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Author Topic: How can fuel cells be efficient?  (Read 1887 times)

Brian Letchford

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How can fuel cells be efficient?
« on: 14/12/2010 14:30:02 »
Brian Letchford asked the Naked Scientists:
   
Fuel cell technology is promoted as a possible solution to CO2 and hydrocarbon polluting engines.

However, I understand that the main method for producing hydrogen comes from processing hydrocarbons. Also, as the by-product of fuel cells is water, would this method not only pollute the atmosphere to produce hydrogen but also directly add to the rising water level?

What do you think?
« Last Edit: 14/12/2010 14:30:02 by _system »


 

Offline CliffordK

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How can fuel cells be efficient?
« Reply #1 on: 14/12/2010 15:25:12 »
There may be a few sources of hydrogen.

If there is adequate electricity, Hydrogen can be made with electrolysis. 

Water --> 2H2 + O2 --> Water (as a cycle).

I had forgotten about the steam reforming method which can either produce Carbon Coke, or Carbon Dioxide along with Hydrogen gas.

Water is also a product of combustion of hydrocarbons, but the total amount is literally a drop in the oceans.  So, the primary concern should be resource depletion, and potential effects of atmospheric carbon dioxide increases (if CO2 is released).
 

Offline peppercorn

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How can fuel cells be efficient?
« Reply #2 on: 14/12/2010 15:37:30 »
If you are talking specifically about hydrogen fuel-cells, the perceived advantage is that they are quite a bit more efficient at turning the chemical energy of hydrogen into mechanical work (via electricity) than a heat-engine is.

In this respect they are closer to a Battery-electric vehicle because, as you imply hydrogen can't be directly mined or collected from a geological source, but has to be 'freed' by an intermediate, energy consuming, process.  Notably battery-electric should be inherently more efficient than fuel-cells but currently batteries don't come close to the energy density of compressed or adsorbed Hydrogen.  Plus the fuel-cell driven motor part of the system is as light and compact as (if not more than) a piston engine, transmission and peripherals.

One of the arguments at the moment is that, although currently the majority of hydrogen produced is made from natural gas (still a fossil fuel, if a relatively low impact one), once the infrastructure is developed there will be a shift away from NG to electrolysing water - powered by renewables, nuclear, etc.

So in the long run, so the argument goes, we have the advantage of more efficient 'engines' with a common 'fuel' that even used inefficiently in a vehicle or other energy sources is only able to produce non-polluting water.


Regarding water (vapour) release - burning a litre of gasoline presently releases a certain amount of water (figures anyone?) and this wouldn't increase that much, even if all cars were replaced by ones running on NG produced hydrogen.  I believe stratospheric water vapour is a solar reflector, so if hydrogen could be used for air-travel there could be a lessening of global heating.
 

Offline CliffordK

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How can fuel cells be efficient?
« Reply #3 on: 14/12/2010 15:44:15 »
Keep in mind that light hydrocarbons (Methane, Methanol, etc) can be used in may fuel-cell applications directly without converting it to hydrogen.
 

Offline peppercorn

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How can fuel cells be efficient?
« Reply #4 on: 14/12/2010 15:45:49 »
All that said, I do particularly buy-into the 'hydrogen fuel-cell' model for the future of road transport.  I think in the long-run BEVs will beat the advantages of FCs when looked from a complete energy cycle perspective.

Just for completion there are also other flavours of fuel-cells that can process other chemical energy sources - including methanol, and potentially operate directly on liquid fuels similar to petrol & Diesel.

(Sorry CliffordK was writing in unison...)
 

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How can fuel cells be efficient?
« Reply #4 on: 14/12/2010 15:45:49 »

 

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