(Press-News.org) Caltech scientists, inspired by a chemical process found in leaves, have developed an electrically conductive film that could help pave the way for devices capable of harnessing sunlight to split water into hydrogen fuel.
When applied to semiconducting materials such as silicon, the nickel oxide film prevents rust buildup and facilitates an important chemical process in the solar-driven production of fuels such as methane or hydrogen.
"We have developed a new type of protective coating that enables a key process in the solar-driven production of fuels to be performed with record efficiency, stability, and effectiveness, and in a system that is intrinsically safe and does not produce explosive mixtures of hydrogen and oxygen," says Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech and a coauthor of a new study, published the week of March 9 in the online issue of the Proceedings of the National Academy of Sciences (PNAS), that describes the film.
The development could help lead to safe, efficient artificial photosynthetic systems--also called solar-fuel generators or "artificial leaves"--that replicate the natural process of photosynthesis that plants use to convert sunlight, water, and carbon dioxide into oxygen and fuel in the form of carbohydrates, or sugars.
The artificial leaf that Lewis' team is developing in part at Caltech's Joint Center for Artificial Photosynthesis (JCAP) consists of three main components: two electrodes--a photoanode and a photocathode--and a membrane. The photoanode uses sunlight to oxidize water molecules to generate oxygen gas, protons, and electrons, while the photocathode recombines the protons and electrons to form hydrogen gas. The membrane, which is typically made of plastic, keeps the two gases separate in order to eliminate any possibility of an explosion, and lets the gas be collected under pressure to safely push it into a pipeline.
Scientists have tried building the electrodes out of common semiconductors such as silicon or gallium arsenide--which absorb light and are also used in solar panels--but a major problem is that these materials develop an oxide layer (that is, rust) when exposed to water.
Lewis and other scientists have experimented with creating protective coatings for the electrodes, but all previous attempts have failed for various reasons. "You want the coating to be many things: chemically compatible with the semiconductor it's trying to protect, impermeable to water, electrically conductive, highly transparent to incoming light, and highly catalytic for the reaction to make oxygen and fuels," says Lewis, who is also JCAP's scientific director. "Creating a protective layer that displayed any one of these attributes would be a significant leap forward, but what we've now discovered is a material that can do all of these things at once."
The team has shown that its nickel oxide film is compatible with many different kinds of semiconductor materials, including silicon, indium phosphide, and cadmium telluride. When applied to photoanodes, the nickel oxide film far exceeded the performance of other similar films--including one that Lewis's group created just last year. That film was more complicated--it consisted of two layers versus one and used as its main ingredient titanium dioxide (TiO2, also known as titania), a naturally occurring compound that is also used to make sunscreens, toothpastes, and white paint.
"After watching the photoanodes run at record performance without any noticeable degradation for 24 hours, and then 100 hours, and then 500 hours, I knew we had done what scientists had failed to do before," says Ke Sun, a postdoc in Lewis's lab and the first author of the new study.
Lewis's team developed a technique for creating the nickel oxide film that involves smashing atoms of argon into a pellet of nickel atoms at high speeds, in an oxygen-rich environment. "The nickel fragments that sputter off of the pellet react with the oxygen atoms to produce an oxidized form of nickel that gets deposited onto the semiconductor," Lewis says.
Crucially, the team's nickel oxide film works well in conjunction with the membrane that separates the photoanode from the photocathode and staggers the production of hydrogen and oxygen gases.
"Without a membrane, the photoanode and photocathode are close enough to each other to conduct electricity, and if you also have bubbles of highly reactive hydrogen and oxygen gases being produced in the same place at the same time, that is a recipe for disaster," Lewis says. "With our film, you can build a safe device that will not explode, and that lasts and is efficient, all at once."
Lewis cautions that scientists are still a long way off from developing a commercial product that can convert sunlight into fuel. Other components of the system, such as the photocathode, will also need to be perfected.
"Our team is also working on a photocathode," Lewis says. "What we have to do is combine both of these elements together and show that the entire system works. That will not be easy, but we now have one of the missing key pieces that has eluded the field for the past half-century."
INFORMATION:
Along with Lewis and Sun, additional authors on the paper, "Stable solar-driven oxidation of water by semiconducting photoanodes protected by transparent catalytic nickel oxide films," include Caltech graduate students Fadl Saadi, Michael Lichterman, Xinghao Zhou, Noah Plymale, and Stefan Omelchenko; William Hale, from the University of Southampton; Hsin-Ping Wang and Jr-Hau He, from King Abdullah University in Saudi Arabia; Kimberly Papadantonakis, a scientific research manager at Caltech; and Bruce Brunschwig, the director of the Molecular Materials Research Center at Caltech. Funding was provided by the U.S. Department of Energy, the National Science Foundation, the Beckman Institute, and the Gordon and Betty Moore Foundation.
