Comment by photochemsyn | Hacker News Reader

Comment by photochemsyn | Hacker News Reader

Parent Full thread

Technically this is about evolving oxygen gas from water more than it is about the hydrogen end of the electrocatalytic reaction. Since this is a cathode (2H+ + 2e- -> H2 gas) vs. anode process (2H2O -> 4H+ + 4e- + O2) linked up by a wire to close the circuit, you have two chemical processes to manage. The oxygen-evolving one tends to be slower, i.e. rate limiting. For an overview:

https://sci-hub.se/10.1039/c9cs00607a

Song, et al. (2020). "A review on fundamentals for designing oxygen evolution electrocatalysts." Chemical Society Reviews.

>"Therefore, the OER is the key process that governs the overall efficiency of electrochemical water splitting. To date, IrO2 and RuO2 have been state-of-the-art OER catalysts. However, both of them are made of precious metals and the cost is high. Therefore, it is imperative to seek low-cost alternative materials that can effectively reduce the kinetic limitation of OER and improve the efficiency of water splitting."

So, they discovered that the catalyst used at the OER end has some light-activation property, which is pretty interesting, i.e. they discovered a kind of photovoltaic electrocatalyst. Whether it will prove to be industrially useful is anyone's guess. There are similar systems but they're not very practical (i.e. they require high-energy UV):

https://physicsworld.com/a/light-activated-catalysts-make-ne...

As far as hydrogen-from-water tech, again it has three plausible large-scale cleantech industrial uses: ammonia from atmospheric N2, reduction of iron ore to sponge iron, and methane (and plausibly jet fuel) production from atmospheric CO2.

Hydrogen has numerous uses. Petroleum refineries produce and consume hydrogen in numerous places, if they find they are steam reforming they could use green hydrogen instead, together with storing waste Carbon dioxide to green operations.

Even if we quit refining oil from the ground we will still be doing chemistry like petrochemisty with other feedstocks.

If you can figure out how to get the carbon feedstock from the atmosphere at scale, why would anyone bother with refining a mixed muck coming out of the ground? What we call 'petrochemistry' today will be called 'aero-hydro-chemistry' tomorrow.

There really is very, very little carbon in the atmosphere, famously ~410 ppm. (Yes, that little bit is enough to absorb significantly more heat from the sun).

So, whatever capture system you use, you'd need to move a lot of air through in order to produce a small amount of something like liquid hydrocarbon fuel.

It will require thousands of times more air, by mass. Since the output fuel product is hundreds of times more dense, it would require a crazy large volume of air to extract the carbon necessary to fill a fuel tank.

A corn field combined with a methanol fermentation and distillation facility is an example of a machine that does that. Very large.

But there are CO₂-rich exhausts in chemical plants and power plants, with concentrations well above 50%. This is where the capture could work efficiently. These likely produce a sizable portion of the carbon dioxide surplus.

Capturing carbon from a jet engine will remain problematic, or slow. Maybe we should just grow more trees, extract solid carbon from them (by burning or otherwise), and bury it in old coal mines.

Even more efficient than carbon capture from power plant exhaust?

not pulling the carbon out of the ground and burning it to begin with

It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place.

> It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place.

It kind of makes sense, if energy is cheap enough. If we have surplus energy, we can remove enough CO2 from the atmosphere to stop or even revert climate change. If we can desalinate water with that surplus energy, we can even use that extracted carbon to increase the amount of biomass on the surface.

Both climate change and fresh water supply are solvable with abundant cheap energy.

You have to do something to the existing power plants, before you build out enough solar, wind, batteries, and nuclear. It capture is cheaper then rebuilding the plant, it may make sense to run it until the end of its planned service life.

Certain things produce CO₂ as a part of non-power-generating chemical processes, like steelmaking, or producing cement for concrete. If the CO₂ can be captured economically, it would be a great win; there are few known remotely viable alternatives.

You're forgetting all the lifecycle emissions and the whole 'if capture is cheaper' part given that running a coal plant without CCS is more expensive than replacing it with new solar panels in many areas already.

Plants pull 100 gigatons of carbon out of the atmosphere every year and convert it to biomass (essentially, oxy-ammonia-hydrocarbons like sugars, proteins, fats, etc.). Humans pull about 6 gigatons of carbon out of the ground each year and pump it into the atmosphere.

The reason this cycle doesn't exhaust the atmospheric pool, of course, is that animals and fungi (more the latter) break down biomass into CO2 and release it back into the atmosphere.

That's not what I'd call 'very very little carbon'.

On a planetary atmosphere level? It’s still tiny.

