemical outer sphere reactions are briefly discussed. This introductory overview includes classical models based on transition state theory, quantum mechanical models that employ first‐order time‐dependent perturbation theory as well as more generalized approaches that are suited for the study of both adiabatic and non‐adiabatic reactions. Stochastic aspects as well as recent computer simulations are also addressed.
Vibrational spectroscopy
Authors: Rodes A. , Pérez J. M. , Aldaz A.
Published: December 2010

Fundamental and experimental aspects of infrared spectroscopy techniques are reviewed in connection with their application to the in situ study of the processes taking place at the metal/solution interphase. Advantages and drawbacks of external and internal reflection experiments are discussed in some detail. Then, typical applications are described, with special emphasis on the spectroscopic characterization of adsorbate layers. The feasibility of gaining structural information from the infrared spectra of adsorbed species at different substrates, ranging from adatom–modified single crystal electrodes to nanoparticles is pointed out. New developments are discussed, including the application of step‐scan interferometry to the kinetic study of fast adsorption processes at the electrode surface.
EXAFS
,
XANES
,
SXS
Authors: Adžić R. R. , Wang J. X. , Ocko B. M. , McBreen J.
Published: December 2010

This chapter describes the application of in situ surface X‐ray scattering (SXS) and X‐ray absorption spectroscopy (XAS) to the problems of fuel cell electrocatalysis. It is shown that SXS is well suited for studying single crystal electrode surfaces during electrocatalytic reactions. The structure of surfaces and surface adlayers which exhibit long range order can be probed with high accuracy and a quantitative measure of potential induced structural phase transitions can be obtained. XAS is sensitive to both structural and chemical information and can be applied to polycrystalline electrocatalysts under in situ conditions. A great advantage is that XAS is element‐specific, and this permits investigation of the chemical environment of a constituent element in a composite material such as alloy catalysts. Since XAS probes only short‐range order, it can provide structural information on amorphous materials, liquids, gases, adsorbed monolayers, as well as hydrated ions and complexes in aqueous solution. A major advantage of XAS in the study of electrocatalysts is its ability to probe the
d
states of Pt catalysts.
Combinatorial catalyst development methods
Authors: Mallouk T. E. , Smotkin E. S.
Published: December 2010

Combinatorial chemistry provides a means of rapidly screening electrocatalysts for use in fuel cells and related applications. The screening methods that have so far been applied to electrocatalyst arrays include indirect fluorescent detection, steady‐state voltammetry, chronoamperometry, and scanning electrochemical microscopy. Several different types of anode and cathode electrocatalysts for polymer electrolyte membrane fuel cells have been studied by these techniques. Heuristic models based on mechanistic and spectroscopic studies of fuel cell catalysis are useful in guiding these searches for new catalyst compositions, and detailed studies of the catalysts already discovered can help to refine or augment these models. One of the outstanding challenges remaining in this area is to find ways to match more closely the synthesis/screening conditions of array catalysts with those of bulk catalysts used in real fuel cells.
Numerical simulations of electrocatalytic processes
Authors: Koper M. T. M.
Published: December 2010

Recent developments in the computer simulation of electrocatalytic processes are discussed. The type of computer simulation chosen for a particular application depends on the time scale of the process and the level of molecular detail desired. Quantum‐chemical electronic structure calculations utilizing the density functional formalism give information about the details of the chemical bonding of molecules at surfaces. Application of the bonding of carbon monoxide to transition metal surfaces and alloys is described, including the role of the electric field. The link to macroscopically measurable kinetics, like voltammetry, can be made by resorting to Dynamic Monte Carlo methods. In this method, reaction events are mapped on to a lattice‐gas model of the catalyst surface and the statistical mechanics is solved
exactly
by Monte Carlo simulation algorithms. The reactant parameters can either be obtained from first‐principles quantum chemical calculations, or be adjusted so as to mimic as closely as possible the experimental results. An example of this method as applied to the oxidation of CO on platinum–ruthenium alloys is discussed.
The hydrogen electrode reaction and the electrooxidation ofCOandH2/COmixtures on well‐characterizedPtandPt‐bimetallic surfaces
Authors: Marković N. M.
Published: December 2010

