DOCSLIB.ORG

The Anode and the Electrolyte in the MCFC Andreas Bodén

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Anode and the Electrolyte in the MCFC Andreas Bodén The anode and the electrolyte in the MCFC Andreas Bodén DOCTORAL THESIS KTH – Chemical Science and Engineering Department of Chemical Engineering and Technology Applied Electrochemistry Kungliga Tekniska Högskolan Stockholm, 2007 AKADEMISK AVHANDLING som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av teknologie doktorsexamen fredagen den 1 juni 2007, kl. 13.00 i sal F3, Lindstedtsvägen 26, Kungliga Tekniska Högskolan, Stockholm © Andreas Bodén 2007 TRITA-CHE-Report 2007:32 ISSN 1654-1081 ISBN 978-91-7178-687-6 ABSTRACT A goal of the Swedish government is to increase the usage of renewable fuels and biomass-based fuels. Fuel cells, and especially the MCFC, are useful for these types of fuels. The Swedish market may benefit from the MCFC in two ways: increased efficiency of the biofuels and also utilisation of produced heat in district heating. Most of the commercial MCFC systems today are optimised for use with methane. The possibility to utilise biomass in Sweden makes it important to study how the MCFC may be adapted or optimised for good performance and low degradation with gas produced from biomass or other renewable fuels. This thesis is focused on methods that may be used to investigate and evaluate MCFC electrodes and electrolytes with renewable fuels i.e. CO2-containing gases. The methods and results are both experimental and mathematically modelled. The objectives of this thesis are to better understand how the performance of the anode is dependent on different fuels. Anode kinetics and the water- gas shift reaction have been investigated as well as the possibility to increase cell lifetime by increasing the initial electrolyte amount by having the anode as a reservoir. The effect of segregation of cations in the electrolyte during operation has also been studied. It was found that if the gas composition at the current collector inlet is in equilibrium according to the water gas-shift reaction the gas composition inside the electrode is almost uniform. However, if the gas is not in equilibrium then the concentration gradients inside the current collector have a large effect on the gas composition inside the electrode. The conversion of the gas in the gas flow channels according to the water-gas shift reaction depends on the gas flow rate. For an anode used in a gas mixture of humidified hydrogen and carbon dioxide that are not in equilibrium some solubility of Ni in a (Li/Na)2CO3 mixture was found. To have the anode act as an electrolyte reservoir to prolong cell lifetime the anode pore size should be carefully matched with that of the cathode and a bimodal pore-size distribution for the anode is preferable to have as good performance as possible for as large electrolyte filling degree interval as possible. Modelling results of segregation of cations in the electrolyte during operation indicate that the electrolyte composition changes during operation and that the lithium ions are enriched at the anode for both types of electrolyte used for the MCFC. The electrolyte composition changes are small but might have to be considered in long-time operation. The results from this thesis may be used to better understand how the MCFC may be used for operation with renewable fuels and how electrodes may be designed to prolong cell lifetime. Keywords: composite electrolytes, electrode kinetics, electrolyte, electrolyte distribution, hydrogen oxidation reaction, ion segregation, mass transport, mathematical modelling, MCFC, molten carbonate fuel cell, nickel solubility, porous electrode, reformate, water-gas shift reaction SAMMANFATTNING Ett av den svenska regeringens mål är att öka användandet av förnyelsebara bränslen och bränslen från biomassa. Bränsleceller och framförallt MCFC är användbara för dessa typer av bränslen. Den svenska marknaden kan dra fördelar av MCFC på två sätt; ökad bränsleutnyttjandegrad och utnyttjande av producerad värme för fjärrvärme. De flesta kommersiella MCFC-systemen idag är optimerade för användning av metan. Möjligheten att använda biomassa på den svenska marknaden gör det viktigt att studera hur MCFC kan anpassas eller optimeras för bra prestanda och låg degradering för användning med gas från biomassa eller andra förnyelsebara bränslen. Fokus i denna avhandling är på metoder som kan användas för att undersöka och utvärdera MCFC-elektroder och -elektrolyter med förnyelsebara bränslen, dvs. gaser innehållande CO2. Metoderna och resultaten är både experimentella