Some background and context from someone tangentially related to the field:
1. The overall idea here is to take an intermittent energy source (e.g. solar power) and "store" it as chemical fuel, in this case hydrogen and oxygen. This is what plants do, and we can also view fossil fuels as resulting from the "storage" of millions of years of solar energy. Note also that you get the water back when you burn the hydrogen, so there is no net consumption of water, it's just a carrier.
2. While you can split water without a catalyst, most of the energy gets wasted as heat, so this is not a great way to go if you're trying to do energy storage.
3. Efficient catalysts exist for this reaction, but they are based on rare and expensive metals, typically Pd, Pt, and Ir. As a result, there has been a search for catalysts involving "first-row" metals such as Fe, Co, Ni, etc.
4. There are variety of metrics for an electrocatalyst (efficiency, stability, cost, etc), but it's a fair bet that if this were significantly better than state-of-the-art, it would be in Science or Nature rather than PNAS.
Beyond the expensive of the metals another problem is duty cycles. Most transition metal catalysis is oxygen sensitive, and it seems like for some reason the first step of splitting water is creating oxygen. Plants go through great lengths to separate oxygen synthesis (photosystem II) from electron consumption. Most hydrogen production in lower organisms (like e coli) occurs entirely in anoxic conditions. Engineered systems for generating hydrogen via algae typically are temporally segregated (harvest light during day, produce hydrogen at night) which defeats the purpose and is also chemically steppy (carbohydrate intermediates).
I suggest going back to your chemistry text and reviewing mass balance, conservation of matter, and balancing equations.
What is that OH? Is it hydroxide radical? Hydroxide? Hydroxyl radical? Where does it go? Does it recombine to make hydrogen peroxide?
Btw... To make oxygen from water the first part of the first step is to split it into H and HO. You can't really break two bonds simultaneously, or anyways it's equivalent to doing them stepwise by the principle of microscopic reversibility.
can you compare storing an intermittent energy source by means of a chemical fuel, hydrogen and oxygen, as compared with in a battery? Just compare and contrast every aspect that matters. Just to be clear, this is (in effect) a battery, right? So what are its characteristics as compared with, say, lithium ion batteries. (I am particularly interested in weight and in number of duty cycles, which sounds like it's "unlimited" as opposed to lithium ion which is really not that many cycles, right?) I'm also far outside the field, just interested. Thanks!
Duty cycles does make sense as the catalytic efficiency decreases per given use period (in this case, day is the most relevant) due to irreversible chemical reactions with the catalyst itself, in this case probably quite a bit of the metaphosphate going to plain rust.
Thank you, but could you translate this to practical terms? I would like you to imagine some totally off-the-wall usage, I don't know, (this is completely illustrative example), imagine a tiny pacemaker that is self-powered through blood circulation and must charge and discharge itself essentially continuously - so, something like tens of thousands of duty cycles per day (low estimate, this is one cycle every few seconds), or 7m cycles per year.
By the end of one year, would it be totally depleted?
Please note that I did not want to name the application, so don't worry about the specifics of my illustrative example, it's totally made-up and I see the problems with it - just about the timing.
Additionally I am interested in the size and weight as compared with other rechargeable battery types.
I am sorry that I seem to be asking really strange questions. If they are not well-defined could you reply with your questions about my question?
Thank you so much for taking the time to understand my question and and reply. Basically, I'm asking if the effect you describe applies to hundreds of thousands, millions, tens of millions, hundreds of millions, or billions of charge/discharge cycles. Is it a tiny little effect or rather more significant than that?
I want you to really think out of the box, please, so just to expand your mind (as an "anchor"), even though it is not relevant to my application, consider:
>Modern automobile engines are typically operated around 2000–3000 rpm (33–50 Hz) when cruising, with a minimum (idle) speed around 750–900 rpm (12.5–15 Hz), and an upper limit anywhere from 4500 to 10,000 rpm (75–166 Hz) for a road car or nearly 20,000 rpm for racing engines such as those in Formula 1 cars (currently limited to 15,000 rpm)
So if the ctypical cruising speed is 2000 RPM, then in an hour of cruising, a piston would go through 120,000 cycles. If an hour of driving gets you, say, 100 miles (obviously higher than average) then 100,000 miles is 1,000 hours (likely actually more), so that we are at 120 million cycles per 100,000 miles. Obviously this is pretty crazy and I don't envision anything that does anything like that, plus it would need an electric generator, but I just wanted to expand your mind as to why in certain, as-yet unspecified, applications, hundreds of millions, billions, or tens of billions of duty cycles might well be completely reasonable to talk about, and therefore whether the answer to my questions is "tens of thousands" or "infinite" is by no means an equivalent answer!
