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Chemistry > Fuel Cells > Flashcards

Fuel Cells Flashcards

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1
Q

what does a fuel cell do? is it a galvanic cell?

A

produces electricity. it is a galvanic cell but has some different features

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2
Q

how is there a continuous supply of electricity?

A

there is a continuous supply of reactants. This is because the electrolyte is replenished by the half reactions so big volumes do not need to be provided

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3
Q

how efficient are fuel cells?

A

40-60% efficient

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4
Q

is a fuel cell expensive?

A

yes

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5
Q

what are the products of fuel cells?

A

water unless an organic fuel is being used in which water and carbon dioxide are produced

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6
Q

what are the reactants of an acidic fuel cell?

A

O2 gas and H2 gas

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7
Q

what is the electrolyte of acidic fuel cells?

A

H+, H2SO4, H3PO4, H3O+

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8
Q

what does the electrolyte do in a fuel cell?

A

govern the type of fuel cell and allow for the movement of charged ions

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9
Q

what is the anode of an acidic fuel cell?

A

H2

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10
Q

what is the cathode of an acidic fuel cell?

A

O2

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11
Q

what is an ammeter?

A

measures current (flow of electrons)

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12
Q

what is a voltmeter?

A

measures voltage (push on electrons)

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13
Q

what are the acidic fuel cell equations?

A

the ones with H+

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14
Q

what are the alkaline fuel cells?

A

the ones with OH- and water

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15
Q

what are the reactants of an alkaline fuel cell?

A

O2 and H2

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16
Q

what is the electrolyte of an alkaline fuel cell?

A

OH-

17
Q

what properties does an electrode have?

A

catalyst, inert, porous

18
Q

what are reactants of other; organic fuel cells?

A

CH4, O2

19
Q

what is the electrolyte of organic fuel cells

A

O2-

20
Q

what is the anode of an organic fuel cell?

A

organic fuel

21
Q

how to balance a straight forward alkaline equation?

A
  1. balance key elements
  2. balance OH-
  3. balance charge
22
Q

how to balance complex alkaline equations?

A
  1. add H+
  2. balance electrons
  3. add OH- to both sides to neutralise
  4. simplify or cancel down water
23
Q

why is a H2-O2 fuel cell zero emissions?

A

only water is produced

24
Q

to make H2-O2 fuel cells more zero emission making, what needs to happen?

A

H2 needs to be made in a renewable way. if made from a non-renewable source, it is not “zero emission”

25
Q

how is most hydrogen made?

A

95% from fossil fuels in a process called steam reforming

26
Q

what are the equations for steam reforming

A

CH4 (g) + H2O(g) —> (Ni solid as catalyst) CO(g) +3H2(g)

CO(g) + H2O(g) —–> (Fe or Cu solid as catalyst) CO2(g) + H2(g)

27
Q

steam reforming produces carbon dioxide, what argument still supports the fuel cell?

A

using fuel cell is still more green than using fossil fuels because it is 40-60% energy efficient compared to the 35% efficiency of fossil fuels (more heat loss and CO2 produced)

28
Q

what is another argument suggesting CO2 gas is ok?

A

can be collected for carbonating drinks

29
Q

how does electrolysis work? what is a criticism?

A

2H2O(l) —> O2(g) + 2H2(g)

  • water is precious
  • energy used to do this is expensive
30
Q

what is another way of making H2 gas?

A

collecting biogas from landfills and feeding it into steam reforming process

31
Q

what is a problem with hydrogen that would cause a need for changes?

A
  • highly flammable

- change pipelines and fuel stations

32
Q

what are two chemical properties of hydrogen?

A
  • energy content 143KJg-1 is higher than petrol 44KJg-1

- found as a gas at room temp

33
Q

describe how hydrogen can be stored as liquid?

A
  • H2 liquid boils at -225 and a lot of energy is needed to achieve this
  • need well insulated tank
  • energy from hydrogen 8MJL-1 is less than petrol 32MJL-1
  • therefore need to carry 4x more hydrogen than petrol so tank may need to be very large
34
Q

describe how hydrogen can be stored when compressed

A
  • stored under pressure (up to 700 bars)
  • tank needs to be larger to store the same amount of H2 liquid
  • tank would need to be as large as boot
35
Q

describe storing hydrogen with adsorb material storage

A

H2 sticks to the surface of metal hydrides as either H atoms or H2 molecules

36
Q

describe storing with absorption

A

H2 can dissociate and be absorbed by lattice structures (solid form)

37
Q

describe the last storing of hydrogen

A

H2 reacts with other chemicals- can react with many

38
Q

advantages of fuel cells

A
  • chemical energy directly into electrical energy which makes it more efficient than the series of conversations that take place in a power plant
  • produce water and heat, no greenhouse gases
  • will generate electricity as long as fuel is supplied, normal batteries need to be recharged or replaced
  • use a variety of fuels
  • electricity can be generated on site and uses are not reliant on a grid. waste heat can be used to heat water or to heat home
39
Q

disadvantages of fuel cells

A
  • need a constant fuel supply
  • expensive because still developing
  • may have expensive electrolytes or catalysts
  • need changes to systems such as hydrogen filling stations will need to be made
  • generate direct current but appliances use alternating current. an inverter will be needed
  • hydrogen is mostly from fossil fuels
  • hard to store and hard to be safe

Chemistry (28 decks)

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