och matematiskt modellerade. Målet med denna avhandling är att bättre förstå hur anodens prestanda beror på användningen av olika bränslen. Anodens kinetik och vattengasskiftreaktionen har studerats liksom möjligheten att förlänga cellens livstid genom att öka den initiala mängden elektrolyt medelst användning av anoden som reservoar. Effekten av segregation av katjoner i elektrolyten under last har också undersökts. Om gassammansättningen är i jämvikt enligt vattengasskiftreaktionen vid inloppet till strömtilledaren kommer gassammansättningen att vara nära uniform inuti elektroden. Om ingående gas inte är i jämvikt kommer stora koncentrationsgradienter uppkomma i strömtilledaren och påverka gassammansättningen i elektroden. Omsättningen med avseende på vattenskiftreaktionen av gasen i flödeskanalen verkar vara beroende av gasens flödeshastighet. För en anod som används i en uppfuktad blandning av vätgas och koldioxid som inte är i jämvikt befanns det att Ni har en viss löslighet i (Li/Na)2CO3. För att kunna använda anoden som reservoar för elektrolyt för att förlänga livstiden för MCFC skall anodens porstorleksfördelning överensstämma med katodens och ha en bimodal porstorleksfördelning för att ge en tillräckligt god prestanda i ett så stort elektrolytfyllnadsgradsintervall som möjligt. Modelleringsresultat för segregering av katjoner i elektrolyten under drift visar att litiumjoner anrikas i anoden för båda typerna av elektrolyt som används i MCFC. Elektrolytkoncentrationsförändringarna är små men kan behövas tas i beaktande vid långa driftstider. Denna avhandlings resultat kan användas för att bättre förstå hur MCFC skall anpassas för drift med förnyelsebara bränslen och hur elektroder kan utformas för att förlänga livstiden. Nyckelord: elektrodkinetik, elektrolyt, elektrolyt fördelning, jonsegregering, kompositelektrolyt, löslighet av nickel, masstransport, matematisk modellering, MCFC, porösa elektroder, reformat, smältkarbonatbränslcell, vattengasskiftreaktionen, vätgasoxidationsreaktionen LIST OF PAPERS This thesis is a summary of the following papers: I. A Steady-State Model of the Porous Molten Carbonate Fuel Cell Anode for Investigation of Kinetics and Mass Transfer Mari Sparr, Andreas Bodén and Göran Lindbergh J. Electrochem. Soc., 153(8), A1525-A1532 (2006) II. The solubility of Ni in molten Li2CO3-Na2CO3 (52/48) in H2/H2O/CO2 atmosphere Andreas Bodén, Masahiro Yoshikawa and Göran Lindbergh J. Power Sources, 166, 59-63 (2007) III. Experimental determination of effective surface area and conductivities in the porous anode of molten carbonate fuel cell Masahiro Yoshikawa, Andreas Bodén, Mari Sparr and Göran Lindbergh J. Power Sources, 158, 94-102 (2006) IV. Influence of the anode pore-size distribution and total electrolyte filling degree on the MCFC performance Andreas Bodén, Masahiro Yoshikawa and Göran Lindbergh Manuscript V. A Model for Mass Transport of Molten Alkali Carbonate Mixtures Applied to the MCFC Andreas Bodén and Göran Lindbergh J. Electrochem. Soc., 153(11), A2111-A2119 (2006) VI. Conductivity of SDC and (Li/Na)2CO3 composite electrolytes in reducing and oxidising atmosphere Andreas Bodén, Jing Di, Carina Lagergren, Göran Lindbergh and Cheng Yang Wang Manuscript submitted to Journal of Power Sources My contributions to the papers in this thesis I would hereby like to point out some significant contributions to the papers in this thesis that I have not been participating in. In Paper I I have not performed the experiments and the derivation of kinetic expression for the reactions. Paper III is the result of Dr. Yoshikawa’s work at our department. I have been involved in the experimental work and the evaluation of the results but I did not perform the measurements and I was not involved in the evaluation of the reaction-rate distribution. In Paper IV I have not made the measurements of the cathode reaction resistance in the symmetrical setup. In Paper VI I have been fully involved except that I have not performed all the measurements. ACKNOWLEDGEMENTS Professor Göran Lindbergh, my supervisor, thank you for your support and guidance through this work. Thanks for accepting me into your group, solving and discussing lab issues and theory in electrochemistry especially in late work hours and for supporting me also in non-work issues. Secondly to my supplement supervisor Dr. Carina Lagergren, thank you for your help and discussion regarding laboratory equipment and MCFC and the help in putting this thesis together. To all my colleagues both former and present at Applied Electrochemistry for creating a friendly and helpful working environment. I will miss all the small events with the group and the discussions in the coffee room. Two special thanks go to Dr. Mari Sparr for our co-operation and interesting discussions and to Thomas Tingelöf for morgonpassan and other crazy things. To my roommate Thomas Vernersson for sharing early bird mornings, too much coffee drinking, eating all those sushi plates, striking each others work, making all the possible
