Some Science!

Note: this post is about the science that I am doing this summer. If you're more interested in my posts about travel, wait until Monday, when I will post about my awesome upcoming weekend with Max and Chris in Amsterdam.

My main project for this summer is entitled "Supercritical synthesis of PtBi nanoparticles for use as a fuel cell catalyst". Now I will explain what this means. It takes a minute, so hang in there.

Fuel cells work by converting chemical energy into electrical energy - that is, they react chemicals together to get electricity out. A fuel cell has 3 main parts, the anode, the electrolyte, and the cathode. In a standard hydrogen fuel cell (the most basic type), hydrogen is supplied to the anode where it is converted to 2 H+ ions and 2 electrons. These H+ ions can travel through the electrolyte, but the electrons cannot. They must travel through an external circuit, which generates the electric current. At the cathode, the H+ ions and the electrons are reunited, and combined with O2- ions (which come from the air) to form water. Here is a simple picture:
However, there are a lot of problems with this standard fuel cell. The first is the problem of using hydrogen as a fuel. It's hard to make, dangerous to store, and, since it's a gas, it takes up a lot of space. So, there has been a lot of research lately into running fuel cells on other fuels. Most of these research is focused on small organic molecules (SOMs) such as methanol, ethanol, formic acid, or ethylene glycol (antifreeze). There is a particular focus on ethanol, since it is less poisonous than the other SOMs, and can be produced from plant sources (but don't even get me started on how much I dislike corn ethanol...).

Additionally, the hydrogen doesn't just split into ions and electrons by itself. It needs a catalyst to do this. The most effective and commonly used catalyst is platinum. However, platinum is very expensive. In fact, it has become so expensive lately, that catalytic converter theft is dramatically on the rise due to the platinum that they contain. Anyways, when the conversion is made to using SOMs as fuel instead of hydrogen, platinum doesn't work so well as a catalyst anymore. Why? Because platinum becomes "poisoned" by carbon monoxide, an intermediate in the oxidation process that must take place at the anode. Basically what this means is that the CO sticks to the platinum atoms really well and won't leave or allow other atoms to bind to the platinum, so the reaction can go no further.

Scientists have found that by adding other metals, such as lead or bismuth, to the platinum, they can prevent this CO poisoning. In a very general sense, this is because the addition of other atoms increases the distance between the platinum atoms, which keeps the CO molecule from forming the "bridge" between two platinum atoms that it needs to stay stuck on them. So, this is really great. The PtPb and PtBi catalysts solve the CO problem, they're cheaper than pure Pt, and they work for lots of different SOM fuels.

Next problem? They take a really long time to make. In order for them to be a feasible solution and bring fuel cells to a mass market, all parts of the cell must be cheap, quick, and easy to manufacture. This is finally where I come in, in case you were lost in here somewhere. I'm working on a new way to make PtBi nanoparticles that could be used as a catalyst. Instead of taking a day or a week like the old methods, this method takes about 1 minute, max. It's also very reproducible, easy to scale up, and doesn't use any toxic reagents.

This synthesis method is called supercritical synthesis. If you look at a simple phase diagram, like this one for water:
you can see that, at high temperatures and pressures, there is something called the "critical point" in the upper right of the graph. Water at temperatures AND pressures higher than this critical point is called supercritical. This is true for any gas/liquid, but the most common species used for supercritical synthesis are water and carbon dioxide. I will be using supercritical water as a solvent to synthsize PtBi nanoparticles. There are all sorts of ways that I can set up the synthesis to hopefully effect the size and structures of these nanoparticles, but I will save that for another post.

In general, fuel cells are sort of depressing to work on (also did some work on them last summer). As you can see, every time one problem is solved, 10 more pop up. I realize this is true for most scientific challenges, but I think fuel cells are worse than most. I think the scientific community has pretty much realized that hydrogen fuel cells are a lost cause, but it's still holding out for the hope that they can be feasible when used with ethanol/methanol. In my opinion (a quite hypocritical one since this is my second summer working on fuel cells), we should be spending a lot less energy (hah, a pun!) on these and a lot more on battery technology. They're similar fields, but battery technologies are way behind where they should be, and I think that they're really holding us back in terms of electrifying a good deal of our transportation. We have the energy generation part down: wind, solar getting better every day, etc. Energy storage, people. That's what we're still missing.