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climate change - renewables > Energy Storage - Batteries > Flashcards

Energy Storage - Batteries Flashcards

1
Q

Battery

A

A device converting stored chemical energy into electrical energy.

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2
Q

Structure of batteries?

A

Composed of electrochemical cells(Electrolytes, anode and cathode)

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3
Q

Electrolyte

A

A material, often in an aqueous solution, allowing ions to pass freely through but does NOT conduct free electrons.

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4
Q

Anode

A

Contain molecules readily ejecting one or more electrons by oxidizing and releasing the residual ion INTO the electrolyte.

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5
Q

Cathode

A

Molecules formed by reduction of ions from the electrolyte by combinding each ion with one or more electrons.

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6
Q

Most common electrochemical cell?

A

Daniel Cell

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7
Q

Daniel Cell

A

A copper-zinc cell beign cathode-anode, both being in sulfate solutiosn.

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8
Q

Mechanism of Daniel Cell

A

Anode zinc is ozidized where two electrosn flow from anode to cathode extenrally, releasing zinc ion into solution,
Electron interaction releases copper in the solution.

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9
Q

Why do daniel cell half-reactions occur spontaneously?

A

Net positive gibbs free energy.

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10
Q

Enthalpy of Reaction

A

Change in enthalpy of a chemical reaction that occurs at constant pressure.

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11
Q

What happens after copper ion release?

A

Sulfate ion in copper soltion transfers to zinc solutiion, balancing net flow of charge.

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12
Q

Calculating cell voltages of cells…

A

Combinding reduction potentials (-0.76 V for zinc and 0.34 V for copper.

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13
Q

Reduction Potential

A

Tendency of a chemical species to be reduced by gaining an electron.

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14
Q

Nernst Equation

A

Permits calculation of reduction potential of a reaction

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15
Q

What determines effective energy upper bound density of battery?

A

Voltage and Gibbs energy

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16
Q

Calculating energy density of daniel cell…

A

Mass of both one Zn and one Cu is 129u, equating to 1.65 MJ/kj, then divided GIBBS of 212 by 0.129kg

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17
Q

Primary Cell

A

One way flow from cathode to anode, being used only once.

18
Q

Secondary Cell

A

Can reverse flow, having multiple uses.

19
Q

Difference of fuel cell..

A

Continous flow of consumables entering the device.

20
Q

Mechanism of hydrogen fuel cell..

A

Input with H2, dissacoiated by catalysis at the cathode, hydrogen then passsing through electrolyte, combining with oxygen at anode

21
Q

Combustion

A

A series of chemical reactions that generate heat.

22
Q

Type of reaction fuel cell..

A

Combustion

23
Q

Energy of hydrogen fuel…

A

Enthalpy of reaction for combustion of H is 285.8kJ/mol whilst gibbs is 237.1 kJ/mol,, with 83% efficiency at 298K and 1 atm.

24
Q

H2 energy density…

A

140 MJ/kg or 120 MJ/kg with standard cell voltage of 1.229 V in reality this is 0.85-1.05

25
Q

Disadvantage of fuel cells…

A

Reacting with atmospheric CO2.

26
Q

Proton Exchange Membrane

A

A semipermeable membrane designed to conduct protons whilst acting as a electornic insulator and reactant barrier.

27
Q

Challenge with catalysis rate in fuel cells…

A

Platinum used at hydrogen/oxygen anode/cathode which is expensive.

28
Q

Hydrogen Economy

A

Refers to an economy relying on hydrogen as the commercial fuel that would deliver a substantial fraction of a natiosn energy and services.

29
Q

Hydrogen economy is based on…

A

Higher energy density and energy storage in hydrogne…

30
Q

Fromation of H2…

A

Not found naturally on Earth, an energy carrier, created by steam reforming.

31
Q

Steam Reforming

A

This reacts natural methane gas with steam in presence of a catalyst, producing H, CO and some CO2.

32
Q

Downside to steam reforming…

A

Produces CO2 so requries carbon capture.

33
Q

Alternative to steam reforming.

A

Electrolysis, splitting water into constituatens with differnet materials to fuel cells.

34
Q

Gas Diffusion Later in fuel cells…

A

Grants reactants access to catalyst with hydrophobic materials preventing water entry.

35
Q

Drawbacks to hydrogen storage…

A

At standard temperature/pressure, H2 has very low energy dnesity, taking up large volume, where compression is unsafe.

36
Q

Volumetric density of gasoline vs H2…

A

30 MJ/L whilst hydrogen at standard ATM and TEMP is 12 kJ/m^3

37
Q

Hydrogen gas often stored at…

A

700 ATM with 5.6MJ/L

38
Q

Alternative to hydrogen gas storage…

A

Liquified.

39
Q

Hydrogen liquified…

A

Liquifies at 20.28 K with 10 MJ/l energy density

40
Q

Liquified hydrogen is useful in…

A

Cryogenic tanks storage in space but not automobiles.

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