Load more

Recommended publications
  • Electrolyte Panel
    Lab Dept: Chemistry Test Name: ELECTROLYTE PANEL General Information Lab Order Codes: LYTE Synonyms: Electrolytes; Lytes CPT Codes: 80051 – Electrolyte panel Test Includes: Carbon Dioxide, Chloride, Potassium, Sodium concentrations reported in mEq/L, and AGAP (Anion Gap). Logistics Test Indications: The maintenance of osmotic pressure and water distribution in the various body fluid compartments is primarily a function of the four major electrolytes, Na+, K+, Cl-, and HCO3-. In addition to water homeostasis, these electrolytes play an important part in the maintenance of pH, regulation of proper heart and muscle functions, involvement in electron transfer reactions, and participation in catalysis as cofactors for enzymes. Lab Testing Sections: Chemistry Phone Numbers: MIN Lab: 612-813-6280 STP Lab: 651-220-6550 Test Availability: Daily, 24 hours Turnaround Time: 30 minutes Special Instructions: N/A Specimen Specimen Type: Blood Container: Green top (Li Heparin) tube, preferred Alternate tube: Red, marble or gold top tube Draw Volume: 0.6 mL blood Processed Volume: 0.2 mL serum/plasma Collection: Routine blood collection. Mix tubes containing anticoagulant by gentle inversion. Note: Venipuncture samples are preferred, but capillary specimens will be accepted. Special Processing: Lab Staff: Sample must be run within one hour of collection for CO2 stability. Centrifuge specimen, remove serum/plasma aliquot into a plastic sample cup. Avoid prolonged contact with separated cells. Store at refrigerated temperatures. Patient Preparation: None Sample Rejection: Mislabeled or unlabeled specimens Interpretive Reference Range: See individual analyte procedures Critical Values: See individual analyte procedures Limitations: See individual analyte procedures Methodology: See individual analyte procedures References: See individual analyte procedures Updates: 2/8/2016: Update alt tube types .
    [Show full text]
  • Next Generation Anodes for Lithium-Ion Batteries
    NEXT GENE ATION ANODES Next Ge eratio A odes for Lithium-Io Batteries Seco d Quarter Progress Report 2018 De is Dees, Poi t-of-Co tact Argonne National Laboratory 9700 South Cass Avenue Argonne, IL 60439 Phone: (630) 252-7349 E-mail: [email protected] Bria Cu i gham, DOE-EERE-VTO Tech ology Ma ager U.S. Department of Energy, Battery R&D Phone: (202) 287-5686 E-mail: [email protected] Table of Co te ts Overview (page 2) 1. Research Facilities Support (page 5) CAMP Facility Support Activities (ANL) (page 5) Characterization and Optimization of Si Slurry by Zeta Potential (ORNL) (page 7) Thermodynamic Understanding and Abuse Performance (SNL) (page 9) Hydro/Solvothermal Synthesis and Scale-up of Silicon and Silicon-containing Nanoparticles (ANL) (page 10) 2. Characterization, Diagnostics, and Analysis (page 12) Spectroscopic Characterization of Cycled Si Electrodes: Understanding the Role of Binder (ORNL) (page 12) EQCM Studies of Silicon Anodes (ANL) (page 13) Effect of silicate thickness on the electrochemical performance of silicate-coated silicon nanoparticles (ANL) (page 15) Calendar-life versus Cycle-life aging of Lithium-ion Cells with Silicon-Graphite Composite Electrodes – Electrolyte Analysis (ANL) (page 17) 3. Materials Advancements (page 18) Continued Study of Lithiation Effect of the Poly(Acrylic Acid) Binders on the Silicon Anode of Lithium-Ion Batteries (ANL) (page 19) Probe the relationships between functional electrolytes structure and SEI property for Si materials (LBNL) (page 21) Silicon Surface Modification Using
    [Show full text]
  • Elements of Electrochemistry