People of differing competence tend to give each other's views equal weight, preventing them from making the best group decisions, finds new UCL-led research.
This suggests that people with similar levels of competence make the best decision-making groups, as otherwise the tendency to assume equal competence can give undue weight to the opinions of less capable members.
The new study, published in Proceedings of the National Academy of Sciences, investigated how pairs of people with differing competence weighted their own judgements against each other's.
Researchers ...
This news release is available in German.
Reproduction at old age involves risks that may impact one's own life and may impose reduced biological fitness on the offspring. Such evidence, previously obtained in humans and other taxa under laboratory conditions, has now been confirmed by researchers from the Max Planck Institute for Ornithology in Seewiesen together with colleagues from the UK and New Zealand for the first time in free-living animals. In a long-term study on a population of house sparrows they found that offspring of older parents themselves produced ...
Nearly three out of four Chinese adults have poor cardiovascular health, with poor diet and growing rates of obesity compounding the risks associated with continuing high rates of smoking, according to a new survey published in the Journal of the American College of Cardiology.
The 2010 China Noncommunicable Disease Surveillance Group collected cardiovascular health data from a nationally representative sample of more than 96,000 men and women in the general Chinese population. According to estimates derived from the survey results, just 0.2 percent of Chinese men and ...
People in a society are bound together by a set of connections - a social network. Cooperation between people in the network is essential for societies to prosper, and the question of what drives the emergence and sustainability of cooperation is a fundamental one.
What we know about other people in a network informs how much we are willing to cooperate with them. By conducting a series of online experiments, researchers explored how two key areas of network knowledge effect cooperation in decision-making: what we know about the reputation and social connections of those ...
A new study suggests that increases in atmospheric CO2 could intensify extreme droughts in tropical and subtropical regions -- such as Australia, the southwest and central United States, and southern Amazonia -- at much a faster rate than previously anticipated, explains University of Texas at Austin professor Rong Fu in a commentary in the March 9 edition of Proceedings of the National Academy of Sciences.
Fu, a professor at the university's Jackson School of Geosciences, writes about a new study by William K.M. Lau of the University of Maryland and Kyu-Myong Kim of the ...
Once green, the Sahara expanded 5,500 years ago, leading ancient herders to follow the rain and grasslands south to eastern Africa. But about 2,000 years ago, their southward migration stalled out, stopped in its tracks, archaeologists presumed, by tsetse-infested bush and disease.
As the theory goes, the tiny tsetse fly altered the course of history, stopping the spread of domesticated animal herding with a bite that carries sleeping sickness and nagana, diseases often fatal for the herder and the herded.
Now, isotopic research on animal remains from a nearly 2,000-year-old ...
Despite extensive historical knowledge about the African slave trade - including trends in the volume and demographics of the roughly 12 million people shipped from West and West Central Africa to the New World between 1500 and 1850 - fundamental details about their ethnic and geographical origins remain elusive. Dr. Hannes Schroeder from the Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who led the study, explains:
- There are historical records - merchant ledgers, shipping records and the like - but they tend to refer to coastal shipping ...
In the ongoing Ebola outbreak in West Africa, whose death toll is approaching 10,000, little information has been available about how the human immune response unfolds after infection.
Researchers from Emory and the Centers for Disease Control and Prevention have now obtained a first look at the immune responses in four Ebola virus disease survivors who received care at Emory University Hospital in 2014, by closely examining their T cells and B cells during the acute phase of the disease. The findings reveal surprisingly high levels of immune activation, and have implications ...
March 9, 2015
PITTSBURGH--To fully understand how nanomaterials behave, one must also understand the atomic-scale deformation mechanisms that determine their structure and, therefore, their strength and function.
Researchers at the University of Pittsburgh, Drexel University, and Georgia Tech have engineered a new way to observe and study these mechanisms and, in doing so, have revealed an interesting phenomenon in a well-known material, tungsten. The group is the first to observe atomic-level deformation twinning in body-centered cubic (BCC) tungsten nanocrystals. ...
COLUMBUS, Ohio - Children whose parents think they're God's gift to the world do tend to outshine their peers - in narcissism.
In a study that aimed to find the origins of narcissism, researchers surveyed parents and their children four times over one-and-a-half years to see if they could identify which factors led children to have inflated views of themselves.
Results showed that parents who "overvalued" their children when the study began ended up with children who scored higher on tests of narcissism later on.
Overvalued children were described by their parents ...
