Protein nanowires + Geobacter + humidty = electric potential

[jim mcnamara]

https://phys.org/news/2020-02-green-technology-electricity-thin-air.html

I am not competent to judge this (what seems very edgy to me) article. Basically it says: a ten micron thick protein layer with Geobacter on the surface and protein nanowires arranged in a mesh, when exposed to humidity, generates electricity.

Maybe @TeethWhitener who is knowledgeable in nanoscience can help.

Source:
Power generation from ambient humidity using protein nanowires, Nature (2020).
DOI: 10.1038/s41586-020-2010-9 ,
https://nature.com/articles/s41586-020-2010-9

On a lighter note - if this has merit the Pacific Northwest will become Power Central (with a capital P and capital C) for the Western US.
Forecasts for places like Eugene OR, talk about 'sun breaks'. A few minutes when you can see the sun.

I think @OmCheeto or @BillTre may be able to comment on the humidity aspect of life up there. I live in a desert...

 

[Borek]

It is not nanowires that make me doubt, but the thermodynamics - they have not explained where the energy comes from.

"Out of a thin air" would make a nice twist if it was published on April 1st.

 

[fresh_42]

My thought was as I read it: For an industrial scale we would need much humidity, hence solar or geothermal energy first, plus whatever those bacteria eat.

Funny idea, but I would put my money on algae first.

 

[chemisttree]

I’ve seen a potato provide enough electricity to power small electronics too!

I think ultimately you will find the secret to this redox battery is hiding in the “surface chemistry” of the wires or some redox occurring at the electrodes. I prefer potatoes to smelly sulfurreducens anyway!

 

[Borek]

I’ve seen a potato provide enough electricity to power small electronics too!

Sure, but there is a dissolving wire there, it is obvious where the energy comes from (and when it will end).

I think ultimately you will find the secret to this redox battery is hiding in the “surface chemistry” of the wires or some redox occurring at the electrodes.

In both cases something would be consumed. The way the article is written it doesn't say what is consumed to produce the energy, it just juggles humidity, nanowires, proteins and geobacters.

This is level of reporting that fits tabloid.

 

[chemisttree]

But it’s “Nature!” We must submit to it...

The way its written it is hard to distinguish it from a perpetual motion black box or free energy.

 

[TeethWhitener]

I’ll look at the full paper at work tomorrow when I have access. There’s a fair amount of work being done right now on evaporation and condensation-based energy harvesting (full disclosure: I pitched a program on nanoscale electrokinetic phenomena last year that didn’t get funded ). From what I can tell from various press releases (this one in particular), this device falls into the same category. I’m not sure how they’re maintaining their moisture gradient, but apparently neither are they. Hopefully the paper will be clearer.

 

[berkeman]

But it’s “Nature!” We must submit to it...

You beat me to posting that! Is there a difference between "Nature" and "nature" journal articles?

 

[nsaspook]

More details.
https://static-content.springer.com...9/MediaObjects/41586_2020_2010_MOESM1_ESM.pdf

 

[BillTre]

A couple years ago, for while, I became interested in geobactor making these little nanotube things to apparently conduct electrons from an anoxic layer in sediment to the better oxygenated surface of the sediment.
This allowed the bacteria deep in the sediment (a few centimeters) to make better use of the local resources they had at their disposal (as well IIRC) improving nourishment of the bacteria along the filaments leading to the better oxygenated higher up regions.
It was not clear to me (did not have access to a lot of the journals) how this was happening at a molecular level, but it was interesting. Since I could not figure out what was going on and my journal access was limited, my interest in the subject waned.
I could understand how an electron pipeline between an oxygenated area and non-oxygenated area could be beneficial in a fairly straightforward way, it was not clear how this could benefit a bunch of bacterial along the filament and still provide benefit to the most deeply buried bacteria.
It seemed to be doing more than just conducting the electrons.

This case seems to be doing something similar, maybe conducting electrons to a surface where they are dissipated to a humid atmosphere by shedding molecules with a charge.

