battery and energy density Flashcards

Question

Fuel cells

Answer 1

Galvanic cell which converts chemical energy of a fuel oxidant system directly into electrical energy by means of redox reactions Do not store energy but convert chemical energy in the fuel to electrical energy * Fuel and oxidising agents have to be continuously supplied at the respective electrodes * Generate power as long as the electroactive material is supplied

Answer 2

H2, CO, CH3OH(methyl alcohol), C2H5OH (ethanol), HCHO(formaldehyde/ methanal), N2H4(Hydrazine)

Answer 3

O2 ,H2O2, halogens

Answer 4

ADV High power efficiency (about 50 - 80% ) * Ecofriendly - products formed are not toxic * Silent operation DIS Cost of the power is high as a result of the use of expensive electrodes and catalysts * Power out put is moderate * Fuels in the form of gases and oxygen need to be stored in tanks under high pressure

Answer 5

Space exploration; as auxiliary power generators in space vehicles * Vehicle traction for cars, buses and commercial vehicles * Large scale power generation

Answer 6

Thermodynamic efficiency the ratio of work output (ΔG) to heat input (ΔH)

Answer 7

Anode : Porous carbon impregnated with Pt catalyst * Cathode : Porous carbon impregnated with Ag catalyst * Fuel : Hydrogen gas * Oxidant : Oxygen gas * Electrolyte : 30-45 % KOH(warm)

Answer 8

Aqueous solution of KOH is used as electrolyte * Low temperature fuel cell (operates at 100 C) * Oxygen reduction is more rapid than in acid electrolytes * Use of non noble metal electro-catalyst is feasible * Carbon containing fuels cannot be used as CO2 + KOH, to form K2CO3 => reduced efficiency of cell

Answer 9

* H2 gas diffuses through anode ,gets adsorbed on the electrode surface ,reacts with OH- to form water * At cathode O2 diffuses through electrode, is adsorbed and reduced to OH- * Product is water which dilutes the KOH * Cell operates at 100oC, so that water from KOH escapes as steam *The water was used by astronauts for drinking on Apollo spacecraft Emf = 1.23 V

Answer 10

ADV Operates at low temperature * Alkali is used as electrolyte hence non noble metal catalyst can be used so less expensive DIS Reactants must be free from C, because on oxidation CO2 is formed .alkali reacts with CO2 to form carbonates = reduced efficiency of the cells; pure fuel and oxidant which are free of carbon compounds must be used * Liquid electrolytes pose handling problems

Answer 11

Concentrated phosphoric acid is used as electrolyte * Intermediate temperature(160 – 220C) * Platinum is used as electro-catalyst * Use only H2 as fuel * H2 used as fuel must be very pure as sulphur compounds and CO poison the Pt catalyst

Answer 12

(mixture of LiAlO2 + K2CO3 +Li2CO3) used as electrolyte * High temperature fuel 600 – 650C) * Catalyst is not required since it operates at high temperature * H2 or CO can be used as fuel

Answer 13

Known as proton exchange membrane fuel cell * Polymer membrane or proton exchange membrane is used as electrolyte *Fluorocarbon backbone (-CF2-CF2-) similar to Teflon to which sulphonic acid groups(-SO3H) are attached. The protons on sulphonic acid group are free to migrate through the hydrated membrane. e.g., (A) Aquivion and (B)Nafion *New membranes are being used especially when CH3OH is used as fuel - Polyelectrolyte membranes e.g., SPEEK - sulphonated poly(ether ether ketone) *Low temperature fuel cell ( 60- 90 °C ) *Polymer membrane must remain hydrated to maintain H+ conductivity *Water produced from the reaction must be removed from the cathode * High temperatures may dehydrate the polymer so H+ conductivity cannot take place and the polymer may degrade and crack resulting in short circuit * Low temperatures will result in flooding of the cell thereby reducing efficiency of the cell and a higher catalyst loading will be required *Low weight and volume * High energy density * Noble metal catalyst usually Pt is used * CO, if present poisons the catalyst , so pure fuel and oxidant should be used

Answer 14

* Ceramic oxide capable of conducting oxide ions is used as electrolyte, e.g. ZrO2 doped with Y2O3 * Very high temperature fuel cell (operates at 650 - 1000oC) * Due to high temperature , expensive catalyst need not be used * CO can also be used as a fuel * Slow start - up

Answer 15

ability to store energy in the form of electrical charge * Has two conducting plates separated by a dielectric * When a DC voltage is connected across the capacitor, one plate becomes +,- * charge accumulation on the plates causes a voltage or p. d across the capacitor

Answer 16

the charge accumulation capability of a capacitor * Charge (Q) proportional to (V) Q = C × V C ∝ A/d

Answer 17

AKA ultra capacitors or electrochemical double-layer capacitors(EDLC) energy storage devices that have high capacitance used to store large amounts of electrical charge * Charge and discharge very quickly * Capacitance is several thousand times that of a Capacitor

Answer 18

Electrodes: high surface area materials such as porous carbon, graphene, carbon nanotubes and certain conducting polymers or carbon aerogel Electrolyte: KOH, H2SO4, Na2SO4 Separator: an ion permeable separator is placed between the electrodes in order prevent electrical contact, but still allows ions from electrolyte to pass through e.g., porous polypropylene

