Since ages the natural photosynthesis has sustained human civilization by providing food, fuel and the life sustaining environment, which is now threatened by the twin challenges of energy security and global warming. Researchers all over the world have turned to artificial photosynthesis for future sustainable life on this planet. Artificial photosynthesis (AP) is a chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen, without requiring chlorophyll. The process has great potential for creating a technology that could significantly reduce greenhouse gases linked to climate change, while also creating a clean way to produce energy.
Artificial photosynthesis (AP) aims to split water in oceans, and possibly even rivers, into its hydrogen, oxygen, and carbon components such as alcohol using sunlight. The process uses a special kind of solar cell that absorbs sunlight and conveys electricity to a pool of carbon dioxide dissolved in water. Catalysts spur a chemical transformation that yields oxygen and a carbon-based byproduct.
“The oxygen is then released into the air, just like plants do. The other product is captured and stored, for instance in depleted oil fields,” said Matthias May, a physicist at the HZB Institute for Solar Fuels in Berlin, and a co-author of the article, published in the journal Earth System Dynamics. Artificial photosynthesis, it turns out, is more efficient than natural photosynthesis. “The big difference is that we use artificial, inorganic materials for this, which effectively allow much higher conversion efficiencies,” he added. “This is exciting, as the high efficiency translates to a much lower land and water footprint.” Scientists say these artificial leaves could be installed in deserts, where are there are no trees or farms already capturing carbon dioxide.
The main challenge presented by AP is that photosynthesis in nature is inefficient. Plants convert only about 1 percent of carbon and water into carbohydrates. That efficiency has increased to about 10 percent in the lab, however, and researchers at Monash University in Melbourne, Australia, have hit a level of 22 percent efficiency. Several exciting advances are being made that have started turning this highly ambitious goal into realistic technology.
The technological challenge is to develop cheap, efficient catalysts and durable solar cells. “This will require a long-lasting, worldwide research effort, probably similar to fusion energy, which does, however, not guarantee success in due time,” he said. Countries would also need to find a way to pay for it.
HyperSolar, Inc. , the developer of a breakthrough technology to produce renewable hydrogen using sunlight and any source of water, announced in May 2019 that the stability test of its proprietary fully integrated hydrogen production device has surpassed 1000 hours. The device will serve as the foundation of the Company’s first-generation commercial renewable hydrogen generator.
New research describes a highly efficient and cheap device that could be used to turn waste carbon dioxide into methane. Natural gas, which mainly consists of methane, is a cleaner fuel than coal and has been characterized as a “bridge fuel” prior to transitioning to renewable energy sources, but not everyone thinks it’s a good idea to burn yet more hydrocarbons.
The natural photosysnthesis process uses chlorophyll, which captures sunlight, and a collection of proteins and enzymes that use that sunlight to break down H2O molecules into hydrogen, electrons and oxygen (protons). The electrons and hydrogen are then used to turn CO2 into carbohydrates, and the oxygen is expelled. The artificial photosynthesis process involve the four basic steps of light harvesting, charge separation, water splitting, and fuel production.
In artificial photosynthesis (the ‘artificial leaf’), sunlight is converted directly into solar fuel, without making use of biomass as in the production of biofuels from plants, and without involving an electricity network, as in electrolysis using power from photovoltaic cells.
One of the solar fuels is Hydrogen; the other may be carbon based fuels. Hydrogen is an attractive carbon-free energy carrier, which may play a lead role in future renewable energy technology. The drawback of hydrogen is that it is a highly explosive gas, while the existing energy infrastructure is based on liquids.
The carbon-based fuels that may be produced by means of artificial photosynthesis are not complex molecules like carbohydrates, but simpler molecules such as methane, methanol and carbon monoxide. The processes by which these fuels are produced are more complex than those involved in the production of hydrogen, However, carbon-based fuels have the advantage that many are liquid and could therefore be integrated into the existing energy infrastructure relatively easily.
There are a number of different approaches that can be taken to artificial photosynthesis. The first approach is a photovoltaic cell that supplies the current to the electrodes in a separate cell called electrolyzer that splits water molecules into their constituents, hydrogen and oxygen. One problem associated with this method is that it currently relies on the rare metals and is economically unattractive.