Please note that both the heart-valve driven pacemaker, and the hybrid engine with per-cycle electric recovery, are not the domains I'm talking about. So I'm interested in a more pure or abstract description of the possible specifications here.
By the way if you happen to know off-hand of other kinds of energy storage (example: graphene supercapacitor; flywheel) that you happen to know are good for the mentioned hundreds of millions of cycles, then you could mention this as well. However, in this thread I was primarily asking about the number of duty cycles (and, to a lesser extent, the possible weight) of a reversible fuel cell - whether via water splitting or some other mechanism.
This is kind of out-there, but it also sounds like you are saying the catalyst may be thought of as an additional "fuel" to be added over time. Like, for the engine made-up example, someone might think of topping up their engine with both petrol and catalyst-fuel, every time they top up. So in this case it would matter how much in quantity we are talking about - if the catalyst is thought of as a consumable that gets used over time and adding some more is part of operations. If it gets used exceedingly slowly, this is no greater a burden than engine oil changes, which are already used regularly.
Thank you so much for your time. I hope I've been clear about my questions.
If all this is pretty crazy, then please just name the number of duty cycles until the catalyst is 50% depleted. (And please name a definition for what 50% depleted means.) Or, any other alternative measure you can think of, as long as it's well-defined. I would just like to know within 1-2 orders of magnitude! Thank you!
(you might want to mention you're not OP in cases like this, as I addressed my comment specifically to them and almost thought I was still talking to them.)
of course, I appreciate your reply too. epistasis, why do you say "cycles don't make sense" -- is it because it's "infinite" or because it can't be run as a fuel cell immediately in the same place? Like you can't go back and forth immediately?
I read most of the article you linked (which had a couple of occurrences of the term 'fuel cell' - not many - therefore leading me to be confused as to why you said what you just said).
I am talking about using it as a fuel cell, same as a battery. If daily cycling means 1 cycle per day, then 10 years means 3650 cycles. How does "power to gas" compare? Infinite cycles?
Apologies for the confusion. You were asking for an awful lot, in way that didn't make much sense, so I thought I would chip in a bit.
OP was talking about burning the hydrogen, as was I. Burning is not typically the term used with what goes on in fuel cells.
A battery has a fixed capacity attached to it, it has a fixed power to energy ratio. The component that stores the energy is directly attached to the part that discharges the energy. This is what makes "cycles" make sense.
With power to gas, or using fuel cells to consume energy from the process described in the article, the component that stores energy is not directly connected to the part that consumes energy. It's not necessary that they even have a fixed fuel stores attached to them, they could just be hooked up to a pipeline. The rate at which parts wear out would better be described in terms of total energy stored or consumed.
That's why I mentioned the cost estimates (€0.10/kWh for hydrogen in that article), because it's perhaps the best way to compare. The rapid drop of lithium ion grid storage has put it at $250/kWh capacity with 3650 cycles, which is ~$0.07/kWh before accounting for taxes, maintenance, siting, etc., which may or may not be included in that above estimate for hydrogen.
Both of these numbers blow me away by how small they are. We're in for a wild ride on tech changes over the next few years...
Thanks. So after the fuel is burned for energy, it can't be unburned again, all in the same closed loop? (Reversible fuel cell?). That is not possible/practical?
I emailed Jeannie and she sent me the paper. I'm an idiot about finding a place to post it or host it (or find it), but the title of the paper is:
"Highly active catalyst derived from a 3D foam of Fe(PO3)2/Ni2P for extremely efficient water oxidation"
As a former chemist in another but related field, this phrase is telling and part of why it is not in a higher impact journal: "We find that this catalyst, which may be associated with the in situ generated nickel–iron oxide/hydroxide and iron oxyhydroxide catalysts at the surface". This is generally code for "we're getting some sort of nano surface effect we're not 100% sure we understand or can replicate." I can't access the full paper, but the downfall of catalysts are usually: cost, durability, or unreproduciblity\creation cost. Getting nano surfaces to grow properly at industrial (10s of grams scale as one researcher said to me) is still more of an art than a science, with maybe one guy in a 10 person group able to get the substrate to perform.
