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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.

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