“concentrating photovoltaic (cpv) systems leverage the cost of high efficiency multi-junction solar cells by using inexpensive optics to concentrate sunlight onto them,” said noel c. giebink, assistant professor of electrical engineering, penn state. “current cpv systems are the size of billboards and have to be pointed very accurately to track the sun throughout the day. but, you can’t put a system like this on your roof, which is where the majority of solar panels throughout the world are installed.”

giebink notes that the falling cost of typical silicon solar cells is making them a smaller and smaller fraction of the overall cost of solar electricity, which also includes “soft” costs like permitting, wiring, installation and maintenance that have remained fixed over time. improving cell efficiency from about 20 percent for silicon toward greater than 40 percent with multi-junction cpv is important because increasing the power generated by a given system reduces the overall cost of the electricity that it generates.

to enable cpv on rooftops, the researchers combined miniaturized, gallium arsenide photovoltaic cells, 3d-printed plastic lens arrays and a moveable focusing mechanism to reduce the size, weight and cost of the cpv system and create something similar to a traditional solar panel that can be placed on the south-facing side of a building’s roof. they report their results today (feb. 5) in nature communications.

“we partnered with colleagues at the university of illinois because they are experts at making small, very efficient multi-junction solar cells,” said giebink. “these cells are less than 1 square millimeter, made in large, parallel batches and then an array of them is transferred onto a thin sheet of glass or plastic.”

to focus sunlight on the array of cells, the researchers embedded them between a pair of 3d-printed plastic lenslet arrays. each lenslet in the top array acts like a small magnifying glass and is matched to a lenslet in the bottom array that functions like a concave mirror. with each tiny solar cell located in the focus of this duo, sunlight is intensified more than 200 times. because the focal point moves with the sun over the course of a day, the middle solar cell sheet tracks by sliding laterally in between the lenslet array.

previous attempts at such translation-based tracking have only worked for about two hours a day because the focal point moves out of the plane of the solar cells, leading to loss of light and a drop in efficiency. by sandwiching the cells between the lenslet arrays, the researchers solved this problem and enabled efficient solar focusing for a full eight hour day with only about 1 centimeter of total movement needed for tracking.

to lubricate the sliding cell array and also improve transmission through the lenslet sandwich they used an optical oil, which allows small motors using a minimal amount of force for the mechanical tracking.

“the vision is that such a microtracking cpv panel could be placed on a roof in the same space as a traditional solar panel and generate a lot more power,” said giebink. “the simplicity of this solution is really what gives it practical value.”

because the total panel thickness is only about a centimeter and 99 percent of it — everything except the solar cells and their wiring — consists of acrylic plastic or plexiglas, this system has the potential to be inexpensive to produce. giebink cautions, however, that cpv systems are not suitable for all locations.

“cpv only makes sense in areas with lots of direct sunlight, like the american southwest,” he said. “in cloudy regions like the pacific northwest, cpv systems can’t concentrate the diffuse light and they lose their efficiency advantage.”

the researchers tested their prototype concentrator panel outside over the course of a day in state college, penn. even though the printed plastic lenses were not up to specification, they were able to demonstrate over 100 times solar concentration.

others working on this project include jared price, graduate student, penn state; xing sheng, postdoctoral fellow; john a rogers, professor of materials science and engineering, university of illinois, urbana champaign; and bram m. meulblok, technical representative, luxexcel group b.v., the netherlands.

the u.s. department of energy funded this research.

“the use of waste heat for power production would allow additional electricity generation without any added consumption of fossil fuels,” said bruce e. logan, evan pugh professor and kappe professor of environmental engineering. “thermally regenerative batteries are a carbon-neutral way to store and convert waste heat into electricity with potentially lower cost than solid-state devices.”

low-grade waste heat is an artifact of many energy-generating methods. in automobiles, waste heat generated in winter is diverted to run the vehicle heating system, but in the summer, that same waste heat must be dissipated to the environment. coal, nuclear and other power plants require high heat to produce electricity, but after producing electricity the excess waste heat is routed to cooling towers to dissipate. many industrial sites, geothermal sources or solar generating plants also create low-grade heat that is wasted.

the researchers want to take this waste heat and capture it to produce more power. other researchers have tried a variety of methods, but most produce too little power to be workable, or they cannot provide a continuous resource. logan and his team are using a thermally regenerated ammonia-based battery that consists of copper electrodes with ammonia added only to the anolyte — the electrolyte surrounding the anode.

