Fuel Cells; PEMFC; Cause of Proton Movement

In summary, the movement of protons towards the cathode in a proton exchange membrane fuel cell is due to concentration gradients created by the continuous production and consumption of hydrogen on either side of the membrane. This movement is in accordance with an electrochemical gradient caused by the loss and gain of electrons at the electrodes. The constant flow of current in the fuel cell maintains the negative and positive potentials at the electrodes, allowing for the continuous production of electricity.
  • #1
Menninger
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Lately I've started learning about fuel cells, particularly proton exchange membrane fuel cells (PEMFC), and a fairly basic question that has been bugging me is: Since the cathode is positive, it is clear why the electrons flow through the load and to the cathode, but why do the protons/hydrogen ions also move towards the cathode given that their charge ought to repel such movement?

From the very rudimentary knowledge I possess, the only thing I can think of is concentration gradients created by the continuous production of hydrogen on one end and consumption on the other. But I want to be sure - and I ask my question here because the answer has, for whatever reason (my incompetence or something else), been nontrivial to look up.

http://upload.wikimedia.org/wikipedia/en/5/5c/Fc_diagram_pem.gif [Broken]
Thanks
 
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  • #2
I'm not 100% sure, but from what I can remember from my chem classes is that hydrogen loses electrons at the electrode on the left in your diagram and this makes it negative. Consequently, this causes electrons to move to the electrode on the right, which intially makes this one negative and the left one positive. This causes the protons to move to the electrode on the right and accept these electrons. Hydrogen molecules are continuously losing electrons to the left electrode, and therefore this electrode (the source of the electrons) has a more negative electric potential (more electrons) than the right one at any particular instant (which are immediately transported away). Electrons are continuously accepted at the right electrode (electrons move towards it) and hence it has the more positive electric potential (fewer electrons) in the circuit at any instant (which are immediately accepted by the protons).

Remember that a current is being generated in the fuel cell, so the electron producing electrode is always negative and the accepting one positive. The accepting electrode only stays positive because any incoming electrons combine with the H+ ions and this maintains its positive potential (which would otherwise make the electrode become more negative over time till the potential difference reaches 0). I've not used the terms cathode and anode to avoid confusion here because contrary to a battery, current is generated here and the roles are reversed.
 
  • #3
Yes, thanks.

That is eventually what I found in a paper on another website. The movement is in accordance with an electrochemical gradient. The electric gradient is caused by what you say. The "chemical" gradient refers to the fact that random motion of the atoms tends towards equal concentrations on either side of the membrane - and of course the chemical reactions catalyzed ensure that equal concentrations never actually occur.
 

1. What is a fuel cell?

A fuel cell is an electrochemical device that converts the chemical energy from a fuel, such as hydrogen, into electricity through a chemical reaction. This process does not involve combustion and produces very little pollution.

2. What is a PEMFC?

A PEMFC (proton exchange membrane fuel cell) is a type of fuel cell that uses a proton exchange membrane as an electrolyte to facilitate the movement of protons from the anode to the cathode. This type of fuel cell is commonly used in transportation and stationary power applications.

3. How do PEMFCs work?

PEMFCs work through a process known as the proton exchange reaction. Hydrogen gas is fed into the anode side of the fuel cell, where it is split into protons and electrons. The protons are then able to pass through the proton exchange membrane to the cathode side, while the electrons flow through an external circuit, creating an electrical current. At the cathode, the protons and electrons combine with oxygen to produce water as a byproduct.

4. What causes the movement of protons in a PEMFC?

The movement of protons in a PEMFC is caused by the presence of the proton exchange membrane. This membrane is made of a polymer material that is able to selectively allow protons to pass through, while blocking the flow of electrons. This creates an imbalance of positive and negative charges, causing the protons to move towards the cathode.

5. What are the main benefits of using PEMFCs?

Some of the main benefits of using PEMFCs include their high efficiency, low operating temperature, and minimal environmental impact. They also have the potential to be powered by renewable sources of hydrogen, making them a promising alternative to traditional fossil fuel-based energy systems.

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