Fuel Cells Flashcards
what does a fuel cell do? is it a galvanic cell?
produces electricity. it is a galvanic cell but has some different features
how is there a continuous supply of electricity?
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
how efficient are fuel cells?
40-60% efficient
is a fuel cell expensive?
yes
what are the products of fuel cells?
water unless an organic fuel is being used in which water and carbon dioxide are produced
what are the reactants of an acidic fuel cell?
O2 gas and H2 gas
what is the electrolyte of acidic fuel cells?
H+, H2SO4, H3PO4, H3O+
what does the electrolyte do in a fuel cell?
govern the type of fuel cell and allow for the movement of charged ions
what is the anode of an acidic fuel cell?
H2
what is the cathode of an acidic fuel cell?
O2
what is an ammeter?
measures current (flow of electrons)
what is a voltmeter?
measures voltage (push on electrons)
what are the acidic fuel cell equations?
the ones with H+
what are the alkaline fuel cells?
the ones with OH- and water
what are the reactants of an alkaline fuel cell?
O2 and H2
what is the electrolyte of an alkaline fuel cell?
OH-
what properties does an electrode have?
catalyst, inert, porous
what are reactants of other; organic fuel cells?
CH4, O2
what is the electrolyte of organic fuel cells
O2-
what is the anode of an organic fuel cell?
organic fuel
how to balance a straight forward alkaline equation?
- balance key elements
- balance OH-
- balance charge
how to balance complex alkaline equations?
- add H+
- balance electrons
- add OH- to both sides to neutralise
- simplify or cancel down water
why is a H2-O2 fuel cell zero emissions?
only water is produced
to make H2-O2 fuel cells more zero emission making, what needs to happen?
H2 needs to be made in a renewable way. if made from a non-renewable source, it is not “zero emission”
how is most hydrogen made?
95% from fossil fuels in a process called steam reforming
what are the equations for steam reforming
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)
steam reforming produces carbon dioxide, what argument still supports the fuel cell?
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)
what is another argument suggesting CO2 gas is ok?
can be collected for carbonating drinks
how does electrolysis work? what is a criticism?
2H2O(l) —> O2(g) + 2H2(g)
- water is precious
- energy used to do this is expensive
what is another way of making H2 gas?
collecting biogas from landfills and feeding it into steam reforming process
what is a problem with hydrogen that would cause a need for changes?
- highly flammable
- change pipelines and fuel stations
what are two chemical properties of hydrogen?
- energy content 143KJg-1 is higher than petrol 44KJg-1
- found as a gas at room temp
describe how hydrogen can be stored as liquid?
- 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
describe how hydrogen can be stored when compressed
- 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
describe storing hydrogen with adsorb material storage
H2 sticks to the surface of metal hydrides as either H atoms or H2 molecules
describe storing with absorption
H2 can dissociate and be absorbed by lattice structures (solid form)
describe the last storing of hydrogen
H2 reacts with other chemicals- can react with many
advantages of fuel cells
- 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
disadvantages of fuel cells
- 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