Literally .0441%

Getting anything at that concentration out is… generally not easy.

Doable! But not easy.

That it’s chemically low reactivity makes it even harder.

Plants have spent billions of years evolving to do it, and from an energy perspective aren’t very efficient at it.

Unless we want to burn even more oil trying to power the process or just make a tiny dent in it, we’ll need to not only figure out a somewhat efficient way to do it, but also figure out how to generate a massive amount of power without burning oil to power it.

For even more perspective, human breath can be easily composed of somewhere between 20,000 ppm and 40,000 ppm, and tens of thousands greater than that with enough energy expenditure. (I know this because I've actually measured this myself with research grade NDIR CO2 sensors)

441 ppm can be "a lot" depending on the gas and the expected effect. You don't want to breathe in 441 ppm of chlorine gas. But CO2 being fairly non-reactive makes 441 ppm of it relatively minuscule in contrast to the other predominant atmospheric gases. It's also nowhere near enough to cause outright catastrophe.

441 ppm CO2 turns out to be quite close to enough to cause global catastrophe.

Eventually. But no one is going to keel over dead due to suffocation today because of global CO2 concentration, which is ‘outright’.

Pretty sure global minimum temperatures above 100F would also count as ‘outright’.

There are already places where being without a cooling method other than sweating would be fatal, at least one day of the year.

In many more places, crops are failing.

People necessarily leaving these places will need to go where other people already are.

That happened before too, and has been (at lower frequency) for all of recorded history, near as we can tell. As noted, not an outright catastrophe right now.

The discussion is about avoiding it becoming one, and relative impacts. Humanity isn’t going to be dead tomorrow because of this, but may be in more pain in a decade or two, and longer term even more so.

Regional collapses have happened. This will be the first global collapse.

If it happens, it will be much earlier than you hope, as millions, then tens of millions, then hundreds of millions force their way across borders, and fascist governments ride that into power and then start a global thermonuclear war. The refugees will only be fleeing crop failure and increasingly murderous kleptocratic government.

It is already starting. Lots of governments are flirting with dictatorship, and many have got there already. US and Brazil have drawn back a hairsbreadth from the brink, but for how long?

You might want to slow down and breath a little.

Just like the people who were entering the Capitol about 20 months ago.

I favorited that comment. When I feel anxious about something, I’ll read it again and realize anxiety can always be worse.

It is a fact that almost half the US voting population is ready and willing to vote in somebody who would arrange never to leave office. Numerous billionaires support that outcome.

I'm not saying that you're wrong (or right). There is a LOT of scary stuff going on right now, for a lot of people.

I'm just asking you to slow down a bit, and take care of how you are now.

Otherwise, you'll never get to the point of any of the other stuff mattering anyway - and likely make it a lot worse for yourself in the meantime.

Really? Thanks an amazing claim! I'm sure you can provide us some evidence to support this.

Multiple Megatonnes of many different materials are mined at much lower concentration, and that requires digging up rocks. CO2 has many properties that make it fairly easy to select for.

We've already figured out that last part, it's called putting a few tens of square km of solar panels and heliostats (don't need it all to be electricity) in egypt or bolivia. A square metre nets you enough energy for a few tonnes per year in realistic current tech. This will never stem the tide if we don't go to net zero first, but reversing the damage in a century is doable by covering one medium sized desert.

Sounds easy and we’ve got it all worked out at scale. Problem solved then?

Maybe. Just maybe there's a middle ground between something being unfathomably difficult and impossible because big number bad, and being trivial?

There are lots of potential avenues for stuffing the genie back in the bottle with a small fraction of the energy we got out of releasing it. All that's lacking is the political will to hold the fossil fuel industry accountable, stop them doing more damage, and confiscate the proceeds of their crimes to start undoing the damage.

This last part isn't helped by reactionaries constantly screaming 'big number mean impossible' and 'der entropy'. Almost as if the goal of such discourse is to prevent solutions.

Who are you talking to exactly?

I never said anything of the sort, nor did anyone else near as I can tell?

You were concern trolling to try to shit on the best plan we have for a planet that remains habitable by vaguely gesturing about how hard it is with no context.

Then you sullenly implied I was saying it was trivial when I contextualised the actual scale involved.

This is part of the standard reactionary fud playbook.

Now you're playing the victim and trying to imply that's never what you meant.

Literally completely false.

You might want to re-read the thread and actually follow the site rules this time?

Feel free to read my prior comments if you want to see how completely false your perception seems to be of my motivations too.

My point is this takes time and treasure, and it isn’t yet solved - and incremental improvement helps, because if we were to try to actually do things at scale with our current level of knowledge, we lack the infrastructure to do so without burning more oil.

