C7.5 Fuel Cells Flashcards
what is a fuel cell?
an electrochemical cell in which a fuel donates electrons at one electrode and oxygens GAINS ELECTRONS at the other electrode
How do hydrogen fuel cells work?
- hydrogen fuel provides a source of ELECTRONS, setting up a voltage
-when hydrogen fuel enters the cell, it becomes OXIDISED
HYDROGEN + OXYGEN –> WATER
Example of how a chemical cell/battery works using zinc and copper electrodes
you can use the DIFFERENCE IN REACTIVITY to make cells/batteries
- electrons flow from MOST REACTIVE (zinc) to LEAST(copper)
-2 metals join together by a wire and put into ELECTROLYTE - electrons will flow from zinc to copper
why do electrons flow from most reactive to least?
more reactive metals have a greater tendency too give away electrons / form positive ions
The greater the difference in reactivity…
the higher the voltage produced
difference between normal cells, rechargeable cells and fuel cells?
Normal cell - goes flat as chemicals are used up
fuel cells- chemicals pumped in to replace those used up
rechargeable cells - when recharging, chemical reactions are reversed to REPRODUCE chemicals used up
what factors affect the voltage produced ?
- greater difference in reactivity
- concentration of electrolyte
- type of electrolyte
- type of electrode
ADVANTAGES OF HYDROGEN FUEL CELLS
1) no pollution
2) produce more energy per kg than petrol
3) continuous process until fuel stops being supplied
DISADVANTAGES OF HYDROGEN FUEL CELLS
1) hydrogen is expensive to produce/store
2) High pressure tanks needed to store , which are dangerous
3) fuel cells affected by low temps - less efficient
how does the recharging process of cells occur ? 4mks
- chemical reaction is reversible
when external current is applied - so product ca turn back into reactants
- hence movement of electrons continue to take place
half equns for reactions at the electrodes in hyrdrogen fuel cell?
H2 –> 2H+ + 2e-
o2 + 4H+ + 4e- –> 2H2O
why do non-rechargable cells stop produding electricity/gov example of one?
alkaline batteries
- one of reactants used up - stops chemical reactions
- no flow of electrons so cell stops producing electricty