In the second approach, the photovoltaic cell also acts as an electrode in contact with water, and the voltage it produces splits the water directly. Having these two functions, photoelectricity generation and electrolysis into one unit makes it more usable, says Thomas Hannappel of the Technical University Ilmenau in Germany. “We have a greater range for cost reduction with one unit than with two different units,” says Hannappel who has created New record energy efficiency for artificial photosynthesis
DOE, Lawrence Berkeley Lab Making Strides In Artificial Photosynthesis
Scientist Heinz Frei and his team at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed an artificial photosynthesis system, made of nanosized tubes, that appears capable of performing all the key steps of the fuel-generating reaction. Their latest paper, published in Advanced Functional Materials, demonstrates that their design allows for the rapid flow of protons from the interior space of the tube, where they are generated from splitting water molecules, to the outside, where they combine with CO2 and electrons to form the fuel. That fuel is currently carbon monoxide, but the team is working toward making methanol. Fast proton flow, which is essential for efficiently harnessing sunlight energy to form a fuel, has been a thorn in the side of past artificial photosynthesis systems.
The individual unit of the system will be small square “solar fuel tiles” (several inches on a side) containing billions of the nanoscale tubes sandwiched between a floor and ceiling of thin, slightly flexible silicate, with the tube openings piercing through these covers. Frei is hopeful that his group’s tiles could be the first to address the major hurdles still facing this type of technology. Each tiny (about 0.5 micrometer wide), hollow tube inside the tile is made of three layers: an inner layer of cobalt oxide, a middle layer of silica, and an outer layer of titanium dioxide. In the inner layer of the tube, energy from sunlight delivered to the cobalt oxide splits water (in the form of moist air that flows through the inside of each tube), producing free protons and oxygen.
“These protons easily flow through to the outer layer, where they combine with carbon dioxide to form carbon monoxide now – and methanol in a future step – in a process enabled by a catalyst supported by the titanium dioxide layer,” said Won Jun Jo, a postdoctoral fellow and first author of the paper. “The fuel gathers in the space between tubes, and can be easily drained out for collection.” Importantly, the middle layer of the tube wall keeps the oxygen produced from water oxidation in the interior of the tube, and blocks the carbon dioxide and the evolving fuel molecules on the outside from permeating into the interior, thereby separating the two very incompatible chemical reaction zones.
This design mimics actual living photosynthetic cells, which separate oxidation and reduction reactions with organic membrane compartments inside the chloroplast. Similarly in line with nature’s original blueprint, the team’s membrane tubes allow the photosynthetic reaction to occur over a very short distance, minimizing the energy loss that occurs as ions travel and preventing unintended chemical reactions that would also lower the system’s efficiency.
“There are two challenges that have not yet been met,” said Frei, who is a senior scientist in Berkeley Lab’s Biosciences Area. “One of them is scalability. If we want to keep fossil fuels in the ground, we need to be able to make energy in terawatts – an enormous amount of fuel. And, you need to make a liquid hydrocarbon fuel so that we can actually use it with the trillions of dollars’ worth of existing infrastructure and technology.”
HyperSolar Achieves Major Breakthrough in Splitting Water into Renewable Hydrogen Fuel
HyperSolar, Inc. has announced that it had successfully produced renewable hydrogen using commercially available low-cost silicon solar cells (supplied by Midwest Optoelectronics, LLC “MWOE”) protected with HyperSolar’s proprietary coating.
Recently, the Company’s research team used a patent pending solar-cell/membrane assembly that produces hydrogen and oxygen separately on two different sides of the solar cells. The membrane prevents mixing of hydrogen and oxygen (hazardous gaseous mixture) resulting in the extraction of “pure hydrogen,” necessary for use in fuel cells that can power cars like the Toyota Mirai and Honda Clarity, as well as industrial power equipment. This integrated assembly also prevents recombination of hydrogen and oxygen into water at the catalyst surface, greatly improving the overall hydrogen utilization efficiency.
In addition, the key to this success is the use of HyperSolar’s patent pending electroactive coating formulated to protect the solar cells from corrosion during prolonged hydrogen production. The success of utilizing silicon solar cells provided by outside manufacturers represents yet another indication of the potential of HyperSolar’s technology for economically viable production of hydrogen.
Earlier, HyperSolar recently achieved major breakthrough in splitting water into renewable hydrogen fuel. It achieved the 1.25 volts of water splitting voltage required for artificial photosynthesis to split water into hydrogen and oxygen using only the power of the sun, through an inexpensive but efficient solar absorber.
The theoretical minimum voltage needed to split water molecules into hydrogen and oxygen is 1.23 V. However, in real world systems, 1.5 V or more is generally needed because of the low reaction kinetics. So far, other researchers have only been able to achieve this voltage level through the use of either inefficient materials, such as titanium oxide, or very expensive semiconductors, such as gallium arsenide. Also, overcoming the corrosive degradation of these “artificial photosynthesis” systems remains a monumental challenge and has thus far eluded commercialization.
