Korea-led team develops hybrid solid oxide electrolysis cell for efficient production of H2
27 December 2017
Solid oxide electrolysis cell (SOEC) has the potential to be cost-effective, environmentally friendly, and highly efficient for the production of hydrogen from water. There are two types of SOECs, based on the electrolyte materials: oxygen ion conducting SOECs (oxygen-SOECs) and proton conducting SOECs (proton-SOECs).
Researchers in South Korea, with colleagues at Georgia Tech, have now developed an SOEC based on a mixed-ion conductor that can transport both oxygen ions and protons at the same time; they call it a “Hybrid-SOEC”. In a paper in the journal Nano Energy, the researchers reported that the hydrogen yield from their Hybrid-SOEC was 1.9 L per hour at a cell voltage of 1.5 V at 700 °C—four times higher hydrogen production efficiency of the existing high-efficient water electrolytic cells.
The proposed system has attracted much attention as a new promising option for the cost-effective and highly-efficient hydrogen production, as it shows excellent performance compared with other water-electrolysis systems, they said.
The work was led by Professor Guntae Kim in the School of Energy and Chemical Engineering at UNIST in collaboration with Professor Tak-Hyoung Lim of Korea Institute of Energy Research (KIER) and Professor Jeeyoung Shin of Sookmyung Women’s University.
An SOEC consists of two electrodes and a solid-state electrolyte; the solid-state electrolyte obviates the need to replenish lost electrolytes, while eliminating corrosion problems. SOECs also operate at relatively high temperatures (700-1000 °C), helping to offer reduced electrical energy consumption.
Existing SOEC electrolytes allow the transport of either only one of the hydrogen or oxygen ions to the other electrode. For SOEC electrolytes that transport oxygen ions, water electrolysis occurs at the anode and this results in the production of hydrogen. The SOEC electrolytes that transport hydrogen ions cause water electrolysis to occur at the cathode and this results in the production of oxygen. Here, hydrogen travels through the electrolyte to the anode.
The Hybrid-SOEC concept is based on the mixed ionic conducting electrolyte, allowing water electrolysis to occur at both hydrogen and air electrodes.
Theoretically, using electrolytes that transport both hydrogen and oxygen ions allows the production of two electrolysis products—hydrogen and oxygen—on both sides of the cell. This could improve hydrogen production rate greatly. In the study, the research team focused on the control of properties of electrolytes.
In comparison to other SOECs and representative water-electrolysis devices reported in the literature, the proposed system demands less electricity for hydrogen production, while exhibiting outstanding electrochemical performance with stability. Moreover, the Hybrid SOEC exhibits no observable degradation in performance for more than 60 hours of continuous operation, implying a robust system for hydrogen production.
By controlling the driving environment of the hydrogen ion conductive electrolyte, a mixed ion conductive electrolyte in which two ions pass can be realized. In Hybrid-SOEC where this electrolyte was first introduced, water electrolysis occurred at both electrodes, which results in significant increase in total hydrogen production.
—Junyoung Kim, lead author
Resources
Junyoung Kim, Areum Jun, Ohhun Gwon, Seonyoung Yoo, Meilin Liu, Jeeyoung Shin, Tak-Hyoung Lim, Guntae Kim (2017) “Hybrid-solid oxide electrolysis cell: A new strategy for efficient hydrogen production,” Nano Energy, Volume 44, Pages 121-126 doi: 10.1016/j.nanoen.2017.11.074
This is excellent news for near future, much lower cost clean H2 production, from water and electricity from clean excess/surplus REs. Clean Solar and Wind energies would become usable 24/7 for increased effectiveness and efficiency.
Surplus clean low cost H2 could be stored and/or used for various tasks and/or to produce e-energy to meet peak demands.
Posted by: HarveyD | 27 December 2017 at 06:16 AM
HarveyD
Go back and read the article. This is not a path to use excess/surplus REs (which mostly do not exist anyway). It requires a temperature in excess of 700 deg C (1292 deg F) which is above the melting point of aluminum. I am not sure how they claim 4 time more efficiency but I assume that they are just taking the electrical input and ignoring the heat energy input. There is no free lunch -- particularly when it come to generating hyrdrogen from electricity. Much better to use the energy as electricity and if you really have a surplus either turn down the fossil fuel plants or used pumped storage or some other storage where you will get back more than 25% of the input.
Posted by: sd | 27 December 2017 at 08:32 AM
The talk of efficiency doesn't appear to be about energy efficiency, but production rate per unit area.
The advantage of high-temperature electrolysis is that the water is already partly dissociated by heat, so the electric power requirement is smaller. This lends itself to operation with high-temperature nuclear reactors to supply feed steam at much higher efficiency than converting all cell input power to electricity.
Posted by: Engineer-Poet | 27 December 2017 at 09:43 AM
So, what is the exact:
- full-energy efficiency (thermal+electric input vs gained H2 energy content)
- electric energy efficiency (electric input vs gained H2 energy content)
of this new electrolysis system?
700C is high-grade heat which is not easy/cheap to come by. It will either need dedicated CSP plant or integration into a nuclear powerplant right?
Posted by: soltesza | 27 December 2017 at 10:27 AM
ignoring the heat energy input...
If you have waste heat from a power plant that helps.
