Hiroshima University researchers have blended together various polymer and molecular semiconductors as photo-absorbers to create a solar cell with increased power efficiencies and electricity generation.

These types of solar cells, known as organic photovoltaics (OPV), are devices that generate electricity when light is incident upon their photo-absorbers. The efficiency of a solar cell is determined by comparing how much electricity is generated to how much light is incident upon the cell. This is referred to as “photon harvest,” or how many particles of light are converted into electrical current. The more efficient the solar cell, the more cost effective and pragmatic the cell is for commercial use.

Schematic illustration of the distribution of the materials in the semiconductor layer for the OPV cell.  ITIC is selectively located at the interface of PTzBT and PCBM domains, which leads to an efficient charge carrier (photocurrent) generation. Image Credit: Hiroshima University. Click Image for the largest view.

The team at the Graduate School of Advanced Science and Engineering added only a small amount of a compound that absorbs long wavelengths of light resulting in an OPV that was 1.5 times more efficient than the version without the compound. The compound was able to enhance the absorption intensity due to the optical interference effect within the device. The group went on to show that how they are distributed is key to further improved power generation efficiency.

Itaru Osaka, corresponding author of the paper, published in Macromolecules said, “The addition of a very small amount of a sensitizer material to an OPV cell, which consists of a semiconducting polymer that we developed previously and along with other materials.”

Osaka explained, “This leads to a significant increase in the photocurrent and thereby the power conversion efficiency due to the amplified photon absorption that originates in the optical interference effect. A key is to use a very specific polymer, one that allows us to have a very thick semiconductor layer for OPV cells, which significantly enhances optical interference effect compared to a thin layer.”

As for future work, Osaka has his eye set on pushing the boundaries of state of the art solar cells.

“Our next step is to develop better semiconducting polymers as the host material for this type of OPV and better sensitizer materials that can absorb more photons in the longer wavelength regions. This would lead to the realization of the world’s highest efficiency in OPV cells.”

A 150% gain in efficiency is quite an achievement. Admittedly, organic photovoltaics do have a long way to go to catch semi-conductor solar cells. But, they shouldn’t have to, as they are vastly less expensive to make, and contain way less objectionable material. You can bet manufacturers in this field are taking notice.

Incheon National University scientists encapsulated a methanol fuel cell catalyst in a protective molecular sieve that selectively prevents undesired reactions.

Direct methanol fuel cells (DMFCs), which produce electricity using methanol, will be an alternative solution in the transition away from fossil fuels and toward a ‘hydrogen’ economy. However, undesired methanol oxidation on the cathode side in DMFCs degrades the essential platinum catalyst, causing performance and stability problems. Now, scientists from Korea have found a simple method to coat platinum nanoparticles with a protective carbon shell. This selectively excludes methanol from reaching the catalyst’s core on the cathode, solving a long-standing problem in DMFCs.

Graphic of a synthesized carbon-encapsulated Pt cathode catalyst. Image Credit: Incheon National University. Click image for the largest view.

Many scientists worldwide are focused on finding efficient alternatives. Though high hopes have been placed on hydrogen fuel cells, the reality is that transporting, storing, and using pure hydrogen comes with a huge added cost, making this process challenging with current technology. In contrast, methanol (CH3O3), a type of alcohol, does not require cold storage, has a higher energy density, and is easier and safer to transport, making a transition into a methanol-based economy is a more realistic goal.

However, producing electricity from methanol at room temperature requires a direct methanol fuel cell (DMFC); a device that, so far, offers subpar performance. One of the main problems in DMFCs is the undesired “methanol oxidation” reaction, which occurs during “methanol crossover”, that is, when it passes from the anode to the cathode. This reaction results in the degradation of the platinum (Pt) catalyst that is essential for the cell’s operation. Although certain strategies to mitigate this problem have been proposed, so far none has been good enough owing to cost or stability issues.

In a recent study published in ACS Applied Materials & Interfaces, a team of scientists from Korea came up with a creative and effective solution. They fabricated – through a relatively simple procedure – a catalyst made of Pt nanoparticles encapsulated within a carbon shell. This shell forms an almost impenetrable carbon network with small openings caused by nitrogen defects. While oxygen, one of the main reactants in DMFCs, can reach the Pt catalyst through these “holes,” methanol molecules are too big to pass through.

