Catalyst seems to be a magic word. But, a catalyst does not change the energy balance of a reaction. The reactant(s) potential energy and the product(s) potential energies are not changed. The difference between them is not changed. The Gibbs free energy is changed. For a reaction to proceed there is often some amount of additional energy that has to be added to the system to drive the reaction. This energy is recovered as the reaction proceeds, except for losses due to inefficiencies and thermodynamic limits which can be minimized but not eliminated. Catalysts essentially reduce this Gibbs free energy and this eases driving the reaction, it is easier, and probably faster (perhaps much faster), but the energy balance is not effected, except as mentioned, by reducing inefficiencies. If you have to heat reactants to 1000 degrees C to have the reaction proceed at a desired rate, a catalyst might reduce the necessary heat input to only 100 degrees C. Insulation- conduction, convection and radiation losses may then be less for the system (smaller delta T), but the energy balance between reactants and product is not changed. There are all sorts of advantages that a catalyst can contribute to a chemical or other process, but it cannot change the basic thermodynamics. If you need to add 10 units of energy to drive the system (overcome Gibbs free energy) that energy is recovered as the potential well between the Gibbs free energy peak to the products is increased the same amount
A better catalyst does not make it energy cheaper to make hydrogen from water, except for reducing inefficiencies in the system. If the inefficiencies are great, the gains may be great, if the inefficiencies are small, possible gains are also small. You reach a point of diminishing returns.
If you have 100 units of solar power, you might be able to convert it to hydrogen gas and have retained energy of 50 to 99 units, depending on inefficiencies. You might be able to convert it to similar levels of battery power. Then other questions about the cost per energy unit storage of batteries and hydrogen (with it's associated energy costs for compression of liquefaction) has to be considered.
I don't know the details, but that solar power storage seems to emphasize use of batteries, holt salts, water elevation or gass compression would seem to argue that the hydrogen route is less favorable. Remember that the conversion of the stored energy back to electricity or mechanical energy is important, and may be the dominate issue, especially as the processes for making the stored energy medium becomes more efficient. This would seem to favor fuel cells or batteries over thermal modalities as the efficiencies are significantly better. I'm not sure how gravity storage would compare.
If hydrogen is pressurized or liquified you may need need to use ~ 5-40% of the hydrogens energy content to do so. Such concentrated hydrogen may be convenient for mobile uses, but it does have a penalty that has to be figured into the final picture.
http://www.hydrogen.energy.gov/pdfs/901 ... ession.pdf
An example- with very good electrolysis efficiency you might obtain 99 units of hydrogen energy from 100 units of input energy. But final use efficiency may be ~ 60% to 94% of the input energy. If you burn coal with CO2 sequestration you might obtain 100 units of input energy by burning ~ 150 units of coal energy (I have heard that sequestration consumes ~ 50% of initial coal energy). From an environmental standpoint you may get a fraction of the original power potential and not produce significant atmospheric CO2. But you need to add in other considerations like coal mining and transport costs (environmentally and cost) , increased power plant costs and in terms of the number of equivalent plants needed, etc. I'm not sure much, if any gain can be achieved.
This picture changes if the power source is relatively cheap fusion energy (this leaves out tokamaks). Fission is similar though it is not very cheap, though good supplies exist if thorium is used. Fission also has it's own environmental issues.
I wonder if hydrogen is the ideal final product. Synthesis of hydrocarbons (methane and on up) with cheap and non polluting energy sources avoids much of the problems of hydrogen and would be mostly CO2 neutral. Heavier hydrocarbons are already part of the infrastructure. They are safer and more convenient. My vague picture of the least disruptive and cheapest evolution is electric cars with supplemental gasoline powered generators. These hybird cars are carbon neutral with solar power or nuclear power derived synthetic fuels. are not range or use limited, and might help with energy storage with a smart, two way electrical grid.
There are choices for the end product used to meet your goals, but the real problem that has to be answered first is the energy source. Coal sequestration might answer some environmental issues but it is expensive, it would increase coal usage by at least 50% and perhaps by as much as 100%. With additional uses across the energy use spectrum, duration of the supply and World politics become more prevalent. Fission may be less supply limited, but is again a limited duration solution, even if all of the concerns can be met. Fusion, and especially cheap fusion is the ideal answer. Solar might be pushed to adequate levels, though land use would be huge, considerable excess capacity would be needed, and painful conservation regimens would probably be needed. A mixed bag of solutions, including continuing expansion of fossil fuel reserves eases the acuteness of the problem, except of course for those who believe global warming due to man made CO2 is a dire and immediate threat...
Dan Tibbets
To error is human... and I'm very human.