“the battery will run until the reaction uses up the ammonia needed for complex formation in the electrolyte near the anode or depletes the copper ions in the electrolyte near the cathode,” said fang zhang, postdoctoral fellow in environmental engineering. “then the reaction stops.”

this type of battery would be useless as a constant source of electricity if the reaction were not regenerative. using low-grade waste heat from an outside source, the researchers distill ammonia from the effluent left in the battery anolyte and then recharge it into the original cathode chamber of the battery.

the chamber with the ammonia now becomes the anode chamber and copper is re-deposited on the electrode in the other chamber, now the cathode, but formerly the anode. the researchers switch ammonia back and forth between the two chambers, maintaining the amount of copper on the electrodes.

“here we present a highly efficient, inexpensive and scalable ammonia-based thermally regenerative battery where electrical current is produced from the formation of copper ammonia complex,” the researchers report in the current issue of energy and environmental science. they note that the ammonia liquid stream can convert the thermal energy to electrical energy in the battery. “when needed, the battery can be discharged so that the stored chemical energy is effectively converted to electrical power.”

one of the problems with previous methods was that the amount of energy produced in, for example, a system using salty and less salty water to generate electricity, was too small relative to the amount of water used.  the thermally regenerative ammonia battery system can convert about 29 percent of the chemical energy in the battery to electricity and can be greatly improved with future optimization.

the researchers produced a power density of about 60 watts per square meter over multiple cycles, which is six to 10 times higher than the power density produced by other liquid-based thermal-electric energy conversion systems. the researchers note that the current thermally regenerative ammonia battery is not optimized, so that tinkering with the battery could both produce more power and reduce the cost of operating the batteries.

the researchers were able to increase power density by increasing the number of batteries, so that this method is scalable to something that might be commercially attractive.

other researchers on this project were jia liu, postdoctoral fellow and wulin yang, graduate student, both in environmental engineering. the researchers have filed a preliminary patent on this work.

the king abdullah university of science and technology supported this work.

the project, called fast farming: feeding a hot, dry world, uses a genetic screening technique known as activation tagging to identify genes that improve a plant’s ability to tolerate environmental stresses. these stresses, such as drought and extreme heat, are worsening as a result of climate change and already are threatening the ability of farmers around the world to grow enough food.

the team has launched a crowdfunding campaign to support the project. it’s the first to launch under a new partnership between penn state and useed, a crowdfunding platform that partners with universities to support research projects.

the team is aiming to sustain an intensive research program for a full year, allowing them to test many different environmental conditions with an expanded set of plant varieties and giving them the chance to identify many more new stress-tolerance genes.

the team uses brachypodium distachyon, a small, fast-growing grass species related to wheat and barley. they grow many thousands of brachypodium plants in greenhouses and growth chambers to mimic soil and weather conditions faced by farmers around the world. they can harvest valuable data from one generation of plants in as little as one month. the research team also hopes to make direct contact with farmers and plant breeders around the world, learning about the specific challenges they face as a result of climate change and helping them to efficiently identify the best hardy, high-yielding crop varieties that will grow well under fluctuating climate conditions.

the students involved in the project include nikki kapp, a master’s degree student in plant biology, and penn state undergraduate students liam farrell, jaime jarrin and samantha roa.

anderson’s group studies the dynamics of plant cell walls, with a focus on improving our ability to sustainably produce food, materials and energy from plants. before joining the penn state biology department in 2011, he completed postdoctoral research at the energy biosciences institute at the university of california berkeley, which focuses on the scientific, technical and societal aspects of developing sustainable sources of bioenergy. he is currently a principal investigator in the center for lignocellulose structure and formation, an energy frontiers research center funded by the u.s. department of energy.

for more information on anderson’s research, visit his laboratory website.

in the decade since nobel laureates konstantin novoselov and andre geim proved the remarkable electronic and mechanical properties of graphene, researchers have been hard at work to develop methods of producing pristine samples of the material on a scale with industrial potential. now, a team of penn state scientists has discovered a route to making single-layer graphene that has been overlooked for more than 150 years.

