What the fuel cell is going to do is make an electrical current and it’s going to do that by splitting hydrogen atoms into their component parts of protons and electrons and make the electrons move through a wire.
The fuel cell consists of just a few parts including two electrodes.
Each electrode is made from carbon and is coated with the catalyst platinum.
The two electrodes are separated by a special plastic membrane of a material called NafionTM.
When I say ‘special’, among its other properties, it’s very porous and yet repels water, it’s hydrophobic.
The membrane sits between the two electrodes and being plastic, acts as an insulator preventing the two electrodes from touching each other.
The pores of the membrane are filled with water.
The two electrodes form the anode and cathode of the cell.
Manifolds provide H2 to the anode and air as a source of O2 to the cathode.
The electrodes have wires connected to them, and the wires are connected to a load. In this case a bulb, but on a car, an inverter.
How fuel cell works
Something must make this cell work, and it’s all to do with catalysts, electronegativity and electrical charges.
The first thing that happens, is the effect of the catalyst, and just like in a catalytic converter, the catalyst splits molecules into their individual atoms and so when O2 meets the cathode, the oxygen molecules are each split into two oxygen atoms.
The atom, oxygen, is neutral, but, it’s very electronegative.
It’s looking for electrons to fill its outer shell, and so, on the oxygen side (the cathode), there’s a force attracting electrons in.
On the anode side, the H2 settles on the platinum and is immediately split into two separate hydrogen atoms.
The electronegativity of the oxygen needing two electrons is greater than the hold that the proton of the hydrogen atom has on its own electron.
The electrons on the hydrogen atoms are attracted to the oxygen.
It may look like there is a great distance between the oxygen and hydrogen, but remember, the wires connecting the two electrodes are already full of electrons.
The attraction causes two electrons to move onto each of the oxygen atoms, creating a pull on the electrons in the wire, which in turn, pulls the electrons off the hydrogen atoms creating hydrogen ions.
It’s worth noting that a hydrogen atom without its electron is called a hydrogen ion even though it’s actually just a proton.
So, now we have electrons moving through the wire, onto the oxygen atoms, and an electrical current has been established.
Once the oxygen atoms have filled their ‘seats’, they now have ten electrons and only eight protons, and suddenly, they become very negatively charged, creating a second force.
Left over on the anode we have hydrogen atoms without electrons, which I’m going to call, protons.
These positively charged protons on the anode, are being pulled by the very negatively charged oxygen atoms on the cathode.
If protons could pass through the wire, they would, but they can’t, they’re too big, so they need another way of getting to the oxygen atoms.
This is where the water in the membrane comes in.
Water is H2O, and a water molecule has one oxygen and two hydrogen atoms.
The pull from the negatively charged oxygen atoms on the cathode is enough to make the protons on the anode ‘take the plunge’ and jump onto the water molecules.
This makes the water molecules they jump onto positively charged.
The positively charged protons (hydrogen ions), then make their way towards the negatively charged oxygen using the water molecules as ‘steppingstones’.
Every time a water molecule (H2O) gains a proton/hydrogen ion it becomes H3O+, and H3O+ is an acid.
Effectively the water becomes an acid electrolyte, and just like in a lead acid battery, the electrolyte is capable of transporting charged particles which water (H2O) cannot do.
It’s in this way that the protons are transported towards the negatively charged oxygen.
When the protons reach the oxygen, two protons jump onto the oxygen atom and both take an electron.
These two protons cancel out the double negative charge of the oxygen atom, and each proton, having picked up an electron, now becomes hydrogen again.
Effectively the oxygen atom finds itself with two hydrogen atoms stuck to it, oh, and did I mention that an oxygen atom with two hydrogen atoms stuck to it, is water.
This makes water the by-product of the whole process.
What a proton exchange membrane fuel cell does, is take hydrogen and oxygen, and make electricity, and water.
It splits the hydrogen atoms into protons and electrons on the anode and it pushes the electrons through an electrical circuit.
The protons pass through the membrane, hence the term proton exchange membrane, using acidified water molecules as electrolyte, and, the electrons and protons meet up again on the cathode, and become hydrogen, which joins with oxygen, to make water.
The water exhausts out of the fuel cell, and the more hydrogen and oxygen we feed into the cell, the more electricity and water is made.
Each cell produces a voltage in a range between 0.45V and 1.1V and this alone isn’t very much, but, the cells are very thin, and if you have 400 of them connected in series, you’ve got a potential to produce 400V and, sufficient power to drive a medium sized SUV along.
There’s no doubting about it, there’s some pretty clever chemistry going on to make a fuel cell work, but, if the future is to include vehicles which can be easily and rapidly fuelled up in a relatively conventional way, this is certainly a solution which fits that bill.
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