Energy Storage - Batteries

Question 1

Battery

Answer 1

A device converting stored chemical energy into electrical energy.

Question 2

Structure of batteries?

Answer 2

Composed of electrochemical cells(Electrolytes, anode and cathode)

Question 3

Electrolyte

Answer 3

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

Question 4

Anode

Answer 4

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

Question 5

Cathode

Answer 5

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

Question 6

Most common electrochemical cell?

Answer 6

Daniel Cell

Question 7

Daniel Cell

Answer 7

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

Question 8

Mechanism of Daniel Cell

Answer 8

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.

Question 9

Why do daniel cell half-reactions occur spontaneously?

Answer 9

Net positive gibbs free energy.

Question 10

Enthalpy of Reaction

Answer 10

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

Question 11

What happens after copper ion release?

Answer 11

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

Question 12

Calculating cell voltages of cells…

Answer 12

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

Question 13

Reduction Potential

Answer 13

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

Question 14

Nernst Equation

Answer 14

Permits calculation of reduction potential of a reaction

Question 15

What determines effective energy upper bound density of battery?

Answer 15

Voltage and Gibbs energy

Question 16

Calculating energy density of daniel cell…

Answer 16

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

Question 17

Primary Cell

Answer 17

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

Question 18

Secondary Cell

Answer 18

Can reverse flow, having multiple uses.

Question 19

Difference of fuel cell..

Answer 19

Continous flow of consumables entering the device.

Question 20

Mechanism of hydrogen fuel cell..

Answer 20

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

Question 21

Combustion

Answer 21

A series of chemical reactions that generate heat.

Question 22

Type of reaction fuel cell..

Answer 22

Combustion

Question 23

Energy of hydrogen fuel…

Answer 23

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.

Question 24

H2 energy density…

Answer 24

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

Question 25

Disadvantage of fuel cells...

Answer 25

Reacting with atmospheric CO2.

Question 26

Proton Exchange Membrane

Answer 26

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

Question 27

Challenge with catalysis rate in fuel cells...

Answer 27

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

Question 28

Hydrogen Economy

Answer 28

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

Question 29

Hydrogen economy is based on...

Answer 29

Higher energy density and energy storage in hydrogne...

Question 30

Fromation of H2...

Answer 30

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

Question 31

Steam Reforming

Answer 31

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

Question 32

Downside to steam reforming...

Answer 32

Produces CO2 so requries carbon capture.

Question 33

Alternative to steam reforming.

Answer 33

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

Question 34

Gas Diffusion Later in fuel cells...

Answer 34

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

Question 35

Drawbacks to hydrogen storage...

Answer 35

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

Question 36

Volumetric density of gasoline vs H2...

Answer 36

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

Question 37

Hydrogen gas often stored at...

Answer 37

700 ATM with 5.6MJ/L

Question 38

Alternative to hydrogen gas storage...

Answer 38

Liquified.

Question 39

Hydrogen liquified...

Answer 39

Liquifies at 20.28 K with 10 MJ/l energy density

Question 40

Liquified hydrogen is useful in...

Answer 40

Cryogenic tanks storage in space but not automobiles.