 

[TeethWhitener]

It was not clear to me (did not have access to a lot of the journals) how this was happening at a molecular level, but it was interesting. Since I could not figure out what was going on and my journal access was limited, my interest in the subject waned.

It’s still an open question. It looks to be some combination of remarkably high proton conductivity coupled with electron conduction through stacks of cytochromes, but that’s just a guess. I have a number of colleagues working on Geobacter for that very reason.

 

[TeethWhitener]

First glance at the paper:
1) Their device consists of a gold electrode as a base, a film of protein nanowires, and a small gold electrode at the top that does not cover the nanowires completely and allows them access to humidity in the air.
1) Power density is about 4 mW/cm³
2) It's not photovoltaic.
3) the I-V curve does not pass through the origin. This is usually indicative of leakage current or charging of some kind. But the authors assert that it isn't charging (at least not transient charging) because the effect lasts for >12 hours.
4) It's not coming from oxygen or nitrogen in the air, and they did some work to support the assertion that it's not coming from chemical changes in the nanowires.
5) Stable DC voltage of around 0.5V for 2 months.
6) There's a gradient of water adsorption in the device that correlates with the open circuit voltage. This goes away if the top electrode is made to cover the protein nanowires entirely.

The authors' best guess is that the nanoporous structure of the nanowire mesh is extremely slow to saturate with adsorbed water, and the distribution of carboxyl groups in the structure is such that the adsorption gradient corresponds to a potential gradient in the device.

A brief primer on the nanoscale electrokinetic effect that is likely responsible for this: at a solid/electrolyte interface, the solid has a surface potential which impacts the distribution of ions in the electrolyte. This ion distribution has a characteristic length scale (the Debye length), beyond which the ions effectively screen the surface potential from the bulk electrolyte. The Debye length is on the order of 1-50 nm for typical electrolyte strengths. If you shrink nanochannels/nanopores down to this scale, the linearized Poisson-Boltzmann equation that governs the behavior of the electrolyte no longer works, and nonlinear effects start creeping in. Large boosts in the efficiency of the electrokinetic effect are observed, and you can exploit lots of transient gradients (both chemical and physical) in these types of systems to harvest energy (my own interest was in pressure gradients for tidal/current energy harvesting).

 

[BillTre]

A brief primer on the nanoscale electrokinetic effect that is likely responsible for this: at a solid/electrolyte interface, the solid has a surface potential which impacts the distribution of ions in the electrolyte. This ion distribution has a characteristic length scale (the Debye length), beyond which the ions effectively screen the surface potential from the bulk electrolyte. The Debye length is on the order of 1-50 nm for typical electrolyte strengths. If you shrink nanochannels/nanopores down to this scale, the linearized Poisson-Boltzmann equation that governs the behavior of the electrolyte no longer works, and nonlinear effects start creeping in. Large boosts in the efficiency of the electrokinetic effect are observed, and you can exploit lots of transient gradients (both chemical and physical) in these types of systems to harvest energy (my own interest was in pressure gradients for tidal/current energy harvesting).

It seems to me that for this effect to be maintained for such long periods, the charge has to go somewhere so that it does not build up and inhibit the effect.
My guess above, is that some charge gets shed as gaseous molecules in the humidity and can then diffuse away. However, I don't know if this is reasonable or even possible.

The electronics of living things can be quite complex and interesting.

 

[zoki85]

I’ve seen a potato provide enough electricity to power small electronics too!

I've also heard that and was enthusiastic to test it. I tried that and even more (combinations of potatoes,lemons, various electrodes to stick in parallel or series threads).
Complete disappointment...Less than miliwatt in best case. I destroyed few kilos of good food in a process

It is not nanowires that make me doubt, but the thermodynamics - they have not explained where the energy comes from.

"Out of a thin air" would make a nice twist if it was published on April 1st.