Professor Oh Joong Kwon from Incheon National University, Korea, who led the study explained, “The carbon shell acts as a molecular sieve and provides selectivity toward the desired reactants, which can actually reach the catalyst sites. This prevents the undesirable reaction of the Pt cores.”

The scientists conducted various types of experiments to characterize the overall structure and composition of the prepared catalyst and proved that oxygen could make it through the carbon shell and methanol could not. They also found a straightforward way to tune the number of defects in the shell by simply changing the temperature during a heat treatment step. In subsequent experimental comparisons, their novel shelled catalyst outperformed commercial Pt catalysts and also offered much higher stability.

Prof Kwon has been working on improving fuel cell catalysts for the past 10 years, motivated by the many ways in which this technology could find its way into our daily lives.

Prof Kwon noted, “DMFCs have a higher energy density than lithium-ion batteries and could therefore become alternative power sources for portable devices, such as laptops and smartphones.”

This development looks very intuitive and clever. The insight from 10 years of effort surely played a role and the results must be very gratifying indeed. The idea of a squirt of methanol powering up a device instead of long charging cycle certainly has a high consumer attraction level and methanol is very common, relatively safe, and cheap.

Lets hope this will economically scale up to commercial manufacturing for consumer applications. Your humble writer would certainly look eagerly at a reliable methanol power source for several devices.

Efficiently mass-producing hydrogen from water is closer to becoming a reality thanks to new findings. The research came from Oregon State University College of Engineering researchers and collaborators at Cornell University and the Argonne National Laboratory.

The scientists used advanced experimental tools to forge a clearer understanding of an electrochemical catalytic process that’s cleaner and more sustainable than deriving hydrogen from natural gas.

The group’s findings have been published in Science Advances.

Hydrogen is found in a wide range of compounds on Earth, most commonly combining with oxygen to make water, and it has many scientific, industrial and energy-related roles. It also occurs in the form of hydrocarbons, compounds consisting of hydrogen and carbon such as methane, the primary component of natural gas.

Oregon State’s Zhenxing Feng, a chemical engineering professor who led the study said, “The production of hydrogen is important for many aspects of our life, such as fuel cells for cars and the manufacture of many useful chemicals such as ammonia. It’s also used in the refining of metals, for producing human-made materials such as plastics and for a range of other purposes.”

The data at the U.S. Department of Energy shows the United States produces most of its hydrogen from a methane source such as natural gas via a technique known as steam-methane reforming. The process involves subjecting methane to pressurized steam in the presence of a catalyst, creating a reaction that produces hydrogen and carbon monoxide, as well as a small amount of carbon dioxide.

The next step is referred to as the water-gas shift reaction in which the carbon monoxide and steam are reacted via a different catalyst, making carbon dioxide and additional hydrogen. In the last step, pressure-swing adsorption, carbon dioxide and other impurities are removed, leaving behind pure hydrogen.

Feng explained, “Compared to natural gas reforming, the use of electricity from renewable sources to split water for hydrogen is cleaner and more sustainable. However, the efficiency of water-splitting is low, mainly due to the high overpotential – the difference between the actual potential and the theoretical potential of an electrochemical reaction – of one key half-reaction in the process, the oxygen evolution reaction or OER.”

A half-reaction is either of the two parts of a redox, or reduction-oxidation, reaction in which electrons are transferred between two reactants; reduction refers to gaining electrons, oxidation means losing electrons.

The concept of half-reactions is often used to describe what goes on in an electrochemical cell, and half-reactions are commonly used as a way to balance redox reactions. Overpotential is the margin between the theoretical voltage and the actual voltage necessary to cause electrolysis – a chemical reaction driven by the application of electric current.

Feng, in outlining the basics said, “Electrocatalysts are critical to promoting the water-splitting reaction by lowering the overpotential, but developing high-performance electrocatalysts is far from straightforward. One of the major hurdles is the lack of information regarding the evolving structure of the electrocatalysts during the electrochemical operations. Understanding the structural and chemical evolution of the electrocatalyst during the OER is essential to developing high-quality electrocatalyst materials and, in turn, energy sustainability.”

(Left) The formed amorphous IrOx layer appears to reach a steady-state thickness by 0.25 hours. (Right) Cross-section transmission electron microscopy (TEM) images of the pristine SrIrO3 film after 4 hours of potential cycling between 1.05 and 1.75 V versus RHE.

Feng and the collaborators used a set of advanced characterization tools to study the atomic structural evolution of a state-of-the art OER electrocatalyst, strontium iridate (SrIrO3), in acid electrolyte.

