Understanding PEM Fuel Cells: Exploring the Process and Benefits

In summary, Proton Exchange Membrane (PEM) fuel cells work by using a thin plastic sheet called a proton exchange membrane, which allows hydrogen ions to pass through it. The membrane is coated on both sides with metal alloy particles, mostly platinum, that serve as active catalysts. The fuel cell also uses a solid organic polymer as an electrolyte, which reduces corrosion and management problems. Hydrogen is fed to the anode side of the fuel cell where it is encouraged by the catalyst to release electrons and become hydrogen ions. The electrons travel in the form of an electric current that can be utilized before returning to the cathode side of the fuel cell, where oxygen is fed. At the same time, the protons diffuse through the
  • #1
Alex
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Being fairly new to the whole fuel cell thing (or at least how it works), I have a couple questions.

I have learned so far that Proton Exchange Membrane (PEM) fuel cells work using the following device and process:

The proton exchange membrane is a thin plastic sheet that allows hydrogen ions to pass through it. The membrane is coated on both sides with highly dispersed metal alloy particles (mostly platinum) that are active catalysts. The electrolyte used is a solid organic polymer poly-perflourosulfonic acid. The solid electrolyte is an advantage because it reduces corrosion and management problems. Hydrogen is fed to the anode side of the fuel cell where the catalyst encourages the hydrogen atoms to release electrons and become hydrogen ions (protons). The electrons travel in the form of an electric current that can be utilized before it returns to the cathode side of the fuel cell where oxygen has been fed. At the same time, the protons diffuse through the membrane (electrolyte) to the cathode, where the hydrogen atom is recombined and reacted with oxygen to produce water, thus completing the overall process.
*

Why must the hydrogen be combined with oxygen at the end of the process? Why can't you recycle the hydrogen and do the process over again?

*http://www.fuelcells.org/fctypes.htm#proton
 
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  • #3
Alex said:
Why must the hydrogen be combined with oxygen at the end of the process? Why can't you recycle the hydrogen and do the process over again?

I think you answered your own question. You can recycle the hydrogen but you have to put energy into split the water molecules. You can't have a perpetual motion machine so the hydrogen must react in some way at the end. When hydrogen is burned it forms water as the energy is released.

I am guessing here but is the driving force simply diffusion of the hydrogen from a high concentration to low concentration? If so, you must react the hydrogen in order to get a low conc. at the output. If you didn't react the H then diffusion would stop.
 
  • #4
It is probably better that the used hydrogen reacts with water to form H2O, because as mmwave said, it is probably too impractical to reuse the hydrogen.

H2O emissions are generally a lot better to the environment than CO2 and other hydrocarbons :smile:
 
  • #5
motai said:
It is probably better that the used hydrogen reacts with water to form H2O, because as mmwave said, it is probably too impractical to reuse the hydrogen.
Quick clarification here: its not a matter of practicality, combining hydrogen with oxygen is how you get the energy - its the whole point of having a fuel cell.
H2O emissions are generally a lot better to the environment than CO2 and other hydrocarbons
...until you factor in where the energy required to make the hydrogen came from, of course.
 
  • #6
Hmm I must have misunderstood, then. I was thinking that the hydrogen broke up into an electron and a proton, with the proton traveling through the proton exchange membrane and the electron going through a separate wire. I assumed that the electron could simply combine with the h again and the process could be repeated.

So in order for the hydrogen proton and electron to recombine, they must combine with the O2 to form water?
 
  • #7
russ_watters said:
Quick clarification here: its not a matter of practicality, combining hydrogen with oxygen is how you get the energy - its the whole point of having a fuel cell. ...until you factor in where the energy required to make the hydrogen came from, of course.

So the whole process could not occur without the water in the cathode. I see now. Doh! :biggrin:

Thanks everyone.
 
  • #8
Alex said:
Hmm I must have misunderstood, then. I was thinking that the hydrogen broke up into an electron and a proton, with the proton traveling through the proton exchange membrane and the electron going through a separate wire. I assumed that the electron could simply combine with the h again and the process could be repeated.
The force propelling the proton through the membrane is the same force propelling the electron through the wire. This is almost exactly the same as how any other battery works: ions flow one direction through the battery and electrons flow the other direction through the wire, meeting back in the battery.
So in order for the hydrogen proton and electron to recombine, they must combine with the O2 to form water?
Essentially yes.
 
  • #9
It could also be so that the consumer will buy more hydrogen. This hydrogen car is going to be just like a gasoline car. Big, bulky, amp-consuming machines are going to be needed in order to take the water and convert it into hydrogen, so that we the people may buy it for $5.00 a gallon. Of course, with proper research one day we might be able to make a small enough water to hydrogen converter, to where it could fit in the hydrogen car, and we can simply fill our cars up with free water, but they won't let that research happen.
 
  • #10
Dual Op Amp said:
but they won't let that research happen.

Not true. There is no real evidence that industry has stymied research in any way. In fact, both government and industry have worked hard for innovations in new fuel systems.
 