“there are lots of layered materials similar to graphene with interesting properties, but until now we didn’t know how to chemically pull the solids apart to make single sheets without damaging the layers,” said thomas e. mallouk, evan pugh professor of chemistry, physics, and biochemistry and molecular biology at penn state. in a paper first published online on sept. 9 in the journal nature chemistry, mallouk and colleagues at penn state and the research center for exotic nanocarbons at shinshu university, japan, describe a method called intercalation, in which guest molecules or ions are inserted between the carbon layers of graphite to pull the single sheets apart.

the intercalation of graphite was achieved in 1841, but always with a strong oxidizing or reducing agent that damaged the desirable properties of the material. one of the most widely used methods to intercalate graphite by oxidation was developed in 1999 by nina kovtyukhova, a research associate in mallouk’s lab.

while studying other layered materials, mallouk asked kovtyukhova to use her method, which requires a strong oxidizing agent and a mixture of acids, to open up single layers of solid boron nitride, a compound with a structure similar to graphite. to their surprise, she was able to get all of the layers to open up. in subsequent control experiments, kovtyukhova tried leaving out various agents and found that the oxidizing agent wasn’t necessary for the reaction to take place.

mallouk asked her to try a similar experiment without the oxidizing agent on graphite, but aware of the extensive literature saying that the oxidizing agent was required, kovtyukhova balked.

“i kept asking her to try it and she kept saying no,” mallouk said. “finally, we made a bet, and to make it interesting i gave her odds. if the reaction didn’t work i would owe her $100, and if it did she would owe me $10. i have the ten dollar bill on my wall with a nice post-it note from nina complimenting my chemical intuition.”

mallouk believes the results of this new understanding of intercalation in boron nitride and graphene could apply to many other layered materials of interest to researchers in the penn state center for two-dimensional and layered materials who are investigating what are referred to as “materials beyond graphene.” the next step for mallouk and colleagues will be to figure out how to speed the reaction up in order to scale up production.

their results appear in the nature chemistry article titled “non-oxidative intercalation and exfoliation of graphite by brønsted acids” by nina i. kovtyukhova, yuanxi wang, ayse berkdemir, mauricio terrones, vincent h. crespi, and thomas e. mallouk — all of penn state — and rodolfo cruz-silva of the research center for exotic nanocarbons, shinshu university, nagano, japan. their work was supported by the u.s. army research office muri grant w911nf-11-1-0362.

for more information, please visit: http://news.psu.edu/story/325381/2014/09/08/research/rethinking-basic-science-graphene-synthesis

the surface area of this porous silicon is high,” said donghai wang an assistant professor of mechanical engineering at penn state. “it is widely used and has a lot of applications.”

the standard method for manufacturing porous silicon is a subtraction method, similar to making a sculpture.

“silicon is an important material because it is a semiconductor,” said wang. “typically, porous silicon is produced by etching, a process in which lots of material is lost.”

wang’s team uses a chemically based method that builds up the material rather than removing it. the researchers start with silicon tetrachloride, a very inexpensive source of silicon. they then treat the material with asodium potassium alloy.

“the bonds between silicon and chlorine in silicon tetrachloride are very strong and require a highly reducing agent,” said wang. “sodium potassium alloy is such an agent.”

once the bonds break, the chlorine binds with the sodium, potassium and silicon, potassium chloride and sodium chloride — table salt — become solid, forming a material composed of crystals of salt embedded in silicon. the material is then heat-treated and washed in water to dissolve the salt, leaving pores that range from 5 to 15 nanometers. the researchers report their results in today’s (apr. 10) issue of nature communications.

because sodium potassium alloy is highly reactive, the entire procedure must be done away from the oxygen in the air, so the researchers carry out their reaction in an argon atmosphere.