The Company has focused on increasing the stability of the proprietary all-in-one hydrogen production device, working toward the 1000-hour target, since 2018. The stability test was conducted under continuous simulated peak sunlight illumination by the research team at the University of Iowa. The solar cell at the core of the hydrogen panel remained operational after the completion of the stability test. However, the hydrogen production rate began to decrease after 600 hours. The components integrated onto the device were identified to be the cause of the deteriorating device performance. The company is currently in process of improving the device components to remain stable for longer periods of operational time.
Stability of solar hydrogen device over 1000 hours translate to 6 months of lifetime in sunny states like California, or to 1 year of lifetime in average. Extension of lifetime of the device can significantly lower the levelized cost of hydrogen making it more economical for users.
“This is a landmark achievement for our research team,” said Tim Young, CEO of HyperSolar. “This step brings us considerably closer to being able to produce hydrogen panels for our pilot plant, referenced in previous announcements Furthermore, as we finalize work on other elements of the device, we will continue to improve the panel’s stability performance without compromising the hydrogen production efficiency, which will, in turn, reduce the cost of the hydrogen even further. We are very encouraged by this progress.”
HyperSolar’s research is centered on developing a low-cost and submersible hydrogen production particle that can split water molecules under the sun, emulating the core functions of photosynthesis. Each particle is a complete hydrogen generator that contains a novel high voltage solar cell bonded to chemical catalysts by a proprietary encapsulation coating. “Our teams at the University of California, Santa Barbara and at the University of Iowa have been working diligently to achieve efficient renewable hydrogen production,” said Tim Young, CEO of HyperSolar.
Latest bionic leaf now 10 times more efficient than natural photosynthesis
In 2016 Harvard researchers showed that water-splitting catalysts could be augmented with bacteria that combines the resulting hydrogen with CO2 to create oxygen and biomass, fuel, or other useful products. The approach was more efficient than plants at turning CO2 to fuel and was built using cheap materials, but turning it into a commercially viable technology will take time.
Harvard scientists Daniel Nocera and Pamela Silvers, in partnership with their co-authors, developed a “bionic leaf” that could capture and convert 10 percent of the energy in sunlight, a big step forward for the field. It’s also about 10 times better than the most efficient plants. The researchers use catalysts made from a cobalt-phosphorous alloy to split the water into hydrogen and oxygen, and then set specially engineered bacteria to work gobbling up the carbon dioxide and hydrogen and converting them into liquid fuel.
Scientists at Harvard developed the “bionic leaf 2.0,” which increases the efficiency of the system well beyond nature’s own capabilities, and used it to produce liquid fuels for the first time.” We developed a hybrid water splitting–biosynthetic system based on a biocompatible Earth-abundant inorganic catalyst system to split water into molecular hydrogen and oxygen (H2 and O2) at low driving voltages.”
“We designed a new cobalt-phosphorous alloy catalyst, which we showed does not make reactive oxygen species,” says Nocera. “That allowed us to lower the voltage, and that led to a dramatic increase in efficiency.” With this new catalyst, the system is able to convert sunlight into biomass with 10 percent efficiency, which is 10 times that of even the most efficient plants. But that’s not the only potential application for the technology.
When grown in contact with these catalysts, Ralstonia eutropha consumed the produced H2 to synthesize biomass and fuels or chemical products from low CO2 concentration in the presence of O2. Already, the researchers have demonstrated how the system can be used to create compounds such as isobutanol, isopentanol and PHB, a bio-plastic precursor.
This scalable system has a CO2 reduction energy efficiency of ~50% when producing bacterial biomass and liquid fusel alcohols, scrubbing 180 grams of CO2 per kilowatt-hour of electricity. Coupling this hybrid device to existing photovoltaic systems would yield a CO2 reduction energy efficiency of ~10%, exceeding that of natural photosynthetic systems.
Technion-Israel Institute of Technology researchers’ breakthrough in solar fuels
Technion-Israel Institute of Technology researchers have found a novel way to split water molecules into hydrogen and oxygen by trapping light in ultrathin films of iron oxide. Iron oxide is a common semiconductor material, inexpensive to produce, stable in water, and – unlike other semiconductors such as silicon – can oxidize water without itself being oxidated, corroded, or decomposed.