Not super aimed at this particular paper, but those are probably the reasons you don't see fireworks going off over inorganic labs around the country about this paper.
"Hydrogen is the cleanest primary energy source we have on earth,” said Paul C. W. Chu, TLL Temple Chair of Science and founding director and chief scientist of the Texas Center for Superconductivity at UH.
This seems like sensationalism and poor science communication to me. Hydrogen isn't a primary energy source.
"Primary energy source" is a term with a specific meaning. I'm not talking about market share.
Primary energy sources do not require any type of conversion. Fossil fuels, nuclear, wind, and solar are all primary energy sources. Free hydrogen isn't found in nature. It can be made by splitting water using energy from a primary source. The catalyst described in this press release makes that process more efficient, but it still takes energy from a primary source to create hydrogen.
Sure it is; you just have to go kind of far out of the solar system before you'll start running into it. Molecular clouds of hydrogen are what makes those pretty Hubble pictures of nebulae. :)
And then in the very next sentence he says “Water could be the most abundant source of hydrogen if one could separate the hydrogen from its strong bond with oxygen in the water by using a catalyst.”
"Sensationalism and poor science communication" is not the half of it. He's lying outright.
I am (was) a chemist but I find this research area somewhat puzzling. Electrolytic hydrogen production has been industrialized for more than a century. Put nickel electrodes in an aqueous solution of potassium hydroxide. Separate anode and cathode with a porous diaphragm. Run direct current through it. Get pure hydrogen. "Simple" alkaline electrolysis is only ~50% efficient, but that means there's only a factor of two efficiency gain possible no matter how good your catalyst. Large commercial electrolyzers from a decade ago reached ~70%. Why so much research on further marginal efficiency gains from new catalysts? Are there other costs that fall faster-than-linearly with improved efficiency?
Large commercial electrolyzers from a decade ago reached ~70% (efficiency)."
That's good to know. No "breakthrough" can improve the process by more than another 30%. NREL says the best commercial systems are at 73% today.[1] There's also an additional energy cost for compressing the hydrogen.
That's pretty good. Getting any chemical or electrochemical process up to 73% efficiency is a good result.
That was actually the data source I was thinking of. It's reviewing units commercially available by the end of 2003. More time had passed than I thought.
I agree that the efficiency is already pretty good and even a "perfect" system would not drastically lower energy inputs further.
>“Cost-wise, it is much lower and performance-wise, much better,”
Having lower catalyst costs may allow for more installations that are used only intermittently. I know very little about the research in this particular field, but am not surprised that it's seeing more attention.
As intermittent renewable electricity generation continues to get cheaper and replace fossil fuel sources, there's going to be a massive interest in using the large amounts of curtailed energy in someway. California is currently curtailing GWh per day of solar, and there's still a fairly low amount of renewable penetration. The question isn't necessarily about storing hours of energy, but perhaps weeks or maybe even months.
Power to gas to electricity is currently only about 1/3 efficient, but depending on the cost curve of various battery technologies, there could be a big case for generating and storing a few months worth of methane mixed with hydrogen for winter months in the northern hemisphere.
I bet there are likely to be far more research into combining electrolysis with methanation (perhaps with CO2 that's already dissolved in the water) or even chains of carbon.
CNG automobiles, fueled with methane made from surplus renewable energy, might be a way for natural gas to be used in the future. We'll see if its ever economical, but there may be some great use cases for it.
I agree that cheap-but-intermittent renewable electricity calls for differently optimized electrolyzer designs. Optimize for "cheap to manufacture and maintain" so you can afford to use them at a low duty cycle. If that is the underlying objective for this research, it's great, but doesn't come through clearly in the linked report. They mention efficiency in the headline, efficiency 7 times more in the body, and cost only twice, only in the body.
Does the electrolysis of water in the presence of the currently-used catalysts gradually corrode the anode/cathode, reducing efficiency and requiring eventual maintenance? If so, this could simply be a Total-Cost-of-Ownership thing: reducing maintenance costs or extending cycle time by decreasing corrosion.
The general goal of the research grants is to create a technology stack that takes sunlight as input and provides hydrogen as output. Such a thing would allow production of storable energy in the open ocean, immediately making the rest of the planet inhabitable by people.
> That would solve one of the primary hurdles remaining in using water to produce hydrogen, one of the most promising sources of clean energy.
