Forschungszentrum Juelich researchers with American Oak Ridge National Laboratory scientists have now successfully observed with nano-scale precision how deposits form at the iron electrode during operation. A deeper understanding of the charging and discharging reactions is viewed as the key for the further development of this type of rechargeable battery to gain market maturity.

The study results have been published in the journal Nano Energy.

Iron-air batteries promise a considerably higher energy density than present-day lithium-ion batteries. Additionally, their main constituent – iron – is an abundant and therefore quite a low cost material, The Forschungszentrum Jülich scientists are among the driving forces in the renewed research into this concept that was discovered in the 1970s.

Schematic of the measuring method: the tip of the in situ electrochemical atomic force microscope scans the surface of the iron electrode. Laser-beam deflection reveals spatial irregularities, which can be compared to each other over the course of several cycles.  Image Credit: Copyright: Forschungszentrum Jülich / H. Weinrich. Click image for the largest view.

For reasons including insurmountable technical difficulties, research into metal-air batteries was abandoned in the 1980s for a long time. The past few years, however, have seen a rapid increase in research interest. Iron-air batteries draw their energy from a reaction of iron with oxygen. In this process, the iron oxidizes almost exactly as it would during the rusting process. The oxygen required for the reaction can be drawn from the surrounding air so that it does not need to be stored in the battery. These material savings are the reason for the high energy densities achieved by metal-air batteries.

Iron-air batteries are predicted to have theoretical energy densities of more than 1,200 Wh/kg. By comparison, present-day lithium-ion batteries come in at about 600 Wh/kg, and even less (350 Wh/kg) if the weight of the cell casing is taken into account. Lithium-air batteries, which are technically considerably more difficult and complicated to realize, can have energy densities of up to 11,400 Wh/kg. When it comes to volumetric energy density, iron-air batteries perform even better: at 9,700 Wh/l, it is almost five times as high as that of today’s lithium-ion batteries (2,000 Wh/l). Even lithium-air batteries have “only” 6,000 Wh/l. Iron-air batteries are thus particularly interesting for a multitude of mobile applications in which space requirements play a large role.

Institute head Prof. Rüdiger-A. Eichel explained, “We consciously concentrate on research into battery types made of materials that are abundant in the Earth’s crust and produced in large quantities. Supply shortages are thus not to be expected. The concept is also associated with a cost advantage, which can be directly applied to the battery, particularly for large-scale applications such as stationary devices for the stabilization of the electricity grid or electromobility.”

The insights obtained by the Jülich researchers create a new basis for improving the properties of the battery in a targeted manner. Using in situ electrochemical atomic force microscopes at the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, they were able to observe how deposits of iron hydroxide particles (Fe(OH)2) form at the iron electrode under conditions similar to those prevalent during charging and discharging.

Henning Weinrich from Jülich’s Institute of Energy and Climate Research (IEK-9) explained this point, “The high pH of 13.7 alone represents a borderline condition for the instrument. We were the first at Oak Ridge to successfully conduct such an experiment under realistic conditions.” Weinrich stayed in the U.S.A. for three months especially for the measurements.

The deposits do not decrease the power of the battery. On the contrary, since the nanoporous layer increases the active surface area of the electrode, it contributes to a small increase in capacity after each charging and discharging cycle. Thanks to the investigations, the researchers have for the first time obtained a complete picture of this layer growth.

Dr. Hermann Tempel from Jülich’s Institute of Energy and Climate Research (IEK-9 explained, “It was previously assumed that the deposition is reversed during charging. But this is obviously not the case.” Furthermore, a direct link was verified for the first time between the layer formation at the electrode surface and the electrochemical reactions.

There is, however, still a long way to go until market maturity. Although isolated electrodes made of iron can be operated without major power losses for several thousand cycles in laboratory experiments, complete iron-air batteries, which use an air electrode as the opposite pole, have only lasted 20 to 30 cycles so far.

This research project may well be seen as a breakthrough before long. Those energy densities are just a huge diamond in the rough for battery manufactures, device manufacturers and consumers. Plus the raw materials costs are way lower. This research not only has “legs”, it put new legs on other researchers that have stalled.

