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SRNL Hits Milestone in Nuclear Hydrogen Production

The Hybrid Sulfur Process has two stages. First, the electrolysis of sulfur dioxide and water to generate hydrogen and sulfuric acid, followed by the thermochemical conversion of the sulfuric acid back to sulfur dioxide. Click to enlarge.

The US Department of Energy’s Savannah River National Laboratory (SRNL) recently successfully completed a 100-hour long demonstration of a sulfur dioxide depolarized electrolyzer (SDE), designed and fabricated by SRNL, to produce hydrogen from water. The SDE is a core component of the Hybrid Sulfur Process.

The demonstration, which showed that the electrolyzer can successfully operate continuously without significant loss of performance, represents a milestone in the development of an efficient, economical process for generating large quantities of hydrogen using advanced nuclear reactors. In previous demonstrations, the electrolyzer had only been operated for short durations.

The Hybrid Sulfur Process (HyS) is one of the variants on sulfur-based thermochemical cycles for the production of hydrogen and is derived from a Westinghouse process. The electrolyzer oxidizes sulfur dioxide to form sulfuric acid (H2SO4) at the anode and reduces protons to form hydrogen at the cathode.  The overall electrochemical cell reaction consists of the production of H2SO4 and H2:

SO2 + 2H2O → H2SO4 + H2

The initial electrolysis reaction of sulfur dioxide and water occurs at low temperature. The resulting sulfuric acid is decomposed into steam and sulfur trioxide, which is then further decomposed into sulfur dioxide and oxygen at high temperature (850-950 °C) with heat obtained from the nuclear reactor.

The sulfur dioxide in the electrolyzer reduces the required electrode potential well below that required for electrolysis of pure–water, thus reducing the total energy consumed by the electrolyzer. An electrolyzer operating in the range of 500-600 mV per cell can lead to an overall HyS cycle efficiency in excess of 50%, which is superior to all other currently proposed thermochemical cycles, according to the researchers at SRNL.

An important factor in the efficiency of the Hybrid Sulfur Process is the low amount of cell voltage required by the electrolyzer, which determines the amount of electricity needed. In the 100-hour test, SRNL’s electrolyzer required about 0.8 volts per cell, leaving researchers optimistic that the commercial goal of 0.6 volts per cell can be achieved when operating the electrolyzer at higher temperature and pressure.

Future work will seek to further improve the cell performance and extend its operational durability. SRNL is currently building a larger, multi-cell electrolyzer. Plans call for beginning construction of an integrated labscale Hybrid Sulfur Process, including the larger electrolyzer, during the next fiscal year.

The long-term goal is to build an engineering demonstration of the HyS Process that can be operated in conjunction with DOE’s planned Next Generation Nuclear Plant, scheduled for operation after 2017 at the Idaho National Laboratory.




Roger will like this one. It just seems to me that you could run this off of geothermal or solar heat instead of using a nuclear station.


Oh great. Nuclear Hydrogen. Now we can have a Hindeberg that glows weather it's on fire or not.

Actually, in spite of the many challenges of hydrogen, this seems like good fundamental research. I continue to hope we can have more efficient large scale storage of excess energy than Hydrogen, though. Even, "in excess of 50% efficiency" still sounds like we lose almost half the electric potential when storing energy as H2.

Paul Dietz

Roger will like this one. It just seems to me that you could run this off of geothermal or solar heat instead of using a nuclear station.

Yeah, from all those 900 C geothermal sources we have out there. Planning to tap the magma from an active volcano?

Max Reid

Yes Solar & Geothermal will also work, but is there anyway to store Heat instead of converting to Hydrogen.

Paul Dietz

Even, "in excess of 50% efficiency" still sounds like we lose almost half the electric potential when storing energy as H2.

Since that's the conversion ratio from heat energy, that's actually rather good. It's better than you'd get from putting nuclear-generated electricity into an ordinary electrolyzer, since producing that electricity throws away about 2/3 of the heat energy in a typical nuclear powerplant.


Hey, if geothermal gets you a third of the way there, why not use it? Top it up with whatever other energy you have around. No magma needed.


Anyway you look at it an improvement in catalysts is good news.

Max: a little off topic but heat can be stored. For geothermal it is already stored. For solar heat up something and use the heat at night.

I have idly speculated that solar thermal be used to heat a large mass of iron or another cheap material. Something rather nontoxic, and noncorrosive, with an appropriate melting point. That would be a commercial scale operation.

At the residential level the analogue would heat a water mass by solar and let that help the heat pump in winter.

I am too old and long retired to be at all concerned with the calculations. Might pan out. Might not.


The nukular power industry power mongers will use any ruse/technofix to create and maintain a monopolistic hold over the basic commodity of energy. No doubt, the military/industrial complex is involved in this Machiavellian nukular power charade.


This is interesting research, but electricity is still used to create the hydrogen. To put this process into widespread use would mean either electricity demand would have to be reduced somewhere, or more plants of some type (goal, gas, nuke) built. Perhaps a combination of waste heat and intermittent electricity (wind, solar) would be fruitful.

