A cheap and efficient way to directly convert industrial CO₂ offgas into oxygen and solid carbon

By Community last

October 17, 2021

WN: Wow! Shout it from the housetops!

excerpts:

We can’t go on belching CO₂ into the atmosphere at the rate we’ve been doing it.  But CO₂ is a product of combustion, and combustion’s not going to disappear in time to meet any climate goals.  Far from it.  We’ve painted ourselves into a corner on that one.

So what can we do in the meantime?  The whole carbon capture and sequestration idea, which would pipe CO₂ for miles and bury it underground, seems frankly kind of nuts.  Not only is it literally sweeping the problem under the rug, but it also seems to help continue funneling big bucks to oil companies, who conveniently are the only ones who have the technology to shove stuff miles underground.  Plus, in practical terms, it hasn’t gone well at all.

So … what else can we do in the meantime?  After years of experimentation with different catalyst formulations, an Australian team of researchers has devised a cheap and scalable way — with the help of simple mechanical energy, of all things — to split CO₂ into C and O₂.  I got so excited I split an infinitive right in my title.

They reported the finding in the October 6 edition of Advanced Materials, the top American materials science journal.

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Our Aussie friends here used a totally different approach: mechanical energy.  But how do you convert motion into electrochemistry?  The key here was the triboelectric effect.  The formal way of describing this is “a type of contact-induced electrification in which a material becomes electrically charged after it comes into frictional contact with another, dissimilar material”.  But the relatable way of getting it across is this:

 
There are certain materials that match up really well this way, like polystyrene and cat fur, or a balloon and your hair.  By rubbing them together, we can transfer electrons from one surface to another, or we can induce charge separation in a material.

So maybe there could be a way to use this phenomenon to transfer electrons to CO₂ and activate it so that it will react with something and cease to be CO₂.  Well, there is!  But it wasn’t too easy to find.  That’s what these researchers have been tirelessly working on for years, and after an awful lot of tinkering, they hit on a system that really gets it done.

Before we go into the details, let’s step back and appreciate the big picture.  They got a 92% efficiency of conversion of CO₂ into solid carbonaceous product — at only around 100°F — with an energy input of only 230 kW∙h per ton of CO₂.  The cost of electricity in the U.S. is about 12 cents per kW∙h.  So that’s about $27.60 to get rid of a ton of CO₂.  Errr, OK!  I’ll buy!

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The authors gallantly try to explain what the fork happens when a crystal of Ag_0.72Ga_0.28 strikes a gallium droplet.  They do know that when this happens, an ultrathin layer of gallium oxide (region A in the figure below) quickly forms on the surface of the liquid gallium droplet.  The triboelectric effect of the collision induces a charge separation across layer A, and from then on this thin layer acts like a tiny battery, until its charges come back together.

 
Electrons are compelled to flow away from the gallium (region C), leaving some Ga⁺ (gallium missing an electron and hence positively charged) at the surface of the droplet.  These electrons circulate up to region B, and ultimately return to C again, but on the way they encounter CO₂, and convert it to CO₂^{· ‒}.  So there’s the key to this whole thing.  Mechanical energy — the friction between the Ag-Ga crystals and liquid gallium — makes this happen:

Ga  +  CO₂  →  Ga⁺  +  CO₂^{· ‒}

Separation of charge, folks.  The same principle behind photosynthesis, the process that literally runs all life on the planet.

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There’ll be technical hurdles, to be sure.  Nobody just slaps up a plant and has everything go peachy right away.  And no, of course this won’t singlehandedly solve all the world’s problems.  But if this really is a practical and cost-effective way to stop CO₂ pollution at large scale before it even starts, it could be a highly implementable way to help us meet the climate goals we’re all pining for.  We could really use the help.

Please click on: Convert Industrial CO₂ Offgas Into Oxygen And Solid Carbon

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