Congratulations folks!

University of Michigan researchers recommend replacing all incandescent and halogen light bulbs in your home now with compact fluorescent lamps (CFLs) or LEDs.

With LED light bulbs are getting cheaper and more energy efficient every year, does it make sense to replace less-efficient bulbs with the latest light-emitting diodes now, or should you wait for future improvements and even lower costs?

According to the study published in Environmental Research Letters immediate replacement is not advised for existing CFLs and LEDs, unless your main concern is helping to reduce power-plant emissions. They team offered up a general replacement rule.

Image Credit: University of Michigan. Click image for the largest view.

Lixi Liu, first author of the study and a doctoral student at the University of Michigan School for Environment and Sustainability and at the Department of Mechanical Engineering said, “Estimating the right time to switch over to LEDs is not a straightforward problem. If your goal is to help reduce carbon dioxide emissions, then maybe you should switch to LEDs now. But if your main concern is lowering costs and home energy use, then holding on to existing CFLs and LEDs, and waiting until LEDs use even less energy and are even lower in cost, may be desirable.”

For a CFL that’s used an average of three hours per day, it may be best – both economically and energetically – to delay the adoption of LEDs until 2020, she noted.

Lighting accounted for 10 percent of U.S. residential energy use in 2016. Home lighting upgrades are an easy way to lower your utility bill, reduce energy use and help cut greenhouse gas emissions.

LEDs are long-lasting light bulbs that use less energy than incandescent, halogen or fluorescent bulbs to provide the same light output. But the initial purchase price for LEDs is higher than other types of bulbs, so many consumers haven’t made the switch.

Previous studies have noted that LEDs reduce spending on energy over time and are a cost-effective alternative to other light bulbs. But those studies did not look at the best time to replace an existing bulb.

In their newly published study in Environmental Research Letters, the University of Michigan researchers examined cost, energy use and greenhouse gas emissions for different types of 60-watt-equivalent bulbs and created a computer model to generate multiple replacement scenarios, which were then analyzed.

Specifically, they used a method called life cycle optimization to construct a lighting replacement optimization model. The life cycle optimization method has previously been used by researchers at the University of Michigan’s Center for Sustainable Systems to study replacement of automobiles, refrigerators, washing machines and air conditioners.

Gregory Keoleian, director of the center and a co-author of the paper said, “Replacement decisions can be complex and often confusing.”

Keoleian, who is also a professor at the School for Environment and Sustainability added, “Research at the Center for Sustainable Systems over the past dozen years has focused on helping consumers navigate this complexity and identify opportunities for cost savings and lower environmental impact.”

In the lighting study, the University of Michigan researchers considered factors such as how often the current bulb is used and its condition. And they looked at trajectories for lighting technology and energy generation: light bulb technologies are improving, costs continue to drop, and electricity generation in this country is becoming cleaner.

By 2040, the share of U.S. electricity from natural gas is expected to increase by 6 percent, and the share from renewables is expected to increase 13 percent. By 2040, the share of U.S. electricity from nuclear power is expected to decrease by 4 percent, and the share from coal is expected to decrease 15 percent.

The new lighting study provides specific replacement strategies for maximizing the cost, energy and emissions savings from home lighting.

Kazuhiro Saitou, a University of Michigan mechanical engineering professor and the other co-author of the paper said, “It was a challenging optimization problem to solve accurately. Because it involved various types of decision variables – years of use, number of replacements and type of lighting technology – and multiple objectives – cost, energy and emissions – that can compete with each other.”

In addition to the previously mentioned results, the study found that:

In general, bulbs that are used more often should be replaced first to maximize energy savings.

Replacing a bulb before it burns out may seem wasteful, but consumers can cut energy use by doing so.

Strategies for replacing light bulbs vary from place to place, depending on regional energy costs and the power-generation mix (i.e., coal, natural gas, nuclear and renewables).

Strategies for replacing light bulbs vary from place to place, depending on regional energy costs and the power-generation mix (i.e., coal, natural gas, nuclear and renewables).

In general, LED upgrades should be made earlier and more frequently in places – such as California, Washington, D.C., and Hawaii – where electricity costs are high.