Using waste heat alone to drive a chemical reaction directly would be ideal, but since this is fairly obvious, I guess there is nothing useful that can happen at the temperatures of a typical secondary cooling circuit.

Stan Peterson

Its nice to know that the Peakist's End of the (civilized) World will not arrive,for yet another reason. I view this technology as a last step to be taken if all the other interim and preferable technological efforts run into unblock-able obstacles.

I see little need for a full Gen IV high temperature reactor development based on Fission. It is a aways off anyhow. It won't be there before 2030. By then Fusion and even the He3+ He3 reaction may be the answer of choice.

That is not in the cards however. Li-Ion and Electrified Ground Transport has been demonstrated and cost is a manageable issue. It will arrive long before this technology matures.

I would prefer a Gen III+ standardized Nuke providing half the temperature, a pre-heating if you will. to around 400 degrees C. The technology is here, safety margins are just much better.

There are certainly enough advanced Nukes being built to supply the pre-heat. By last count, there are 251 Nukes being built outside the USA. Within the USA there are 29 Nukes in the process of seeking "Combined Operating and Construction" license approval as well.

Although there are 102 Nukes active in the USA, the latest 50 produce 67% of the electrical energy, as the early ones were significantly smaller. The new standardized designs up rate these last 50 by a small amount of output too.

As a consequence by 2020, the USA will be generating about twice as much electricity from Nukes as is does today, when the oldest Nukes start to retire. So the USA will have 35-40% of its electrical energy coming for m Nukes, with another 16% from Hydro and a few 4-5% from other "renewables" as well. That places half of the US load from non fossil sources. It is also a source of a lot of low level waste heat.

Secondary use of the waste heat has not been used, so using any of it will only improve the plant economics some more. I would think that large scale desalinization would be preferable use, but some H2 preparation is another possible use, as is Nitrogen (fertilizer) creation.


So how much energy does it take to turn the Sulfuric Acid back into water?

Or are we just going to turn all of our freshwater into Sulfuric Acid?

Mike Z

An Ideal combination to add to the hydrogen to biomass gasification to significantly increase biofuel yields, and possibly displace 100% of our liquid energy consumption.


It may be possible to convert nuclear heat (from reactors not yet slated for construction) to hydrogen at 50% efficiency, but it has to be converted at the other end.  PEM fuel cells are ~60% efficient, so end-to-end would be 30% minus gas compression and other losses.  Used in an internal combustion engine at 25% instead of a PEMFC, end-to-end becomes 12.5%.

The electrical efficiency of a nuke plant is about 33%.  Transmission efficiency, ~90%.  Batteries, motor and such, 70%.  End to end, 21%, all losses included and no cost or reliability issues stemming from PEMFC's.


Greyflcn: you may want to take a closer look at the insert chart. There are two reactions involved. The first one uses the Sulfuric acid as a reactant.

richard schumacher

Cheap H2 made from non-fossil fuels is a good thing. Electrolyze CO from atmospheric CO2 (again with non-fossil energy), use that plus the H2 to make synthetic liquid hydrocarbons, and we can keep using internal combustion engine vehicles with no net contribution of greenhouse gasses.

Herm Perez

One advantage that no one is mentioning is that hydrogen can be stored, then used in a turbine by burning, or in a fuel cell during a peak demand period.. and it can be piped to the final location easily if so desired.

Herm Perez,

We are mentioning that Hydrogen can be stored. We also explicitly state that much energy is lost in creating, storing, and burning much so that we want a more efficient storage medium. For example, if you have two reservoirs (one 1,000 feet above the other), then you can use excess electricity to pump water up to the higher reservoir, and when you need peak power, let it flow back down hill through turbines. This is a much more efficient form of energy storage than electrolysis, pressurization and combustion, and it works on a huge scale at reasonably low cost with well-established technology. Just because Hydrogen burns cleanly does not make it optimally efficient, or even the most environmentally friendly form of energy storage.

Roger Pham

Thanks, Neil, for the thought of me. This is happy news, indeed, but minus the nuclear energy, though. I've just read in the current Scientific American edition that wider utilization of nuclear energy will increase the risk of nuclear weapon proliferation. This is exactly what we are trying to avoid happening in Iran and other unstable and unfriendly regimes in the world! Much safer to concentrate on solar and wind electricity, but with a major caveat, due to the unreliability of both of these renewable energy sources!

I figure that since over 50% of electrical generation in the US is from coal-fired plants, the heat from the coal combustion itself can be used in conjunction with renewable electricity from wind or solar sources to produce H2, in order to double (?) the electrical efficiency of room-temp electrolysis. Why? Because steam turbines in coal-fired plants cannot change their output rapidly enough to respond to the fluctuating output of wind or solar electricity. Because of the unreliability of wind or solar electricity, utility companies must invest extra in back-up fossil fuel generation capacity, and this greatly reduce the appeal of renewable electricity. Unless, of course, if unreliable but renewable electricity can be used very efficiently to generate transportation-grade fuels, in the form of hydrogen for the future, or, for now, via Fischer-Trophs synthesis when the H2 can be combined with the CO2 output of the coal-fired plants to produce liquid hydrocarbon fuels.

