Generation, storage, and time-delayed release of electrons in graphitic carbon nitride material for artificial photosynthesis
The storage of photogenerated electric energy and its release on demand are still among the main obstacles in artificial photosynthesis.
Scientists have now explored a modified form that can produce light-generated electrons and store them for catalytic hydrogen production even after the light has been switched off.
They present this biomimetic photosynthesis approach in the journal Angewandte Chemie.
Berkeley Lab approach could lead to more stable, efficient artificial photosystems
Scientists have found a way to engineer the atomic-scale chemical properties of a water-splitting catalyst for integration with a solar cell, and the result is a big boost to the stability and efficiency of artificial photosynthesis.
Led by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), the project is described in a paper published this week in the journal Nature Materials.
The research comes out of the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub established in 2010 to develop a cost-effective method of turning sunlight, water, and carbon dioxide into fuel. JCAP is led by the California Institute of Technology with Berkeley Lab as a major partner.
The goal of this study was to strike a careful balance between the contradictory needs for efficient energy conversion and chemically sensitive electronic components to develop a viable system of artificial photosynthesis to generate clean fuel.
Striking the right balance
“In order for an artificial photosystem to be viable, we need to be able to make it once, deploy it, and have it last for 20 or more years without repairing it,” said study principal investigator Ian Sharp, head of materials integration and interface science research at JCAP.
The problem is that the active chemical environments needed for artificial photosynthesis are damaging to the semiconductors used to capture solar energy and power the device.
“Good protection layers are dense and chemically inactive. That is completely at odds with the characteristics of an efficient catalyst, which helps to split water to store the energy of light in chemical bonds,” said Sharp, who is also a staff scientist at Berkeley Lab’s Chemical Sciences Division. “The most efficient catalysts tend to be permeable and easily transform from one phase to another. These types of materials would usually be considered poor choices for protecting electronic components.”
By engineering an atomically precise film so that it can support chemical reactions without damaging sensitive semiconductors, the researchers managed to satisfy contradictory needs for artificial photosystems.
“This gets into the key aspects of our work,” said study lead author Jinhui Yang, who conducted the work as a postdoctoral researcher at JCAP. “We set out to turn the catalyst into a protective coating that balances these competing properties.”
Doing double duty
The researchers knew they needed a catalyst that could not only support active and efficient chemical reactions, but one that could also provide a stable interface with the semiconductor, allow the charge generated by the absorption of light from the semiconductor to be efficiently transferred to the sites doing catalysis, and permit as much light as possible to pass through.
They turned to a manufacturing technique called plasma-enhanced atomic layer deposition, performed at the Molecular Foundry at Berkeley Lab. This type of thin-film deposition is used in the semiconductor industry to manufacture integrated circuits.
“This technique gave us the level of precision we needed to create the composite film,” said Yang. “We were able to engineer a very thin layer to protect the sensitive semiconductor, then atomically join another active layer to carry out the catalytic reactions, all in a single process.”
The first layer of the film consisted of a nanocrystalline form of cobalt oxide that provided a stable, physically robust interface with the light-absorbing semiconductor. The other layer was a chemically reactive material made of cobalt dihydroxide.
“The design of this composite coating was inspired by recent advances in the field that have revealed how water-splitting reactions occur, at the atomic scale, on materials. In this way, mechanistic insights guide how to make systems that have the functional properties we need,” said Sharp.
Using this configuration, the researchers could run photosystems continuously for three days—potentially longer—when such systems would normally fail in mere seconds.
“A major impact of this work is to demonstrate the value of designing catalysts for integration with semiconductors,” said Yang. “Using a combination of spectroscopic and electrochemical methods, we showed that these films can be made compact and continuous at the nanometer scale, thus minimizing parasitic light absorption when integrated on top of photoactive semiconductors.”
The study authors noted that while this is an important milestone, there are many more steps needed before a commercially viable artificial photosystem is ready for deployment.
