8 ms·

New Catalyst Efficiently Produces Hydrogen from Seawater

67 points by EndXA 7y ago

EndXA 7y ago
The original study can be found at: https://www.nature.com/articles/s41467-019-13092-7 https://www.nature.com/articles/s41467-019-13092-7 Abstract: > Seawater is one of the most abundant natural resources on our planet. Electrolysis of seawater is not only a promising approach to produce clean hydrogen energy, but also of great significance to seawater desalination. The implementation of seawater electrolysis requires robust and efficient electrocatalysts that can sustain seawater splitting without chloride corrosion, especially for the anode. Here we report a three-dimensional core-shell metal-nitride catalyst consisting of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam, which serves as an eminently active and durable oxygen evolution reaction catalyst for alkaline seawater electrolysis. Combined with an efficient hydrogen evolution reaction catalyst of NiMoN nanorods, we have achieved the industrially required current densities of 500 and 1000 mA cm−2 at record low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. This discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production.
Accujack 7y ago
This is interesting for cleaning up internal combustion engine use, but it's not so useful for climate change because although burning hydrogen doesn't produce carbon dioxide or methane, it does produce water vapor. See this page for info on that: https://www.acs.org/content/acs/en/climatescience/climatesciencenarratives/its-water-vapor-not-the-co2.html https://www.acs.org/content/acs/en/climatescience/climatesci... Also, the big issue with hydrogen as a fuel is that while it has a high energy density per unit mass, it has a very low energy density per unit volume... IE, from an engineering point of view you have to carry a large volume of the stuff to have a vehicle with any significant range. Discussion of how that could potentially be done here: https://www.energy.gov/eere/fuelcells/hydrogen-storage https://www.energy.gov/eere/fuelcells/hydrogen-storage In a way, this sort of research addresses the same problem as improved battery technology - we need mobile energy sources for moving things. I think a major reason we haven't gotten where we need to go with this problem is that researchers tend to look for a way to replace gasoline - to find another fuel that can simply be used in place of gas/diesel using the same engine technology (and associated control, fuel handling, and other tech). That's very, very difficult to do, because gasoline is uniquely suited to what we use it for - it has high energy density per unit volume and mass, it's moderately volatile at standard temperature and pressure, and most interestingly we don't have to expend much energy to produce it, because all that energy was stored aeons ago. We just have to get it out of the ground and separate it into usable fractions. It's essentially a "free ride" as far as energy sources go. It's too bad continual use will destroy us.
- theandrewbailey 7y ago
  There's also the fact that metals become brittle when exposed to hydrogen. Hydrogen seeps through the crystal/atomic lattice and combines with oxygen or carbon, and tears the metal apart. https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
  - jeffreyrogers 7y ago
    The high pressure containers are made from composites though. Are they susceptible to embrittlement as well?
  - syntaxing 7y ago
    I thought hydrogen embrittlement only effects mainly steel that under go high temperature. That's why the rebake stuff in inert environments that was forged like screws.
- derefr 7y ago
  Water vapour is pretty easily re-condensed, though, no? Cars emit their waste products into the air because it’s kind of hard to capture gaseous waste (you would need a compressor, which would use almost as much energy as the car itself.) But if your waste was water vapour, you could just route your gas waste through a condenser column, and then dump it into a storage tank. And, since the waste product is literally just water, that tank could be emptied pretty frequently—any time you’re near a municipal storm drain, in fact. So you wouldn’t need to worry about your car taking on that much mass.
  - logfromblammo 7y ago
    A condenser column would need to be cooled. Even a passive radiator adds weight. Another step in the engine cycle can cool and condense the water vapor to liquid, and extract additional energy from the exhaust. The weight of the required additional engine parts, and the cooler in particular, tends to erase all the actual benefit in an automobile. Cargo ships and train locomotives could do it.
- 7y ago
zentiggr 7y ago
Partially in reply to Accujack but to frame the question in general: Is hydrogen a reasonable power source for non-mobile applications? I know its volatility makes it dangerous for household use, but are there controlled industrial/outdoor/other uses that it would be suitable for?
- theandrewbailey 7y ago
  An immediate application would be to replace steam reforming processes. (methane (natural gas) in, hydrogen out) https://en.wikipedia.org/wiki/Steam_reforming https://en.wikipedia.org/wiki/Steam_reforming
- jeffreyrogers 7y ago
