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Articles 661 - 690 of 914

Full-Text Articles in Chemical Engineering

Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov Jan 2002

Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov

Faculty Publications

Anodic formation of oxide films on titanium surfaces, in various concentrations of aqueous KOH solutions, have been studied using ellipsometry and micro-Raman spectroscopy. By in situ ellipsometric measurements the coefficient of film thickness growth and indexes of refraction of anodic oxide films have been determined. The voltage at which the oxide film breaks down is strongly dependent on the KOH concentration. Further, the solution concentration strongly influences the potential at which the oxide film is transformed from the amorphous state to crystalline form. Using micro-Raman spectroscopy four crystalline forms of titanium oxides, namely, anatase, brookite, corundum, and rutile, have been …

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Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti Jan 2002

Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti

Faculty Publications

Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, …

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Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn Jan 2002

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn

Faculty Publications

This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …

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Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn Jan 2002

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn

Faculty Publications

This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …

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Green Electrochemistry. Examples And Challenges, Michael A. Matthews Aug 2001

Green Electrochemistry. Examples And Challenges, Michael A. Matthews

Faculty Publications

Electrochemical methods have been proposed for synthesis of organic compounds, including conversion of CO2. Such methods may provide a basis for environmentally friendly and sustainable methods for chemical production. Nevertheless, electrochemical syntheses are not widely utilized. Several examples of ongoing research are presented that illustrate both the opportunities as well as the challenges associated with the utilization of electrochemistry for green chemical manufacturing.

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Determination Of An Ethane Intermolecular Potential Model For Use In Molecular Simulations From Ab Initio Calculations, Richard L. Rowley, Tapani A. Pakkanen, Yan Yang Apr 2001

Determination Of An Ethane Intermolecular Potential Model For Use In Molecular Simulations From Ab Initio Calculations, Richard L. Rowley, Tapani A. Pakkanen, Yan Yang

Faculty Publications

Counterpoise-corrected, supermolecule, ab initio energies obtained at the MP2/6-311+G(3df, 2pd) level were computed for 22 different relative orientations of two ethane molecules as a function of the separation distance between the molecular centers. These energies were used to regress the parameters in several simple, analytical, interatomic or site-site models that can be used for implementation in molecular simulations. Sensitivity analysis indicated that the inter molecular potential surface is insensitive to the C-C interactions and that the parameters in the C-C model are coupled and unobtainable from the dimer energies. Representation of the potential surface can be made in terms of …

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Simultaneous Capture And Mineralization Of Coal Combustion Flue Gas Carbon Dioxide (Co2), Morris D. Argyle, Katta J. Reddy, Sanil John, Hollis Weber, Pradip Bhattacharyya, David T. Taylor, Mikol Christensen, Thomas Foulke, Paul Fahlsing Apr 2001

Simultaneous Capture And Mineralization Of Coal Combustion Flue Gas Carbon Dioxide (Co2), Morris D. Argyle, Katta J. Reddy, Sanil John, Hollis Weber, Pradip Bhattacharyya, David T. Taylor, Mikol Christensen, Thomas Foulke, Paul Fahlsing

Faculty Publications

The mineral carbonation, a process of converting CO2 into stable minerals (mineralization), has been studied extensively to capture and store CO2. However, most of the mineral carbonation studies have been largely investigated at lab scale. Preliminary and pilot scale studies for accelerated mineral carbonation (AMC) were conducted at one of the largest coal-fired power plants (2120 MW) in the USA by reacting flue gas with fly ash particles in a fluidized bed reactor. In the preliminary experiments, flue gas CO2 and SO2 concentrations decreased from 13.0 to 9.6% and from 107.8 to 15.1 ppmv, respectively during the first 2 min. …

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Electrochemical Generation Of Superoxide In Room-Temperature Ionic Liquids, Inas M. Alnashef, Matthew L. Leonard, Matthew C. Kittle, Michael A. Matthews, John W. Weidner Jan 2001

Electrochemical Generation Of Superoxide In Room-Temperature Ionic Liquids, Inas M. Alnashef, Matthew L. Leonard, Matthew C. Kittle, Michael A. Matthews, John W. Weidner

