Q & A: High pH ’Lemon’ Batteries

We are doing the lemon battery thingie, but we are just testing the electrical current and comparing them to battery, but we are also using high ph foods, will they work also? why or why not?
- Amy
Sumter, sc, USA

Amy -

We know from experience that copper-zinc batteries can be made with potatoes, and those seem by taste like they're higher pH than lemons, although we haven't measured that pH. We tried playing around changing the pH of solutions some by dumping baking soda in vinegar, and it didn't change the battery voltage much. At first glance, this seems surprising, because at the copper electrode, the H+ ions (the ones present in acids) combine with electrons to make H2 molecules. The more acidic, the more H+ ions around, and the more easily that reaction should happen. What we guess is that in the more acidic foods, copper dissolves off the copper electrode, generating H2 and raising the pH (lowering the acidity) right near the copper electrode. So as as far as the electrical battery is concerned, the more acidic foods may end up not acting very acidic. Then the voltage generated won't depend much on the initial pH, because the copper electrode doesn't really see that pH. One little piece of evidence supporting that guess was that the initial battery voltage after the solution was stirred in was a bit over 2 V, but it would drop to about 1.5 V after a few seconds. Maybe that drop was caused by the copper gradually dissolving and changing the pH near the electrode. We only tried measuring battery voltage. You might also measure how much current the battery can supply before its voltage starts to drop. Maybe that will depend more on pH. For more information on how food batteries work, check out our section on Homemade Batteries.

-Mike W.

(published on 10/22/2007)