    Page 1 of 8 Chem 201 Winter 2006 ELEM ENTS OF ELEC TROCHEMIS TRY I. Introduction A. A number of analytical techniques are based upon oxidation-reduction reactions. B. Examples of these techniques would include: 1. Determinations of Keq and oxidation-reduction midpoint potentials. 2. Determination of analytes by oxidation-reductions titrations. 3. Ion-specific electrodes (e.g., pH electrodes, etc.) 4. Gas-sensing probes. 5. Electrogravimetric analysis: oxidizing or reducing analytes to a known product and weighing the amount produced 6. Coulometric analysis: measuring the quantity of electrons required to reduce/oxidize an analyte II. Terminology A. Reduction: the gaining of electrons B. Oxidation: the loss of electrons C. Reducing agent (reductant): species that donates electrons to reduce another reagent. (The reducing agent get oxidized.) D. Oxidizing agent (oxidant): species that accepts electrons to oxidize another species. (The oxidizing agent gets reduced.) E. Oxidation-reduction reaction (redox reaction): a reaction in which electrons are transferred from one reactant to another. 1. For example, the reduction of cerium(IV) by iron(II): Ce4+ + Fe2+ ! Ce3+ + Fe3+ a. The reduction half-reaction is given by: Ce4+ + e- ! Ce3+ b. The oxidation half-reaction is given by: Fe2+ ! e- + Fe3+ 2. The half-reactions are the overall reaction broken down into oxidation and reduction steps. 3. Half-reactions cannot occur independently, but are used conceptually to simplify understanding and balancing the equations. III. Rules for Balancing Oxidation-Reduction Reactions A. Write out half-reaction "skeletons." Page 2 of 8 Chem 201 Winter 2006 + - B. Balance the half-reactions by adding H , OH or H2O as needed, maintaining electrical neutrality.
    [Show full text]
  • All-Carbon Electrodes for Flexible Solar Cells
    applied sciences Article All-Carbon Electrodes for Flexible Solar Cells Zexia Zhang 1,2,3 ID , Ruitao Lv 1,2,*, Yi Jia 4, Xin Gan 1,5 ID , Hongwei Zhu 1,2 and Feiyu Kang 1,5,* 1 State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China; [email protected] (Z.Z.); [email protected] (X.G.); [email protected] (H.Z.) 2 Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 3 School of Physics and Electronic Engineering, Xinjiang Normal University, Urumqi 830046, Xinjiang Province, China 4 Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094, China; [email protected] 5 Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong Province, China * Correspondences: [email protected] (R.L.); [email protected] (F.K.) Received: 16 December 2017; Accepted: 20 January 2018; Published: 23 January 2018 Abstract: Transparent electrodes based on carbon nanomaterials have recently emerged as new alternatives to indium tin oxide (ITO) or noble metal in organic photovoltaics (OPVs) due to their attractive advantages, such as long-term stability, environmental friendliness, high conductivity, and low cost. However, it is still a challenge to apply all-carbon electrodes in OPVs. Here, we report our efforts to develop all-carbon electrodes in organic solar cells fabricated with different carbon-based materials, including carbon nanotubes (CNTs) and graphene films synthesized by chemical vapor deposition (CVD). Flexible and semitransparent solar cells with all-carbon electrodes are successfully fabricated.
    [Show full text]
  • A Review of Cathode and Anode Materials for Lithium-Ion Batteries
    A Review of Cathode and Anode Materials for Lithium-Ion Batteries Yemeserach Mekonnen Aditya Sundararajan Arif I. Sarwat IEEE Student Member IEEE Student Member IEEE Member Department of Electrical & Department of Electrical & Department of Electrical & Computer Engineering Computer Engineering Computer Engineering Florida International University Florida International University Florida International University Email: [email protected] Email: [email protected] Email: [email protected] Abstract—Lithium ion batteries are one of the most technologies such as plug-in HEVs. For greater application use, commercially sought after energy storages today. Their batteries are usually expensive and heavy. Li-ion and Li- based application widely spans from Electric Vehicle (EV) to portable batteries show promising advantages in creating smaller, devices. Their lightness and high energy density makes them lighter and cheaper battery storage for such high-end commercially viable. More research is being conducted to better applications [18]. As a result, these batteries are widely used in select the materials for the anode and cathode parts of Lithium (Li) ion cell. This paper presents a comprehensive review of the common consumer electronics and account for higher sale existing and potential developments in the materials used for the worldwide [2]. Lithium, as the most electropositive element making of the best cathodes, anodes and electrolytes for the Li- and the lightest metal, is a unique element for the design of ion batteries such that maximum efficiency can be tapped. higher density energy storage systems. The discovery of Observed challenges in selecting the right set of materials is also different inorganic compounds that react with alkali metals in a described in detail.
