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### Topic: Fuel cells  (Read 7058 times)

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#### 777888

• Guest
##### Fuel cells
« on: October 28, 2004, 01:58:00 PM »
Can someone teach me what a Hydrogen fuel cell is? How is it different than a dry cell? And why those fuel cells are better for electric cars?

Thanks
« Last Edit: October 28, 2004, 02:15:40 PM by 777888 »

#### Demotivator

• Guest
##### Re:Fuel cells
« Reply #1 on: October 28, 2004, 03:50:25 PM »

#### 777888

• Guest
##### Re:Fuel cells
« Reply #2 on: October 28, 2004, 08:58:51 PM »
Thanks, I read it but I can't find the answer for why dry cell has a higher voltage than a fuel cell, ie when a fuel cell is replaced by a fuel cell in an open circuit, the voltage of the dry cell is measured to be more while the current stays neaerly the same. And why dry cell has more power than fuel cell? Is that a good thing?

#### Demotivator

• Guest
##### Re:Fuel cells
« Reply #3 on: October 28, 2004, 09:49:08 PM »
I don't know. I guess the half reactions of a dry cell add up to a greater emf. However, voltage can be boosted for any battery if cells are connected in series.
« Last Edit: October 28, 2004, 10:13:06 PM by Demotivator »

#### 777888

• Guest
##### Re:Fuel cells
« Reply #4 on: October 31, 2004, 01:09:03 AM »
H2(g) and O2(g) passed into a hydrogen fuel cell. The voltage measured with an open circuit. Different resistances are added to the circuit and the voltage and current are measured for each load. The fuel cell is disconnected and replaced by a dry cell. Same procedure is used to measure the voltage and current for the same resistances in the circuit.

-The measurements are given. I plot the voltage-current graph(voltage as vertical axis), and I observe that the negative slope of the line of the dry cell is steeper, which implies as current increases, voltage decreases faster in dry cell than in fuel cell. But does that mean that fuel cells are more efficient(higher efficiency)? If so, why?(Besides, the line of the dry cell starts at a higher point, which means dry cell has a higher voltage than fuel cell for the same current.)

Thanks for teaching me!
« Last Edit: October 31, 2004, 01:12:49 AM by 777888 »

#### Mitch

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##### Re:Fuel cells
« Reply #5 on: October 31, 2004, 01:19:49 AM »
Remember also that liquid hydrogen has a density of 0.07g/ml so you can't store that much with out needing a very large tank. The latest research involves hydrogen absorption onto surfaces so that you can get a higher packing of hydrogen in the same volume.
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#### Demotivator

• Guest
##### Re:Fuel cells
« Reply #6 on: November 01, 2004, 10:54:24 AM »
1) Efficiency is the capability of converting energy to work without wasting it as heat. In that sense, the dry cell is more efficient. However, efficiency is not the sole parameter that would make a dry cell preferable to a fuel cell.

2) It doesn't matter that the voltage is less than a dry cell. Fuel cells can be stacked to increase voltage.

3) As far as the graphs are concerned, it is desirable for power output to be the larger. Power = VI, so the graph that exhibits the bigger number over a range of I is preferable. I would think that would be the graph with the less steep slope.
Practically, fuel cells can also increase power by increasing the flow of fuel into the cell. Dry cells can not do this.