Skip to comments.Solar Fuels Take Two Steps Forward
Posted on 10/03/2011 8:55:35 PM PDT by neverdem
Two independent research teams report today in Science that they've taken key strides toward harnessing the energy in sunlight to synthesize chemical fuels. If the new work can be improved, scientists could utilize Earth's most abundant source of renewable energy to power everything from industrial plants to cars and trucks without generating additional greenhouse gases.
Today, humans consume an average of 15 trillion watts of power, 85% of which comes from burning fossil fuels such as oil, coal, and natural gas. That massive fossil fuel consumption produces some nasty side effects, including climate change, acidified oceans, and oil spills. These problems are likely to grow far worse in coming years, as worldwide energy use is expected to at least double by 2050.
Renewable power sources, such as solar photovoltaics and wind turbines, aim to fill this demand, and they are making steady progress at providing electricity at ever cheaper costs. But electricity has a key drawback as an energy carrier. It's difficult to store in large quantities, which means it can't be used for most heavy industry and transportation applications, such as flying planes or driving heavy trucks. So researchers have long sought to use the energy in sunlight to generate energy-rich chemical fuels, such as hydrogen gas, methane, and gasoline, that can be burned anytime anywhere. And though they have demonstrated that this goal is possible, the means for doing so have been inefficient and expensive.
That's where the new advances come in. In the first, researchers led by Daniel Nocera, a chemist at the Massachusetts Institute of Technology in Cambridge, report that they've created an "artificial leaf" from cheap, abundant materials that splits water into molecular hydrogen (H2) and oxygen (O2), somewhat similar to the way plants carry out the first step in photosynthesis. The leaf consists of a thin, flat, three-layered silicon solar cell with catalysts bonded to both faces of the silicon. When placed in a beaker of water and exposed to sunlight, silicon absorbs photons of sunlight, generating electrons with enough energy to conduct through the silicon.
The process leaves behind positively charged electron vacancies called "holes" that can also move through the material. The holes migrate to a cobalt-containing catalyst painted on one face of the silicon cell, where they strip electrons from water molecules, breaking them into hydrogen ions (H+), and oxygen atoms. The catalyst then knits pairs of oxygens together to make O2. Meanwhile, the H+ ions migrate to another catalyst on the opposite face of the silicon cell, where they combine with conducting electrons to make molecules of H2. In principle, the H2 can then be stored and either burned or run through a fuel cell to generate electricity.
In the second study, a team led by chemists Richard Masel of Dioxide Materials in Champaign, Illinois, and Paul Kenis of the University of Illinois Urbana-Champaign, report that they've come up with a more energy-efficient approach to converting carbon dioxide (CO2) into carbon monoxide (CO), the first step to making a hydrocarbon fuel. Other researchers have worked for decades to devise catalysts and the right reaction conditions to carry out this conversion. But converting CO2 to CO has always required applying large electrical voltages to CO2 to make the change. That excess voltage is an energy loss, meaning it takes far more energy to make the CO than it can store in its chemical bonds.
But Masel, Kenis, and colleagues found that when they use a type of solvent for CO2 in their setup called an ionic liquid, it reduces the extra voltage needed approximately 10-fold. Ionic liquids are liquid salts that are adept at sabilizing compounds such as CO2 when they are given an extra negative charge, the first step in converting CO2 to CO. And the Illinois researchers suspect that this added stability reduces the need for applying an external charge to do the job.
"These papers are nice advances," says Daniel DuBois, a chemist at Pacific Northwest National Laboratory in Richland, Washington, who works on catalysts for both splitting water and reenergizing CO2. But he cautions that neither solves all of their respective issues. The oxygen-forming catalyst in the artificial leaf, for example, remains slow, DuBois says. And the efficiency of the overall leaf is only 4.7% at most, and just 2.3% in its most simplest design. The catalyst in the CO2 system is even slower. But DuBois says that because other researchers in the field now have a good examples of systems that work, they can now focus on designing improved catalysts to speed them up.
Interesting approach, eventually I think we’ll get there. Hard to beat the energy density of chemical fuels, but it sucks to have to wait around 50 million years for them.
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Okay, ready to be shot down here, but if you could find a catalyst that when it came into contact with water, split it into hydrogen and oxygen inside the fuel line of a hydrogen burning engine.
Then the hydrogen would be burned mixed with oxygen and the exhaust product would be water vapor that when condensed became water again.
So, if this was all in a closed loop, why wouldn't it be an almost perpetual motion engine?
Ready and waiting to be told... I am full of crap here—
So, once again... with these catalysts being developed, why am I full of crap on the above?
Key word is IF. IF I could find a catalyst that would break CO2 into carbon and oxygen, I could make oxygen and piles of carbon that I could burn again. IF I could find a substance that would turn lead into gold... etc.
Hydrogen and oxygen react to release energy. To reverse the reaction, the energy has to be put back in in the form of heat, light, electricty. Catalysts don't do rapid, large scale break down of more stable compounds into less stable compounds in the absence of energy. Catalysts are used to increase the rate of a reaction that would normally proceed slowly on its own. Water doesn't want to break down into H and O nearly as much as O and H want to react to form water.
That reaction has a preferred direction. It will go one way very well if a small amount of energy gets it started. A spark in a container of O and H will do it nicely. A container of water will not break down into water without a huge input of energy. Yes, a catalyst will make the breakdown more efficient, but it will not magically breakdown water without that energy.
No perpetual motion machine here.
Step 2: Run
I suppose we could just burn wood...
The system may be closed, but the heat is not. The heat escapes through the metals via friction. You would have to have one heck of a catalyst to break the H2 from the O, and it would have to be fast to supply the amount of H2 necessary to power the engine.............
>> “but it sucks to have to wait around 50 million years for them.” <<
Nobody ever waited 50 million years for anything, and we’re not waiting now.
The Earth is making hydrocarbon fuels faster than we are using them, but to promote serfdom and socialism we need bogus old earth propaganda, and ‘alternative’ energy schemes. Solutions without problems.
>> “I suppose we could just burn wood.” <<
We should be burning way more of it than we are. We would then have more healthy young plants and less dead ones making our forests burn to death in unnaturally intense wild fires, and less newsprint fouling up our land fill dumps.
Fire is the environmentally sensitive way of disposing of waste.