Posted by: SJC | 27 December 2017 at 10:40 AM
The same and/or equivalent/similar process could possibly be fine tuned to work at lower temperatures with similar efficiency?
Secondly, the high (700C) temperature used could be maintained-contained in an isolated environment with reduced heat loss.
Another good use for NPPs would be to supply most of the heat required (at very low cost). Alternatively, excess heat from future Small transportable mass produced NPPs and/or solar furnaces could also be used.
At the current development rate, much lower cost clean H2 will be available within 5 to 10 years.
Posted by: HarveyD | 27 December 2017 at 11:21 AM
700 C temperatures are not achievable with water-cooled reactors, and that's too close to the boiling point of sodium. This application would require either a gas-cooled reactor or molten-salt reactor.
Posted by: Engineer-Poet | 27 December 2017 at 01:42 PM
This whole research effort appears to be an interesting lab experiment which is OK if it adds to our base knowledge. However, it does not appear to be a practical way to make cheaper hydrogen.
700 C is definitely not waste heat and any talk of efficiency has to take into account the heat energy that is put into the water. You can not just keep it hot. The energy is going into the process. There is no free lunch especially if it involves violating the laws of thermodynamics. The absolute minimum energy involved in transforming water into hydrogen and oxygen has to be greater than the energy that you would recover by transforming the hydrogen and oxygen back to water. Otherwise, you could build a perpetual motion machine.
Posted by: sd | 28 December 2017 at 08:33 AM
With an MCFC or SOFC you get the heat you need for SOEC electrolysis. With fossil power plant waste heat you preheat the water which improves efficiency.
Posted by: SJC | 28 December 2017 at 11:04 AM
Nobody said otherwise. The difference is that the steam is made directly from reactor heat at almost 100% efficiency, while the electric side will probably have 50% thermal efficiency or less. If the unit is dedicated to hydrogen production, the electric side can be considerably smaller and cheaper.
There is nothing more ridiculous than proposing to burn fossil fuel in a fuel cell to make electricity and heat to run electrolysis to make hydrogen. Gasification of the fuel in steam is vastly more efficient and cheaper.
Posted by: Engineer-Poet | 28 December 2017 at 04:40 PM
Engineering-Poet
My previous post came after yours but the comment about the heat energy was not intended for you. I am sure that you understand this. If was for HarveyD who seemed to think that just keeping the water or water vapor at 700 C in an insulated container was all that was required. There are a number of people on this site that do not seem to understand basic thermodynamics.
Also, your comment on ridiculous idea of burning fossil fuel in a fuel cell to make electricity and heat for electrolysis is spot on.
Posted by: sd | 29 December 2017 at 03:11 PM
Sometimes I do exposition/elaboration for the lurkers.
Carry on.
Posted by: Engineer-Poet | 29 December 2017 at 07:56 PM
Many times you insult as if your opinion is the ONLY opinion.
Posted by: SJC | 30 December 2017 at 04:28 PM
Many times I insult as if some ignoramus has failed basic science or even basic arithmetic. Wait, that actually happens. A lot.
If you don't want to be on the receiving end, don't be that guy.
Posted by: Engineer-Poet | 30 December 2017 at 08:14 PM
SJC
You are welcome to have your opinion just as I feel that I am allowed to have my opinion. However, you can not have your own facts or you own laws of physics. You and some others think that hydrogen will become an important commodity and fuel cells an important power source for cars, trucks, trains, etc. That is OK. I do not think that it will happen. I have some reasons why I think that but maybe I am wrong. I worked long enough as an engineering faculty member to know that most research efforts will come to nothing. But I also feel that we should have more basic research as you never know what might turn up and currently I believe that we are living somewhat off what research has been done in the past and not replenishing it.
Posted by: sd | 31 December 2017 at 10:07 AM
I would like to weigh in to this debate regarding the use of waste heat at 700 dgr C.
Actually, NO waste heat would be necessary. Just feed in the electricity from Solar PV and Wind turbine to supply the initial heating to 700 dgr C. Then, with good insulation, the heating will continue, with the difference being that low-temp PEM electrolyzer is around 70%-efficient, while this SOEC may be around 95%-99% efficiency. So, we may be looking at a vast improvement in efficiency with the use of SOEC.
Alternatively, Concentrated Solar thermal heat can be used to maintain 700 dgr temp, while solar PV electricity can be used in order to get well over 100% efficiency with respect to supplied electricity.
Posted by: Roger Pham | 31 December 2017 at 01:27 PM
Per the steam calculator at TLV.com, the enthalpy of superheated steam at 700 C and 10 bar is 3.92352 MJ/kg. This is about 1.1 kWh/kg, roughly 3.3% of the total energy of the hydrogen produced.
You can calculate the enthalpy of the gas products, which energy must either be used to heat input steam, put to secondary use or be lost. I'm not interested enough in this to put forth the effort. Only then can you do a full energy balance and see why high-temperature electrolysis is so interesting (or look up where someone else has done the work for you).
Posted by: Engineer-Poet | 01 January 2018 at 12:59 PM
Correction: water is only 1/9 hydrogen so the enthalpy of the steam would be 29% of the energy of the hydrogen product.
Posted by: Engineer-Poet | 01 January 2018 at 03:14 PM