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C12 > Fuel Cells as a Source of Energy > Flashcards

Fuel Cells as a Source of Energy Flashcards

1
Q

State what fuel cells use to generate electricity

A

Chemical energy of hydrogen or other fuels to cleanly and efficiently generate electricity.

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2
Q

State whether or not a fuel cell is a type of galvanic cell

A

Yes.

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3
Q

State whether or not fuel cells run down or need recharging

A

No

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4
Q

Electricity is available for as long as fuel cells are supplied with…

A

Fuel

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5
Q

State what the major limitation of primary/secondary cells are

A

Cell must be discarded or recharged when the reaction reaches equillibrium

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6
Q

State an alternative term to describe primary and secondary cells

A

Galvanic cells

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7
Q

State the key difference between a fuel cell and a primary or secondary cell

A

Reactants do not have to be stored in the fuel cell, but must be continuously supplied from an external source.

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8
Q

State what fuel cells transform chemical energy into

A

Electrical energy

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9
Q

Compare and contrast the efficiency of fuel cells with thermal power stations

A

Fuel cells > Thermal Power Station Energy Efficiency because they directly convert chemical - electrical energy

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10
Q

State what a fuel cell employing hydrogen produces

A

Electricity, water, heat and very small amount of nitrogen dioxide and other emissions

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11
Q

State the 2 major parts of a fuel cell

A
  1. Hydrogen gas input

2. Oxygen gas input

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12
Q

State what the two gas compartments of a fuel cell are separated by

A

Two porous electrodes and an electrolyte solution

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13
Q

State what the electrode at the hydrogen compartment is termed

A

Anode

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14
Q

State what the electrode at the oxygen compartment is termed

A

Cathode

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15
Q

State what the electrodes within a fuel cell can be classified as

A

Porous

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16
Q

State whether the anode in a fuel cell is positively or negatively charged

A

Negatively

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17
Q

State whether the cathode in a fuel cell is positively or negatively charged

A

Positively

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18
Q

State what process occurs at the cathode of a fuel cell

A

Reduction

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19
Q

State what process occurs at the anode of a fuel cell

A

Oxidation

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20
Q

State how higher voltages can be obtained from fuel cells

A

Connecting a number of fuel cells in series to form a battery/fuel cell stack

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21
Q

State what the electrodes within a fuel cell must be

A
  • porous

- conducting

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22
Q

State why electrodes within a fuel cell must be both porous and conducting

A

Allow the hydrogen and oxygen to come into contact with the ions in the electrolyte and to allow the redox half reactions to occur at their surface.

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23
Q

State what the size of the current that can be drawn from a fuel cell depends upon

A

The surface area of the electrodes

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24
Q

State why catalysts are employed within fuel cells

A

To increase the rate of reaction and the current that can be produced from a cell

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25
Q

Outline the purpose of porous electrodes

A

Allow reactants to diffuse through them to react with ions in the electrolyte

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26
Q

State what fuel most fuel cells are designed to use

A

Hydrogen

27
Q

State what a fuel cell using hydrogen as a fuel source can be described as

A

A ‘zero-emission’ device

28
Q

State whether the production of hydrogen can result in the production of significant levels of greenhouse gases/pollutants

A

Yes. Especially if produced via steam reforming (of natural gas, oil or coil)

29
Q

State 2 practical methods of harvesting hydrogen gas sustainably

A
  1. Using electrical energy to convert water to hydrogen (electricity can be generated from renewable sources such as solar-power farms and wind farms)
  2. Collecting biogas from landfill sites and converting the methane to hydrogen via steam reforming
30
Q

State what the widespread adoption of hydrogen as a primary fuel source would require

A

Massive expenditure on infrastructure

31
Q

State the major reasons supporting challenges associated with hydrogen gas storage

A

Hydrogen is a gas at room temperature

32
Q

State what temperature liquid hydrogen generally boils at

A

Extremely low temperatures

33
Q

State whether a large or small quantity of energy is needed to liquify hydrogen

A

Large quantity

34
Q

State what the requirements of a hydrogen gas tank are

A

Good insulation

35
Q

State whether or not hydrogen gas must be stored in high pressure tanks

A

Yes. Hydrogen gas must be stored in high pressure tanks,

36
Q

State why hydrogen gas pressure tanks must be so large to effectively replace a standard hydrocarbon fuel tank