Now then, why not charge your PHEV or BEV with renewable electricity instead of bother to make H2? WEll, because your PHEV or BEV is not always plugged into the grid when the wind blows the strongest nor when the sun is at its peak of luminosity. The cost of battery is too high for utility providers to use it to store excess wind or solar electricity output. H2 storage is much cheaper and not dependent on scarce materials if deployed in massive quantity.

Roger Pham

Hi Ben, if you're the author of the anonymous last posting?
Storing energy in the form of H2 is not inefficient if one uses the H2 ,or methane, or synthetic hydrocarbon via FT when H2 is combined with waste CO2, as transportation fuels, or via local pipeline for home heating or for distributed generation whereby both heat and electricity can be harnessed from the H2 (or methane, when H2 is combined with CO2) at 80-90% overall efficiency!

Hydrostatic energy storage is well known, and occurs in the natural form as lakes with dams and hydro-electricity, but costs too much when all the structures have to be built from scratch. Plus, how do you put these hydrostatic energy storage into your car? Battery? Aye, there's the rub! Current A123 battery costs $2000/kwh, and there's concern of shortage of Lithium upon massive adoptation of PHEV's.


Roger: Yes the batteries still cost too much. But IMO that problem is much smaller than working out all the remaining wrinkles in hydrogen (hydrogen ICE is inefficient and fuel cells make batteries look cheap). Batteries are no longer so much a science problem as they are a manufacturing/engineering problem now. As for Lithium, the oceans are full of the stuff.


NiMh battery systems are more appropriate for more classes of PHEV vehicles than Li-ion batteries. The notion of reducing weight to increasing driving range is Neanderthalic.

Carefully distributed battery weight lowers vehicle center-of-gravity, thus improves stability and handling and offers a major safety feature especially applicable to top-heavy roll-prone SUVs. Furthermore, the crash test rule of thumb 'the lighter car always loses' is still valid.

Battery weight becomes less of an issue and more of an advantage with larger vehicles.

The heavier the battery, the more the battery recycling and maintenance industries are likely to remain localized, rather than outsourced to 3rd World slave labor states.

Batteries are likely to have additional use as household electricity storage for low-demand uses, when wear reduces their utility in vehicles. Do NOT forget that a portable, household battery supply can be a lifesaver in an emergency or grid failure, not to mention the ideal means to wrest control of energy systems out of the hands of corporate bourgeoise.

The foremost issue with future automobiles is that their use be limited and travel by other means improved as necessary replacements. Current and predicted numbers of future 'better' cars cannot be supposedly accommodated via high-tech Li-ion batteries, fuel cells, hydrogen, super-light hypercars, computerization, etc. The PHEV vehicle, particularly because of its batteries, offers substantial technological advancement and revolutionary reform for travel, land-use, development and energy.

This forum is habited by nearsighted nerds playing science fiction games.


Mr. Wells,

If you don't like the company you keep, it is not the fault of the establishment you frequent.



Wells: Who's playing sci-fi games? If you actually owned an EV then you might actually know what you're talking about. Weight is a lot more than just range. It's also the ability to get up a steep hill and accelerate at a reasonable rate. In my experience, NiMh are a damn site better than lead-acid but still only marginally acceptable. I could even wish for an improvement over my current LiFePO4.

Roger Pham

Hi Neil,
ICE like the diesel cycle can attain up to 45% efficiency. ICE, when optimized strictly for Hydrogen fuel, can attain as high as 50% efficiency without requiring the high compression ratio of traditional Diesel engine, due to the much faster combustion rate of Hydrogen. The high compression of Diesel engine creates more friction loss in comparison to net output at part load or even at high load, but the slower combustion (isobaric combustion) of heavy petroleum like diesel fuel requires high compression for proper expansion. Fast combustion rate of H2 allowing near-isochoric combustion at TDC, hence efficient expansion of combusted gas without requiring very high compression like 1:20 in a Diesel. Compression ratio of 1:13 is sufficient for optimal H2-ICE efficiency, leading to less engine internal friction.

Now, with a full hybrid ICE-HEV drive train, the optimal efficiency of the ICE can be maintained throughout all driving mode, allowing the H2-ICE-HEV to get close to the FCV-HEV in term of overall efficiency.

Your posting sounded real intelligent until the last sentence. For the record, I have 20/20 vision without the use of corrective lenses. Never needed them. :)

Herm Perez

You cant store energy hydrostatically in S Florida, it is flat as a pancake, so hydrogen can take the place of natural gas if it can be made cheap enough for peak demand power generation.. if you burn it in simple gas turbines you can get up to 46% efficiency, up to 90% if you can reuse the heat in co-generation schemes..

If large fuel cells can beat this then even better.

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