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.
Carbon bonded to other carbon, which is a kind of reduced carbon, is what we use for energy. What kind of energy you ask? Well, how about food, which is a kind of reduced carbon. Food is sugars, proteins, fats, etc, which are all carbon chains. Also how about fossil fuels like gasoline (let’s call that octane). The bonds between the carbons have energy in them, and we get that energy out by digesting them or burning them.
Other carbon chains you might like: animals (which you eat), plants (which you eat), you, everyone you know, fossil fuels (which you burn), most polymers like plastic bags, soda bottles, and on and on and on.
The Clear Science staff is kind of over-simplifying here: there are other elements in these molecular chains, like H, O, and N. But anything organic is based on carbon chains, so you can think of them as being reduced carbon.
The Clear Science staff was going to answer the question"Is there a decay rate in heat at distance from a flame/heat source?" To do that let’s consider one way that heat transports from one place to another: conduction.
Heat is energy. Say we have a flame on the left and no flame on the right. The flame is there because some chemical reaction is happening: chemical bonds are breaking and their energy is being liberated. Because of this the temperature of the flame is high, like 1500 degrees. On the right temperature is only room temperature or 20 degrees.
Heat moves by conduction from high temperatures to low ones. This is a basic property of the universe, and it is described by Fourier’s law. Written above in “math language,” what it says in English is "heat flux is proportional to the negative of the temperature gradient." Or: heat fluxes from high temp to low.
We mentioned a recent paper that examined silicon/carbon fibers for use in batteries. Shown above is a TEM image from the paper. From it you can tell the fibers are essentially hollow carbon fibers with a layer of silicon around the outside edge.
Transmission electron microscopes (TEMs) work by shooting a beam of electrons through a sample. The sample has to be quite thin to let the electrons through, but since these fibers are around 100 nm thick that is fine. The important thing is that the image is made with electrons. This is different than the sort of images you’re used to, such as those made with cameras, regular microscopes, or even your eyes: all of those images are made by light. Electrons have a smaller wavelength than light, and so electron microscopes work at extremely high resolution: in some cases you can make out individual atoms with them.
Why would anyone care about silicon-coated nano-fibers? Because lithium ions can be stored inside silicon, and that makes these fibers well-suited to storing lithium for lithium ion batteries. Some researchers think we may be able to extend the life of batteries using these.
Let’s talk about some recent science work on lithium-ion batteries, and the journal article reporting the work. Scientists tell each other about their work through articles (or “papers”). This one is called: In Situ TEM Investigation of Congruent Phase Transition and Structural Evolution of Nanostructured Silicon/Carbon Anode for Lithium Ion Batteries.
Sometimes titles are hard to understand unless you break them down into pieces:
TEM is transmission electron microscopy
in situ means they’re doing some experiment and watching it happen inside the TEM
phase transition means atoms are going from one arrangement to another
structural evolution means the experiment is changing the material somehow
nanostructured means the size they’re looking at is less than 1000 nanometers
an anode is the negative electrode in a battery
lithium ion batteries are like computer or cell phone batteries
This paper is in a journal called Nano Letters. Under the title is a list of names. These are the authors. Basically that is everyone who did the science work, dreamed it up, paid for it, or wrote the paper. (This C&EN article on the paper summarizes and contains a link to it.)
The Clear Science staff has been spending time doing experiments to probe the hidden secrets of battery materials. A battery is a device that converts chemical energy to electrical energy, which you can then use to power something. A battery has two electrodes, and each one has a different chemical.
We’re using light reflections to study these chemicals. Let’s talk about what that means. Pictured above is a coin cell battery, like you might see in a watch. We’ve modified it to have a window on each side to shine light through, and we’ve put it in a special holder.
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.)
Reading about Energy Critical Elements (or ECEs) the other day, the Clear Science Staff found ourselves thinking of this plot of elemental abundance in the Earth’s crust. The data comes from this US Geological Survey website. This can give you a good idea of how easy certain elements are to come by. The most common are oxygen (O) and silicon (Si), otherwise known as sand or glass when you put them together (silica SiO2).
Precious metals like platinum (Pt), gold (Au), and osmium (Os) are in the group of lowest occurrence. Rare earths are labeled in blue, and you can easily see they are not the most common but also not the rarest elements. However, this numerical “abundance” is only part of the story. There are other considerations when deciding how easy an element is to come by …