It's possible from "a thin air". The device is called a windmill :)

 

[Swamp Thing]

There has been a new burst of interest in this from the popular media, for example:

https://www.telegraph.co.uk/news/20...hin-air-cloud-lightning-clean-energy-machine/

https://newatlas.com/energy/lightning-like-energy-from-air/

 

[guyp]

Comments on "Generic Air-Gen Effect in Nanoporous Materials for Sustainable Energy Harvesting from Air Humidity", authored by Xiaomeng Liu, Hongyan Gao, Lu Sun, and Jun Yao, at the Univ of Mass and published in Advanced Materials on 5 May 2023:
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In any system or device used to transform energy to do useful work, there are two well-established principles in our description of nature that should be considered: They are

1. The Law of Energy Conservation. It is also call the First Law of Thermodynamics, and can be shown to be deeply rooted in nature due to nature’s symmetry in time translations.

2. The Law that the Entropy of a Closed Macroscopic System Cannot Spontaneously Decrease. Entropy is a measure of the disorder in a system. This law is also called the Second Law of Thermodynamics, and can be derived from the statistical behavior of interacting particles.

Both laws have never been found violated in any careful observation of nature over the last one hundred and fifty years.

Liu, et al’s paper does not mention either, even though they describe getting energy in a sustainable process with no depletion of its source and with an accompanying order generation without loss of order elsewhere.

It is no surprise that water in the air (determining the air humidity) contains energy. In fact, all matter contains energy. If one wishes to produce work from any other form of energy, a system should be devised that converts energy from that other form to mechanical energy, such as the energy a piston supplies in exerting a force over a distance, or the kinetic energy of an electric current. It is also desirable that one is able to bring the system back to its original state in a cycle, so that the process can be repeated.

When water vapor changes from a gas phase to a liquid or bonds with another molecule or adsorbs to a surface, the entropy of that water necessarily decreases. If one surrounds the materials taking part in the process with a boundary impervious to energy or material transfer, then somewhere in that closed system the entropy must increase to a value at least as large as the amount that the water lost. This entropy most often is derived from the heat release in the process. A useful example is a hurricane. Hurricanes are formed over warm water. That warm water heats the air above, and releases water vapor. Because the air in the atmosphere several thousand feet above is colder than the warmed air below, and because warmed air is lighter than colder air, the warm air rises, carrying water vapor with it. As that moist warm air rises into the colder air above, the cooling causes the water vapor to condense into liquid water (droplets). In the process, heat is released, warming the air, which then rises even faster. In the meantime, the water droplets drop back to the ocean, tending to cool its surface. But rising moist air draws more moist air from the surrounding water surface, intensifying the hurricane. The net result is that heat flows from the warm surface air and ocean into the colder stratosphere while work is done in the motion of the air, i.e. there is a conversion of heat energy into some work. Air conditioners take advantage of the inverse process by changing the phase of a liquid into a gas to produce cooling. None of these processes violate the first or second law of thermodynamics.

Note that extracting energy to produce just work in a non-cyclical process does not violate the laws of thermodynamics. A good example is a very long insulated cylinder containing a gas, with one end wall being a piston. One can let the gas push the piston while expanding. The piston can do mechanical work, all coming from the kinetic energy of the gas. (For an ideal gas in an adiabatic (no heat exchange) process, the entropy of the gas does not change during an expansion of the gas, so the overall entropy change is zero. Neither the first nor the second law is violated. But this expansion is not a sustainable (i.e. cyclic) process.

Now, in Liu et al’s work, some water vapor presumably adheres to the surface of a material (inside small channels). This reaction must reduce the entropy of the water. In the process, it may also produce free electrons which could cause an electric potential gradient along the channels. The freed charges can make a current. However, once all those charges are removed, the process stops. Liu noted that other research groups had observed this loss of current in similar setups. However, if Liu and workers had a much larger effective surface, the total in all the channels, then they may not have waited long enough to see the current drop (i.e. longer than 48 hours). Again, since the charge depletes, the process is non-sustainable. One could rejuvenate the system by purging the channels of water. But this would require an energy input. As the initial adsorption of water molecules into the channels required a production of entropy, the efficiency of this now thermodynamic engine will be less than 100%.---------------------------------------------------------------------