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Question about fuel cells.


blackhole123
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I was discussing the future of cars and breaking out dependence on oil with a friend, and fuel cells came up.

 

I thought that fuel cells would be a major breakthrough because they are more efficient than combustion engines, and hydrogen is a lot easier to get than fossil fuels. He claimed that fuel cells would not increase efficiency because you would still need electricity to power the car, to carry out the reaction of the hydrogen that would give energy.

 

I'm sure he is mistaken, or else fuel cells would be worse than a straight up electric car, but I was shaky on my understanding of fuel cells so I couldn't successfully rebut him.

 

I believe I am correct that fuel cells produce electricity with a chemical reaction. How is the electrochemical reaction started, does it take energy? And how costly is hydrogen production?

 

What should I say the next time he claims that fuel cells won't work since "you still need electricity to power the car"?

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The factors that determine if a fuel cell is more efficient, or better for the environment, compared to something else are based upon things like what kind of fuel cell it is, what reactants are used to run it, and where those reactants have come from.

 

You probably should have a read about fuel cells, that will make the argument between you and your friend more understandable.

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A fuel cell is essentially a battery which uses (usually) hydrogen and oxygen, converting them into water. Most hydrogen is currently gotten from fossil fuels, but could be produced via electrolysis of water, which would require electricity rather than fossil fuels.

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What should I say the next time he claims that fuel cells won't work since "you still need electricity to power the car"?

 

He's right that they require electricity to power the car (if you go with the popular idea to use hydrogen as a fuel - this clean hydrogen comes from a sustainable origin, like wind and/or solar energy. Both produce electricity.).

 

So, the popular description of fuel cells is: sustainable electricity (wind/solar) is used to make hydrogen. Hydrogen goes into the tank of the car. Hydrogen powers the fuel cell, and is combusted, forming electricity (and heat). The electricity powers the electric engine of the car.

 

However, you can also make hydrogen from fossil sources, as Mr Skeptic already mentioned. Today, in 2009, the "fossil hydrogen" is a lot cheaper than the "clean hydrogen". And it's exactly the same hydrogen, so everybody will go for the fossil hydrogen.

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To put it even more basically: a hydrogen car is an electric car. The hydrogen fuel cell replaces the battery in a conventional electric car. It's advantage is that it can be "refueled" quickly and with high energy density, like gasoline, while batteries are heavy and take hours to charge. It works (very basically) like this:

 

*Electricity can be used to separate water into hydrogen and oxygen.

*Combining hydrogen and oxygen back into water can produce electricity (which can run an electric motor).

*Oxygen is abundant in the air, but hydrogen is not. So you need to supply your own hydrogen, but not your own oxygen to do so.

*So the inputs are oxygen from the air and hydrogen from your fuel tank, and the outputs are electricity and water.

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I was discussing the future of cars and breaking out dependence on oil with a friend, and fuel cells came up.

 

I thought that fuel cells would be a major breakthrough because they are more efficient than combustion engines, and hydrogen is a lot easier to get than fossil fuels. He claimed that fuel cells would not increase efficiency because you would still need electricity to power the car, to carry out the reaction of the hydrogen that would give energy.

 

I'm sure he is mistaken, or else fuel cells would be worse than a straight up electric car, but I was shaky on my understanding of fuel cells so I couldn't successfully rebut him.

 

I believe I am correct that fuel cells produce electricity with a chemical reaction. How is the electrochemical reaction started, does it take energy? And how costly is hydrogen production?

 

What should I say the next time he claims that fuel cells won't work since "you still need electricity to power the car"?

That's PARTLY true. I'm not a chemistry major, but I've learned a bit about water electrolysis both in high school and university chemistry, and typically electrolysis uses more electrical energy in producing hydrogen than you'd get in terms of chemical energy by using the hydrogen.

 

But still, to have a way of converting electrical energy to chemical energy, even if you lose a little in the process, still means that you could fuel cars with a chemical that in turn gets its energy from the electrical grid. So this wouldn't depend ONLY on fossil fuels, but on nuclear, wind, solar, hydroelectric, etc... and the variety of power sources could still ease dependence on fossil fuels.

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