“In general, we need to know more about how these systems fail so we can identify areas to target for future improvement,” said Sharp. “Understanding degradation is an important avenue to making something that is stable for decades.”
Researchers create the first practical design for photoelectrochemical water splitting
Scientists from Forschungszentrum Jülich have developed the first complete and compact design for an artificial photosynthesis facility. This is a decisive step towards applying the technology. The concept is flexible both with respect to the materials used and also the size of the system. The researchers have now published their findings in the journal Nature Communications (DOI: 10.1038/NCOMMS12681).
In future, sun and wind will supply the lion’s share of our energy. The fluctuating nature of these renewable energy sources means that current research is focusing more intensively on efficient storage technologies. Like the energy sources themselves, these technologies should be environmentally friendly and affordable. This trend is particularly apparent in research on direct photoelectrochemical water splitting, that is to say artificial photosynthesis employing a combination of solar cell and electrolyser. In this way, solar energy can be directly converted into the universal storage medium of hydrogen. This process was first investigated in the 1970s, but has only begun to attract increasing attention in recent years. As yet, research has focused on materials science for new absorber materials and catalysts to further improve efficiency.
Jülich solar cell researchers Jan-Philipp Becker and Bugra Turan, however, are concentrating on an aspect that has so far largely been neglected: a realistic design that can take this technology from the scientists’ laboratories and put it into practical applications. “To date, photoelectrochemical water splitting has only ever been tested on a laboratory scale,” explains Burga Turan. “The individual components and materials have been improved, but nobody has actually tried to achieve a real application.”
Compact, complete, and expandable
The design created by the two experts from Jülich’s Institute of Energy and Climate Research is clearly different from the usual laboratory experiments. Instead of individual components the size of a finger nail that are connected by wires, the researchers have developed a compact, self-contained system – constructed completely of low-cost, readily available materials.
With a surface area of 64 cm2, their component still appears relatively small. The trick is in its flexible design. By continuously repeating the basic unit, it will in future even be possible to fabricate systems that are several square metres in size. The basic unit itself consists of several solar cells connected to each other by a special laser technique. “This series connection means that each unit reaches the voltage of 1.8 volt necessary for hydrogen production,” says Jan-Philipp Becker. “This method permits greater efficiency in contrast to the concepts usually applied in laboratory experiments for scaling up.”
Compatible with a wide range of technologies
At the moment, the solar-to-hydrogen efficiency of the prototype is 3.9 %. “That doesn’t sound like much,” admits Bugra Turan. “But naturally this is only the first draft for a complete facility. There’s still plenty of room for improvement.” In fact – the scientists add – natural photosynthesis only achieves an efficiency of one per cent. Jan-Philipp Becker is of the opinion that within a relatively short time the Jülich design could be increased to around 10 % efficiency using conventional solar cell materials. However, there are also other approaches. For instance, perovskites, a novel class of hybrid materials, with which it is already possible to achieve efficiencies of up to 14 %.
“This is one of the big advantages of the new design, which enables the two main components to be optimized separately: the photovoltaic part that produces electricity from solar energy and the electrochemical part that uses this electricity for water splitting.” The Jülich researchers have patented this concept, which can be flexibly applied for all types of thin-film photovoltaic technology and for various types of electrolyser. “For the first time, we are working towards a market launch”, says Becker. “We have created the basis to make this reality.”
Learn and see more: From Leaf to Tree: Large-Scale Artificial Photosynthesis
Scientists discover a process that could enhance our ability to harvest energy from the Sun for electricity and fuels.
A process to enhance the performance of solar technologies such as solar cells and photocatalysts, and potentially make their production cheaper, has been discovered by scientists.
Solar cells take energy from the Sun and convert it into electricity. But energy from the Sun can also be harnessed to create other fuels such as hydrogen, which could be used for example in cars. These ‘solar fuels’ are produced by mimicking photosynthesis, the process used by plants to create energy from sunlight.
