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Solar reactor for the two-step thermochemical production of fuels from water and carbon dioxide

Schematic of the solar reactor for the two-step, solar-driven thermochemical production of fuels. Click to enlarge.

A team from Caltech, ETH Zürich and the Paul Scherrer Institute have devised a solar reactor for the two-step, solar-driven thermochemical production of fuels. In a paper published in the journal Science, they report stable and rapid generation of fuel over 500 cycles. They achieved solar-to-fuel efficiencies of 0.7 to 0.8%, and showed that the efficiency was largely limited by system scale and design, rather than by its chemistry.

The basis for the system is a solar-driven thermochemical cycle for dissociating H2O and CO2 using nonstoichiometric ceria (CeO2). The design of the reactor exposes porous ceria directly to concentrated solar radiation, heating it to between 1,420 and 1,640 °C, thereby liberating oxygen from its lattice. The material then readily strips oxygen atoms from carbon dioxide and water, forming CO and hydrogen, respectively, which are combined to create fuels.

Solar-driven thermochemical approaches to CO2 and H2O dissociation inherently operate at high temperatures and use the entire solar spectrum; as such, they provide an attractive path to solar fuel production at high rates and efficiencies in the absence of precious metal catalysts...Cerium oxide (ceria) has emerged as a highly attractive redox active material choice for two-step thermochemical cycling because it displays rapid fuel production kinetics and high selectivity, where such features result, in part, from the absence of distinct oxidized and reduced phases. However, ceria-based thermochemical studies to date have largely been limited to bench-top demonstrations of components or individual steps of the solar fuel production cycle; assessment of cyclability has been limited, and the energy conversion efficiency has remained uncertain because of the relatively low gravimetric fuel productivity inherent to the nonstoichiometric process.

Here, we demonstrate high-rate solar fuel production from both CO2 and H2O using a solar reactor subjected directly to concentrated radiation under realistic operating conditions relevant to large-scale industrial implementation, without the need for complex material microstructures and/or system design (e.g., additional quench or separation steps). The results provide compelling evidence for the viability of thermochemical approaches to solar fuel generation while clarifying the efforts required to transform the concept into a central technology in a sustainable energy future.

—Chueh et al.

The solar-to-fuel energy conversion efficiency obtained in the work for CO2 dissociation was about two orders of magnitude greater than that observed with state-of-the-art photocatalytic approaches. The gravimetric hydrogen production rate exceeds that of other solar-driven thermochemical processes by more than an order of magnitude.

The researchers found that both the efficiency and the cycling rates in the reactor were limited largely by thermal losses, resulting from conductive and radiative heat transfer. A thermodynamic analysis of efficiency based solely on the material properties of CeO2 suggests that values in the range of 16 to 19% are attainable, even in the absence of sensible heat recovery.

Given that, the team anticipates that reactor optimization and system integration will result in substantial increases in both efficiency and fuel production rates. Furthermore, they note, the abundance of cerium, which is comparable to that of copper, is such that the approach is applicable at scales relevant to global energy consumption.


  • William C. Chueh, Christoph Falter, Mandy Abbott, Danien Scipio, Philipp Furler, Sossina M. Haile, and Aldo Steinfeld (2010)High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria. Science Vol. 330 no. 6012 pp. 1797-1801 doi: 10.1126/science.1197834



Recycle CO2 would be a good idea if it can be done with higher efficiency. Who knows, the world may one day learn to recycle most pollutants and GHG. Wonder how the current oil/coal/NG allk prowerful lobbies would react, specially if it cost more than the raw products.


From the efficiency, I guess we can infer the BTUs of H2, CO and O2 per acre.
This might be another form of energy generation and/or CO2 reduction for the future (near I hope).

I think the current Bank/ Oil/ Coal/ Pharmaceutical/ NG/ SEIU/ UAW/ Auto/ allk prowerful lobbies will be unconcerned with this for many years
– and then Caltech, ETH Zürich and the Paul Scherrer Institute will just create their own lobby.

Government by powerful special interests.

So what’s the answer?
Elect those with a history of opposing earmarks, lobbies and graft.


While I find this very interesting, and promising, I note they only compare their idea to other solar photocatalytic and thermochemical processes. What's it's end-to-end efficiency when compared to the more mature solar-electrolysis technology?


Ceria is used in SOFCs. I have read of a process where the concentrated solar thermal energy is used to heat an SOFC where water and electricity are used to create H2 and O2 at lower temperatures. This look good also.


I guess the question I have is what does it cost to produce a gallon of gas now and what will the cost be at volume?


TT...powerful lobbies and financially interested groupuscules have gained such a tight hold on politicians that elections have become more and more meaningless. We are effectively back to the middle ages and are more or less governed by as many few. We the people has lost its real meaning and does not apply any longer. Instead of Kings and Lords we now have puppets elected with $500M+ propaganda campaigns.

The only way that 'We the People' could effectively elect our representatives and government leaders would be to break the financial ties that make our politicians so utterly dependent on the few powerful people/groups mentioned above.

This could be done by banning all financial contributions by individuals, lobbies, groupuscules, religious groups, small and large firms etc. Election cost (expenses) should be limited to $5 to $10 by legal voters for each of the 2 major parties and paid for 100% with public money. An independent body should oversee the process and candidates that have transgressed the rules and limits should be disqualified and banished from elected offices for at least 20 years.

However, the majority may prefer the current masquerade. That's what we have become.


Right now you can check a box on your tax form to contribute $5 towards campaigns, but few do. If $5 per tax payer per year were put towards campaigns we would have over $500 million per year and could limit corporate and union contributions.