Interrelationships between the kinetics of fuel cell reactions and the structure/composition of anode catalysts are reviewed. Model systems like Pt single crystals and well characterized Pt(hkl)/Pd and Pt3Sn(hkl) bimetallic surfaces are used to establish a link between the macroscopic kinetic rates and thermodynamic properties of the reacting system and the microscopic level of understanding of the bonding and reactivity of the reaction intermediates and spectator species. The results show that the hydrogen reaction is a structure sensitive process, with Pt(110) being an order of magnitude more active than either of the atomically “flatter” (100) and (111) surfaces. The difference in the activity at the crystal face is attributed to the structure sensitive adsorption of hydrogen (Hupd) and hydroxyl anions (OHad) and the effect these species have on the formation of an active intermediate (Hopd). The significant differences of the hydrogen reaction in alkaline versus acid electrolytes are thought to arise due to the presence of OHad, even close to the reversible potential of the hydrogen reaction in the alkaline electrolyte. The hydrogen reaction on Pt(hkl) modified by pseudomorphic Pd (sub)monolayers shows “volcano‐like” behavior, having the maximum rate on Pt(111) modified by 1 ml of Pd. The physical model based on differences in the adsorption energies of Hupdand Hopdon Pd vs. Pt is used to rationalize the catalytic activity of Pd atoms. For the Pt(111)/CO system, a remarkable difference in both activity and stability of thep(2 × 2)–3CO ordered structures is observed between alkaline and acid solutions. The pH‐effect is explained as the pH‐dependent adsorption of OHad, which starts in the Hupdpotential region at defect sites. The oxidation of H2in the presence of CO occurs concurrently with CO oxidation on Pt and Pt bimetallic surfaces. The PtSn(111) system is used to demonstrate that both the bifunctional effect and the ligand effect contribute to the influence of Sn on the CO oxidation rate and for H2oxidation process in the presence of CO.
Oxidation reactions in high‐temperature fuel cells
Authors: McEvoy A. J.
Published: December 2010

The high temperature fuel cell anode is activated thermally and therefore does not require noble metal catalysts to maintain the oxidation kinetics. Consequently, the high temperature devices are fuel‐tolerant, so an important advantage for their commercial future is the adaptability to commercial fuels. At most a simple pre‐reforming is all that is required to provide an acceptable fuel stream.

The anode is part of an overall electrochemical system in which the other principal components are the oxygen ion source, either the molten carbonate electrolyte in which the oxygen carrier is the carbonate ion, CO32−, or the solid electroceramic electrolyte in which oxygen ions are mobile, and the gas phase fuel stream. Reactions are generally considered as taking place at a three‐phase boundary, which for low polarization must be delocalized to form a volumetrically functioning anode by appropriate materials selection. Concentration overpotential effects are due to diffusion problems for the ingress of the fuel gas, or inhibition of discharge of reaction products.

The functioning of the current state‐of‐the‐art cermet anode is described, as are the considerations motivating the search for new and innovative anode materials, particularly metal oxides and perovskites; in principle these should permit direct oxidation of at least the lower hydrocarbons without restriction by carbon formation and other degradation mechanisms.

Operation of anodes at lower temperatures is also a motivation for current development work, so that the oxidation kinetics are maintained at a lower level of thermal activation of the system.
Poisons for the
O
2
reduction reaction
Authors: Paulus U. A. , Schmidt T. J. , Gasteiger H. A.
Published: December 2010

We reviewed the influence of various kinds of impurities on the oxygen reduction reaction mainly on platinum as electrocatalyst. Our discussion includes data obtained from work with smooth polycrystalline platinum electrodes or platinum single crystals, data obtained from supported catalysts and as far as available results obtained with membrane electrode assemblies in fuel cells. It is shown that the oxygen reduction reaction activity can be affected significantly by the presence of contaminants which may or may not change its reaction pathway (transition from a 4e
−
reduction to a 2e
−
reduction or vice versa).