  I haven't done the calculations, but my gut reaction is that you're better off using electricity for non-mobile applications. Hydrogen production looks like: electricity -> electrolysis -> hydrogen. And then you use the hydrogen in a fuel cell to generate electricity. Since you already need electricity to produce the hydrogen it seems to make more sense just to use it directly for whatever non-mobile application you have. There are other (cheaper) ways to produce hydrogen but they require hydrocarbon feedstocks.
  - m_eiman 7y ago
    Storing hydrogen for seasonal use could be neat. Split water using summer sun, use hydrogen to generate electricity in winter.
    - jeffreyrogers 7y ago
      I hadn't thought of that. One potential problem is long-term storage of hydrogen. Hydrogen is so small that it will eventually escape from whatever container you put it in. This diffusion is faster at higher pressures, and depends a lot on the materials involved. So I think it could work, but you'd have to be careful about what materials you used for your storage container.
sfink 7y ago
Producing water vapor is irrelevant. The water will just condense and come back out in one form or another. Produce all you want, humidity is naturally limited. As your linked article puts it: "water vapor does not control the Earth’s temperature, but is instead controlled by the temperature".
aazaa 7y ago
> ... Direct electrolysis of seawater rather than freshwater is highly significant, especially for the arid zones, since this technology not only stores clean energy, but also produces fresh drinking water from seawater. ... There seems to be a step missing from that statement, specifically, oxidation of the electrolytically-generated H2 through combustion or in a fuel cell. Assuming that step, the water is pure, and there's no need for reverse osmosis which is itself quite energy-intensive. This might be a key point to consider with industrial hydrogen generation rather than, say direct capture of solar energy in a battery. Direct capture yields energy only, whereas electrolysis of seawater yields potable drinking water and energy.
- mrspuratic 7y ago
  > ... electrolysis of seawater yields potable drinking water and energy. And salts, or typically, brine. That's a harder problem to solve (i.e. dispose of safely).
  - vkou 7y ago
    Why not just dump them right back in the ocean? Compared to the environmental shit-show of coal and oil extraction, wringing your hands over brine ending up in the ocean, seems entirely misdirected.
    - klyrs 7y ago
      I'd have concerns about the effects of hypersalination on the ecology local to wherever you propose to dump this brine. This isn't "wringing hands," it's learned caution by somebody who doesn't believe in free lunch.
      - vkou 7y ago
        So put it on a tanker, and dump it out, bit by bit, in the middle of the ocean. This isn't a difficult problem to solve. It is absolutely wringing hands, compared to what we do with far more damaging products and byproducts of petroleum extraction.
gwbas1c 7y ago
> Zhifeng Ren, director of the Texas Center for Superconductivity at UH and a corresponding author for the paper, said a major obstacle has been the lack of a catalyst that can effectively split seawater to produce hydrogen without also setting free ions of sodium, chlorine, calcium and other components of seawater, which once freed can settle on the catalyst and render it inactive. Chlorine ions are especially problematic, in part because chlorine requires just slightly higher voltage to free than is needed to free hydrogen. Which gets to one of my big questions about generating hydrogen from seawater: I assume there will be waste products, which in the best case, is either brine or salt. If we're making hydrogen in mass from seawater, what is the environmental impact?
- throwanem 7y ago
  You get hydrogen gas and chlorine gas; one is fuel, the other feedstock for any number of industrial processes. (Electrolysis of an NaCl solution is already one of the standard methods of producing elemental chlorine for lab and industry use. The efficiency isn't great, but the method described in this paper appears to improve considerably on that, assuming it can itself be efficiently implemented at industrial scale.)
- contravariant 7y ago
  If it's just salt then it's basically just a matter of figuring out how much seawater we need to evaporate. Which we can find out by dividing the total energy consumption by the energy density of hydrogen [1], this results in a figure of 120 tons a year, or about 2.8 billionth of the ocean [2], or about .001 cm a year [3] (until the area of the ocean starts shrink noticeably). Assuming the evaporated water returns to the ocean after a while I reckon we should be fine. [1]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum... [2]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+volume+of+the+ocean%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum... [3]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+area+of+the+ocean%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum...
dr_dshiv 7y ago
Or use a non-electrode approach, like using 13.56mhz radio frequencies to split salt water: https://www.tandfonline.com/doi/abs/10.1179/143307508/270875?journalCode=ymri20 https://www.tandfonline.com/doi/abs/10.1179/143307508/270875...