Much of the lobbying has to do with fund raising. The lobbyists promise to raise money for the politicians campaign which is all legal. When most Congress members spend more of their time fund raising, that looks like an attractive offer.

Roger Pham

The temperature required (1400-1600 C) is too high! This will create a lot of design and operational problems. Solid Oxide high-temp electrolytic cells can do the same at 800-1000 degrees C. Electrical current is required for solid oxide electrolysis, but the heat loss from the insulation and cooling of the cells can be used in steam turbine to generate electricity to power the high-temp electrolysis.


That temperature is high to be using nuclear power too, which since it can run day and night has advantages in capital cost over solar, as you still need to buy the hydrogen production equipment.


If little but the CeO2 needs to hit the 1400-1600°C level, perhaps the rest of the system can be made less refractory. However, the efficiency will have to be many times higher to compete with electric power production using a similar collector field; even with an ICE efficiency of 40%, the photons-to-work efficiency is going to be extremely low compared to solar thermal or PV.

Account Deleted

Reforming at 1640° C or 3000° F - we used to call this thermal reforming - disassociation of molecules is 'easy' if not fast - however the environment is difficult.

These high temperatures call for rather exotic refractory! Forget valves etc!


This is off topic to some degree. I am addressing the comments regarding campaign financing. A way to break corporate grip on representatives of the people is to remove their capability to fund political campaigns as everyone knows. What we need in my opinion is a grass roots campaign for both state and federal constitutional amendments that state:
The financing of elections for the offices of United States President or Vice President, for electors for President or Vice President, or for Senator or Representative in Congress, shall be raised from only those individuals that are citizens of the United States eligible to vote specifically for the candidate.

Please comment.


It's not a scientific, economic problems or fraud of any kind if they start to commercialize this machine for small-scale home-leisure use or hobby use. Many hobby kits are selled on internet these days, no reasons not to sell this one too. Im interrested to learn and practice at home with a kit, how to replace exxon-mobil, shell, opec, texas crude, texaco branded products. These branded products like bunker fuel, diesel, ethanol e 85, super gasoline of 94 octane, super gasoline of 92 octanes, 87 octans gasoline, 10-30 saw engine oils with additives, kerosene, natural gas, methanol can be learned by folks at home of how to produce it. For testing these fuels, it's more easy. Let's say you just brew your own butanol, then just poor this butanol into you gasoline car and drive with it, till the tank need a refill. If the ride was normal, then just add some more butanol instead of gasoline and stay with it, you are now ready to check regurlarly the quality of your own brew butanol for years. Check the qualities of your other fuels if you have more then needed for your car by selling this fuel to neibors and friends, they surrely need butanol, ethanol, bio-diesel, chimical diesel, n.gas, kerosene, acytylene, white powder, methanol, hydrogen gas, so on. Happy fuel production.


SJC & dwinstonel. I find a (compulsory) $5/year per tax payer/voter a very interesting solution as long as other shadow donations are banned. Some kind of election finance control board would have to be set up to distribute election funds properly and ensure that no under the table dirty money is introduced or find its way to candidates. That way, elected politicians would have a free hand to govern for the PEOPLE and not for powerful lobbies.

By the way, you would have to find ways to stop lobbies and all interested groups to finance political propaganda materials. Those (parallel campaigns) may be the hardest to stop within current constitutional rights. A constitution amendment and an election reform law may be required. That would not be easy to do but something has to be done sooner or latter. The election masquerade has degenerated to a shameful level and is no longer democratic.



Since corporations are considered people, they contribute $5 each as well. Lobbying is considered free speech, but they would not be able to contribute more than $5 for each lobbying corporation and they could not fund raise because there would be none.


Here in Canada each party that gets more than 2% of the vote in the last election is given funding for the next election campaign. Each vote they got in the last election is worth approximately $1.75 in future funding.

A buck+75 per voter can go a long way when then campaigning only lasts 5 weeks.


So an acre of desert (4047 m2) with 3 kWh per m2 per day solar insolation (non-tilt flat plane average over the year) could yield:

328 gallons of gasoline-equivalent per day at 100% efficiency
62 gallons per day at 19% efficiency
2.3 gallons per day at 0.7% efficiency

For comparison, algae to bio-oil is currently around 8 gallons per acre per day at best.


Harvey and others

The problem I have with any federally run election system is the Federal Bureaucracy required to manage it. If you have the Feds running the election system it will be quickly corrupted. The Feds already have too much centralized power. We need to force power away from Washington DC and Big Business and into the hands of the electorate.


"The Feds already have too much centralized power."

We'd like to invite you downtown for a debrief Mr. Winstone...)


Presidential Elections is a Federal affair an it could hardly be delegated to the States or other bodies. Federal Supreme Court appointed guru or equivalent body may be tasked with it?

State and local elections is another matter. Some kind of effective oversee organisation is also required for them.

Locally, we are also having problems with election financing. Limited public money is used but private donations are still allowed up to $1000 per people and/or firm. The problem is with this $1000. It could be lowered to $5 or so. We already have an election guru to oversee the process. It is not perfect but it works to avoid undue influence.


I think a $5 donation by all citizens would be money well spent if it helped end corruption. I would like to see contributions to state elections limited to voters that reside in that state as well. Californians shouldn't help decide elected officials in Texas.


I fully agree with you KGC


I second that.


I would like to see contributions to state elections limited to voters that reside in that state as well. Californians shouldn't help decide elected officials in Texas.

I third that... And I think it should go double for contributions coming from outside the country. Corporations in China and Saudi princes shouldn't help decide elected officials in America.



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