4 ms·

From the abstract[0]: they have a promising catalyst that could be used for a "direct ammonia fuel cell" operating at room temperature. It involves ruthenium, w

From the abstract[0]: they have a promising catalyst that could be used for a "direct ammonia fuel cell" operating at room temperature. It involves ruthenium, which is an expensive rare earth element. For context, it's possible to 'crack' ammonia into hydrogen and nitrogen & feed that to a PEM fuel cell, but this requires extra equipment, high temperatures, and consumes some of the output energy. Solid oxide fuel cells can also run directly on ammonia, but that's b/c they operate at high temperature [650 C].[1] Solid acid fuel cells can turn ammonia into hydrogen at 250 C -- but this is still extra equipment & consumes energy.[2] Ammonia can also be burned in modified gas turbines, which IMO would be a great way to quickly displace natural gas in peaker plants, to enable higher renewables penetration w/o relying on fossil fuels to take up the slack. Ammonia is a better hydrogen carrier than liquid or compressed hydrogen because storage is easier due to high energy density. The round-trip energy efficiency could also be higher.[3] It's less flammable, but more toxic. For more, see [4]. It sounds like the real enabling technology would be direct fuel cells and direct electrosynthesis (reverse fuel cells) to get higher efficiency. [0] https://www.nature.com/articles/s41557-021-00797-w https://www.nature.com/articles/s41557-021-00797-w [1] https://www.ammoniaenergy.org/articles/ammonia-for-fuel-cells-afc-sofc-and-pem/ https://www.ammoniaenergy.org/articles/ammonia-for-fuel-cell... [2] https://news.northwestern.edu/stories/2020/11/ammonia-to-green-hydrogen/ https://news.northwestern.edu/stories/2020/11/ammonia-to-gre... [3] https://www.ammoniaenergy.org/articles/round-trip-efficiency-of-ammonia-as-a-renewable-energy-transportation-media/ https://www.ammoniaenergy.org/articles/round-trip-efficiency... [4]https://www.intechopen.com/chapters/40233 https://www.intechopen.com/chapters/40233

R0b0t1 5y ago
I think this is an interesting development for smaller generating needs, maybe even personal, but: > Ammonia can also be burned in modified gas turbines, which IMO would be a great way to quickly displace natural gas in peaker plants, to enable higher renewables penetration w/o relying on fossil fuels to take up the slack. Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous. It's just in some markets they must telegraph their moves and get approval, which can take ~4 hours or more. I bring up nukes because how are we going to make the ammonia? Nitrogen fixing reactions take loads of power. You could get it from nukes until we figure out higher capacity solar collection, but I don't know of anything else that would work well.
- djsbs 5y ago
  “ Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous.” But the physical thermal stress from throttling it significantly shorten its lifespan. Throttling nukes is not a trivial task; I know one plant (Bruce?) doesn't even bother changing the reactor power, they just inject steam into the bay instead of putto g it through a turbine
  - R0b0t1 5y ago
    Sounds like red tape or other stupidity. Ramping up very hot yes, but matching loads like you would with a gas plant no.
    - djsbs 5y ago
      Its a bit complicated. Disclaimer: Im not a nuke engineer, I just took some nuke classes and was surrounded by then for a while. New reactor designs promise to throttle, but I don’t know if any have been deployed. This is a bit more complicated than a gas turbine. With a gas turbine, you just inject more gas as needed to keep the turbine turning at a constant speed. The combustion chamber is a violently small part of the whole. The heat producing part of a reactor, by contrast, is massive. As a result you have thermal gradients, and these gradients are different at different power. They’re also larger at larger power. A large thermal gradient isn’t a huge problem by itself (engineers have been accounting for this since the steam engine). The problem is the change of gradient itself. As the gradient changes, the materials inside change shape and this causes large mechanical stresses. The situation is pretty much the same as when you turn off an ICE car: ever hear those ringing or popping sounds it makes? That is the various hot parts cooling and changing shape abruptly. The problem for a reactor is made worse because material selection is very difficult: you cant just pick any alloy that has good thermal expansion, or good fatigue characteristics. Every alloy must be from a very narrow set of isotopes (not elements!!) that are compatible with the reactor’s neutron environment (balance, distribution, energy spectrum, etc).
      - R0b0t1 5y ago
mojomark 5y ago
Good, thoughtful, comment, but the statement that ammonia is more "energy dense than H2 is innacurate and misleading. Ammonia has very slightly higher Volumetric Energy desnity than H2, but it has an extremely lower Gravimetric (mass) energy density.[1] The difference has significant implications for the intended application. 1. https://commons.wikimedia.org/wiki/File:Energy_density.svg https://commons.wikimedia.org/wiki/File:Energy_density.svg
- Turing_Machine 5y ago
  Hmm... I don't think that takes into account the weight of the tankage. 700 bar tanks aren't light, especially not ones that can resist hydrogen embrittlement.
  - coderenegade 5y ago
    The best metric is %-wt of hydrogen. Compressed hydrogen tanks go from 4.5-7% hydrogen by weight. I've read state-of-the-art vessels can get as high as 10%. Liquid ammonia is 17% hydrogen by weight, so as long as the tanks don't erode this too much, you're still doing better than compressed H2.
  - ncmncm 5y ago
    LH2 tanks may be very lightweight. Given good insulation, that is much preferred, particularly for aviation.
    - lambdatronics 5y ago
      Right, for large aircraft LH2 might be the way to go. General aviation is more likely to be looking at pressurized H2 due to boil-off.
      - ncmncm 5y ago
        LH2 will not be practical for most small aircraft, although "business jets" will probably take it up. Most of the rest will continue to rely on gasoline or propane. Eventually it will be cheaper to synthesize this from atmospheric CO2 than to mine it.
joe_the_user 5y ago
Technically, Ruthenium is a platinum group element, not a "rare earth" element, though it is rare. https://en.wikipedia.org/wiki/Ruthenium https://en.wikipedia.org/wiki/Ruthenium
- inter_netuser 5y ago
  On this, supposedly STEM-oriented forum, such a grave violation of chemistry nomenclature should be a bannable offence. I've lost count of how many times everything is "rare earth", including Magnesium. An alkaline earth metal that's nearly as common as iron.

