Nanosheet Catalyst Discovered To Sustainably Split Hydrogen From Water | Hacker News Reader

Nanosheet Catalyst Discovered To Sustainably Split Hydrogen From Water

bnl.gov

25 pointspwg10 comments

There are perfectly good industrial electrolysis cells that can split water with 85% efficiency, and that does not require platinum, only nickel (and by that I mean elemental nickel, not nickel-molybdenum-nitride). They need to be big and operate under high temperature and use sodium or potassium hydroxide in the water, so for industrial purposes only, but essentially a solved problem.

The unsolved problem is a good catalyst for the reverse process that takes place in hydrogen fuel cells. For that platinum is currently required, and no alternatives are known. I have read dozens of reports of catalysts for electrolysis, but not a single one for a replacement catalyst in hydrogen fuel cells. That would actually be a breakthrough.

Even with the latter problem solved (where I'm optimistic), the problem of storing hydrogen in an efficient way is way harder, and there I'm less optimistic. For that reason alone I'm very sceptic to how realistic a hydrogen economy is.

It's only far away if you want to work in pure hydrogen, which is ideologically simple but not really required. Synthesis of methane from hydrogen is easy and efficient and (pretty) cheap - use atmospheric co2 as carbon feedstock. A German company is working on this and has proven solution at small scale, I'm sure they're not the only ones.

More of a pain than simply burning/recombining hydrogen with oxygen, but has the upside that there is already a huge and established global network for transport and storage of methane - cheap and proven and currently being rapidly scaled.

So what is the idea?

You place a bunch of solar panels in a sunny place that also has water.

Then you directly power the grid when it is sunny and all power is needed.

When not needed, you power the catalyst, storing the hydrogen.

When it is dark, you use the hydrogen to create power and (maybe) heat.

Besides the current costs (especially the solar PV part), there's the problem that you're throwing away most of your energy in the [electricity => hydrogen => electricity] loop. Electrolysis isn't perfect [1], but the big waste is electricity generation, with the best hydrogen fuel cells being only 50-60% efficient [2, SOFC "predicted"] (turbines smaller than utility scale would be far worse). In the most optimistic case you lose half of your stored energy (more likely 2/3rd).

Realistically you'd have to store almost all of your electricity -- compare solar output, a very short midday peak, with electricity demand, which in many places is nearly constant over time. Almost of all of it would go through the 50%+ storage losses, which means the solar part (PV + inverter + etc.) of your costs are more than doubled, amortized per kWh. So economically, practically anything is better than local hydrogen storage. (Under the premise that solar PV is not effectively free, which is an understatement to put it mildly).

[1] http://en.wikipedia.org/wiki/Electrolysis#Electrolysis_of_wa...

[2] http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/f...

Pretty much. One of the biggest problems with a lot of renewable energy is it's not reliable. Sun doesn't shine, wind isn't blowing, etc. So you need a way to store energy in a buffer to smooth out fluctuations. Hydrogen is looking like the best long term bet for that. You might even be able to use it for hydrogen cars, but then you run into problems with transportation and crash-proof storage that you don't have with just a tank in your back yard.

Punchline: nearly as good as platinum, without being expensive like platinum. Not sure whether it's actually easy and cheap to make in large quantities. Still lots of other problems with hydrogen as a fuel.

If it were really likely to be incredibly useful, there'd be a patent number in this article, not a reference to a publication in Angewandte Chemie.

Also: requires external electricity ... exceeding the minimum required by thermodynamics

Of course, there's no getting around those pesky laws of thermodynamics.

Right, so with the perfect catalyst, you get as much energy out as you put in. With imperfect catalysts (anything real), you have to apply a voltage higher than when thermodynamics says is necessary to get the reaction to happen at an appreciable rate. The excess voltage cannot be recovered. The better the catalyst, the lower the excess voltage necessary, so a cheap and very effective catalyst essentially promises an efficient way to store and transport energy as hydrogen gas, which would be excellent.

Your platinum, water connection made me think again about the recently announced space mining venture for some reason...

It's a good reason. The cheaper and easier it is to split water the more cost effective it will be to manufacture Oxygen and Hydrogen from in situ water ice resources throughout the Solar System (on Mars, on the moon, or on an asteroid). The uses of Water and Oxygen for inhabited structures in orbit should be obvious, but liquid Oxygen and Hydrogen are also quite excellent rocket propellants which would be equally valuable on orbit.

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