    [Show full text]
  • A Highly-Active, Stable and Low-Cost Platinum-Free Anode Catalyst Based on Runi for Hydroxide Exchange Membrane Fuel Cells
    ARTICLE https://doi.org/10.1038/s41467-020-19413-5 OPEN A highly-active, stable and low-cost platinum-free anode catalyst based on RuNi for hydroxide exchange membrane fuel cells Yanrong Xue1,2,5, Lin Shi3,5, Xuerui Liu1,2, Jinjie Fang1,2, Xingdong Wang2, Brian P. Setzler3, Wei Zhu 2, ✉ ✉ Yushan Yan 1,3 & Zhongbin Zhuang 1,2,4 1234567890():,; The development of cost-effective hydroxide exchange membrane fuel cells is limited by the lack of high-performance and low-cost anode hydrogen oxidation reaction catalysts. Here we report a Pt-free catalyst Ru7Ni3/C, which exhibits excellent hydrogen oxidation reaction activity in both rotating disk electrode and membrane electrode assembly measurements. The hydrogen oxidation reaction mass activity and specific activity of Ru7Ni3/C, as measured in rotating disk experiments, is about 21 and 25 times that of Pt/C, and 3 and 5 times that of PtRu/C, respectively. The hydroxide exchange membrane fuel cell with Ru7Ni3/C anode can −2 −2 deliver a high peak power density of 2.03 W cm in H2/O2 and 1.23 W cm in H2/air (CO2-free) at 95 °C, surpassing that using PtRu/C anode catalyst, and good durability with less than 5% voltage loss over 100 h of operation. The weakened hydrogen binding of Ru by alloying with Ni and enhanced water adsorption by the presence of surface Ni oxides lead to the high hydrogen oxidation reaction activity of Ru7Ni3/C. By using the Ru7Ni3/C catalyst, the anode cost can be reduced by 85% of the current state-of-the-art PtRu/C, making it highly promising in economical hydroxide exchange membrane fuel cells.
    [Show full text]
  • Galvanic Cell Notation • Half-Cell Notation • Types of Electrodes • Cell
    Galvanic Cell Notation ¾Inactive (inert) electrodes – not involved in the electrode half-reaction (inert solid conductors; • Half-cell notation serve as a contact between the – Different phases are separated by vertical lines solution and the external el. circuit) 3+ 2+ – Species in the same phase are separated by Example: Pt electrode in Fe /Fe soln. commas Fe3+ + e- → Fe2+ (as reduction) • Types of electrodes Notation: Fe3+, Fe2+Pt(s) ¾Active electrodes – involved in the electrode ¾Electrodes involving metals and their half-reaction (most metal electrodes) slightly soluble salts Example: Zn2+/Zn metal electrode Example: Ag/AgCl electrode Zn(s) → Zn2+ + 2e- (as oxidation) AgCl(s) + e- → Ag(s) + Cl- (as reduction) Notation: Zn(s)Zn2+ Notation: Cl-AgCl(s)Ag(s) ¾Electrodes involving gases – a gas is bubbled Example: A combination of the Zn(s)Zn2+ and over an inert electrode Fe3+, Fe2+Pt(s) half-cells leads to: Example: H2 gas over Pt electrode + - H2(g) → 2H + 2e (as oxidation) + Notation: Pt(s)H2(g)H • Cell notation – The anode half-cell is written on the left of the cathode half-cell Zn(s) → Zn2+ + 2e- (anode, oxidation) + – The electrodes appear on the far left (anode) and Fe3+ + e- → Fe2+ (×2) (cathode, reduction) far right (cathode) of the notation Zn(s) + 2Fe3+ → Zn2+ + 2Fe2+ – Salt bridges are represented by double vertical lines ⇒ Zn(s)Zn2+ || Fe3+, Fe2+Pt(s) 1 + Example: A combination of the Pt(s)H2(g)H Example: Write the cell reaction and the cell and Cl-AgCl(s)Ag(s) half-cells leads to: notation for a cell consisting of a graphite cathode - 2+ Note: The immersed in an acidic solution of MnO4 and Mn 4+ reactants in the and a graphite anode immersed in a solution of Sn 2+ overall reaction are and Sn .