Faculty Publications

We have demonstrated that superoxide ion can be generated electrochemically in room-temperature ionic-liquid solvents. In the absence of impurities, cyclic voltammetry showed that the super oxide ion is stable in these solvents. Similar superoxide ion chemistry has previously been demonstrated in volatile and environmentally suspect aprotic solvents such as dimethyl formamide and acetonitrile. However, ionic liquids are nonvolatile and should minimize the problems of secondary solvent waste. It is proposed that the resultant superoxide ion can be used to perform low temperature oxidation of wastes. Low-temperature oxidation of waste solvents can provide a much needed alternative to high-temperature waste incinerators, …

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Hysteresis During Cycling Of Nickel Hydroxide Active Material, Venkat Srinivasan, John W. Weidner, John Newman Jan 2001

Hysteresis During Cycling Of Nickel Hydroxide Active Material, Venkat Srinivasan, John W. Weidner, John Newman

Faculty Publications

The nickel hydroxide electrode is known to exhibit a stable hysteresis loop, with the potential on charge being higher than that on discharge at every state-of-charge (SOC). What we show here is that this loop created during a complete charge and discharge (i.e., boundary curves) is not sufficient to define the state of the system. Rather, internal paths within the boundary curves (i.e., scanning curves) can be generated that access potentials between the boundary curves. The potential obtained at any SOC, as well as how the material charges and discharges from that point, depends on the …

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Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. S. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. E. Lofland, Jason R. Hattrick-Simpers, H. Chang Jan 2001

Multimode Quantitative Scanning Microwave Microscopy Of In Situ Grown Epitaxial Ba1-XSrXTio3 Composition Spreads, K. S. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. E. Lofland, Jason R. Hattrick-Simpers, H. Chang

Faculty Publications

We have performed variable-temperature multimode quantitative microwavemicroscopy of in situepitaxial Ba1−xSrxTiO3 thin-film composition spreads fabricated on (100) LaA1O3 substrates. Dielectric properties were mapped as a function of continuously varying composition from BaTiO3 to SrTiO3. We have demonstrated nondestructive temperature-dependent dielectric characterization of local thin-film regions. Measurements are simultaneously taken at multiple resonant frequencies of the microscope cavity. The multimode measurements allow frequency dispersion studies. We observe strong composition-dependent dielectric relaxation in Ba1−xSrxTiO3 at microwave frequencies.

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Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White Jan 2001

Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White

Faculty Publications

Approximate models are developed, based on second, fourth, and sixth order polynomials, that describe the concentration profile of an electrochemically active species in a spherical electrode particle. Analytical expressions are obtained that describe the way the concentration profiles, surface concentrations, and electrode utilization change during the galvanostatic discharge of an electrode particle. Based on a comparison with an exact analytical model over a wide range of dimensionless current densities, all three approximate models performed extremely well in predicting these quantities. Quantitative criterion for the validity of these models is also developed and shows that the sixth order, four parameter approximate …

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Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White Jan 2001

Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White

Faculty Publications

No abstract provided.

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Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White Jan 2001

Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White

Faculty Publications

No abstract provided.

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Synthesis And Characterization Of Hydrous Ruthenium Oxide-Carbon Supercapacitors, Manikandan Ramani, Bala S. Haran, Ralph E. White, Branko N. Popov Jan 2001

Synthesis And Characterization Of Hydrous Ruthenium Oxide-Carbon Supercapacitors, Manikandan Ramani, Bala S. Haran, Ralph E. White, Branko N. Popov

Faculty Publications

It is shown that composite Ru oxide-carbon based supercapacitors possess superior energy and power densities as compared to bare carbon. An electroless deposition process was used to synthesize the ruthenium oxide-carbon composites. Ru is dispersed on the carbon matrix as small particles. The effect of electrochemical oxidation and temperature treatment on the material performance has been studied extensively. Increasing the oxidation temperature reduces the proton transport rate and also increases the degree of crystallinity of the deposits. This adversely affects the performance of the composite. Loading a small amount of Ru oxide (9 wt %) on carbon increases the capacitance …

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Transformations Of Coal-Derived Soot At Elevated Temperature, Thomas H. Fletcher, Jim Rigby, Jinliang Ma, Brent W. Webb Jan 2001

Transformations Of Coal-Derived Soot At Elevated Temperature, Thomas H. Fletcher, Jim Rigby, Jinliang Ma, Brent W. Webb