What? No. Hydrogen is not a source of energy, it's a storage format. A more efficient catalyst will certainly help with losses when storing the energy, but there's no net gain.
Yeah, this doesn't make sense. Also the problem isn't getting hydrogen, its to burn the hydrogen for energy efficiently and safely, which we currently have not found a way to do ... yet.
Got any reference on the efficiency and longevity of their fuel cells?
Hydrogen fuel cells have a sweat spot at around 30% efficiency lasting for several years, and another at around 50% efficiency lasting for a few months. I have never seen anybody get a different set of numbers.
The Toyota hydrogen fuel-cell car has a high price and not so great performance, so it's safe to say that the answer to your question is "not good enough for a car, yet".
They are competing with batteries, not combustion engines. That's because the hydrogen must be generated somehow (and stored).
If you go and generate the hydrogen from natural gas (so you have a natgas powered car, not much gain) you'll have to multiply those by a 40% to 50% conversion efficiency. If you generate it from water and electricity, your equivalent battery will have that 30% efficiency multiplied by another ~30% efficiency of electrolysis.
Could this also be used in desalination? Turn into hydrogen, burn to convert back to water, feed it catalyst material like a fuel? (I'm not really sure how these catalysts work, do you like push water through them? and out comes gases?)
So, uh, do catalysts like this reduce the waste heat you get when electrolyzing water with a cruder setup? Because there's nothing but a specific minimum energy input that's going to break the bonds between hydrogen and oxygen.
hydrogen makes metals brittle and there can be catastrophic failure of valves, regulators etc.
there are only 3 significant problems with hydrogen as an energy carrier to solve before it becomes ubiquitous:
1. how to make it
2. how to store it & transport it
3. how to use it
IMO there was a time in the late 80s, early 90s when there was a chance it could be useful but the battery tech development over the last 25 years has nailed the coffin shut - hydrogen research persists because people with jobs know how to research hydrogen production.
What are the key metrics for catalysts? Obviously cost is one. Round-trip energy efficiency? How does this measure up to existing commercial alternatives? How about against no-catalyst electrolysis?
There's a reason why different gasses are used in different applications. Combustiblity, pressure required for liquefaction, flashpoint, safety and so on.
There's a lot of overlap between these in some areas like home heating and BBQs, but each application requires some engineering to make it work with any particular fuel.
The energy storage density of hydrocarbons make them more practical as a fuel in situations where portability is a concern. For example: You could have a hydrogen BBQ, but the tank would probably have to be much larger for the same amount of burn time.
No, hydrogen gas is less dense than hydrocarbons (at the same pressure) since it has a lower molar mass (volume is inversely proportional to the molar mass).
As soon as we can convert CO2 into hydrocarbons using solar or wind power in a way that's cost-competitive with conventional extraction we'll have turned an important corner in developing as a society.
Growing sugarcane does a pretty good job of converting CO2 into hydrocarbons using solar power.
But to be cost-competitive with fracked methane, I'm pretty sure we're going to need some heavily genetically-engineered strains of algae, growing in artificial forests of pipes.
The irony is that algae can be used to clean up fracking wastewater, so it makes methane production cheaper as it competes.
Sugarcane and switchgrass might be able to close the loop, but these take a lot of mechanical processing and land to do so, which could introduce additional costs.
The promise of syntetic fossil fuels from things like water and CO2 is that you don't need a lot of land, you just need energy, and that energy can be renewable.
If you can discover a way to cost-effectively synthesize hydrocarbons (CH chains) from CO2 and H2O, which contain all of the necessary components, you're pretty much guaranteed a Nobel prize.
So far the process to do this involves a lot of messy intermediate steps, like hundreds of millions of years and enormous pressure in the mantle of the Earth.
We need energy in portable forms (and have other uses for hydrocarbons). Getting that energy from clean sources and storing it with atmospheric CO2 is better than burning fossil sources of energy.
IIRC one "infrastructure-scale" battery idea is compressing hydrogen into salt domes. While I can't speak to the intersection of the article and this idea, people can clearly store hydrogen in massive amounts.
Unlike natural gas (which we can mine from the earth), hydrogen can't be an energy source because there's no place you can mine it. It can only be a medium of transmitting energy: you need some other source of energy in order to create hydrogen, and then you can transport it somewhere else and use it there.
