Is it the perfect energy solution? Where solar, carbon capture and bio collide

March 22, 2016 |

BD-cover-032316-smOne of these days your personal transportation system might look like this. A solar or wind energy facility generates renewable electricity, which is converted into a solar fuel using electrofuel technology that converts CO2 and water to a fuel using electricity (rather than photosynthesis) to power the operation. That fuel is then used in a Microbial fuel cell that is loaded on your vehicle, which translates the fuel back into an electric current for an electric motor.

Advantages? First, renewable electricity. Second, we bypass the metal battery which causes range anxiety and the endless re-charge blues in transport vehicles. Third, we switch to higher-efficiency electric motors.

You could even power a plane this way — since the problem with the solar plane is not the electric motor itself, but rather the weight of the conventional batteries compared to their energy storage capacity.

Back to school with Microbial Fuel Cells, for a sec

Microbial fuel cells have been around since the end of the 1990s, so you might ask — where are they? Especially since a proposed first application in wastewater treatment has happened, either.

According to the resident guru of MFC, Penn State’s Bruce Logan, two problems have proven stubborn. He observed last year in Environmental Science & Technology Letters:

One main reason is the cost of the electrodes. It was estimated that the electrode materials would need to cost less than 100 € per square meter (∼$110 USD) to make them economically viable. This now seems to be possible with advances in inexpensive anodes, separators, and cathodes based on activated carbon catalysts. Another factor that could limit the development of larger-scale MFCs is diminished power at larger scales. 

Science took a step forward recently in both these challenges with work in carbon nanotubes. A team of researchers reporting in the Journal of Power Sources observed:

Microbial fuel cells (MFCs) are a promising technology capable of directly converting the abundant biomass on the planet into electricity. Prior studies have adopted a variety of nanostructured materials with high surface area to volume ratio, yet the current and power density of these nanostructured materials do not deliver a significant leap over conventional MFCs. 

The results show that CNT-based materials attract more exoelectrogens, Geobacter sp., than bare gold, yielding thicker biofilm formation. Among CNT-based electrodes, low sheet resistance electrodes result in thick biofilm generation and high current/power density. The miniaturized MFC having an SSLbL CNT anode exhibits a high volumetric power density of 3320 W m−3. This research may help lay the foundation for future research involving…2D and 3D nanostructured electrodes.

OK, let’s do that again in everyday language. Two key takeaways. One, a carbon nanotube material is outperforming gold in aspects of a microbial fuel cell. Uh, that helps on cost. Two, the power density is around 3X of what we usually see with microbial fuel cells. Though this does not predict results at engine-scale, starting with a lot more power density is sure to help.

Several types of microbial fuel cells.

Several types of microbial fuel cells.

Now, you might be asking at this stage what is happening to make carbon nanotube production more predictable — since nanotubes look like spaghetti when you make them today, even if they have tremendous improvement in conducting electricity.

So, it’s also good news that a research team out of Australia is reporting that a technology that won some notoriety last year for unboiling an egg, is now being used to standardize the length of carbon nanotubes. This is a spinning reactor, rotating at up to 15 revolutions per second — the energy environment created inside the reactor has the capability to produce a “kink” in a carbon nanotube. Not unlike making a kink in a paperclip or folding a sheet of paper, making it easier to break at a desired location. And with a guided laser, the team has been producing same-length nanotubes around 170 nanometers.

And yes, that technology really can unboil an egg. The reactor unfolds and refolds proteins, which allows it to refold the gelatinous whites of an egg back into their original liquid form.

(By the way, if those spinning reactors sound familiar, they’ve been experimented with for almost a decade now as a low-cost, low-temp, low-pressure means of making biodiesel from virgin or waste oils).

OK, let’s put all that together again

The precision-length nanotubes, it is believed, will allow for more elegant design of 3D anodes in a microbial fuel cell, sharply improving the efficiency and reducing the cost. We’ll have to see about scale-up, that’s for later.

Assuming it scales effectively to transport-scale, that microbial fuel cell uses selected cyanobacteria or bacteria to generate electricity for an electric motor, from an energy-dense fuel. That is to say, a bio-battery that has immense range compared to an electric battery.

In turn, that fuel is solar fuel, which is to say that it is made using solar or wind energy, plus CO2 and water (one day, might be wastewater, and even now it can be brackish non-potable water).

So, if you see a solar facility providing power, a wastewater facility providing water, and a coal-fired power plant providing captured CO2 — all working together symbiotically to provide utility services to a metro area, but also the elements for a solar fuel — well, that’s the picture. No emissions of course — it’s all captured for an industrial symbiosis.

That fuel can be distributed as liquid energy via pipeline, truck and rail to conventional re-fueling facilities. No need to depend in the long-term on slow-charging electric battery stations, only.

If you’ve considered the range efficiency, the charging time, and the zero emissions — you might think that’s a really great way to power an industrial economy going forward. And that’s true zero emissions, not Obamemissions where only the tailpipe output is considered regardless of whether you are producing electricity using renewables, or coal or oil.

How possible is it?

Feeding a Joule or Algenol solar fuel to a fuel cell to produce electricity, that can be done. There are direct-ethanol fuel cells, and a vehicle using an early-stage of this technology competed in a Shell Eco-marathon in France in 2007. But we probably have a while to wait for true electrofuels, that use renewable energy, CO2 and water — rather than photosynthetic technologies. More about the Electrofuels, here.

The Bottom Line

We’ve identified this technology — if made robust and scaled — as a real candidate for “natuional energy solution” because it wraps up so many societal goals ranging from low-carbon, low-cost, high performance and affordable infrastructure, all in one.

So, one to watch.

Further reading

We looked at the biobattery in depth last year, here.

More on microbial fuel cells and nanotechnology here.

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