Which will slowly change over the next couple decades and centuries, but not without a lot of fallout first due to the speed of change.

I looked at your previous comments and retract my accusation. Apologies.

Most of the time when someone mentions CO2 air concentration it's as a prelude to pushing CCS or some vague idea about producing 100s of kW of energy per person using nuclear abundanceand I pattern matched a little preemptively.

This doesn't excuse your rhetoric about it not being urgent though. The damage may take effect later, but it is being done right now.

Thanks for acknowledging that, it isn’t easy.

You might want to recheck again though on that urgency claim. I never said that either.

To recap some discussions in other threads, what I’m pointing out is due to the sheer size of the problem, this will take decades to centuries to get under control (if the models are right, barring some truly revolutionary technology), no matter what.

Depending on the level of force used, it can and likely will lead to large scale war, which burns even more oil based on the way military operations are run now (and for the foreseeable future).

Even if we did things at the urgency level of the Manhattan project with infinite resources - unless we burned more oil. Even then, probably.

This is a heavily overloaded train that has been building up speed for 150+ years.

As to if any individual should be panicking or calm about this is up to them, but I personally find panic to put someone in a place where they are easily misled and results in bad and poorly thought out decisions which can often make it worse.

Which tends to be why folks go to fascism when they’re overloaded and scared, IMO.

As to if this discussion is useful or not? I don’t know. But I figured I’d throw it out there.

The advantage of attempting it mechanically is that you might use less water and less fixed nitrogen. Water consumption is directly linked to how plants absorb CO₂ from the atmosphere, see https://ripe.illinois.edu/blog/difference-between-c3-and-c4-...

You mean ethanol, right? I don't think it's produced by fermentation, at least not without a secondary process that removes the other hydrocarbon.

That aside, yes, plant biomass to alcohol is a carbon-neutral tech that has already existed for a really long time. Let plants take carbon out of the atmosphere, ferment the starches and sugars into fuel alcohol, feed the remaining cellulose to animals, burn the fuel, eat the animals, and return most (but not all!) of the carbon back to where it came from. It's really an incredible process, but obviously its existence is a threat to the oil industry. If you've ever noticed the propaganda that ethanol is bad for engines and worse for the environment, well, just follow the money.

D'oh! Yes, ethanol. Thanks for the correction!

It takes a very great deal of hydrocarbon fuel to produce the ethanol going into our engines. When EVs displace gasohol-burning cars, the ag production, 30% of the maize crop, can go back to feeding people (or, more likely, feeding chickens); and we may hope the fuel used will be synthetics from atmospheric feedstocks.

Brazil's sugar cane operations seem to produce more fuel than the process consumes.

Direct carbon capture makes sense whenever you have a high concentration of CO₂ emissions. The most obvious are cases where you can get pure carbon, not CO₂. Other times, it might be also worth capturing the CO₂ from something burning. Direct carbon capture from the air will probably be the most expensive solution, but it is still doable. You figure that eventually it will be subsidized.

Home furnaces burn a lot of natural gas and put the water in the sewer and the CO2 in the air. I wonder how much tweaking the sewer system would need to start acting as a CO2 return system also. If it were a closed loop system you could at least be carbon neutral, and stockpiling methane for the winter is easier than stockpiling electricity.

I think the upgrade to far, far more efficient heat pumps would be small compared to the cost of that...

The other problem with carbon capture (if you could overcome the low concentration issue somehow) is that the result of the tragedy of the commons isn't just "oops the temperature went up by 2°", it's "oops we killed off all plant life on Earth simultaneously and now nearly every living thing on Earth will be dead within a few years".

It took centuries to increase atmospheric CO2 to problematic level.

If we are so lucky as to have to worry about overcorrection, I'm confident we'll be able to find the 'off' switch to whatever solution in time.

This comment is inaccurate, the way CO2 traps heat isn't from the sun, but the thermal black body radiation from the surface.

Do you have a link to something where I can read more about this?

I’ve looked into the chemistry you’d use to turn a carbonaceous asteroid into useful products such as plastic films or material for a biosphere and the old C1 chemistry (manufactured gas and PVC from acetlyene) and the new stuff for utilization of CO2 turns out to be very relevant.

For instance you are going to get CO2 as a waste product and you will not throw it away because it is precious so you will add energy to recycle it. You might just get O2 from processing of metals and stones, burn the carbon and feed the CO2 into some system for further processing. The difference with earth is you have 24 hour sunlight and the anility to concentrate it with weightless mirrors.

Reply on news.ycombinator.com