“i believe that the process can be scaled up to manufacturing size,” said wang. “there are some processes that use sodium potassium alloy at industrial levels. so we can adapt their approaches to make this new type of porositic silicon.”

because these silicon particles have lots of pores, they have a large surface area, and act as an effective catalyst when sunlight shines on this porous silicon and water. the energy in sunlight can excite an electron that then reduces water, generating hydrogen gas. this process is aided by the material’s larger-than-normal band gap, which comes from the nanoscale size of the silicon crystallites.

“this porous silicon can generate a good amount of hydrogen just from sunlight,” said wang.

the researchers are also looking into using this porous silicon as the anode in a lithium ion battery.

other researchers on this project were fang dai, jiantao zai and hiesang sohn, all postdoctural researchers in mechanical engineering; and ran yi, mikhail l gordin and shuru chen, graduate students in mechanical engineering.

the u.s. department of energy and the defense threat reduction agency funded this work.

it’s a scene worthy of the modern reboot of “fantastic voyage.” a tiny rocket-shaped projectile breaches the border of a cell wall and begins to work, like an egg beater, to whip up the cell’s innards, or puncture its membranous wall with a battering-ram motion.

although a scene like this might take place in james cameron’s modern retake on the 1966 film classic (if it ever comes out), it’s something scientists at penn state university and weinberg medical physics in maryland have already witnessed.

in their work, which will appear in the journal angewandte chemie international edition, the researchers developed microscopic metallic motors known as nanomotors and then injected them into living human cells, marking what they say is the first time such an experiment had ever been done.

“our first-generation motors required toxic fuels and they would not move in biological fluid, so we couldn’t study them in human cells,” said researcher tom mallouk, evan pugh professor of materials chemistry and physics at penn state. “that limitation was a serious problem.”

the scientists overcame that problem when they discovered that the nanomotors could be powered by ultrasonic waves, which make them spin. because they didn’t need to use the toxic fuel anymore, the way was cleared for use in living cells.

the nanomotors measure 3,000 nanometers wide, which means about 33 of them could be stacked end-to-end along the width of a human hair. in addition to using sonic frequencies to spin them, the researchers employed magnetic fields to steer them around inside the cells. they also discovered that different motors could be controlled independently of the others, making them able to do very precise work.

“autonomous motion might help nanomotors selectively destroy the cells that engulf them,” mallouk said in a statement. “if you want these motors to seek out and destroy cancer cells, for example, it’s better to have them move independently. you don’t want a whole mass of them going in one direction.”

doing battle with cancerous cells is just one potential application of the research. according to mallouk, “nanomotors could perform intracellular surgery and deliver drugs non-invasively to living tissues.”

mallouk adds that a future goal in a “fantastic voyage”-like world would be to have the nanomotors link up in a network and create an environment “where nanomotors would cruise around inside the body, communicating with each other and performing various kinds of diagnoses and therapy.” he adds, “there are lots of applications for controlling particles on this small scale, and understanding how it works is what’s driving us.”

organic pollutants are found in many industrial wastewaters, including those of textile companies, pharmaceutical companies and agriculture. they are an increasing problem, because they are often resistant to environmental degradation and cannot be processed with conventional biological or chemical water treatments.

micromotors could help. last year, building on previous uses of micromotors as on-chip biosensors and cell transporters, joseph wang, at the university of california, san diego in the us, and colleagues developed self-propelled micromotors that could capture oil droplets – thereby offering a means to clean up small oil spills. only now, however, have micromotors been used to actually degrade pollutants. ‘this study indicates the great potential of micromotors for environmental monitoring and remediation,’ says wang.

developed by samuel sanchez and colleagues at the max planck institute for intelligent systems and at the leibniz institute for solid state and materials research the latest micromotors consist of a tubular core of platinum that is surrounded by iron. releasing them into polluted water containing dilute hydrogen peroxide results in the motors’ platinum cores converting the peroxide into oxygen bubbles and the surrounding iron produces hydroxyl radicals. the bubbles propel the micromotors along, while the hydroxyl radicals oxidise organic pollutants.