67 points by EndXA 7y ago

The original study can be found at: https://www.nature.com/articles/s41467-019-13092-7 https://www.nature.com/articles/s41467-019-13092-7 Abstract: > Seawater is one of the most abundant natural resources on our planet. Electrolysis of seawater is not only a promising approach to produce clean hydrogen energy, but also of great significance to seawater desalination. The implementation of seawater electrolysis requires robust and efficient electrocatalysts that can sustain seawater splitting without chloride corrosion, especially for the anode. Here we report a three-dimensional core-shell metal-nitride catalyst consisting of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam, which serves as an eminently active and durable oxygen evolution reaction catalyst for alkaline seawater electrolysis. Combined with an efficient hydrogen evolution reaction catalyst of NiMoN nanorods, we have achieved the industrially required current densities of 500 and 1000 mA cm−2 at record low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. This discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production.

Accujack 7y ago

This is interesting for cleaning up internal combustion engine use, but it's not so useful for climate change because although burning hydrogen doesn't produce carbon dioxide or methane, it does produce water vapor. See this page for info on that: https://www.acs.org/content/acs/en/climatescience/climatesciencenarratives/its-water-vapor-not-the-co2.html https://www.acs.org/content/acs/en/climatescience/climatesci... Also, the big issue with hydrogen as a fuel is that while it has a high energy density per unit mass, it has a very low energy density per unit volume... IE, from an engineering point of view you have to carry a large volume of the stuff to have a vehicle with any significant range. Discussion of how that could potentially be done here: https://www.energy.gov/eere/fuelcells/hydrogen-storage https://www.energy.gov/eere/fuelcells/hydrogen-storage In a way, this sort of research addresses the same problem as improved battery technology - we need mobile energy sources for moving things. I think a major reason we haven't gotten where we need to go with this problem is that researchers tend to look for a way to replace gasoline - to find another fuel that can simply be used in place of gas/diesel using the same engine technology (and associated control, fuel handling, and other tech). That's very, very difficult to do, because gasoline is uniquely suited to what we use it for - it has high energy density per unit volume and mass, it's moderately volatile at standard temperature and pressure, and most interestingly we don't have to expend much energy to produce it, because all that energy was stored aeons ago. We just have to get it out of the ground and separate it into usable fractions. It's essentially a "free ride" as far as energy sources go. It's too bad continual use will destroy us.

theandrewbailey 7y ago
There's also the fact that metals become brittle when exposed to hydrogen. Hydrogen seeps through the crystal/atomic lattice and combines with oxygen or carbon, and tears the metal apart. https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
- jeffreyrogers 7y ago
  The high pressure containers are made from composites though. Are they susceptible to embrittlement as well?
- syntaxing 7y ago
  I thought hydrogen embrittlement only effects mainly steel that under go high temperature. That's why the rebake stuff in inert environments that was forged like screws.
derefr 7y ago
Water vapour is pretty easily re-condensed, though, no? Cars emit their waste products into the air because it’s kind of hard to capture gaseous waste (you would need a compressor, which would use almost as much energy as the car itself.) But if your waste was water vapour, you could just route your gas waste through a condenser column, and then dump it into a storage tank. And, since the waste product is literally just water, that tank could be emptied pretty frequently—any time you’re near a municipal storm drain, in fact. So you wouldn’t need to worry about your car taking on that much mass.
- logfromblammo 7y ago
  A condenser column would need to be cooled. Even a passive radiator adds weight. Another step in the engine cycle can cool and condense the water vapor to liquid, and extract additional energy from the exhaust. The weight of the required additional engine parts, and the cooler in particular, tends to erase all the actual benefit in an automobile. Cargo ships and train locomotives could do it.
7y ago

zentiggr 7y ago

Partially in reply to Accujack but to frame the question in general: Is hydrogen a reasonable power source for non-mobile applications? I know its volatility makes it dangerous for household use, but are there controlled industrial/outdoor/other uses that it would be suitable for?