A

High pressure hydrogen storage tanks need to be large to meet the energy availability within smaller hydrocarbon fuel tanks

37
Q

Compare and contrast the energy availability of liquid hydrogen and a liquid hydrocarbon (e.g. petrol)

A

Petrol has a energy availability of four times greater

38
Q

State what hydrogen can absorb to

A

The surface of materials such as metal hydrides, either as hydrogen molecules or as hydrogen atoms

39
Q

State whether or not hydrogen can dissociate

A

Yes

40
Q

State what hydrogen would dissociate and become absorbed into

A

Lattice structure of some solid materials

41
Q

State whether or not hydrogen can react reversibly with a range of different chemicals

A

Yes.

42
Q

Provide reasons supporting the levels of danger associated with hydrogen

A

Hydrogen burns more readily and a flame/spark will ignite almost any combination of hydrogen and air

43
Q

State what the low density of hydrogen means for its levels of flammability

A

Low density means that hydrogen can rise rapidly and quickly disperse in ventilated areas - often without ignition

44
Q

Compare and contrast danger associated with a fire in a petrol powered vehicle vs a hydrogen powered vehicle

A

Hydrogen-powered vehicle is less dangerous due to low density of hydrogen gas

45
Q

Compare and contrast the fuel efficiency and emissions of fuel cells with internal combustion engines

A

Higher fuel efficiency and lower emissions overall from fuel cells

46
Q

State what fuel cells convert chemical energy directly into

A

Electrical energy

47
Q

State why the electrical energy conversion in fuel cells is more efficient than the series of energy conversions that take place in power stations

A

Fuel cells: chemical - electrical energy

Power stations: chemical - heat - mechanical - electrical energy

48
Q

State what hydrogen fuel cells produce as by products

A

Water and heat

49
Q

State whether any greenhouse gases are released from hydrogen fuel cells

A

No greenhouse gases are released

50
Q

State for how long fuel cells will generate electricity

A

As long as the fuel is supplied

51
Q

State whether or not fuel cells can use a variety of fuels

A

Yes

52
Q

State whether or not fuel cells are expensive.

A

Yes. Still a developing technology.

53
Q

State what alterations will be required for fuel cells to be used extensively for transport

A

Extensive network of hydrogen filling stations will need to be established

54
Q

State a possible disadvantage of fuel cells generation of DC current

A

Many electrical appliances in the home require AC current and an inverter is thus required to change DC to AC at the appropriate voltage.

55
Q

Identify a possible disadvantage associated with the sourcing of hydrogen for fuel cells

A

Mainly sourced from fossil fuels - which involves energy losses and generates greenhouse gases

56
Q

State the major disadvantage of using hydrogen fuel in fuel cells

A

Safety associated with storage of fuel

57
Q

Compare and contrast the function of primary/secondary cell with fuel cells

A

Primary/secondary cells - source of portable electrical energy
Fuel cells - continuous source of high electric current for portable/fixed applications

58
Q

Compare and contrasts the life of the reactants within primary/secondary cells and fuel cells

A

Primary/secondary cells - reactants in primary & secondary cells are contained and can thus be depleted
Fuel cells - air/oxygen are supplied continuously

59
Q

Compare and contrast the site of oxidation in primary/secondary cells and fuel cells

A

Primary/secondary cells - negatively charged anode

Fuel cells - negatively charged anode

60
Q

Compare and contrast the site of reduction in primary/secondary cells and fuel cells

A

Primary/secondary cells - positively charged cathode

Fuel cells - positively charged cathode

61
Q

Compare and contrast the porous region of primary/secondary cells and fuel cells

A

Primary/secondary cells - salt bridge

Fuel cells - porous electrodes

62
Q

Compare and contrast the position of the electrolyte for primary/secondary cells and fuel cells

A

Primary/secondary cells - salt bridge (carries charge between electrodes)
Fuel cells - between two porous electrodes (carries charge between electrodes)

63
Q

Compare and contrast the energy transformations of primary/secondary cells and fuel cells

A

Chemical - electrical energy

64
Q

Compare and contrast the energy efficiency of primary/secondary cells and fuel cells

A

Primary/secondary cells - 60-90% efficient

Fuel cells - 40-60% efficient

C12 (7 decks)

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