Thanks to the University of Michigan team! Perhaps that three hour daily use idea will pay off well.

Massachusetts Institute of Technology researchers have created a material for a chemical heat ‘battery’ that could release its energy on demand. The new phase-change material provides a way to store heat in a stable chemical form, then release it later, on demand, using light as a trigger.

A good example for its use is that in large parts of the developing world, people have abundant heat from the sun during the day, but most cooking takes place later in the evening when the sun is down, using fuel – such as wood, brush or dung – that is collected with significant time and effort.

The new chemical composite developed by researchers at MIT could provide an alternative. It could be used to store heat from the sun or any other source during the day in a kind of thermal battery, and it could release the heat when needed, for example for cooking or heating after dark.

In its chemically stored form, the energy can remain for long periods until the optical trigger is activated. Image Credit: MIT. Click image for the largest view.

A common approach to thermal storage is to use what is known as a phase change material (PCM), where input heat melts the material and its phase change – from solid to liquid – stores the energy. When the PCM is cooled back down below its melting point, it turns back into a solid, at which point the stored energy is released as heat. There are many examples of these materials, including waxes or fatty acids used for low-temperature applications, and molten salts used at high temperatures. But all current PCMs require a great deal of insulation, and they pass through that phase change temperature uncontrollably, losing their stored heat relatively rapidly.

But the new system uses molecular switches that change shape in response to light; when integrated into the PCM, the phase-change temperature of the hybrid material can be adjusted with light, allowing the thermal energy of the phase change to be maintained even well below the melting point of the original material.

The new findings, by MIT postdocs Grace Han and Huashan Li and Professor Jeffrey Grossman, have been published in the journal Nature Communications.

Professor Grossman explains, “The trouble with thermal energy is, it’s hard to hold onto it,” So his team developed what are essentially add-ons for traditional phase change materials, or, “little molecules that undergo a structural change when light shines on them.” The trick was to find a way to integrate these molecules with conventional PCM materials to release the stored energy as heat, on demand. “There are so many applications where it would be useful to store thermal energy in a way lets you trigger it when needed,” he said.

The researchers achieved this by combining the fatty acids with an organic compound that responds to a pulse of light. With this arrangement, the light-sensitive component alters the thermal properties of the other component, which stores and releases its energy. The hybrid material melts when heated, and after being exposed to ultraviolet light, it stays melted even when cooled back down. Next, when triggered by another pulse of light, the material resolidifies and gives back the thermal phase-change energy.

“By integrating a light-activated molecule into the traditional picture of latent heat, we add a new kind of control knob for properties such as melting, solidification, and supercooling,” said Grossman, who is the Morton and Claire Goulder and Family Professor in Environmental Systems as well as professor of materials science and engineering.

The system could make use of any source of heat, not just solar, Ms Han noted. “The availability of waste heat is widespread, from industrial processes, to solar heat, and even the heat coming out of vehicles, and it’s usually just wasted.” Harnessing some of that waste could provide a way of recycling that heat for useful applications.

“What we are doing technically,” Han explained, “is installing a new energy barrier, so the stored heat cannot be released immediately.” In its chemically stored form, the energy can remain for long periods until the optical trigger is activated. In their initial small-scale lab versions, they showed the stored heat can remain stable for at least 10 hours, whereas a device of similar size storing heat directly would dissipate it within a few minutes. And “there’s no fundamental reason why it can’t be tuned to go higher,” Han said.

In the initial proof-of-concept system “the temperature change or supercooling that we achieve for this thermal storage material can be up to 10º C (18º F), and we hope we can go higher,” Grossman said.

Already, in this version, “the energy density is quite significant, even though we’re using a conventional phase-change material,” Han said. The material can store about 200 joules per gram, which she says is “very good for any organic phase-change material.” And already, “people have shown interest in using this for cooking in rural India,” she said. Such systems could also be used for drying agricultural crops or for space heating.

“Our interest in this work was to show a proof of concept,” Grossman said, “but we believe there is a lot of potential for using light-activated materials to hijack the thermal storage properties of phase change materials.”