Faculty Publications

Coal pyrolysis experiments were performed in the post-flame region of a CH4/H2/air flat-flame burner operating under fuel-rich conditions, where the temperature and gas compositions were similar to those found in the near-burner region of an industrial pulverized coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles surrounding a centrally fed coal/char particle stream. Soot samples were collected from the cloud at different residence times using a water-cooled, nitrogen-quenched probe. The soot samples were then analyzed for their elemental compositions of carbon, hydrogen, nitrogen, sulfur, and (by difference) oxygen plus inorganic matter. …

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Small-Angle X-Ray Studies Of Soot Inception And Growth, Jan P. Hessler, Soenke Seifert, Randall E. Winans, Thomas H. Fletcher Jan 2001

Small-Angle X-Ray Studies Of Soot Inception And Growth, Jan P. Hessler, Soenke Seifert, Randall E. Winans, Thomas H. Fletcher

Faculty Publications

The high spectral intensity of X-rays produced by the undulator at the Basic Energy Sciences Synchrotron Radiation Center of Argonne's Advanced Photon Source has allowed us to perform small-angle X-ray scattering (SAXS) studies of the initial distribution of soot particles formed by various fuels. SAXS provides an in situ probe of the morphology of soot in the region between 1 and 100 nm and complements the ex situ technique of electron microscopy. The basic aspects of SAXS and its potential are illustrated with measurement on a laminar flame of acetylene in air. The more complex fuel toluene has been studied …

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Nitrogen Transformations During Secondary Coal Pyrolysis, Haifeng Zhang, Thomas H. Fletcher Jan 2001

Nitrogen Transformations During Secondary Coal Pyrolysis, Haifeng Zhang, Thomas H. Fletcher

Faculty Publications

A CO/H2/O2/N2 flame was operated under fuel-rich conditions in a flat flame reactor to provide a high-temperature, oxygen-free environment to study secondary reactions of coal volatiles. The distributions of fuel nitrogen in the devolatilization products of four coals, ranging from high volatile bituminous to lignite, were obtained at gas temperatures ranging from 1159 to 1858 K. It was found that the initial nitrogen released was contained almost exclusively in the tar for all coals. Release of nitrogen from the char as light gases started at a later stage than tar nitrogen release. During secondary reactions, …

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Simulation Of Coal Pyrolysis In Plasma Jet By Cpd Model, Yajun Tian, Kechang Xie, Suyu Zhu, Thomas H. Fletcher Jan 2001

Simulation Of Coal Pyrolysis In Plasma Jet By Cpd Model, Yajun Tian, Kechang Xie, Suyu Zhu, Thomas H. Fletcher

Faculty Publications

Reaction of coal in a plasma jet is complex and extremely rapid, and acetylene and carbon monoxide are the main products in the pyrolysis gas. Coal pyrolysis is assumed as the first step reaction when coal is injected into hot plasma jet with initial average temperature of 3700 K. Chemical percolation devolatilization (CPD) is employed first to simulate this procedure in mechanism. The calculation results indicate coal pyrolysis rate in plasma jet is very fast and the retention time of coal staying in reactor is only several milliseconds. Comparing the calculation with experiment result, it was concluded that the CPD …

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13-C Nmr Analysis Of Soot Produced From Model Compounds And A Coal, Mark S. Solum, Adel F. Sarofim, Ronald J. Pugmire, Thomas H. Fletcher, Haifeng Zhang Jan 2001

13-C Nmr Analysis Of Soot Produced From Model Compounds And A Coal, Mark S. Solum, Adel F. Sarofim, Ronald J. Pugmire, Thomas H. Fletcher, Haifeng Zhang

Faculty Publications

Soot samples, including the associated organics, produced from an Illinois No. 6 coal (five samples) and two model compounds, biphenyl (three samples) and pyrene (two samples), have been studied by 13C NMR methods. The coal soot data served as a guide to selection of the temperature range that would be most fruitful for investigation of the evolution of aerosols composed of soot and tars that are generated from model compounds. The evolution of the different materials in the gas phase followed different paths. The coal derived soots exhibited loss of aliphatic and oxygen functional groups prior to significant growth …

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Molecular Dynamics Calculations Of The Electrochemical Properties Of Electrolyte Systems Between Charged Electrodes, Richard L. Rowley, Paul S. Crozier, Douglas Henderson Nov 2000