  • #11
I'm opening a parenthesis here. If all present car emissions were H20 instead of CO etc. wouldn't the humidity considerably rise in some regions? Are people starting to forecast what are the consequences of this or is it still too early for serious thought? I predict some new health problems.
 
  • #12
Dual Op Amp said:
Of course, with proper research one day we might be able to make a small enough water to hydrogen converter, to where it could fit in the hydrogen car, and we can simply fill our cars up with free water, but they won't let that research happen.
An electrolysis machine can be made as big or small as you want it - the problem is energy. And no, conspiracy theory has nothing to do with it: just the laws of science.
I'm opening a parenthesis here. If all present car emissions were H20 instead of CO etc. wouldn't the humidity considerably rise in some regions? Are people starting to forecast what are the consequences of this or is it still too early for serious thought? I predict some new health problems.
Car emissions are already mostly water and water already makes up a much larger fraction of our air than CO2 (in the summer and in temperate climates). More water in the air just means more fog and more rain (but an insignificant amount more) - the cycle is already closed. Not a big deal.
 
  • #13
Dual Op Amp said:
Of course, with proper research one day we might be able to make a small enough water to hydrogen converter, to where it could fit in the hydrogen car, and we can simply fill our cars up with free water, but they won't let that research happen.

Nonsense.

Water is not a fuel. If you're going to use that idea, you need a supply of fuel onboard the car. (Batteries anyone?)
 
  • #14
Pedals. We're all too fat, and all too fast.
 
  • #15
Electrons and pem

Physics cw and my basic understanding at stake here!

please can someone explained to me why electrons are unable to travel through the menbrane and are forced to travel around creating an electrical circuit?
 
  • #16
matthewh2712 said:
please can someone explained to me why electrons are unable to travel through the menbrane and are forced to travel around creating an electrical circuit?
Ostensibly, the electric resistance of the conductor is less than the resistance through the membrane, and the voltage is such to attract the electrons through the conductor to the load.
 
  • #17
Protons

Thank you for your reply, kind of understand and i was just also wondering, why the protons travel through the membrane at all, when they are positively charged and yet on the other side of the membrane is another positively charged electrode, so why would they be attracted this way ? any wesites that you think i wuld find useful would be very much appreiciated. Because i have found most to be confusing because they seem to say that the anode can be negatively charged, can this happen ? i need help! :)
 

1. How does a PEM fuel cell work?

A PEM (Proton Exchange Membrane) fuel cell works by converting the chemical energy from hydrogen and oxygen into electrical energy through a process known as electrochemical reaction. This reaction takes place within the fuel cell's membrane electrode assembly (MEA) which consists of an anode, a cathode, and a proton exchange membrane. Hydrogen is fed into the anode side of the MEA and oxygen is fed into the cathode side. The hydrogen molecules split into protons and electrons, with the protons passing through the membrane while the electrons are forced to flow through an external circuit, creating an electrical current. The protons and electrons then combine with oxygen at the cathode side, producing water and heat as byproducts.

2. What are the benefits of using PEM fuel cells?

There are several benefits to using PEM fuel cells. One of the main benefits is their high efficiency, with some fuel cells reaching up to 60% efficiency. They also have low emissions, producing only water and heat as byproducts. PEM fuel cells are also quiet and have a long lifespan, making them suitable for various applications. They can be used in transportation, stationary power generation, and portable devices. Additionally, they can operate at low temperatures and are lightweight and compact, making them easy to integrate into different systems.

3. How is the performance of PEM fuel cells measured?

The performance of PEM fuel cells is measured by several factors, including efficiency, power density, and durability. Efficiency is measured by the amount of energy produced from a given amount of hydrogen, and power density is the amount of power produced per unit of cell area. Durability is measured by how long the fuel cell can operate without significant degradation. These measurements help determine the overall effectiveness and reliability of PEM fuel cells.

4. What are some key components of a PEM fuel cell?

The key components of a PEM fuel cell include the anode, cathode, proton exchange membrane, and the catalyst layers. The anode and cathode are made of porous carbon materials and are coated with catalyst layers, typically made of platinum, to facilitate the electrochemical reaction. The proton exchange membrane, often made of a polymer material, separates the anode and cathode sides and allows for the transfer of protons. Other important components include the bipolar plates, which distribute gases and collect the electrical current, and the gas diffusion layers, which help evenly distribute reactant gases over the catalyst layers.

5. What are the challenges in implementing PEM fuel cells?

While PEM fuel cells have many benefits, there are also some challenges in implementing them on a larger scale. One challenge is the cost of materials, particularly platinum, which is a crucial catalyst in the fuel cell. Another challenge is the need for a reliable and steady source of hydrogen, which is currently primarily produced from non-renewable sources. There are also challenges in the storage and transportation of hydrogen, as it is a highly flammable gas. Finally, the durability and longevity of PEM fuel cells are still being improved, as they can be affected by factors such as temperature, impurities, and mechanical stress.

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