New Catalyst Efficiently Produces Hydrogen from Seawater | Hacker News Reader

New Catalyst Efficiently Produces Hydrogen from Seawater

uh.edu

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The original study can be found at: 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.

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".

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/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

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.

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

The high pressure containers are made from composites though. Are they susceptible to embrittlement as well?

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.

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.

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.

505,000 cubic kilometres of water falls from the sky every year as rain across 510.1 million km² of surface area. Directly adding water vapor like this would have an impact so small as to be undetectable change in the global average humidity.

What that link is talking about is changing systems that operate at a scale it’s hard to fathom.

I think you misunderstand the cited article on water vapor.

The water cycle is self regulating, unlike other green house gases.

>> "However, water vapor does not control the Earth’s temperature, but is instead controlled by the temperature. This is because the temperature of the surrounding atmosphere limits the maximum amount of water vapor the atmosphere can contain."

The other non condensing gases, largely from man made sources, contribute to global warming and elevate the amount of water that can be vaporized per unit volume of air.

Cutting down on emissions by replacing oil based vehicles with electric/hydrogen fuel cell powered vehicles absolutely helps the environment. Cutting emission sources makes job of scrubbing the atmosphere of the green houses gases already present more achievable.

Okay, exhaust water from engines does not add greenhouse gases to the atmosphere in significant quantity to increase the rate of climate change - that happens naturally according to the temperature of the atmosphere. Not sure what I was thinking exactly when I wrote that.

However, there are other reasons not to use hydrogen powered IC engines instead of electric engines, like the efficiency of electric motors vs. IC engines, the need to transport hydrogen fuel in greater volume than gasoline for the same range and power, potential issues with corrosion due to immediate condensation, safety issues in cold climates with exhaust immediately freezing on road surfaces, and others.

If someone had a way to create liquid hydrogen with little energy, store it safely in a vehicle, and have an engine able to use it, that might change the game. Gaseous hydrogen, not so much.

Hydrogen fuel from seawater is a neat idea compared to gasoline, but the chances of wide deployment of hydrogen fuels being a significant contribution to saving ourselves from climate change are minimal, in my opinion.

> 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.

Water vapour is exactly something we want from sea water, in addition to the hydrogen we can use as fuel. It's easily condensed into fresh water, which will likely become increasingly scarce over the next century. Looks like a win-win.

With regards to fuel cells for transportation, wouldn't it be easier to generate electricity from the hydrogen and use that to charge EVs?

> 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?

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.)

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+consum...

[2]: https://www.wolframalpha.com/input/?i=%28world+energy+consum...

[3]: https://www.wolframalpha.com/input/?i=%28world+energy+consum...

I believe you meant to say 120 tons per second. Your [1] link shows 3.8x10^15 grams, which is 3.8x10^9 (metric) tons, not 120. That is in mass of hydrogen. Multiply by ~9 to get the total mass of water used to electrolyze that quantity of hydrogen.

However, the water cycle is pretty fast on average, and has incredibly high throughput, and the cycle quickens as water vapor concentrations increase. If hydrogen generation is sufficiently distributed, you could likely just wait for the next rainfall to release the brine.

You're right I seem to have misread. Good point about the factor ~9, but even then it doesn't look like we'll be draining the oceans dry any time soon.

Although it would be a problem of unimaginable scale to use it as the sole source of energy, which is bound to create some of its own problems, I just don't see any obvious ones.

> ... 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.

> ... 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).

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.

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.

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.

And then what fraction of energy production are you spending on disposal, can you trust the folks disposing it [1], and will it properly circulate? Ocean currents and chemistry are extremely complex, and fisheries are an emergently fragile food source.

I am, by no means, a fan of petroleum. But dismissing concerns about dumping chemical waste into the ocean as "hand wringing" is not a reasoned argument.

[1] https://en.m.wikipedia.org/wiki/Toxic_waste_dumping_by_the_%...

It's not "chemical waste". It's what was already in the ocean.

(Yes, I know, the same thing in concentrated form is different. But dilute it reasonably, and we're good. It's not like it's mercury or something.)

Indeed, a better characterization is "toxic waste." Mercury, uranium, etc., is present in ocean water and concentrating it isn't great, but it's the salt that kills.

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...

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?

An immediate application would be to replace steam reforming processes. (methane (natural gas) in, hydrogen out)

https://en.wikipedia.org/wiki/Steam_reforming

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.

Storing hydrogen for seasonal use could be neat. Split water using summer sun, use hydrogen to generate electricity in winter.

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.

Yes, it's not uncomplicated. There's a guy somewhere in Sweden running his house in this way - he's got a bunch of hydrogen tubes in the basement that get filled up during summer. He's obviously an enthusiast and has paid a lot of money to build this, but at least it's somewhat practically possible.

Edit: found an article about him (in Swedish, but the images are interesting and I think Translate would do a decent job): https://www.nyteknik.se/nyheter/fri-fran-elnatet-med-egen-va...

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