Molecular Dynamics Calculations Of The Electrochemical Properties Of Electrolyte Systems Between Charged Electrodes, Richard L. Rowley, Paul S. Crozier, Douglas Henderson

Faculty Publications

We investigate the interfacial electrochemical properties of an aqueous electrolyte solution with discrete water molecules in slab geometry between charged atomistic electrodes. Long-range intermolecular Coulombic interactions are calculated using the particle particle particle mesh method with a modification to account for the slab geometry. Density distribution profiles and potential drops across the double layer are given for 0, 0.25, and 1 M aqueous electrolyte solutions each electrode surface charges. Results are compared qualitatively with experimental x-ray scattering findings, other computer simulation results, and traditional electrochemistry theory. The interfacial fluid structure characteristics are generally in good qualitative agreement with the conclusions …

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Comparison Of Charged Sheets And Corrected 3-D Ewald Calculations Of Long-Range Forces In Slab Geometry Electrolyte Systems With Solvent Molecules, Richard L. Rowley, Paul S. Crozier, Eckhard Spoht, Douglas Henderson Jun 2000

Comparison Of Charged Sheets And Corrected 3-D Ewald Calculations Of Long-Range Forces In Slab Geometry Electrolyte Systems With Solvent Molecules, Richard L. Rowley, Paul S. Crozier, Eckhard Spoht, Douglas Henderson

Faculty Publications

Two methods of calculating long-range intermolecular potentials are compared for an approximately 3 M aqueous electrolyte solution confined between two charged surfaces. We investigate the ionic density profiles using the charged-sheets method and the corrected three-dimensional (3D) Ewald method at two different system sizes and also compare the Coulomb forces directly. The corrected 3D Ewald method is recommended for the calculation of long-range potentials in systems of this nature because it is less system size dependent than the charged sheets method and the resultant forces are more consistent with periodic boundaries. However, the charged-sheets method for estimating long-range potentials in …

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The Character Of Ash Deposits And The Thermal Performance Of Furnaces, T. F. Wall, S. P. Bhattacharya, Larry Lin Baxter 8507091, G. Richards, J. N. Harb Mar 2000

The Character Of Ash Deposits And The Thermal Performance Of Furnaces, T. F. Wall, S. P. Bhattacharya, Larry Lin Baxter 8507091, G. Richards, J. N. Harb

Faculty Publications

The character of fireside ash deposits depend on the processes by which deposits are formed and subsequent reactions within the deposit and with furnace gases. The properties influencing furnace heat transfer, absorptivity for radiative transfer and thermal conductivity for conductive transfer are shown from many measurements to depend on this character. Illustrative trends in these properties as deposits mature and grow are presented together with their effect on furnace exit temperature and efficiency. The reflective character of initial deposits from particular coals is then considered with predictions and measurements of the spectral character of such deposits, during the first three …

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Pulsed Ultrasound Enhances The Killing Of Escherichia Coli Biofilms By Aminoglycoside Antibiotics In Vivo, Andrea M. Rediske, Beverly L. Roeder, Jared L. Nelson, Rachel L. Robison, Bruce Schaaije, Richard A. Robison, William G. Pitt Mar 2000

Pulsed Ultrasound Enhances The Killing Of Escherichia Coli Biofilms By Aminoglycoside Antibiotics In Vivo, Andrea M. Rediske, Beverly L. Roeder, Jared L. Nelson, Rachel L. Robison, Bruce Schaaije, Richard A. Robison, William G. Pitt

Faculty Publications

Escherichia coli biofilms on two polyethylene disks were implanted subcutaneously into rabbits receiving systemic gentamicin. Ultrasound was applied for 24 h to one disk. Both disks were removed, and viable bacteria were counted. Pulsed ultrasound significantly reduced bacterial viability below that of nontreated biofilms without damage to the skin.