theandrewbailey 7y ago
An immediate application would be to replace steam reforming processes. (methane (natural gas) in, hydrogen out) https://en.wikipedia.org/wiki/Steam_reforming https://en.wikipedia.org/wiki/Steam_reforming
jeffreyrogers 7y ago
I haven't done the calculations, but my gut reaction is that you're better off using electricity for non-mobile applications. Hydrogen production looks like: electricity -> electrolysis -> hydrogen. And then you use the hydrogen in a fuel cell to generate electricity. Since you already need electricity to produce the hydrogen it seems to make more sense just to use it directly for whatever non-mobile application you have. There are other (cheaper) ways to produce hydrogen but they require hydrocarbon feedstocks.
- m_eiman 7y ago
  Storing hydrogen for seasonal use could be neat. Split water using summer sun, use hydrogen to generate electricity in winter.
  - jeffreyrogers 7y ago
    I hadn't thought of that. One potential problem is long-term storage of hydrogen. Hydrogen is so small that it will eventually escape from whatever container you put it in. This diffusion is faster at higher pressures, and depends a lot on the materials involved. So I think it could work, but you'd have to be careful about what materials you used for your storage container.

sfink 7y ago

Producing water vapor is irrelevant. The water will just condense and come back out in one form or another. Produce all you want, humidity is naturally limited. As your linked article puts it: "water vapor does not control the Earth’s temperature, but is instead controlled by the temperature".

aazaa 7y ago

> ... Direct electrolysis of seawater rather than freshwater is highly significant, especially for the arid zones, since this technology not only stores clean energy, but also produces fresh drinking water from seawater. ... There seems to be a step missing from that statement, specifically, oxidation of the electrolytically-generated H2 through combustion or in a fuel cell. Assuming that step, the water is pure, and there's no need for reverse osmosis which is itself quite energy-intensive. This might be a key point to consider with industrial hydrogen generation rather than, say direct capture of solar energy in a battery. Direct capture yields energy only, whereas electrolysis of seawater yields potable drinking water and energy.

mrspuratic 7y ago
> ... electrolysis of seawater yields potable drinking water and energy. And salts, or typically, brine. That's a harder problem to solve (i.e. dispose of safely).
- vkou 7y ago
  Why not just dump them right back in the ocean? Compared to the environmental shit-show of coal and oil extraction, wringing your hands over brine ending up in the ocean, seems entirely misdirected.
  - klyrs 7y ago
    I'd have concerns about the effects of hypersalination on the ecology local to wherever you propose to dump this brine. This isn't "wringing hands," it's learned caution by somebody who doesn't believe in free lunch.
    - vkou 7y ago
      So put it on a tanker, and dump it out, bit by bit, in the middle of the ocean. This isn't a difficult problem to solve. It is absolutely wringing hands, compared to what we do with far more damaging products and byproducts of petroleum extraction.

gwbas1c 7y ago

> Zhifeng Ren, director of the Texas Center for Superconductivity at UH and a corresponding author for the paper, said a major obstacle has been the lack of a catalyst that can effectively split seawater to produce hydrogen without also setting free ions of sodium, chlorine, calcium and other components of seawater, which once freed can settle on the catalyst and render it inactive. Chlorine ions are especially problematic, in part because chlorine requires just slightly higher voltage to free than is needed to free hydrogen. Which gets to one of my big questions about generating hydrogen from seawater: I assume there will be waste products, which in the best case, is either brine or salt. If we're making hydrogen in mass from seawater, what is the environmental impact?

throwanem 7y ago
You get hydrogen gas and chlorine gas; one is fuel, the other feedstock for any number of industrial processes. (Electrolysis of an NaCl solution is already one of the standard methods of producing elemental chlorine for lab and industry use. The efficiency isn't great, but the method described in this paper appears to improve considerably on that, assuming it can itself be efficiently implemented at industrial scale.)
contravariant 7y ago
If it's just salt then it's basically just a matter of figuring out how much seawater we need to evaporate. Which we can find out by dividing the total energy consumption by the energy density of hydrogen [1], this results in a figure of 120 tons a year, or about 2.8 billionth of the ocean [2], or about .001 cm a year [3] (until the area of the ocean starts shrink noticeably). Assuming the evaporated water returns to the ocean after a while I reckon we should be fine. [1]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum... [2]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+volume+of+the+ocean%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum... [3]: https://www.wolframalpha.com/input/?i=%28world+energy+consumption+%2F+hydrogen+heat+of+combustion%29+%2F+%28density+of+water+*+area+of+the+ocean%29 https://www.wolframalpha.com/input/?i=%28world+energy+consum...

dr_dshiv 7y ago

Or use a non-electrode approach, like using 13.56mhz radio frequencies to split salt water: https://www.tandfonline.com/doi/abs/10.1179/143307508/270875?journalCode=ymri20 https://www.tandfonline.com/doi/abs/10.1179/143307508/270875...