The effect of anionic and cationic (mainly copper) additives is discussed as well as the influence of the presence of methanol (representing the class of organic contaminants). Throughout this discussion, it becomes evident that the various additives affect the oxygen reduction reaction in different ways. Nevertheless, generally it can be stated that the efficient usage of the electrocatalytic oxygen reduction reaction at a platinum catalyst results in a high level of purity during all processes connected with fuel cell assembly and operation.
O
2
‐reduction at high temperature:
MCFC
Authors: Hemmes K. , Selman J. R.
Published: December 2010

Oxygen reduction in molten carbonate is discussed in relation to the molten carbonate fuel cell. The melt chemistry of molten carbonate is found to be crucial in understanding the possible reaction mechanism and the dissolution problems of the cathode. Using concepts form linear algebra a complete set of equilibria describing the melt is constructed, which is used to derive the relative concentrations of species in the melt and possible reaction mechanisms. Experimental results are critically reviewed in the light of the theoretical predictions. Based on the obtained insight in the fundamental processes, research directions are indicated for minimizing cathode dissolution and cathode polarization, including a radical new concept of a MCFC with a separate CO
2
channel.
Methanol and formic acid oxidation on ad‐metal modified electrodes
Authors: Waszczuk P. , Crown A. , Mitrovski S. , Wieckowski A.
Published: December 2010

This chapter describes modification of platinum and some other noble metal electrodes for enhanced catalytic oxidation of methanol and formic acid. The modification was carried out by electrochemical addition of submonolayer‐to‐monolayer quantities of noble metals to noble metal substrates, with the primary focus on the use of spontaneous deposition. In contrast to underpotential deposition (UPD), the term noble metal deposition on noble metal substrates (NM/NM) is introduced to cover high reactivity model and real electrodes for fuel cells. We begin with providing a brief description of the basic mechanistic pathways for methanol and formic acid oxidative decomposition on platinum. Subsequently, we review the modified electrodes utilized for the study of methanol oxidation, such as platinum/ruthenium, platinum/osmium (and ruthenium/platinum for enhanced CO tolerance), and palladium/platinum and gold/palladium electrodes for formic acid oxidation. The Pt/Ru electrodes are reviewed most comprehensively as the Pt/Ru mixed‐metal materials are used as an anode in the direct oxidation methanol fuel cell. Despite progress recently made in the specific catalytic categories interrogated in this chapter, research is still needed to establish a solid and comprehensive base for preparation of new catalytic materials via the rational rather than trial and error principle; the latter has exhausted its utility many years ago.
Hydrazine fuel cells
Authors: Kohnke H.
Published: December 2010

Hydrazine as an oxidant for fuel cells is important for niche applications, as it can be stored in simple lightweight containers. In addition, their energy density is high — the fuel cells can be optimized for long‐term operation without any service. Hydrazine can be converted to hydrogen and nitrogen in an external reactor or the hydrazine is added to the electrolyte of the fuel cell and converted at special hydrazine electrodes. The catalyst for these electrodes is a modified nickel catalyst. Alsthom has shown the high power density (2 kg kW
−1
) of this fuel cell type in submarines.
Electrochemical supercapacitors and their complementarity to fuel cells and batteries
Authors: Conway B. E.
Published: December 2010

In recent years, so‐called supercapacitors have been developed providing specific capacitances on the order of 50–100 Farads g
−1
of high surface area substrates, e.g., carbon powders, fibers or aerogels, and some transition‐metal oxide films having specific real areas up to ca. 2000 m
2
 g
−1
. The capacitance of carbon‐based devices originates from the double‐layer capacity of the carbon/liquid electrolyte interfaces, giving rise to a high degree of reversibility of the charging/discharging processes, leading to perceived operability at large power densities. The large achievable specific capacitance provides systems for substantial charge and electrical energy storage, complementary to that provided by batteries. However, on account of the distributed nature of capacitative,
C
, and ohmic,
R
, components of the impedance, a broad range of
RC
time‐constants arises, corresponding to a power spectrum. Hence high power operation is available from only a fraction of the total capacitance at large current densities or a.c. frequencies, or in short‐time pulses.