Answer 19

Separator is sandwiched btw the electrodes This is placed into a case , impregnated with electrolyte and sealed The electrodes are flanked with current collectors

Answer 20

When a potential is applied, the positive electrode attracts negative ions in the electrolyte, while negative electrode attracts the positive ions * Formation of electrical double layer at entire electrode /electrolyte interface with a charge separation in nanometer scale Only absorption and desorption of ions takes place at the electrode during charging and discharging no redox reactions * Distance between the charged layers in d very small and use of porous electrodes gives very high surface area , A is large C ∝ A/d thus C is HIGH

Answer 21

ADV Rapid charging; charge in a few seconds * High power density as they discharge very fast * High cycle life, can be cycled millions of time * Safe as extremely low internal resistance and extremely low heating rates DIS Low energy density High self discharge Linear discharge voltage High cost Power available for a short duration

Answer 22

Memory back-up * Hybrid cars for start-stop application * Flash photography devices in digital cameras, flash lights, portable media players * As an intermediate energy storage for FM radios, cell phones, and emergency kits

Answer 23

Energy density (Wh/kg) is plotted against Power density (W/kg) * To compare performance of various energy storage devices * Since it uses a double-logarithmic chart, storage technologies with very different storage properties can be compared in one plot

Answer 24

Fuel cells have high energy density as the electroactive species can be continuously supplied but the power density is low due to slow kinetics of redox reactions at electrodes * Battery systems offer moderate energy density and power density. * Ultracapacitors (supercapacitors) can deliver very high power density as they can discharge a large amount of charge quickly (because no redox reaction is involved) but energy density is very limited because the charge cannot be stored for a long time

Answer 25

Sustainable production of Hydrogen from renewable feedstocks and electrolysis of water ADV Abundant in crust Compatibility with fuel cell High efficiency (65%) DIS * High cost * Highly flammable dependent on fossil fuels

Answer 26

Natural gas => produce Hydrogen * Most widespread process

Answer 27

Coal => CO2 => gasification process => CO => water gas shift process =>CO2 and H2 => purified pure H2

Answer 28

thermochemical water splitting at 500C – 2000C in a closed system

Answer 29

light energy => split water potential for sustainable hydrogen production * Low environmental impact * Yet in early stage of research

Answer 30

electricity => water takes place in a unit = electrolyzer carbon-free hydrogen production from renewable and nuclear resources.

Answer 31

* Desulphurization: sulpher removed from feedstocks => poisons catalysts in steam reforming Steam reforming: Steam, fuel and air in the reform chamber in presence of catalyst form syngas CH4 + H2O → CO + 3 H2 850-900C * Ni catalyst * Endothermic reaction * High temperature and low pressure is favoured

Answer 32

CO + H2O → CO2 + H2 * Catalyst: Fe3O4/Cr2O3 * Exothermic reaction * Favoured at low temperature (350C) * H2=traces of CO * CO2 is removed => pure H2 * CO removed by methanation (350 – 450C) * CO + 3H2O → CH4 + H2O

Answer 33

ADV higher yield H2 (50%) * Heat generated = recycled to increase efficiency * Relatively stable during process DIS High level of carbonaceous materials are formed * External heat source is needed to initiate the reaction

Answer 34

Electricity = splitting the H2 and O2 in their gaseous phase 0 emission of CO2 (if this process combined with renewable energy sources like electricity form solar or wind energy) * Electrolysis requires needs DC supply Splitting of water is very small approximately 7- 10 moles/ litre pure water is the very poor conductor of electricity hence acid (H2SO4 in acid electrolyzer) or base (KOH or NaOH in Alkaline electrolyzer) used to improve the conductivity * Solutions split into ions, improving conductivity of the electrolyte. aqueous solution containing either NaOH or KOH used concentration of 20-40 % * 343 – 363 K * up to 3 MPa * Charge carrier: OH- * Anodic materials: Ni and its alloys * Cathodic materials: Cd, Pb, Cu, Ag, Pt, Pd. * Electrolyte materials : KOH, NaOH * Catalyst materials: Ni-Zn, Ni-Co-Au, RuO2, LaCoO3

Answer 35

Adv * No harmful emission * Clean hydrogen * 0 greenhouse gas * Used in Fuel cells DIS * Cost of production is high * Efficiency is low * Need high power source * Storage is challenge

Answer 36

(350–700 bar tank pressure => H2 gas −252.8°C at an ATM pressure => liquid

Answer 37

2 categories: chemisorption: (absorption into matter), binding of hydrogen atoms occur into the surface physisorption (adsorption on surface) H2 molecule is bound onto the surface of adsorbent

Answer 38

a novel class of porous materials unique pore structure high density energy storage of clean fuel gas EXAMPLES Zn-MOF (MOF-5), UiO-66, MIL-53(Al), MIL-101(Cr)

Answer 39

safe and economical large-scale transoceanic transportation and long-cycle hydrogen storage used as storage media for hydrogen Organic compounds that can absorb-release H2 through chemical reactions * Methyl cyclopentane * Dibenzyl toluene

