That is an interesting question. It is not a thought that has occurred to me before.

In principle, if you can have oscillating chemical reactions, there is no reason to doubt that some of them might be a basis for an alternating flow of current, but I cannot help doubting that they would be useful. For one thing, all the chemical oscillations that I can think of offhand oscillate comparatively slowly, and I cannot think of a serious need for a chemical battery that produces  slow AC, and especially not if you cannot provide the current at a defined or controllable frequency. The fact that I cannot does not prove anything of course, and if you have any ideas...

Secondly, the best-known oscillating chemical reactions are not particularly energetic. This is hardly surprising; really energetic reactions tend to go one way, fast! So any such battery is not likely to supply exciting quantities of electric power. The big interest in batteries nowadays is to produce safe, rechargeable, large capacity batteries; come up with something like that, and your fortune is made.

Thirdly, nowadays there are so many cheap, efficient, effective, and convenient mechanical and electronic means of conversion between DC and AC electric power, that even if we could identify such a purely chemical battery, it is hard to know who might prefer it to readily available alternatives.

Still, as I said, quite an interesting idea.

Cheers,

Jon

Maybe not what you had in mind, but most biological membranes allow current to flow in both directions. Typically some form of pump pushes ions across the membrane against the concentration gradient and then a channel allows them to flow back across the membrane, usually doing some form of work in the process.

Possibly the most critical of these is the proton/ATP system in mitochondria.A pH gradient is established by pumping protons out of the mitochondria. As they flow back in the current is used to generate ATP molecules.

None that I know of.

Oscillating chemical reactions are a bit missleading. If you look at any of these reactions, they are not a single reaction. You will find that there are two or more processes taking place, each process may in fact be multiple reactions. What happens is that one process will use the available chemicals to produce a further chemical that is used by a second process. The processes run at different speeds and may even produce chemicals that inhibit each other. This results in the concentration of one or more chemicals oscillating up and down. The change in concentration may be indicated by a change in colour, or if an indicator is included in the original chemical load, the indicator will change colour. The reaction continues until all the chemicals in the original load are used up. All the reactions involved run in one direction.

Probably the best known oscillating reaction is the Briggs-Rauscher reaction. You can find a description of it here:

http://en.wikipedia.org/wiki/Briggs-Rauscher_reaction