R0b0t1 5y ago

I think this is an interesting development for smaller generating needs, maybe even personal, but: > Ammonia can also be burned in modified gas turbines, which IMO would be a great way to quickly displace natural gas in peaker plants, to enable higher renewables penetration w/o relying on fossil fuels to take up the slack. Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous. It's just in some markets they must telegraph their moves and get approval, which can take ~4 hours or more. I bring up nukes because how are we going to make the ammonia? Nitrogen fixing reactions take loads of power. You could get it from nukes until we figure out higher capacity solar collection, but I don't know of anything else that would work well.

djsbs 5y ago
“ Nukes can operate as peaker plants. The feedback from the control rods is nearly instantaneous.” But the physical thermal stress from throttling it significantly shorten its lifespan. Throttling nukes is not a trivial task; I know one plant (Bruce?) doesn't even bother changing the reactor power, they just inject steam into the bay instead of putto g it through a turbine
- R0b0t1 5y ago
  Sounds like red tape or other stupidity. Ramping up very hot yes, but matching loads like you would with a gas plant no.
  - djsbs 5y ago
    Its a bit complicated. Disclaimer: Im not a nuke engineer, I just took some nuke classes and was surrounded by then for a while. New reactor designs promise to throttle, but I don’t know if any have been deployed. This is a bit more complicated than a gas turbine. With a gas turbine, you just inject more gas as needed to keep the turbine turning at a constant speed. The combustion chamber is a violently small part of the whole. The heat producing part of a reactor, by contrast, is massive. As a result you have thermal gradients, and these gradients are different at different power. They’re also larger at larger power. A large thermal gradient isn’t a huge problem by itself (engineers have been accounting for this since the steam engine). The problem is the change of gradient itself. As the gradient changes, the materials inside change shape and this causes large mechanical stresses. The situation is pretty much the same as when you turn off an ICE car: ever hear those ringing or popping sounds it makes? That is the various hot parts cooling and changing shape abruptly. The problem for a reactor is made worse because material selection is very difficult: you cant just pick any alloy that has good thermal expansion, or good fatigue characteristics. Every alloy must be from a very narrow set of isotopes (not elements!!) that are compatible with the reactor’s neutron environment (balance, distribution, energy spectrum, etc).
    - R0b0t1 5y ago

mojomark 5y ago

Good, thoughtful, comment, but the statement that ammonia is more "energy dense than H2 is innacurate and misleading. Ammonia has very slightly higher Volumetric Energy desnity than H2, but it has an extremely lower Gravimetric (mass) energy density.[1] The difference has significant implications for the intended application. 1. https://commons.wikimedia.org/wiki/File:Energy_density.svg https://commons.wikimedia.org/wiki/File:Energy_density.svg

Turing_Machine 5y ago
Hmm... I don't think that takes into account the weight of the tankage. 700 bar tanks aren't light, especially not ones that can resist hydrogen embrittlement.
- coderenegade 5y ago
  The best metric is %-wt of hydrogen. Compressed hydrogen tanks go from 4.5-7% hydrogen by weight. I've read state-of-the-art vessels can get as high as 10%. Liquid ammonia is 17% hydrogen by weight, so as long as the tanks don't erode this too much, you're still doing better than compressed H2.
- ncmncm 5y ago
  LH2 tanks may be very lightweight. Given good insulation, that is much preferred, particularly for aviation.
  - lambdatronics 5y ago
    Right, for large aircraft LH2 might be the way to go. General aviation is more likely to be looking at pressurized H2 due to boil-off.
    - ncmncm 5y ago
      LH2 will not be practical for most small aircraft, although "business jets" will probably take it up. Most of the rest will continue to rely on gasoline or propane. Eventually it will be cheaper to synthesize this from atmospheric CO2 than to mine it.

joe_the_user 5y ago

Technically, Ruthenium is a platinum group element, not a "rare earth" element, though it is rare. https://en.wikipedia.org/wiki/Ruthenium https://en.wikipedia.org/wiki/Ruthenium

inter_netuser 5y ago
On this, supposedly STEM-oriented forum, such a grave violation of chemistry nomenclature should be a bannable offence. I've lost count of how many times everything is "rare earth", including Magnesium. An alkaline earth metal that's nearly as common as iron.