So the question is what is that source of energy, and whether we could simply connect the source directly to where the energy is needed and cut out the middleman H2.
One direct application would be more efficient ways to generate fuel for Hydrogen vehicles [0].
It would also be essential for mining fuel from asteroids or gas giant's moons as ice is not so rare, improving the sustainability of space operations. Hydrogen itself has a pretty big specific impulse, it's just not used more often than Kerosene for rockets due to safety issues.
If you could achieve Metallic Hydrogen [1][2] then you would have the perfect fuel for navigating the solar system.
Abstract: A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO2) for photoelectrochemical oxygen evolution reaction. Metal−organic chemical vapor deposition from a singlesource precursor was used to ensure good contact between the FeMnP and the TiO2. The TiO2/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO2 of 1.8 mA cm−2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm−2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec−1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO2/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.
> The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce.
mods, the original title should be preserved, currently it is :
"U of Houston discovers catalyst that splits water into hydrogen and oxygen"
But the original title is : "UH Researchers Report New, More Efficient Catalyst for Water Splitting"
catalyst for water splitting aren't new. the article even says it :
>The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce.
Hi Dang, I submitted the article. I was trying to use the r/futurology article title which was, "University of Houston physicists have discovered a catalyst that can split water into hydrogen and oxygen, composed of easily available, low-cost materials and operating far more efficiently than previous catalysts, reported in the Proceedings of the Natural Academy of Sciences."
HN has an 80 character limit for titles so I had to cut it down drastically from that.
When I see anything related to splitting water into hydrogen, I'm worried that we're going to use water for energy on top of using to hydrate people.
Still today, over 10% of the world population don't have access to clean water. I'm also curious on how clean the water needs to be to be used with this catalyst. AFAIK, most catalyst conversion need pretty pure water, in which case, we would not only use water, but use _clean_ water, which is even more scare than "dirty" water...
Wouldn't that be a good thing in general though? If we use Hydrogen as our storage format, then you can do the following:
Sea Water (H2O + sea junk) -> H2
Then later when generating electricity:
2 * (H2) + O2 -> H2O (fresh) + energy
Naturally, the resultant H2O can be moved and recycled. I think a catalyst that splits water points towards a potential where we have more fresh water, not less.
It seems like a lot, but it would presumably be decentralized across many many locations. Additionally, you don't need 24 * 60 * 60 * olympic pool volumes -- you can cycle the same amount of water into/out of a fuel cell in a closed system.
1 water molecule has 2 Hydrogen molecules and 1 Oxygen molcule. Hydrogen has a molecular weight of 1, while Oxygen has a weight of 16 [1][2]. This means that, by weight, water is about 1/9th hydrogen. So 9kg of water should give us 142 MJ worth of Hyrdogen.
Gasoline is about 46 MJ/kg [0], so 3kg of water should give us the equivelent of 1kg gasoline.
Gas has a density of .77 kg/L [3], water has a density of 1kg/L [4]. So 3L of water, should be about 2.31L worth of Gas.
Also, if we keep the water that results from burning hydrogen we may be able to avoid needing to re-purify it.
That aspect of it is a big meh. Reverse osmosis uses a great deal less energy than hydrolysis, so if you have so much energy that you are using a meaningful amount of water you also have so much energy that you can just make clean water.
How much water would this process need to make enough energy for this to have an impact? Presuming we wouldn't use up our fresh water resources for this and that it would come from the ocean, but would this process create potential threats to the marine habitat as the mineral/chemical concentrations of the ocean water shifted?
1. The overall idea here is to take an intermittent energy source (e.g. solar power) and "store" it as chemical fuel, in this case hydrogen and oxygen. This is what plants do, and we can also view fossil fuels as resulting from the "storage" of millions of years of solar energy. Note also that you get the water back when you burn the hydrogen, so there is no net consumption of water, it's just a carrier.
2. While you can split water without a catalyst, most of the energy gets wasted as heat, so this is not a great way to go if you're trying to do energy storage.
3. Efficient catalysts exist for this reaction, but they are based on rare and expensive metals, typically Pd, Pt, and Ir. As a result, there has been a search for catalysts involving "first-row" metals such as Fe, Co, Ni, etc.
4. There are variety of metrics for an electrocatalyst (efficiency, stability, cost, etc), but it's a fair bet that if this were significantly better than state-of-the-art, it would be in Science or Nature rather than PNAS.