Chemical Bond Energies

The energy required from the electric source to separate them is exactly equal to that released upon combustion of hydrogen

The possibility of recovering 100% of the input energy in a useful form is only theoretical -- unattainable in practice. Processes in the real world always involve losses ("free-energy" dreamers propose over-unity schemes, not realizing that we can't even reach unity efficiency). But, with this in mind, PWSlack's answer is correct.

In practice, electrolysis is not 100% efficient. 50% is not unusual, and the DofE 2010 target is 75%. Here's an article published by a company located a couple miles from here.

In the US, electricity is produced at about 38% efficiency, and fuel cells operate at about 50%. 38% x 75% x 50% = 14.25% If you consider compression and/or liquefying energy costs, plus transportation, the overall efficiency is probably much less than 10%. In the new BMW, they actually BURN this stuff!!! So rather than 50 % fuel cell efficiency (and 90% elec motor efficiency), they've got 25% ICE efficiency. As if that's not disastrous enough, the BMW looses half its H2 in 9 days, because the liquid boils and has to be vented. If you are an oil guy, the H2 "economy" must look really really attractive. If the electric power plant is running on oil, then you can burn at least 4 gallons of the stuff to give you 1 gallon's worth of energy in your BMW. If the power plant is running on coal, then the carbon footprint of your BMW would be on the order of 8 times that of a similar car powered with diesel fuel.

You guys are awesome, Thank You.

My agenda.

I have been posting to the thread "NRC and the New Nuclear Family." One point being made by another person is that the nuclear waste problem is less problematic than sequestering CO2.

Can CO2 be electrolyzed into its constituent components? Is there a market for pure carbon? How about the oxygen? The concentration of CO2 in the atmosphere is quite rare so pulling it out of the atmosphere may not be a great option, but how about working at the stack of a power plant?

Would there be anyway the CO2 could be scrubbed at the stack and then electrolyzed using the nighttime off peak power production capacity of the plant?

What possible uses would there be for the by products?

Is this idea totally out in left field?

I may be grasping at straws here but I think the American Taxpayer is about to get saddled with fuel recycling costs and waste management of nuclear fuel to be supplied by US based enrichment companies to both domestic and foreign operations. In the referred to thread above I am being told that all these costs are being paid for by the industry. I guess I have to take the guys word for it.

I don't think we have taken the end use efficiencies as high as economically feasible. I think optimizing those efficiencies would be a better investment for the consumer than investing in a bunch of new power plants of any type. It may not fill the trough as fast as increasing production capacity, but it certainly makes more sense for the tax paying consumers.

Are we looking at all the alternatives and capturing all the hidden costs?

A quick note on Electrolysis, could the efficiency of the process be stepped up by pumping the molecules using resonant effect. Maybe reducing the thermal loses? Is this out in left field?

Gavilan

Can CO2 be electrolyzed into its constituent components? Is there a market for pure carbon? How about the oxygen?

Yes, yes, and yes. In principle there is nothing to prohibit decomposition of CO2 back into its constituent elements C and O2 (but I don't know if anyone has ever done it, or if it makes economic sense). Pure carbon would certainly would have a market both as a fuel and a feedstock for synthesis of other chemicals. Oxygen certainly has a market too (medical, scuba, fuel oxidation, sewage treatment, etc.). I agree that if we want to process CO2, we should capture it directly at the smokestack.

A quick note on Electrolysis, could the efficiency of the process be stepped up by pumping the molecules using resonant effect. Maybe reducing the thermal loses? Is this out in left field?

I have heard of this idea of using resonance to facilitate bond dissociation during electrolysis. The problem is that I have heard of this only from proponents of "over-unity" energy devices (who seem to think that violation of the first law of thermodynamic is merely a matter of "thinking outside of the box"). Perhaps vibrating the molecules at a resonant frequency would help, but then one must ask how much energy this extra step consumes. Worth investigating, but I would give an educated guess (as a physical chemist) that resonance would provide at best only a modest enhancement of overall energy efficiency.