Monthly Archives: May 2014

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.

Tesla Gigafactory

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tesla-assembly-lineThe current Tesla plant in California. (photo credit)

The Gigafactory is a giant battery production facility planned by Tesla, to be built in one of the following states: Nevada, Arizona, New Mexico, Texas, or California. It’s a powerful effort to force down lithium-ion battery costs by bringing together all the members of the supply chain and consolidating the process in one location. Tesla can do this because it buys a lot of batteries, but also because it has star power.

Tesla is the most exciting thing in batteries at the moment. Lithium-ion battery cost is about $500/kWh, and Tesla wants to bring that down significantly to make electric vehicles a reality for everyone (not just people who can afford expensive cars). Some analysts believe that lithium-ion batteries, as they are currently constructed, have an inherent limitation between $200-300/kWh. This is due to the production costs and the materials (active material, electrolyte, etc). The target cost for electric vehicle batteries is lower than that, under $200/kWh, but it seems like Tesla’s effort will go a long way to making it work. Other battery applications, like utility-scale stationary batteries, will need to be even cheaper though. So it’s clear other battery chemistries will need to fill that space.