Artificial Photosynthesis in the Absence of Light | Hacker News Reader

Artificial Photosynthesis in the Absence of Light

nature.com

69 pointslr4444lr25 comments

Interesting chemistry, it's kind of like a modified Fischer-Tropsh but at room temperature and pressure (and not a complete reduction to hydrocarbon level)::

> "To achieve maximum selectivity and production of acetate from a direct CO2 feed, a two-step electrolyser system was demonstrated to convert CO2 to CO and then CO to acetate through a tandem process ... [stage one] produces a gaseous product stream containing CO, H2 and trace CO2... The gas product stream was then fed to the cathode chamber of the CO electrolyser... By maximizing the conversion of the first and second electrolysers, as well as specifically targeting acetate over other multi-carbon products, this system was able to achieve a single-pass conversion of CO2 to acetate of 25%..."

That's a respectable yield, but it doesn't look too easy to scale up. That's typical for research prototype work like this (iridium anode seems tricky). They're also using 100% CO2 as the feed gas so there's a preconcentration step from atmospheric CO2 required (400ppm starting -> 100% pure takes some energy input).

Seems fairly promising, they were getting 0.19 g of yeast (marmite basically, or nutritional yeast) per g of produced acetate. Mars colonists take note.

Did you see the recent breakthrough where platinum was dissolved in gallium and worked as a liquid catalyst, but even better than in the solid phase?

I wonder if something similar could be done with iridium or other platinum group metals.

Entire new types of chemistry might become viable at industrial scales…

If it becomes a problem just getting enough iridium for scale, there's lots of iridium in asteroids. Could be worthwhile if you're a space colony, or if reusable rockets make launch cheap enough.

This diagram explains the gist of the paper [1]. This system supposedly enables growing "algae, yeast, mushroom-producing fungus, lettuce, rice, cowpea, green pea, canola, tomato, pepper, tobacco" in the dark with acetate.

[1] https://www.nature.com/articles/s43016-022-00530-x/figures/1

Algae and fungus can be done in the dark, but there seem to be some limitations to full plants still: "Plant tolerance and consumption of acetate as a heterotrophic energy source will need to be increased to fully decouple plants from biological photosynthesis."

Oh you are right. Looks like they did manage grow some "undifferentiated lettuce tissue" in the dark using acetate and then did some preliminary work to show that whole plants can metabolize acetate when grown in the light. I wonder what the plan is, if any, to increase "plant tolerance and consumption of acetate as a heterotrophic energy source".

This should greatly improve the efficiency of growing marihuana indoors. The terrible efficiency of photosynthesis of 1% (as stated in the paper) means that currently 99% of the electricity* used to light up the plants is wasted!

Apart from drugs, other grass-roots indoor farming efforts will also profit from this because this approach allows separating the carbon-fixing from the actual farming.

Edit: to expand on the previous paragraph, there could be a business opportunity for large-scale carbon-fixing businesses that sell the acetate to farms. At least after the kinks in the growing procedures have been figured out.

*: the lamps themselves also don't have 100% efficiency

Your comment about the efficiency isn't correct because you haven't taken into account the fact that grow lights do not emit the same spectrum as the sun.

This is even more relevant with LED grow lights as the diodes are emitting specific wavelengths of light.

Combine this new technique with grow lights, and maybe we do even better.

Not only is PV much more efficient than photosynthesis, it also doesn't require so much water, and can operate at temperatures (hot or cold) that would kill most plants. The downside is that PV modules don't grow themselves.

We also cannot eat PV modules (for now)

But electricity from PV can power various biological systems, or produce chemicals that can be feed to chemoautotrophs.

This would be great for space travel and off planet colonies.

So is this about integrating with solar panel farms (which we are already doing and is pretty damn cool - basically plants under the panels is the simple way) or a completely novel method on its own?

My read of the abstract is that it is about growing food without sunlight or aid the growth of food with sunlight plus their thing. This is the focal sentence in the abstract:

> Here a two-step CO2 electrolyser system was developed to produce a highly concentrated acetate stream with a 57% carbon selectivity (CO2 to acetate), allowing its direct use for the heterotrophic cultivation of yeast, mushroom-producing fungus and a photosynthetic green alga, in the dark without inputs from biological photosynthesis.

My understanding is that they take CO2 from the atmosphere, run it through an electrolyzer to create acetate, then add the acetate to the plants' environment to skip the need of sunlight in and/or aid photosynthesis.

Note that I am not a biologist so this could be completely wrong.

A huge benefit would be to reduce the amount of space we need for farms. These could be turned back into forests or converted to grow crops that are not compatible with the acetate boosting yet. Also, this would enable highly urbanized countries to achieve a greater degree of self-sufficiency, which decreases the need for costly transportation.

I’ve seen lots of people trying to solve the “farms take up too much space” issue, but far less evidence that it is actually an issue in the first place

It's an issue for the areas of the world currently facing food scarcity. Producing on-site is going to be cheaper if there is no distribution set up.

Assuming the reason for the food scarcity is a lack of space. It could also be a lack of funds for efficient farming machines. Or a lack of labor. I wouldn’t assume food scarcity is caused by lack of space in most places experiencing it.

With funds and labor you still cannot reasonably grow food in a desert. Fertile land and compatible climate are actually the limiting factors - I think.

It's not just the lack of space, growing indoors allows you to control the climate. This has a massive impact on efficiency.

The acetate could be used to increase the carbon content of the soil, which should make it possible to bootstrap a richer ecosystem within. The chernozyms of the Eurasian steppe and the terra preta of the Amazon basin are examples of extremely fertile carbon-rich soils.

I know some of these words...is the idea that acetate is the end result of photosynthesis, and they're just skipping that step? Or is there a different metabolic pathway that plants have which accepts acetate if it is in the environment but falls back to photosynthesis if it is not?

So does this mean chlorella can be mass-produced cheaper than crops? This would be a second "Green Revolution" if this scales up, it will free up lots of land.

Is this something that might be directed toward CO2 scrubbing?

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