two experts in micromotors, ayusman sen at penn state university in the us and martin pumera at nanyang technological university in singapore, both say that the big advantage of the micromotors is their self-propulsion, which speeds up reaction rates and, therefore, quickly degrades pollutants. ‘the [hydroxyl radicals] can reach the target pollutant molecules much faster than would be possible by simple diffusion,’ says pumera.

the micromotors would probably not be able to remediate ‘huge amounts’ of waste water, says sanchez. ‘we aim to clean contaminated capillaries, small pipes and places difficult to reach,’ he adds. ‘we are dealing with applications especially for the microscale and environments hard to get to.’

li zhang at the chinese university of hong kong says the results are ‘striking’, and hold promise for environmental applications. ‘to date, though several research groups have been working on micromotors, they have mainly put great efforts on biological and biomedical applications,’ he says. ‘it is apparent that for industrial application, such as wastewater treatment, this process needs to be further scaled-up and the micromotors require multi-functionality. i think it is worth doing those trials and continuing this research topic.’

“we have tried to break this paradigm of tradeoffs in materials (by improving) both the stability and the conductivity of this membrane at the same time, and that is what we were able to do with this unique polymeric materials design,” said michael hickner, associate professor of materials science and engineering.

in solid-state alkaline fuel cells, anion exchange membranes conduct negative charges between the device’s cathode and anode — the negative and positive connections of the cell — to create useable electric power. most fuel cells currently use membranes that require platinum-based catalysts that are effective but expensive.

hickner’s new polymer is a unique anion exchange membrane — a new type of fuel cell and battery membrane — that allows the use of much more cost-efficient non-precious metal catalysts and does not compromise either durability or efficiency like previous anion exchange membranes.

“what we’re really doing here is providing alternatives, possible choices, new technology so that people who want to commercialize fuel cells can now choose between the old paradigm and new possibilities with anion exchange membranes,” hickner said.

creating this alternative took some intuition and good fortune. in work spearheaded by nanwen li, a postdoctoral researcher in materials science and engineering, hickner’s team created several variations of the membrane, each with slightly different chemical compositions. they then ran each variation under simulated conditions to predict which would be optimal in an actual fuel cell. the researchers report their findings in a recent issue of the journal of the american chemical society.

based on these initial tests, the group predicted that the membranes with long 16-carbon structures in their chemical makeup would provide the best efficiency and durability, as measured respectively by conductivity and long-term stability.

chao-yang wang, william e. diefenderfer chair of mechanical engineering, and his team then tested each possibility in an operating fuel cell device. yongjun leng, a research associate in mechanical and nuclear engineering, measured the fuel cell’s output and lifetime for each material variation.

despite predictions, the membranes containing shorter 6-carbon structures proved to be much more durable and efficient after 60 hours of continuous operation.

“we were somewhat surprised…that what we thought was the best material in our lab testing wasn’t necessarily the best material in the cell when it was evaluated over time,” said hickner, who added that researchers are still trying to understand why the 6-carbon variation has better long-term durability than the 16-carbon sample in the fuel cell by studying the operating conditions of the cell in detail.

because the successful membrane was so much more effective than the initial lab studies predicted, researchers are now interested in accounting for the interactions that the membranes experienced while inside the cell.

“we have the fuel cell output — so we have the fuel cell efficiency, the fuel cell life time — but we don’t have the molecular scale information in the fuel cell,” hickner said. “that’s the next step, trying to figure out how these polymers are working in the fuel cell on a detailed level.”

the advanced research projects agency-energy at the u.s. department of energy, funded this project in collaboration with proton onsite, a leading membrane electrolyzer company based in connecticut.

more than 100 elevators on penn state’s campus require hydraulic fluid, which is traditionally petroleum-based and problematic when there’s a sprung leak.

not long ago, the university turned to penn state researcher joe perez, a renowned expert on bio-based fuels and lubricants, to help develop an alternative for the 17,000 gallons of hydraulic fluid used by the school.

now penn state is encouraging other schools to convert to soy-based and showing them how.