Science Buddies: "Ask an Expert"

One of the problems associated with fuel cells is the need for a source of hydrogen. You can get hydrogen from natural gas, but natural gas is a fossil fuel which contributes to climate change when it is burned, which defeats the main purpose of fuel cells. Can you get hydrogen from water by using calcium to create a single replacement reaction, with hydrogen as one of the products?

2 Ca + 2 H2O --> H2+ 2 Ca(OH)

Hello candy4me,

Yes, Ca reacts with water to produce hydrogen as you show. The problem with using this reaction for energy production is obtaining the elemental Ca. Do you have some idea for how to produce Ca economically?

WW

Calcium is indeed very expensive. However, you could use a different reactant; for example, water reacts with magnesium in much the same way it reacts with calcium, but magnesium is a lot cheaper than calcium. However, the magnesium/water reaction is much more explosive.

candy4me,

Perhaps you could find a way to regenerate the Ca after it has been used. If you could economically convert the hydroxide back to Ca, then you would have a "rechargeable" system like a battery. If the amount of energy stored in the Ca is big enough for its size and weight, it would be a good alternative to batteries for electric cars. It is an interesting applied physics problem to figure out a usable system.

WW

Can you add a specific substance to calcium hydroxide (Ca[OH]2) to yield calcium + another base? For example, would barium (or similar elements like lithium, sodium, or potassium) react with Ca(OH)2 to yield Ca + Ba(OH)2 ?

candy4me,

In a solution, adding Ba would just oxidize it as well as the Ca. I am not expert in chemistry, so you will need to find a different "expert" for those questions.

In any case, producing elemental Ba is also an expensive process. We are now in the transition from fossil fuels to renewable energy sources. As this transition progresses, electricity will likely become the least expensive form of energy because the main alternative energy sources make electricity: wind, solar, waves, etc. Biofuels are another form of alternative energy, but they can't produce elemental Ca easily either.

I think the reaction you are looking for would involve electricity in and Ca out. Since batteries don't hold enough energy using currently-known and likely technologies, a useful cycle might be:

Generate Ca using an electrochemical process;
Place the Ca in a removable module with a supply of water in the automobile to generate hydrogen;
Use the hydrogen in a fuel cell to get back to electricity;
and when the Ca is exhausted, swap out the Ca-to-hydrogen module for a fresh one (at a Ca station instead of a gasoline station).

I think you will need to do a bit of study in chemistry to solve this very, very difficult problem. On the other hand, you will certainly become rich and famous if you do it. Seriously, I think working in alternative energy and related technology is likely to be a very interesting and rewarding field for several decades now.

I think you might enjoy studying this material: http://www.ambri.com/storage/documents/ ... ws_LMB.pdf.

Good luck and happy studying, WW

From my understanding, it sounds like you are suggesting to run an electric current through calcium hydroxide to try to split it into Ca and (OH)2 through electrolysis. If this is correct, wouldn't the electrolysis of the Ca(OH)2 use all the electricity generated by the fuel cell?

candy4me wrote:wouldn't the electrolysis of the Ca(OH)2 use all the electricity generated by the fuel cell?

You are likely correct. There aren't any known cyclical processes that don't consume energy.

I believe what Wendle was asking you to consider was "what if Ca was your regenerative energy source fuel" and the process was similar to recharable batteries. Instead of charging batteries at recharging stations, you investigate having stations where you trade Ca(OH)2 for Ca to recharge your portable energy source.

The recovery of Ca from Ca(OH)2 requires energy but so do recharging stations for rechargable batteries. Recharging batteries takes time. Swapping materials is probably significantly faster.

The use of hydrogen filling stations maybe more efficient because you can discard the H2O waste product as you go where you don't want to discard the Ca(OH)2.