[Polosky]

I just registered, and I'm not quite sure where to put this. And this is an idea that just occurred to me, I just started an actual chemistry class this year, but I love it. Anyways, here is what I'm thinking...

Water: H2O
Hydrogen Gas: H2
Oxygen Gas: O2

2H2O + Electricity ---> 2H2 + O2

Is the opposite the same? Such as:
2H2 + O2 + Spark ---> 2H2O

That's my first question.
Next, what would be good cathodes and anodes for electrolysis of water?

And then:
One should be able to convert a standard engine to burn hydrogen. (I've done research, still thinking of just creating one or something).
Here's what I think I could do...

[At Home]
Solar Panels (Not only do they create electricity needed for the process, but they can run your house as well)
--->
Electrolysis of water to yield hydrogen and oxygen gas; contain in pressurized containers for liquid hydrogen and oxygen
--->
[In car]
Fill the pressure tanks in your car, and burn them
--->
Burning of H2 and O2 gas creates H2O
--->
Collect the water produced into a tank
--->
cycle starts over

Here's some things I would like to ask:
1. What would be the best cathode and anode?
2. How much oxygen and hydrogen gas will result from the water, say one gram? and how much voltage is required for one gram?
3. Do solar panels keep a constant stream of voltage so long as the sun is shining?
4. Is this possible?

As of right now, I'm not too worried about total cost. That's at the back of my mind right now. I know there are possibilities for contaminants and inefficiency. As well, I'm not too worried about the inefficiency, since it's pretty much a closed system.

Thank you for the time,
Alex

[cth]

OK, well thought. 

Actually, what you propose is so-called "hydrogen economy" http://en.wikipedia.org/wiki/Hydrogen_economy. It has become a very hot research topic for the last 10 years or so. Millions of dollars are spent in it every year and numerous research groups are working on it, both academic, research institutes and private companies. You may want to have a look at the website of the US DoE (Department of Energy) where there are pages dedicated to that project http://www.hydrogen.energy.gov/. Huge profits are expected for the group(s) that will develop it commercially.

You can imagine that, if it was easy to do, it would have been long done already. 

Technical challenges:
- Hydrogen production from water electrolysis, from “hydrogenase” enzyme,…
- Hydrogen storage into nanoporous compounds, as metal hydrides,…
- Hydrogen conversion into electricity in a fuel cell.

Good luck on your project

[Yggdrasil]

The project you suggest is definitely possible.  In fact, a few companies have produced prototype hydrogen internal combustion vehicles (see http://www.hydrogenhighway.ca.gov/vehicles/ice.htm).

Now for your questions:

1. What would be the best cathode and anode?

I don't know enough about the subject to suggest the best materials, but I've heard graphite is good (and easy to obtain; just shave the wood off of the outside of a pencil).  Unlike using metals for electrode, a graphite electrode will not degrade as much over time.

2. How much oxygen and hydrogen gas will result from the water, say one gram? and how much voltage is required for one gram?

Well, since you are taking a chemistry course, you should be able to write a balanced chemical reaction and calculate the mass of oxygen and hydrogen produced (if you want to calculate the volume, just use the ideal gas law).

A note about electricity.  There are a few terms that get easily confused.  Voltage refers to the difference in potential energy between the cathode and anode.  Current refers to the amount of electricity flowing through a device.  Charge refers to the total amount of electrical energy held by a battery.  As an example, you can consider, the common battery types AA and AAA.  Both put out 1.5 volts and the only difference is the amount of charge they carry.  So, AA batteries would power a device longer than the same amount of AAA batteries.  For devices that require a bit more kick (i.e. more voltage), there are 9 volt batteries or the wall socket (120 V in the US).

Anyway, the rate of hydrogen production from electrolysis is depends on the amount of power (current multiplied by voltage).  The exact amount of electrical energy to produce a certain amount of hydrogen depends on how efficient your electrolysis setup is.

3. Do solar panels keep a constant stream of voltage so long as the sun is shining?

Here I think you mean current, but I don't know enough about solar cells to give you an accurate answer.  I would guess that the voltage and current stay fairly constant given a fairly constant stream of light hitting the panel, but I'm not sure.


Finally something to consider.  One of the big advantages of hydrogen fuel is that hydrogen can be used in fuel cells which convert fuel into energy much more efficiently than internal combustion engines.  In internal combustion engines, most of the energy contained in the fuel is lost as waste heat.  Fuel cells lose much less of the energy from the fuel as heat.  Of course, fuel cells are much more expensive than internal combustion engines, so that has been one factor (of many) holding back fuel cell technology.

But, good luck with your studies.  Changing the way the world uses energy is one of the most important problems facing humanity this century, and chemists will definitely play a big part in solving this problem.

[billnotgatez]

The devil is in the details.

The pitfalls are many.

Examples are

Hydrogen causing brittle metals
Explosive nature of hydrogen
Storage problems of hydrogen
Economic blocks to implementation (very long payback)
Expense of photovoltaic systems
Energy necessary to convert water to hydrogen and oxygen
Competing with vastly less expensive sources of energy.

These and more are being addressed but it is taking a lot of research