Congratulations for your achievement folks, stay with this. There are far more applications than you are imagining now. Far far more.

Lawrence Berkeley National Lab experiments help scientists shed light on fuel-cell physics. Scientists looking for the right balance of moisture and temperature in a specialized type of hydrogen fuel cell have used X-rays to explore the inner workings of its components at tiny scales.

This animated 3-D rendering, generated by an X-ray-based imaging technique at Berkeley Lab’s Advanced Light Source, shows tiny pockets of water (blue) in a fibrous sample. The X-ray experiments showed how moisture and temperature can affect hydrogen fuel-cell performance. Image Credit: Berkeley Lab.  Click the image to view the animation or visit the Berkeley Lab page for a larger view.

Like a well-tended greenhouse garden, a specialized type of hydrogen fuel cell – which shows promise as a clean, renewable next-generation power source for vehicles and other uses – requires precise temperature and moisture controls to be at its best. If the internal conditions are too dry or too wet, the fuel cell won’t function well.

But seeing inside a working fuel cell at the tiny scales relevant to a fuel cell’s chemistry and physics is challenging, so scientists used X-ray-based imaging techniques at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Argonne National Laboratory to study the inner workings of fuel-cell components subjected to a range of temperature and moisture conditions.

The study has been published online in the journal Electrochimica Acta.

The research team, led by Iryna Zenyuk, a former Berkeley Lab postdoctoral researcher now at Tufts University, included scientists from Berkeley Lab’s Energy Storage and Distributed Resources Division and the Advanced Light Source (ALS), an X-ray source known as a synchrotron.

The ALS let researchers image in 3-D at high resolution very quickly, allowing them to look inside working fuel cells in real-world conditions. The team created a test bed to mimic the temperature conditions of a working polymer-electrolyte fuel cell that is fed hydrogen and oxygen gases and produces water as a byproduct.

“The water management and temperature are critical,” said Adam Weber, a staff scientist in the Energy Technologies Area at Berkeley Lab and deputy director for a multi-lab fuel cell research effort, the Fuel Cell Consortium for Performance and Durability (FC-PAD).

The research aims to find the right balance of humidity and temperature within the cell, and how water moves out of the cell.

Controlling how and where water vapor condenses in a cell, for example, is critical so that it doesn’t block incoming gases that facilitate chemical reactions.

“Water, if you don’t remove it, can cover the catalyst and prevent oxygen from reaching the reaction sites,” Weber said. But there has to be some humidity to ensure that the central membrane in the cell can efficiently conduct ions.

The research team used an X-ray technique known as micro X-ray computed tomography to record 3-D images of a sample fuel cell measuring about 3 to 4 millimeters in diameter.

“The ALS lets us image in 3-D at high resolution very quickly, allowing us to look inside working fuel cells in real-world conditions,” said Dula Parkinson, a research scientist at the ALS who participated in the study.

The sample cell included thin carbon-fiber layers, known as gas-diffusion layers, which in a working cell sandwich a central polymer-based membrane coated with catalyst layers on both sides. These gas-diffusion layers help to distribute the reactant chemicals and then remove the products from the reactions.

Weber said that the study used materials that are relevant to commercial fuel cells. Some previous studies have explored how water wicks through and is shed from fuel-cell materials, and the new study added precise temperature controls and measurements to provide new insight on how water and temperature interact in these materials.

Complementary experiments at the ALS and at Argonne’s Advanced Photon Source, a synchrotron that specializes in a different range of X-ray energies, provided detailed views of the water evaporation, condensation, and distribution in the cell during temperature changes.

“It took the ALS to explore the physics of this,” Weber said, “so we can compare this to theoretical models and eventually optimize the water management process and thus the cell performance.”

The experiments focused on average temperatures ranging from about 95º to 122º Fahrenheit, with temperature variations of 60º to 80º (hotter to colder) within the cell. Measurements were taken over the course of about four hours. The results provided key information to validate water and heat models that detail fuel-cell function.

This test cell included a hot side designed to show how water evaporates at the site of the chemical reactions, and a cooler side to show how water vapor condenses and drives the bulk of the water movement in the cell.

