Hydrogen fuel cell Flashcards
What are 4 reasons why hydrogen is used in fuel cells
- Hydrogen has a high energy density (per unit mass).
- The only by product from hydrogen is water.
- Hydrogen fuel cells are more energy efficient than internal combustion
engines / electricity generators. - Hydrogen is readily available as it can use water as a raw material which
is plentiful
What are the three bulk production methods for hydrogen currently used
- Steam reforming of fossil fuels.
- Electrolysis of water using high pressure and temperature.
- Photocatalytic splitting of water.
How does electrolysis provide the bulk production of water (provide equation)
1-Electrodes are placed in water.
2-An electric current is passed through the electrodes.
3-The water is split into hydrogen and oxygen.
2H2O > 2H2 + O2 or 2H2O + 2e- >H2 + 2OH
How does Steam reforming of fossil fuels create hydrogen
Natural gas in the form of methane will release hydrogen when exposed to
superheated steam. Since natural gas is readily available through an existing
gas delivery infrastructure, this method of responsible for a large % of overall
production of hydrogen.
What does steam reforming require
supply if methane (natural gas).
Temperature of 700 to 1,000 degrees Celsius.
Steam.
Pressure of between 3 and 25 bar (atmospheric pressure is 1.01 bar).
A catalyst such as nickel.
What is step 1 and 2 in steam reforming including equations
Step 1 -Steam methane reforming reaction;
CH4 + H2O (+heat) > CO + 3H2
High pressure an temperature required
Step 2 - Water gas shift reaction;
CO + H2 > CO2 + H2O (+ small amount of heat)
Catalyst such as nickel required
How does water slitting occur in photocatalytic water splitting
Water splitting occurs naturally in photosynthesis when photon energy is
absorbed and converted into the chemical energy through a complex biological
pathway.
In this process, energy is used from the sun (or an artificial solar radiation
source) to split water.
What happens when water his the semi conductors and what reaction equation happens at these electrodes
The water is passed over the semi-conductor material with light shining directly
on it. The semiconductor material catalyses the water splitting it, the reaction is
as follows;
H2O > 0.5 O2 + 2H+
Reaction at the semiconductor electrode;
2H++ 2e-> H2
Reaction at the counter electrode.
Describe all three methods of hydrogen bulk production and why do they need to take place
Hydrogen gas is not found naturally on Earth. Hydrogen is very reactive so it
must be extracted from its compounds
Steam reforming involves the reaction of methane with steam.
Steam reforming requires high temperature and high pressure.
Electrolysis of water produces hydrogen gas. This requires a significant energy
input.
Photocatalytic water splitting; water can be split into hydrogen and oxygen
directly by sunlight
Photocatalytic water splitting requires a semiconductor catalyst.
What are the most common forms of hydrogen fuel cells
Polymer Electrolyte Membrane (PEM);
alkaline;
phosphoric acid;
molten carbonate; and
solid oxide
How does hydrogen fuel cell covert energy
The hydrogen fuel cell is an energy conversion device where the chemical energy stored within the hydrogen molecule (H2) can be turned into electric current. Therefore, all hydrogen fuel cells, regardless of design convert;
Chemical Energy > Electrical Energy.
What are the operations of a hydrogen fuel cell
The electrolyte material lies between a selectively permeable anode and
cathode.
The anode layer allows hydrogen gas through to meet the electrolyte
layer.
When the hydrogen gas hits the anode a reduction reaction occurs and H+ ions (protons) are formed. This reaction is :
H2 > 2H++ 2e-
These electrons then flow in a circuit and are used to do such work as operate a motor, a pump or lights for example.
The protons pass on through the selectively porous electrolyte membrane (PEM) and arrive at the cathode to be met there by oxygen gas from the air.
Now the electrons generated at the anode have come back through the circuit and arrive at the cathode.
The electrons, the oxygen gas and the protons react to form water in an
exothermic reaction.
4H++ 4e-+ O2 > 2H2O
If the heat is not absorbed to be used then the water will be emitted as
steam. If the heat is removed the water is emitted as liquid water.
What are other applications for hydrogen fuel cells
stationary generation as back up or in remote locations;
stand-alone power supplies for telecommunications installations; and
transport, including cars, buses, trains, boats, or portable power
generators
why is having a stationary back up beneficial
- Stationary generation as back-up in remote locations: Remote locations
cannot be readily accessed for repairs to the national grid leading to extended
power outages. The presence of stationary fuel cells allows quick restoration of
the power supply
Why is having stand alone power supplies for telecommunication
- Stand-alone power supplies for telecommunications installations:
Telecommunications networks, e.g. phone masts require a continuous supply of
electricity and they tend to be in remote locations. Hydrogen fuel cells have few
moving parts so require little maintenance and are very reliable.
