You may find yourself hunting through all the batteries at the drugstore, trying to find an LR44 to buy instead of a 303/357. All because you want to be ‘faithful’ to MnO2. (By the way, this particular day you won’t find one.)
Functionally, these button cells are essentially interchangeable, but they have different active materials inside them. The LR44 is an “alkaline” battery which has the overall reaction:
3 MnO2 + 2 Zn = Mn3O4 + 2 ZnO
The 303/357 is a silver oxide battery having the overall reaction:
Zn + Ag2O = 2 Ag + ZnO
They both give you a potential of about 1.5 V. Actually, the silver oxide battery voltage is a little higher, and its capacity is a bit bigger. But if you’ve been concentrating on MnO2 for a couple years in your work … you know … your loyalty might kick in.
We called the voltaic pile the first modern battery, because some believe that objects discovered in the 1930s (that date to the biblical era) were early batteries, called “Baghdad batteries.” These have iron rods surrounded by copper tubes, and the two metals could be separated by an electrolyte. This is the basic construction of the electrochemical cell we described earlier, with iron replacing zinc.
However, it is unknown if these objects were used this way, or for some other purpose that has not been thought of. This type of battery would have a very low potential (about 0.44 volts) and would not have a lot of power. (The voltage of the cell is the difference between the individual electrode potentials.)
By connecting zinc and copper discs separated by brine-soaked cloth, a zinc-hydrogen cell in made. Alessandro Volta studied the effect produced when metals were connected this way. One of his papers (from 1769) was called De vi attractiva ignis electrici or “On the attractive force of electric fire.” In the 1800s the concept of a battery began to be developed. By connecting several cells, stacking them, a higher voltage is produced. The word voltage comes from his name.
The Clear Science Staff got an email from a producer for National Geographic a few weeks ago, and they wanted to record us explaining how a citrus battery works. (That’s us in the video BTW.) It’s for a science/comedy show that comes out next year called Duck Quacks Don’t Echo.
You put nails made out of two different metals into some acidic fruit, like an orange. If one is zinc and one is copper, you essentially make a zinc-hydrogen cell.
The battery half-reactions are 1) zinc electrodissolution (anode):
Zn → Zn2+ + 2e-
and 2) hydrogen formation (cathode):
2H+ + 2e- → H2
The zinc electrodissolution obviously happens on the surface of the zinc nail, and releases electrons. These electrons are at a low potential and want to flow to someplace at high potential. The hydrogen formation has a higher potential, and occurs when the protons (H+) in the fruit acid meet the electrons at the copper nail to form hydrogen gas (H2).
So if the two nails are connected, electrons will want to flow from the zinc nail to the copper nail. In between these two nails you place something like a cell phone. Flowing electrons are electricity, and so when they flow through the phone charger it’s electricity to charge the phone. This is how batteries work.
The Clear Science staff has been busy with battery science lately, so we haven’t had a chance to post. Perhaps talking a bit about batteries would be a good way to fill the void.
Did you know sometimes batteries are actually made of other batteries? If you cut open a 6-volt lantern battery, as they do in this video, you will find 4 smaller batteries inside. Usually these are 4 F-cell batteries (as in the video). Sometimes it is 4 D-cell batteries. An F-cell is like a D-cell but taller.
F- and D-cell batteries each have ~1.5 V potential. So that’s how they get 6 V:
Tellurium (Te) is used in a popular kind of solar cell, the CdTe photovoltaic. Only about 150 tonnes (t) of tellurium are produced a year. Looking at the elemental abundance chart we saw before, you see that tellurium is more abundant than gold (Au). But over 2,000 t of gold are produced on Earth per year. Why can’t we produce more tellurium?
It’s because tellurium is a byproduct of copper (Cu) production. The last stage of copper mining is to electrolytically refine copper on flat cathodes in an electrochemical cell. Selenium and tellurium just happen to form at the anodes in these cells, and so they are collected and sold as byproducts.
So using our current technology, you would double tellurium production by doubling copper production. But 16 million tonnes of copper are already produced every year, and that production uses 0.08% of all global energy. Doubling copper production is not realistic. So how would you double tellurium production? You have to start working to figure out another way to get it. The US Department of Energy anticipates a tellurium shortage by 2025 … (and looking back, it was one of the ECEs.)
We mentioned storing electricity in a battery. A battery stores energy electrochemically, meaning that electrons are “stored” in a chemical with high energy. Any chemistry that involves electrons as reactants and products is electrochemistry. A fuel cell is similar to a battery: both have two electrodes (anode and cathode) and an electrolyte.
There is more than one way to distinguish a battery and a fuel cell:
Batteries store their chemicals inside the battery, while fuel cells are fed from outside.
Fuel cells often involve catalysis, while batteries may not.
Fuel cells operate continuously. Batteries operate in a batch manner, i.e. charge/discharge.