Just saw this pop up in my New Scientist feed. Here is the headline:
Platinum-free fuel cell promises cheap, green powerMy first reaction when I saw that was, "No! No! No!" and then I got mad again that the technical press just seems to not care anymore. What am I ranting about? Well lemme explain.
I have talked about fuel cells before. Well mostly one fuel cell in particular. I don't want to go over what they are or the specifics of how they work again. There are great resources on the net for that. for this post, you will need to go to those links to freshen up on what a fuel cell is, and understand the difference between power and energy is. Wikipedia has a nice picture of a PEM fuel cell here it is.
The most common proton exchange membrane (PEM) fuel cell has a layer of catalyst on either side of a membrane. This catalyst is usually Platinum, but could also have some palladium and/or ruthenium in it to achieve different properties. Scientist have been futzing with the catalyst for decades to try to achieve higher and higher power densities (the amount of power per square centimeter of membrane). To some degree they have done this.
Another aspect of fuel cells that has improved is the efficiency of fuel cells. Efficiency is a measure of the amount of energy pulled out of the fuel and used for work (or useful heating) relative to the theoretical energy contained within that fuel. Companies like MTI Microfuel cell has claimed 30% for their microfuel cells (because they get 1800 Wh/kg of fuel, whereas the theoretical limit of methanol is 6000), whereas other PEMs and other fuel cell systems can claim 60% or higher. The only reason a fuel cell is considered green is because it should have greater efficiency than an engine or other fuel burning competing method. If a fuel cell has crappy energy efficiency its simply not a green product.
OK, so what is wrong with the New Scientist article? The claim is that lowering the platinum cost of a fuel cell will lower the cost of the fuel cell. The article claimed that the reason to use platinum is because:
Platinum has so far been the metal of choice because the membranes used in fuel cells create a very acidic environment, and the metal is stable in such corrosive conditions.That may be technically correct but it is hardly the sole reason for using platinum. The bigger reason is that no other catalyst gives as high a power density or energy efficiency. Besides, the membranes don't "create a very acidic environment", they are acidic. The acidity is what makes the protons go through the membrane while the electrons go around.
So then the next claim comes:
Now, though, Lin Zhuang's team at Wuhan University in Hubei province, China, has designed a new membrane that is alkali, not acidic - making it possible to use a much cheaper, nickel, catalyst.Again, not technically wrong. I'm sure this guy has done this. What this is saying is that instead of a membrane in which protons move from one side to the other, negative ions, called anions, like hydroxyls (OH-) are moving from one side to the other. But it is hardly news worthy. Acta sells an anion exchange membrane from Tokuyama. And there have been others. The Medis fuel cell, while it does not have a polymer membrane, it too was a alkaline fuel cell.
Alkaline fuel cells have been around for decades. In fact the first fuel cells that went up to space we also alkaline fuel cells. They do have the advantage that they do not need platinum to achieve their highest power density, they can use nickel or iron. But the alkalinity of the Zhuang fuel cell and the fact that they have an anion exchange membrane are hardly news.
The team's new polymer proves easy to make into fuel-cell membranes, and can also be mixed with the catalyst itself - this increases the contact between the two components and boosts efficiency.Uhhh. the PEM membranes can also come in a form that is a liquid and be mixed with catalyst for better contact. Not news.
Previous attempts to change the acidic conditions inside fuel cells involved using liquids, not solids, says Zhang, but they risked forming carbonate deposits that can clog up the cell.Apparently Zhang is not keeping up with the literature. There have been previous alkaline membranes.
A working prototype of the new low-cost fuel cell shows a "decent" performance of 50 milliwatts per square centimetre at 60 °C. "The power output is still lower than that of fuel cells using platinum, but such a comparison may not be appropriate because platinum fuel cells have been studied and optimised for decades," Zhuang says.Yes and the catalysts for alkaline fuel cells have been worked on for decades also. Not news.
The part that gets me is the idea that platinum is the major cost of a fuel cell. Its simply not. Lets find a fuel cell for sale. Here is one.
This sucker can put out 330W and it weighs in at 1.7 Kg. How much catalyst is that? Well we need to know a few things.
Active area per cell: 19.4 cm2
Number of cells: 60
Total Active Area: 1164 cm2
Pt loading: 0.7 mg/cm2
So the entire amount of platinum in this system is: 815 milligrams.
How much does that cost? As of this writing platinum is costing 830 dollars per ounce. or 26 dollars per gram.
So the entire cost of all the platinum for this entire 3000 dollar system is: 22 dollars.
See what I mean? Even if you double the cost of the platinum to gain performance, and then double it again because it needs to be refined to very small and pure particulate. We are still less than 100 dollars of the 3000 dollar system.
The cost of refined nickel isn't free either. I get antsy whenever I see claims of fuel cell costs dropping because someone figured out a way around the use of platinum. In a fuel cell system, the plates need to be made, the plates need to be assembled with the membrane and gas diffusion layers and gaskets between them. Then the fuel cell stack needs to be installed in a system which has controls and fuel ports, pumps and valves. You get the picture.
My last gripe about that useless article is the following...
Not once was efficiency mentioned. Not once. So how can any sort of claim about "greenness" be made? If the efficiency is not above at least 45% I say you don't get to use the word "Green".
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