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Curious layman

Electricity from rust

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There are many ways to generate electricity-batteries, solar panels, wind turbines, and hydroelectric dams, to name a few examples....and now, there's rust.

New research conducted by scientists at Caltech and Northwestern University shows that thin films of rust -iron oxide- can generate electricity when saltwater flows over them. These films represent an entirely new way of generating electricity and could be used to develop new forms of substantial power production.

Interactions between metal compounds and saltwater often generate electricity, but this is usually the result of a chemical reaction in which one or more compounds are converted to new compounds. Reactions like these are what is at work inside batteries.

In contrast, the phenomenon discovered by Tom Miller, Caltech professor of chemistry and Franz Geiger, Dow Professor of Chemistry at Northwestern, does not involve chemical reactions, but rather converts the kinetic energy of flowing saltwater into electricity.

The phenomenon, the electro kinetic effect, has been observed before in thin films of graphene- sheets of carbon atoms arranged in hexagonal lattice -and it is remarkably efficient. The effect is around 30 percent efficient at converting kinetic energy into electricity. For reference the best solar panels are only about 20 percent efficient..... more at link.

https://phys.org/news/2019-07-ultra-thin-layers-rust-electricity.html

 

 

Edited by Curious layman

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Interesting. However...

"For perspective, plates having an area of 10 square meters each would generate a few kilowatts per hour—enough for a standard US home," Miller says. "Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term."

 

1. kW per hour isn't a thing (Chemists, amirite?)

2. "Remote locations" must be near a source of moving water for this to be used.

One of the things not explained in the story is how they arrive at their efficiency value. This is a surface effect, and you probably have laminar flow. Is the efficiency the fraction of the flow energy converted into electrical energy for the bulk fluid, or the fluid that participates in the reaction? It's only the water close to the plate that contributes.

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35 minutes ago, John Cuthber said:

It is a thing, but not a useful thing.

 

It looks to me as if someone has invented the Edison cell again, but mistaken it for something else

https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery

This isn't being described as a battery - no chemical reactions taking place.

 

"the phenomenon...does not involve chemical reactions, but rather converts the kinetic energy of flowing saltwater into electricity."

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At this rate
"They found that it generated several tens of millivolts and several microamps per cm-2."

 it hardly matters

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"several tens of millivolts and several microamps per cm-2."

So that's about 100 nW per cm^2

About a milliwatt per square metre.

 

According to this page

https://bee-health.extension.org/honey-bee-nutrition/

"A worker bee needs 11 mg of dry sugar each day"

Sugar stores about 4 KCal per gram or 16KJ/g

So 11 mg  of sugar provides 176 J

That's pretty close to 2 mW

So they are producing energy at about the rate needed to keep a bee flying round a 2 square metre flowerbed.

On 7/31/2019 at 6:30 PM, John Cuthber said:

 

 it hardly matters

 

It may be technically interesting, but it's not going to save the world.

9 hours ago, J.C.MacSwell said:

Why would an increasing rate of electrical power not be useful?

Because it's not real.

Edited by John Cuthber

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2 hours ago, John Cuthber said:

"

Because it's not real.

Power output can and does change over time.

kW per hour is real...it just does not have not common usage.

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4 hours ago, J.C.MacSwell said:

Power output can and does change over time.

kW per hour is real...it just does not have not common usage.

OK, it's a real thing.

But it's not a real thing in this thread.

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