Author Archives: joshuagallaway

A simple fuel cell

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When I was a grad student I had to run a lab for undergrads to make their own fuel cells. This was a drawing I made to explain the basic components and how they went together. The metal plates on the outside are the current collectors. At the center is the membrane-electrode assembly or the MEA. It’s a piece of solid electrolyte membrane that feels a bit like a piece of rubber. On each side is a small square of catalyst, usually platinum particles.

I have to tell you, I sort of miss painting platinum onto MEAs. However, I do not miss helping people put these together. Getting all that lined up and sandwiched together is harder than it looks.

A battery scientist’s trivial dilemma

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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.

Battery researchers

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Pictured above are Daniel and Jerome, in the battery lab at CUNY. Both of these guys are going to grad school in the fall after working here for a while. It’s been great having them, and we’ll miss them a lot.

Jerome was a student in my transport phenomena class at NYU three years ago. When class was over he was about to enter his last year, and he asked if he could do his senior project working with me. One day a week he took the train up to Harlem, where CUNY is, and built batteries for a year. He must have liked it, because after graduating he started working here as an engineer, and now has a hand in just about everything we do.

Each year since then I’ve had a new student from NYU working on batteries at CUNY. They get their senior thesis out of it, but also they get a chance to see how research really works, and I think that’s important for someone who wants to work in science and engineering. Interpersonal skills, how to get time on lab equipment, how to organize your data, how to find important variables, how to tell what experimental noise looks like, etc. Back in the 90s I was a co-op student at Owens Corning, and I learned a lot of things there … skills I still use today.

New Book About Enzyme Electrodes

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I wrote Chapter 9 in Enzymatic Fuel Cells: From Fundamentals to Applications, which is coming out May 19th. It’s edited by Plamen Atanassov, Heather Luckarift, and Glenn Johnson. The book grew out of a multi-university research project I was part of as a graduate student, with the goal of using biological catalysts for small power sources.

This is controversial research: it is, trust me. But if it works it has a high payoff. Summarizing just one possible application: we as humanity use an expensive element, platinum, for almost all of our room-temperature catalysis. This is why you don’t own very many things that involve room-temperature catalysis. However, living things do catalysis at physiological temperature (98.6 degrees F, not much higher) all the time. If we could use their tricks, catalysis would get much less expensive.

Some enzyme electrodes actually have incredibly high volumetric energy densities. The ones I was making as a graduate student reduced oxygen at 40 A/cm3 at 0.7 V, which is higher than some old-school platinum electrodes, and they do all the catalysis with copper. The downside is they don’t last a long time. But since platinum is 21,000 times more expensive than copper, it could be worth it.

My chapter gave a me a chance to summarize my graduate research in a unified way, making the point I wanted to make. Essentially I showed you could double the catalytic current of one of these electrodes by being smarter about the transport phenomena involved. I published the results in two papers with dry, academic titles, because let’s face it I sometimes like the dry and academic. Only now, after a few more years of experience, I feel it would have been better to publish them together and title it The Point Is The Current Is Twice As High. Here’s the important graph below (from here):

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See how the curves are S-shaped, and the bottom part is at about -7 mA/cm2 in one case and about -14 mA/cm2 in another? That’s the doubling. There’s actually a more important figure earlier in the paper, but this one is the easiest to explain. Science: it’s also about communication.