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Solid-State 13c Nmr Characterization Of Matched Tars And Chars From Rapid Coal Devolatilization, Steven T. Perry, Eric M. Hambly, Thomas H. Fletcher, Mark S. Solum, Ronald J. Pugmire Jan 2000

Solid-State 13c Nmr Characterization Of Matched Tars And Chars From Rapid Coal Devolatilization, Steven T. Perry, Eric M. Hambly, Thomas H. Fletcher, Mark S. Solum, Ronald J. Pugmire

Faculty Publications

Matched tar/char sets were prepared by pyrolysis of a lignite and a bituminous coal in two entrained flow reactors at temperatures between 900 K and 1650 K and heating rates of 104–105 K/s. Detailed chemical structural characterization of these tars and chars was performed using elemental analysis and solid-state 13C NMR. This is the first set of detailed solid-state 13C nuclear magnetic resonance (NMR) data on coal tar samples. The average aromatic cluster sizes of the primary tars from these experiments are quite similar to those of their parent coals, confirming an assumption often made …

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Measurement Of Soot And Char In Pulverized Coal Fly Ash, John M. Veranth, Thomas H. Fletcher, David W. Pershing, Adel F. Sarofim Jan 2000

Measurement Of Soot And Char In Pulverized Coal Fly Ash, John M. Veranth, Thomas H. Fletcher, David W. Pershing, Adel F. Sarofim

Faculty Publications

The unburned carbon in the fly ash produced by low-NOx pulverized coal combustion has been shown by electron microscopy to be a mixture of porous coal char particles and aggregates of submicron particles, which are thought to be soot. The carbon is bimodally distributed with large soot aggregates mixed with the char in the particles larger than 10 microns and dispersed soot found with the submicron particles. A method for determining the mass of soot and char by liquid-suspension gravity separation was used with both laboratory-scale and power plant fly ash samples. For low-NOx, staged, pilot-scale combustion of bituminous coal …

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Diffusion Of Water In Nafion 115 Membranes, Sathya Motupally, Aaron J. Becker, John W. Weidner Jan 2000

Diffusion Of Water In Nafion 115 Membranes, Sathya Motupally, Aaron J. Becker, John W. Weidner

Faculty Publications

In this paper, experimental and simulated data for the diffusion of water across Nafion membranes as a function of the water activity gradient are presented. The gradient in the activity of water across the membrane was varied by changing the flow rate and pressure of nitrogen gas on one side of the membrane. The other side of the membrane was equilibrated with liquid water. It was found that the model predictions are very sensitive to the value of the diffusion coefficient of water in Nafion. Using the Fickian diffusion coefficient extracted from self-diffusion measurements reported in the literature, the model …

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Modeling The Effects Of Ion Association On Direct-Current Polarization Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn Jan 2000

Modeling The Effects Of Ion Association On Direct-Current Polarization Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn

Faculty Publications

Considerable experimental evidence indicates that ion association occurs in solid polymer electrolytes. This work provides a thorough theoretical analysis of the effect of ion association on the conductivity, general current-potential behavior, and limiting current density in a solid polymer electrolyte. The model employs dilute solution theory to describe the fluxes of cations, anions, and ion pairs in a motionless continuum but neglects higher order association. The predictions of the model highlight the effects of the relative diffusion coefficients and dimensionless association constant on concentration distributions of simple ions and ion pairs, the limiting current density, and the potential drop required …

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Oxygen Diffusion Coefficient And Solubility In A New Proton Exchange Membrane, Andrew T. Haug, Ralph E. White Jan 2000

Oxygen Diffusion Coefficient And Solubility In A New Proton Exchange Membrane, Andrew T. Haug, Ralph E. White

Faculty Publications

No abstract provided.

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Self‐Discharge Model Of A Nickel‐Hydrogen Cell, B. Wu, Ralph E. White Jan 2000

Self‐Discharge Model Of A Nickel‐Hydrogen Cell, B. Wu, Ralph E. White

Faculty Publications

No abstract provided.

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Studies On The Capacitance Of Nickel Oxide Films: Effect Of Heating Temperature And Electrolyte Concentration, Venkat Srinivasan, John W. Weidner Jan 2000

Studies On The Capacitance Of Nickel Oxide Films: Effect Of Heating Temperature And Electrolyte Concentration, Venkat Srinivasan, John W. Weidner

Faculty Publications

Nickel oxide films were prepared by electrochemically precipitating the hydroxide and heating it in air to form the oxide. The resulting oxide films behave as a capacitor. The capacitance of the oxide depends on the heating temperature, showing a maximum at 300°C. The mechanism of charge storage was studied by measuring the capacitance and surface area as a function of heating temperature, and the capacitance in different electrolytes and potential windows. The charge-storage mechanism is believed to be a surface redox reaction involving adsorbed hydroxyl ions.

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