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) aims to split water in oceans, and possibly even rivers, into its hydrogen, oxygen, and carbon components using sunlight. Several exciting advances are being made that have started turning this highly ambitious goal into realistic technology.
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. 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.
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.
A chemistry professor has just found a way to trigger the process of photosynthesis in a synthetic material, turning greenhouse gases into clean air and producing energy all at the same time. 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.
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.
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.
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
Artificial Photosynthesis Projects
Efficiency records for solar-powered hydrogen production have continued to rise over the years, and much more rapidly as the technology and techniques improve
UCF Professor Invents Way to Trigger Artificial Photosynthesis to Clean Air, Produce Energy
Uribe-Romo and his team of students created a way to trigger a chemical reaction in a synthetic material called metal–organic frameworks (MOF) that breaks down carbon dioxide into harmless organic materials. Think of it as an artificial photosynthesis process similar to the way plants convert carbon dioxide (CO2) and sunlight into food. But instead of producing food, Uribe-Romo’s method produces solar fuel.
It’s something scientists around the world have been pursuing for years, but the challenge is finding a way for visible light to trigger the chemical transformation. Ultraviolet rays have enough energy to allow the reaction in common materials such as titanium dioxide, but UVs make up only about 4 percent of the light Earth receives from the sun. The visible range – the violet to red wavelengths – represent the majority of the sun’s rays, but there are few materials that pick up these light colors to create the chemical reaction that transforms CO2 into fuel.
Researchers have tried it with a variety of materials, but the ones that can absorb visible light tend to be rare and expensive materials such as platinum, rhenium and iridium that make the process cost-prohibitive.
Uribe-Romo used titanium, a common nontoxic metal, and added organic molecules that act as light-harvesting antennae to see if that configuration would work. The light harvesting antenna molecules, called N-alkyl-2-aminoterephthalates, can be designed to absorb specific colors of light when incorporated in the MOF. In this case he synchronized it for the color blue.
“This work is a breakthrough,” said Uribe-Romo in a UCF news release. “Tailoring materials that will absorb a specific color of light is very difficult from the scientific point of view, but from the societal point of view we are contributing to the development of a technology that can help reduce greenhouse gases.”
“The idea would be to set up stations that capture large amounts of CO2, like next to a power plant. The gas would be sucked into the station, go through the process and recycle the greenhouse gases while producing energy that would be put back into the power plant.”
Perhaps someday homeowners could purchase rooftop shingles made of the material, which would clean the air in their neighborhood while producing energy that could be used to power their homes. “That would take new technology and infrastructure to happen,” Uribe-Romo said. “But it may be possible.”
HyperSolar Achieves Major Breakthrough in Splitting Water into Renewable Hydrogen Fuel
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.
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
Scientists at Harvard have 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.
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.
“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.
Researchers at Monash University in Melbourne claim new record energy efficiency for artificial photosynthesis
Now researchers at Monash University in Melbourne claim to have created a solar-powered device that produces hydrogen at world-record 22 percent efficiency, which is a significant step towards making cheap, efficient hydrogen production a reality.
To help achieve the required solar-input efficiencies, the team utilized the very best commercial-grade multi-junction (indium gallium phosphide, gallium arsenide, and germanium) solar cells available to ensure the maximum sunlight to electricity conversion.
However, an even greater contribution to efficiency was on the material side, where the use of expanded foam nickel electrodes increased the available electrolysis surface area with such efficiency that the electrolyte in which they were immersed was simply local river water with the addition of a standard pH buffer (generally a salt solution containing sodium phosphate and sodium chloride).
“Electrochemical splitting of water could provide a cheap, clean and renewable source of hydrogen as the ultimately sustainable fuel.” said Professor Leone Spiccia from the School of Chemistry at Monash who led the research. “This latest breakthrough is significant in that it takes us one step further towards this becoming a reality.”
“Hydrogen can be used to generate electricity directly in fuel cells,” said Doug MacFarlane, co-author of the research. “Cars driven by fuel cell electric engines are becoming available from a number of car manufacturers. Hydrogen could even be used as an inexpensive energy storage technology at the household level to store energy from roof-top solar cells.”
Swiss Researchers achieved Record efficiency for converting solar energy to hydrogen without rare metals
The scientists from Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland have achieved a solar energy to hydrogen conversion efficiency of 12.3% using abundant and common materials. Researchers used nickel and iron catalysts for the electrodes in their electrolyzer, and solar absorbers made of perovskite – another abundant material – in the solar cells.
The perovskite cells generate open circuit voltages of 1 V compared with the 0.7 V of a silicon cell, hence only two perovskite cells are needed instead of three silicon cells, to generate the required 1.7 V needed for water electrolysis. One challenge that needs to be solved is the instability of the perovskite PVs, which results in a degradation of the photocurrent over a period of hours.
A low-cost alternative is the use of a semiconductor in a photoelectrochemical (PEC) cell. When illuminating a semiconductor that is immersed in water, oxygen bubbles can evolve from one side, while hydrogen bubbles are formed at the counter electrode (or vice versa). The challenge is to find low cost materials that combine good visible light absorption with a high stability against photocorrosion. Moreover, charge carriers should easily move through the bulk of the material, and the surface of the material should have a high catalytic activity for water splitting. Researchers have struggled for years with the tradeoff between light absorption and the separation and collection of photogenerated charge carriers before they die out by recombination.
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