An important application of supercapacitors has been envisaged in a load‐leveling role in hybrid configuration with fuel cells or rechargeable batteries. To achieve this, the relation between operable power densities and achievable energy densities of each of the components has to be evaluated in terms of so‐called Ragone plots in a complementary way.
Alternative fuels and prosects — overview
Authors: Ogden J. M.
Published: December 2010

Continued reliance on current fuels and end‐use technologies poses serious environmental and energy supply security challenges. Globally, direct combustion of fuels for transportation and heating accounts for over half of greenhouse gas emissions, a significant fraction of air pollutant emissions and about two thirds of primary fossil energy use. A variety of alternative transportation fuels and efficient, low‐polluting vehicle technologies have been proposed to help address these challenges. Vehicle technologies include advanced internal combustion engine vehicles, internal combustion engine/hybrid electric vehicles, battery powered electric vehicles and fuel cell vehicles. Use of lower‐polluting fuels, such as reformulated gasoline or diesel, compressed natural gas, methanol, ethanol, dimethyl ether, Fischer–Tropsch liquids and hydrogen, has been suggested. Fuel cell vehicles are particularly attractive as they have zero or near‐zero tailpipe emissions, offer the potential for near‐zero full fuel cycle emissions and use of diverse primary energy sources. In this chapter, we review the status of alternative fuels for vehicles, with an emphasis on fuel cell vehicles and their fuels. The potential role of fuel cell vehicles in meeting future environmental and energy supply goals is discussed, and fuel strategies for implementing fuel cell vehicles on a wide scale are examined.
Methanol from fossil and renewable resources
Authors: Edinger R. , Isenberg G. , Höhlein B.
Published: December 2010

Today, methanol is primarily used for the purposes of the chemical industry. Methanol as an energy carrier and fuel option could enlarge our energy sources for future mobility. Since methanol can be derived from both fossil and renewable resources, it has the option of allowing an economically viable transition to CO2‐reduced mobility. Methanol from wastes, residues, and biomass could support the fuel market for industrialized and developing nations. For fuel cell vehicle applications, methanol constitutes a liquid fuel that can be conveniently stored under atmospheric conditions. For internal combustion and hybrid vehicle propulsion, blending methanol to conventional fuels promises higher fuel quality and, when produced from renewable resources, significantly lower carbon dioxide emissions in the well‐to‐wheel context. For providing future‐oriented transport and mobility, a fuel source shift from fossil to renewable resources is necessary to achieve global atmospheric protection goals as suggested by the United Nations and the European Union.
Solar and wind energy coupled with electrolysis and fuel cells
Authors: Wurster R. , Schindler J.
Published: December 2010

The types and typical capacity ranges of photovoltaic energy conversion, solar thermal electric power generation and wind power generation are outlined, including their respective energy generation costs. Energy potentials for solar and wind power generation suitable for renewable hydrogen production are presented for selected world key areas (North America, Europe and Asia) and illustrated in various tables.

All technologies directly and indirectly necessary for the generation of hydrogen from renewable electricity based energy sources are presented. This includes electricity transmission and conditioning; hydrogen production via electrolysis; hydrogen compression and compressed storage, respectively; its liquefaction and cryogenic storage; hydrogen transportation, either in compressed gaseous form through pipelines or in liquid form via tanker ship and trailers, and finally hydrogen use in fuel cells.

Centralized and distributed settings of renewable hydrogen generation and utilization are described with the focus on distributed settings. Wind/hydrogen energy systems in the 1 kW
e
–5 MW
e
capacity range are used as an example to explain the implications of system layouts for system availability, investment cost reduction and target markets.

Strategies for the build‐up of renewable electricity/hydrogen systems for power generation and fuel supply are developed, outlining in particular hydrogen's unique capability of facilitating the widespread introduction of a vehicle fuel of defined quality derived from renewable sources into future vehicle fuel markets. The requirements for a coordinated approach will be outlined.
Ammonia crackers
Authors: Hacker V. , Kordesch K.
Published: December 2010

Anhydrous ammonia is discussed as an easy to handle and commercially widely available energy carrier. Facilities for storage and transport by sea and land from ammonia producers to major customers are available throughout the world. Pure liquid ammonia, stored in low pressure vessels, is comparable in energy density as well as in price with methanol. Ammonia is cracked on‐site or on‐board into hydrogen and nitrogen. Traces of residual ammonia in the feed stream have to be removed when an acidic electrolyte fuel cell is used. For alkaline fuel cells no gas purification is necessary.