    [Show full text]
  • Solid Electrolyte Batteries
    SOLID ELECTROLYTE BATTERIES John B. Goodenough and Yuhao Lu Texas Materials Institute The University of Texas at Austin Project ID: ES060 DOE Vehicle Technologies Annual Merit Review Meeting May 9-13, 2011 This presentation does not contain any proprietary or confidential information. 1 The University of Texas at Austin Overview Timeline Barriers • Project Start Date-Oct. 2009 • Lithium-ion solid electrolyte. • Project End Date- Sept. 2010 • Choice of redox couples. • Percent complete: 100% complete • Flow-through- cathode cell design Budget Partners • Funding received in FY09-FY10 – $315K • Karim Zaghib of Hydro Quebec • Funding received in FY10-FY11 – $315K 2 The University of Texas at Austin Milestones Develop and test a suitable test cell. (Jan. 10) Completed Optimize components of the cell. (Apr. 10) Completed Develop a lithium/Fe(NO3)3 cell. (July. 10) Completed Design of a new cell (Sept. 10) Completed Test flow-through cell (Jan. 11) Completed 3 The University of Texas at Austin Typical Lithium Ion Battery (LIB) Cell e- e- - Separator + Li+ Anode Li+ Cathode (Reducing Agent) (Oxidizing Agent) Li+ SEI layer Electrolyte Capacity limited by Li solid solution in cathode and loss in SEI layer Voltage limited by Eg of carbonate electrolyte. 4 The University of Texas at Austin Why Oxides? E E Co: 4s0 Co: 4s0 Co(II): t4e2 µLi 4.0 eV Co(IV): t5e0 EFC EFC (pinned) Co(III): t6e0 Co(III): t6e0 O: 2p6 O: 2p6 N(E) N(E) Li CoO (0<x<0.55) LiCoO2 1-x 2 2- + Holes form peroxide (O2) for x> 0.55 or H inserted from electrolyte.
    [Show full text]
  • Nickel-Metal Hydride Batteries: a New Generation of Secondary Storage
    8 Nickel-Metal Hydride Batteries: A New Generation of Secondary Storage Brian Niece Literature Seminar September 23, 1993 Interest in secondary batteries suitable for use in electric vehicles has increased rapidly in the last decade, as restrictions on vehicle emissions in urban areas have become more stringent. Combustion of fossil fuels in large power plants and storage of the energy electrochemically is more efficient than direct combustion in internal combustion engines [1]. In addition, storage batteries can be charged from alternative sources of electricity, such as solar and hydroelectric plants. In order to be acceptable for use in an electric vehicle, a battery must meet a number of important criteria. It must have a high energy density to make the travel distance between recharges as long as possible. It must be capable of high power output throughout its dis­ charge cycle to provide the high current necessary to operate a vehicle, and it must be capa­ ble of especially high peak power for acceleration. The battery must also have a long cycle life as well as a long physical lifetime. It must not undergo rapid self discharge on standing. Finally, it must not be prohibitively expensive. Theoretical energy densities of secondary battery systems in common use are listed in Table 1. Most of these systems are not practical for electric vehicle use for a variety of rea­ sons. The lead-sulfuric acid battery cannot be sealed, and cannot be produced with a suffi­ ciently high energy density. The sodium-sulfur cell is undesirable because it contains metal­ lic sodium and operates at 300°C.
    [Show full text]
  • Chapter 13: Electrochemical Cells
    March 19, 2015 Chapter 13: Electrochemical Cells electrochemical cell: any device that converts chemical energy into electrical energy, or vice versa March 19, 2015 March 19, 2015 Voltaic Cell -any device that uses a redox reaction to transform chemical potential energy into electrical energy (moving electrons) -the oxidizing agent and reducing agent are separated -each is contained in a half cell There are two half cells in a voltaic cell Cathode Anode -contains the SOA -contains the SRA -reduction reaction -oxidation takes place takes place - (-) electrode -+ electrode -anions migrate -cations migrate towards the anode towards cathode March 19, 2015 Electrons move through an external circuit from the anode to cathode Electricity is produced by the cell until one of the reactants is used up Example: A simple voltaic cell March 19, 2015 When designing half cells it is important to note the following: -each half cell needs an electrolyte and a solid conductor -the electrode and electrolyte cannot react spontaneously with each other (sometimes carbon and platinum are used as inert electrodes) March 19, 2015 There are two kinds of porous boundaries 1. Salt Bridge 2. Porous Cup · an unglazed ceramic cup · tube filled with an inert · separates solutions but electrolyte such as NaNO allows ions to pass 3 through or Na2SO4 · the ends are plugged so the solutions are separated, but ions can pass through Porous boundaries allow for ions to move between two half cells so that charge can be equalized between two half cells 2+ 2– electrolyte: Cu (aq), SO4 (aq) 2+ 2– electrolyte: Zn (aq), SO4 (aq) electrode: zinc electrode: copper March 19, 2015 Example: Metal/Ion Voltaic Cell V Co(s) Zn(s) Co2+ SO 2- 4 2+ SO 2- Zn 4 Example: A voltaic cell with an inert electrode March 19, 2015 Example Label the cathode, anode, electron movement, ion movement, and write the half reactions taking place at each half cell.