Answer 40

a larger quantity of H2 for volume of liquid hydrogen * Certain interstitial hydrides are very suitable for H2 storage and transportation * Example: LiNi5H6

Answer 41

Composed of metal cations (such as Li, Mg, Na, etc.) and hydrogen-containing coordination anions (such as AlH4–, NH2–, BH4– ) * On heating, the metallic hydride decomposes= H2 and finely divided metal Ex: Sodium aluminate => 7.4% of H2 when heated at 200C

Answer 42

H2 => thru chemical reaction and restored * Ammonia Borane (NH3 -BH3 ) * Hydrolysis of NH3-BH3 = H2 stored in it in presence of catalyst

Answer 43

detects and responds to input from the physical environment. could be light, heat, motion, moisture, pressure, or can be any molecule or substance such as analytes

Answer 44

Galium arsenide, Ge, Si, solar cell,

Answer 45

piezo electric materials

Answer 46

platinum foils, conductivity measured in aq solutions

Answer 47

detect any type of metal plastic, wood, paper, glass, and cloth

Answer 48

Thermocouple, Thermister, and semi-conductor based IC's

Answer 49

change in enthaply of chemicals substance

Answer 50

Glucose sensor, measures current

Answer 51

for medical measures in oximeter, 2 lights with diff wavelength passed thru and absorbed in photo detector or the other side

Answer 52

interaction btw analyte and electrolyte interaction -> electric signal electrode = transducer

Answer 53

effect of conc on equilibrium of redox found analyte concentration by measuring the variation of p.d between working and reference electrodes

Answer 54

Glass electrodes (e.g. pH-meter, Na+, K+, Li+ Sensors * Solid membrane electrodes (e.g. based on AgX for X ,and Ag2S for other M+), Liquid membrane electrodes (e.g. containing a ligand for M+ complexation e.g. Ca2+ and K+ sensors).

Answer 55

pH-meter-based gas detectors (e.g. CO2, NH3 etc). * Solid oxide sensors (e.g. zirconia-based O2 sensor (λsensor)

Answer 56

detect various analytes qualitatively and quantitatively Easy to Construct and operate, more accuracy, sensitive and highly selective determination * Smaller Volumes of analytes can be estimated * Economically Viable DIS Requires calibration During estimation * impurities can affect the P.D Values * By varying the temp p.d also varies.

Answer 57

measures current to detect analyte concentration at fixed pd pd => electron transfer due to reactions of analytes => amount of current = analyte concentration quantifies current output btw Working and the reference electrode 3 electrodes: working, auxiliary, and reference electrode reference electrode (Ag/AgCl, Hg/Hg2Cl2) provides a stable pd compared to the working electrode inert conducting material (e.g.; platinum,=auxiliary electrode. supporting electrolyte is used in controlled potential experiments to eliminate electromigration effects, decrease the resistance of the solution and maintain the ionic strength constant.

Answer 58

used for estimation of reducible and non-reducible (Mg2+, PO43-, SO42- ) analytes More accurate and sensitive Traces of reducible species can be found accurately Simple to operate and Easy to Construct DIS Working pd should be for limited time or damage to electrode Coprecipitation gives inaccurate results cannot be used with applied voltage more -2V as hydrogen will be evolved Consumes more time to remove dissolved oxygen

Answer 59

measures the proportion of O2 in the gas or liquid being analysed Divers use to measure partial pressure of O2 in their breathing gas * Scientists use as probes to measure respiration or production of O2 * O2 analyzers used in medical applications such as anesthesia monitors, respirators etc * Used to measure exhaust gas concentrations of O2 in IC engines

Answer 60

air/fuel ratio ideal for combustion of gasoline is 14.7:1 * in the exhaust stream and * O2 sensor allows engine control system to maintain ideal ratio * compares O2 in the exhaust to O2 in atmosphere voltage =diff in O2 concentration in the exhaust and atmosphere 0.2V lean mixture 0.8V rich mixture Ideal 0.45 V V is sent as feedback to Engine control unit * Lean mixture: more of NOX emissions * Rich mixture: more of CO , C particles and unburnt fuel emissions * Based on solid state electrochemical fuel cell * Operates at a minimum temperature of 360C * Automobiles fitted with O2 sensor must use unleaded gasoline as lead poisons the Pt catalyst and reduces its efficiency * Symptoms of failure are – increased tail pipe emissions, increased fuel consumption and hesitation on acceleration

Answer 61

to find presence and concentration of a specific substance in a biological analyte.

Answer 62

Anode : Pt Cathode : Pt Electrolyte : Zirconium oxide (ZrO2 ) doped with Yttrium oxide (Y2O3 ) P1 and P2 are the partial pressures of O2 in reference air and exhaust gas respectively

Answer 63

* Analyte * Bioreceptor * Transducer * Electronics and display number of electron transfers, at electrode surface is directly proportional to the number of glucose molecules present in the blood.

Answer 64

Extreme environmental conditions like haematocrit values, or medication interferences may potentially falsify blood glucose readings.

battery and energy density Flashcards

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