Solar fuels could help tackle climate change, as they can be created without producing carbon dioxide, a greenhouse gas. They could also directly replace fossil fuels in many applications.
However, photosynthesis is complicated process, and there are several challenges to its replication. One of these challenges is that catalysts – materials that help the reaction proceed – are often expensive and inefficient, preventing the process from being easily scaled up.
In a new study, published in the journal Advanced Materials last week, researchers from Imperial College London and Queen Mary University of London (QMUL) demonstrate that a unique property of the material barium titanate could lead to more efficient solar cells and catalyst systems.
A clean, climate-friendly energy source that is virtually inexhaustible: This is the promise artificial photosynthesis holds. Chemists from the University of Würzburg have now got one step closer to reaching this goal. The scientists present their work in the journal Nature Chemistry.
Nature shows how to do it: Photosynthesis is a process used by plants to create energy-rich organic compounds, usually in the form of carbohydrates, and oxygen (O2) from carbon dioxide (CO2) and water (H2O) driven by light. If we succeeded in mimicking this process on a large scale, numerous problems of humanity would probably be solved. Artificial photosynthesis could supply the Earth with fuels of high energy density such as hydrogen, methane or methanol while reducing the amount of carbon dioxide in our atmosphere and slowing down climate change.
Developing the necessary efficient catalysts and associated dyes is a focal area of research at the Chair of Professor Frank Würthner at the University of Würzburg’s Institute of Organic Chemistry. Two of Professor Würthner’s doctoral students, Marcus Schulze and Valentin Kunz, have recently reported a partial success in this regard. They present the results of their research work in the current issue of the journal Nature Chemistry.
New system surpasses efficiency of photosynthesis
The days of drilling into the ground in the search for fuel may be numbered, because if Daniel Nocera has his way, it’ll just be a matter of looking for sunny skies.
Nocera, the Patterson Rockwood Professor of Energy at Harvard University, and Pamela Silver, the Elliott T. and Onie H. Adams Professor of Biochemistry and Systems Biology at Harvard Medical School, have co-created a system that uses solar energy to split water molecules and hydrogen-eating bacteria to produce liquid fuels.
The paper, whose lead authors include postdoctoral fellow Chong Liu and graduate student Brendan Colón, is described in a June 3 paper published in Science.
“This is a true artificial photosynthesis system,” Nocera said. “Before, people were using artificial photosynthesis for water-splitting, but this is a true A-to-Z system, and we’ve gone well over the efficiency of photosynthesis in nature.”
While the study shows the system can be used to generate usable fuels, its potential doesn’t end there, said Silver, who is also a founding core member of the Wyss Institute at Harvard University.
By combining semiconducting nanowires and bacteria, researchers can now produce liquid fuel.
Three pioneers in the field of synthetic photosynthesis discuss the potential of this technology and the challenges that must be overcome to make it commonplace.
Imagine creating artificial plants that make gasoline and natural gas using only sunlight. And imagine using those fuels to heat our homes or run our cars without adding any greenhouse gases to the atmosphere. By combining nanoscience and biology, researchers led by scientists at University of California, Berkeley, have taken a big step in that direction.
Peidong Yang, a professor of chemistry at Berkeley and co-director of the school’s Kavli Energy NanoSciences Institute, leads a team that has created an artificial leaf that produces methane, the primary component of natural gas, using a combination of semiconducting nanowires and bacteria. The research, detailed in the online edition of Proceedings of the National Academy of Sciences in August, builds on a similar hybrid system, also recently devised by Yang and his colleagues, that yielded butanol, a component in gasoline, and a variety of biochemical building blocks.
The research is a major advance toward synthetic photosynthesis, a type of solar power based on the ability of plants to transform sunlight, carbon dioxide and water into sugars. Instead of sugars, however, synthetic photosynthesis seeks to produce liquid fuels that can be stored for months or years and distributed through existing energy infrastructure.