Fuel Cells

Question 1

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

Answer 1

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

Question 2

how is there a continuous supply of electricity?

Answer 2

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

Question 3

how efficient are fuel cells?

Answer 3

40-60% efficient

Question 4

is a fuel cell expensive?

Answer 4

yes

Question 5

what are the products of fuel cells?

Answer 5

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

Question 6

what are the reactants of an acidic fuel cell?

Answer 6

O2 gas and H2 gas

Question 7

what is the electrolyte of acidic fuel cells?

Answer 7

H+, H2SO4, H3PO4, H3O+

Question 8

what does the electrolyte do in a fuel cell?

Answer 8

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

Question 9

what is the anode of an acidic fuel cell?

Answer 9

H2

Question 10

what is the cathode of an acidic fuel cell?

Answer 10

O2

Question 11

what is an ammeter?

Answer 11

measures current (flow of electrons)

Question 12

what is a voltmeter?

Answer 12

measures voltage (push on electrons)

Question 13

what are the acidic fuel cell equations?

Answer 13

the ones with H+

Question 14

what are the alkaline fuel cells?

Answer 14

the ones with OH- and water

Question 15

what are the reactants of an alkaline fuel cell?

Answer 15

O2 and H2

Question 16

what is the electrolyte of an alkaline fuel cell?

Answer 16

OH-

Question 17

what properties does an electrode have?

Answer 17

catalyst, inert, porous

Question 18

what are reactants of other; organic fuel cells?

Answer 18

CH4, O2

Question 19

what is the electrolyte of organic fuel cells

Answer 19

O2-

Question 20

what is the anode of an organic fuel cell?

Answer 20

organic fuel

Question 21

how to balance a straight forward alkaline equation?

Answer 21

1. balance key elements
2. balance OH-
3. balance charge

Question 22

how to balance complex alkaline equations?

Answer 22

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

Question 23

why is a H2-O2 fuel cell zero emissions?

Answer 23

only water is produced

Question 24

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

Answer 24

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

Question 25

how is most hydrogen made?

Answer 25

95% from fossil fuels in a process called steam reforming

Question 26

what are the equations for steam reforming

Answer 26

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)

Question 27

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

Answer 27

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)

Question 28

what is another argument suggesting CO2 gas is ok?

Answer 28

can be collected for carbonating drinks

Question 29

how does electrolysis work? what is a criticism?

Answer 29

2H2O(l) ---> O2(g) + 2H2(g) - water is precious - energy used to do this is expensive

Question 30

what is another way of making H2 gas?

Answer 30

collecting biogas from landfills and feeding it into steam reforming process

Question 31

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

Answer 31

- highly flammable | - change pipelines and fuel stations

Question 32

what are two chemical properties of hydrogen?

Answer 32

- energy content 143KJg-1 is higher than petrol 44KJg-1 | - found as a gas at room temp

Question 33

describe how hydrogen can be stored as liquid?

Answer 33

- 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

Question 34

describe how hydrogen can be stored when compressed

Answer 34

- 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

Question 35

describe storing hydrogen with adsorb material storage

Answer 35

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

Question 36

describe storing with absorption

Answer 36

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

Question 37

describe the last storing of hydrogen

Answer 37

H2 reacts with other chemicals- can react with many

Question 38

advantages of fuel cells

Answer 38

- 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

Question 39

disadvantages of fuel cells

Answer 39

- 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