While the thermal conductivity of the carbon-fiber layers – their ability to transfer heat energy – decreased slightly as the moisture content declined, the study found that even the slightest degree of saturation produced nearly double the thermal conductivity of a completely dry carbon-fiber layer. Water evaporation within the cell appears to dramatically increase at about 120º Fahrenheit, researchers found.

The experiments showed water distribution with millionths-of-a-meter precision, and suggested that water transport is largely driven by two processes: the operation of the fuel cell and the purging of water from the cell.

The study found that larger water clusters evaporate more rapidly than smaller clusters. The study also found that the shape of water clusters in the fuel cell tend to resemble flattened spheres, while voids imaged in the carbon-fiber layers tend to be somewhat football-shaped.

There are also some ongoing studies, Weber said, to use the X-ray-based imaging technique to look inside a full subscale fuel cell one section at a time.

“There are ways to stitch together the imaging so that you get a much larger field of view,” he said. This process is being evaluated as a way to find the origin of failure sites in cells through imaging before and after testing. A typical working subscale fuel cell measures around 50 square centimeters, he added.

This is encouraging. Fuel cells, while on the market now, are far from mass market practical. They’re way too management needy for regular consumers or even attentive businesses. So every step this team and others make to refine and simplify operations is welcome and vitally important for fuel cell enthusiasts.

Universidad Politécnica de Madrid (UPM) researchers have designed a new system that reduces the energy gains and losses of buildings through their façade, managing to reduce the energy consumption due to air flow.

Two researchers from School of Building Engineering at UPM have developed a ventilated façade with a double chamber and flow control device that significantly saves energy in buildings. This sustainable and efficient solution can be applied in both rehabilitation works and new buildings due to its simplicity of implementation.

The team’s work has been published in the Energy and Buildings journal and has also been patented.

The façade is the main constructive element of a building that allows us to meet the requirements of energy efficiency and interior comfort established in the national and international rules and directives of the construction sector. The type of system, the design and the right execution of the façade itself are critical aspects that determine the final energy consumption of the building.

Graphic of the façade functioning in summer (left) and winter (right).  Image Credit: Jaime Santa Cruz and César Porras. Click image for the largest view.

Today, the air flow expenses are of 40% – 65% of the total expenses of a building. Buildings in a Mediterranean-continental climate like in Spain suffer in winter energy losses through their north and east façades due to low temperatures. Likewise, these buildings in summer obtain energy gains through their south and west façades due to solar radiation. In both cases, the air flow is needed in the building in order to maintain suitable inner conditions for their inhabitants, counteracting the energy gains-losses through the building envelope.

In order to improve the energy efficiency of façades, two researchers from the group of Tecnología Edificatoria y Medio Ambiente (TEMA) at UPM have developed a new system of ventilated façade. Today, the conventional ventilated façades are composed of an inner sheet, thermal insulation, ventilation chamber and exterior finish.

The new façade design adds a second air chamber between the existing one and the façade insulation, both chambers are interconnected by the bottom of the façade. Another feature is a new element at the top to regulate the air flow in the chambers, depending on the gradient of the existing temperature between inside and outside the building.

A ventilated façade with a double chamber presents two improvements over the conventional system. Firstly, energy gains-losses are reduced through the façades reducing, on consequence, the energy consumption due to air flow. Secondly, the design of the system helps to reduce the vertical temperature gradient along the envelope, homogenizing the air temperature in the chambers throughout the year.

By minimizing the vertical thermal gradients, global consumption due to energy gains-losses through the façade depends less on the height of the building, preventing the upper levels to present higher or lower indoor comfort and degree of energy efficiency than the lower levels. Beside that, this system is a sustainable and efficient solution that can be applied in both rehabilitation works and new buildings due to its simplicity of implementation.

The initial over cost can be short-term amortized when considering the remarkable energy savings of this design.

The authors of this work said, “this research work highlights the potential energy efficiency of buildings through the redesign of conventional construction systems.”

Building façades or even busy home entryways or foyers all need some attention to air loss. This team’s work is welcome indeed and we hope that the patent doesn’t stand as a barrier to widespread adoption.


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