    [Show full text]
  • Electrochemistry –An Oxidizing Agent Is a Species That Oxidizes Another Species; It Is Itself Reduced
    Oxidation-Reduction Reactions Chapter 17 • Describing Oxidation-Reduction Reactions Electrochemistry –An oxidizing agent is a species that oxidizes another species; it is itself reduced. –A reducing agent is a species that reduces another species; it is itself oxidized. Loss of 2 e-1 oxidation reducing agent +2 +2 Fe( s) + Cu (aq) → Fe (aq) + Cu( s) oxidizing agent Gain of 2 e-1 reduction Skeleton Oxidation-Reduction Equations Electrochemistry ! Identify what species is being oxidized (this will be the “reducing agent”) ! Identify what species is being •The study of the interchange of reduced (this will be the “oxidizing agent”) chemical and electrical energy. ! What species result from the oxidation and reduction? ! Does the reaction occur in acidic or basic solution? 2+ - 3+ 2+ Fe (aq) + MnO4 (aq) 6 Fe (aq) + Mn (aq) Steps in Balancing Oxidation-Reduction Review of Terms Equations in Acidic solutions 1. Assign oxidation numbers to • oxidation-reduction (redox) each atom so that you know reaction: involves a transfer of what is oxidized and what is electrons from the reducing agent to reduced 2. Split the skeleton equation into the oxidizing agent. two half-reactions-one for the oxidation reaction (element • oxidation: loss of electrons increases in oxidation number) and one for the reduction (element decreases in oxidation • reduction: gain of electrons number) 2+ 3+ - 2+ Fe (aq) º Fe (aq) MnO4 (aq) º Mn (aq) 1 3. Complete and balance each half reaction Galvanic Cell a. Balance all atoms except O and H 2+ 3+ - 2+ (Voltaic Cell) Fe (aq) º Fe (aq) MnO4 (aq) º Mn (aq) b.
    [Show full text]
  • Hydrogen Storage Alloys
    www.aladdin-e.com Address:800 S Wineville Avenue, Ontario, CA 91761,USA Website:www.aladdin-e.com Email USA: [email protected] Email EU: [email protected] Email Asia Pacific: [email protected] Hydrogen storage alloys Hydrogen storage alloys are important for a few voltage (with respect to the counter electrode) is electrochemical applications, especially in the applied to the metal/metal hydride electrode energy storage area. The basic of current collector, and electrons enter the metal electrochemical use of the hydrogen storage through the current collector to neutralize the alloy can be described as follows: when protons from the splitting of water that occurs at hydrogen enters the lattice of most transition the metal/electrolyte interface (Figure 1a). This metals, interstitial metal hydride (MH) is formed. electrochemical charging process is The electrons accompanying the hydrogen atoms characterized by the half reaction: form a metal-hydrogen band right below the Fermi level, which indicates that the interstitial (1) MH is metallic in nature. While protons in the interstitial MH hop between neighboring During discharge, protons in the MH leave the occupation sites by quantum mechanical surface and recombine with OH− in the alkaline tunneling, the electrons remain within a short electrolyte to form H2O, and charge neutrality distance (3–10 angstroms) of the protons to pushes the electrons out of the MH through the maintain local charge neutrality. Under the current collector, performing electrical work in the influence of an electric field, electrons and attached circuitry (Figure 1b). The protons will move in opposite directions. In an electrochemical discharge process is given by electrochemical environment, a voltage is applied the half reaction: to cause electrons to flow, and the charges are balanced out by moving conductive ions through (2) a highly alkaline aqueous electrolyte with good ionic conductivity.
    [Show full text]