But it also presents challenges, the greatest of which is finding a way to overcome its poor electrical transport properties. “Our light-trapping scheme overcomes this tradeoff, enabling efficient absorption in ultrathin films wherein the photogenerated charge carriers are collected efficiently,” says Prof. Rothschild. “The light is trapped in quarter-wave or even deeper sub-wavelength films on mirror-like back reflector substrates. Interference between forward- and backward-propagating waves enhances the light absorption close to the surface, and the photogenerated charge carriers are collected before they die off.”
The breakthrough could make possible the design of inexpensive solar cells that combine ultrathin iron oxide photoelectrodes with conventional photovoltaic cells based on silicon or other materials to produce electricity and hydrogen. According to Rothschild, these cells could store solar energy for on-demand use, 24 hours per day. This is in strong contrast to conventional photovoltaic cells, which provide power only when the sun is shining (and not at night or when it is cloudy).
Berkeley Lab Researchers Perform Solar-powered Green Chemistry with Captured CO2
Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have developed a hybrid system of semiconducting nanowires and bacteria that synthesizes the combination of carbon dioxide and water into acetate, the most common building block today for biosynthesis,says a News Releaseby LynnYarris of Berkley Labs.
“We believe our system is a revolutionary leap forward in the field of artificial photosynthesis,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division and one of the leaders of this study. “Our system has the potential to fundamentally change the chemical and oil industry in that we can produce chemicals and fuels in a totally renewable way, rather than extracting them from deep below the ground.
“In natural photosynthesis, leaves harvest solar energy and carbon dioxide is reduced and combined with water for the synthesis of molecular products that form biomass,” says Chris Chang, an expert in catalysts for carbon-neutral energy conversions. “In our system, nanowires harvest solar energy and deliver electrons to bacteria, where carbon dioxide is reduced and combined with water for the synthesis of a variety of targeted, value-added chemical products.
The system starts with an “artificial forest” of nanowire heterostructures, consisting of silicon and titanium oxide nanowires, developed earlier by Yang and his research group. “Our artificial forest is similar to the chloroplasts in green plants,” Yang says. “When sunlight is absorbed, photo-excited electron−hole pairs are generated in the silicon and titanium oxide nanowires, which absorb different regions of the solar spectrum. The photo-generated electrons in the silicon will be passed onto bacteria for the CO2 reduction while the photo-generated holes in the titanium oxide split water molecules to make oxygen.”
Once the forest of nanowire arrays is established, it is populated with microbial populations that produce enzymes known to selectively catalyze the reduction of carbon dioxide. For this study, the Berkeley team used Sporomusa ovata, an anaerobic bacterium that readily accepts electrons directly from the surrounding environment and uses them to reduce carbon dioxide.
“S. ovata is a great carbon dioxide catalyst as it makes acetate, a versatile chemical intermediate that can be used to manufacture a diverse array of useful chemicals,” says Michelle Chang. “We were able to uniformly populate our nanowire array with S. ovata using buffered brackish water with trace vitamins as the only organic component.”
Once the carbon dioxide has been reduced by S. ovata to acetate (or some other biosynthetic intermediate), genetically engineered E.coli are used to synthesize targeted chemical products. To improve the yields of targeted chemical products, the S. ovata and E.coli were kept separate for this study. In the future, these two activities – catalyzing and synthesizing – could be combined into a single step process.
A key to the success of their artificial photosynthesis system is the separation of the demanding requirements for light-capture efficiency and catalytic activity that is made possible by the nanowire/bacteria hybrid technology. With this approach, the Berkeley team achieved a solar energy conversion efficiency of up to 0.38-percent for about 200 hours under simulated sunlight, which is about the same as that of a leaf.
The yields of target chemical molecules produced from the acetate were also encouraging – as high as 26-percent for butanol, a fuel comparable to gasoline, 25-percent for amorphadiene, a precursor to the antimaleria drug artemisinin, and 52-percent for the renewable and biodegradable plastic PHB. Improved performances are anticipated with further refinements of the technology.
“We are currently working on our second generation system which has a solar-to-chemical conversion efficiency of three-percent,” Yang says. “Once we can reach a conversion efficiency of 10-percent in a cost effective manner, the technology should be commercially viable.”
“Our system represents an emerging alliance between the fields of materials sciences and biology, where opportunities to make new functional devices can mix and match components of each discipline,” says Michelle Chang, an expert in biosynthesis. “For example, the morphology of the nanowire array protects the bacteria like Easter eggs buried in tall grass so that these usually-oxygen sensitive organisms can survive in environmental carbon-dioxide sources such as flue gases.”
“Our goal is to make each home its own power station,” he said. “One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology,” said MIT professor Daniel Nocera