“We wanted to understand the origin of its record-high activity for the OER – 1,000 times higher than the common commercial catalyst, iridium oxide,” Feng said. “Using synchrotron-based X-ray facilities at Argonne and lab-based X-ray photoelectron spectroscopy at the Northwest Nanotechnology Infrastructure site at OSU, we observed the surface chemical and crystalline-to-amorphous transformation of SrIrO3 during the OER.”

The observations led to a deep understanding of what was going on behind strontium iridate’s ability to work so well as a catalyst.

Feng summed up, “Our detailed, atomic-scale finding explains how the active strontium iridate layer forms on strontium iridate and points to the critical role of the lattice oxygen activation and coupled ionic diffusion on the formation of the active OER units.”

Feng added that the work provides insight into how applied potential facilitates the formation of the functional amorphous layers at the electrochemical interface and leads to possibilities for the design of better catalysts.

This post comes from one of the best press releases seen in quite some time. Your humble writer thanks Steve Lundeberg for both the research information as well as a brief and yet highly instructive review of current hydrogen production and the issues faced in getting to economical water splitting.

This research isn’t a slam dunk solution to the water splitting dilemma. But it sure does illuminate the research in catalysts such that more progress can be made. For that – it might well be a breakthrough.

A team of researchers at the University of California San Diego and the California-based company ZPower have developed a flexible, rechargeable silver oxide-zinc battery with a five to 10 times greater areal energy density than today’s state of the art. The battery also is easier to manufacture; while most flexible batteries need to be manufactured in sterile conditions, under vacuum, this one can be screen printed in normal lab conditions. The device can be used in flexible, stretchable electronics for wearables as well as soft robotics.

The team described their findings in the journal Joule.

“Our batteries can be designed around electronics, instead of electronics needed to be designed around batteries,” said Lu Yin, one of the paper’s co-first authors and a Ph.D. student in the research group of UC San Diego’s nanoengineering Professor Joseph Wang.

The areal capacity for this innovative battery is 50 milliamps per square centimeter at room temperature, a result that is 10-20 times greater than the areal capacity of a typical Lithium ion battery. So for the same surface area, the battery described in Joule can provide 5 to 10 times more power.

“This kind of areal capacity has never been obtained before,” Yin said. “And our manufacturing method is affordable and scalable.”

The new battery has higher capacity than any of the flexible batteries currently available on the market. That’s because the battery has a much lower impedance (the resistance of an electric circuit or device to alternative current). The lower the impedance, the better the battery performance against high current discharge.

“As the 5G and Internet of Things (IoT) market grows rapidly, this battery that outperforms commercial products in high current wireless devices will likely be a main contender as the next-generation power source for consumer electronics” said Jonathan Scharf the paper’s co-first author and a Ph.D. candidate in the research group of UC San Diego’s nanoengineering Professor Ying Shirley Meng.

The batteries successfully powered a flexible display system equipped with a microcontroller and Bluetooth modules. Here too, the battery performed better than commercially available Lithium coin cells.

The printed battery cells were recharged for more than 80 cycles, without showing any major signs of capacity loss. The cells also remained functional in spite of repeated bending and twisting.

“Our core focus was to improve both battery performance and the manufacturing process,” said Ying Shirley Meng, director of the UC San Diego Institute for Materials Discovery and Design and one of the paper’s corresponding authors.

To create the battery, the researchers used a proprietary cathode design and chemistry from ZPower. Wang and his team contributed their expertise in printable, stretchable sensors and stretchable batteries. Meng and her colleagues provided their expertise in advanced characterization for electrochemical energy storage systems and characterized each iteration of the battery prototype until it reached peak performance.

The battery’s exceptional energy density is due to its silver oxide-zinc, (AgO-Zn) chemistry. Most commercial flexible batteries use a Ag2O-Zn chemistry. As a result, they usually have limited cycle life and have low capacity. This limits their use to low-power, disposable electronics.

AgO is traditionally considered unstable. But ZPower’s AgO cathode material relies on a proprietary lead oxide coating to improve AgO’s electrochemical stability and conductivity.

As an added benefit, the AgO-Zn chemistry is responsible for the battery’s low impedance. The battery’s printed current collectors also have excellent conductivity, which also helps achieve lower impedance.

But AgO had never been used in a screen-printed battery before, because it is highly oxidative and chemically degrades quickly. By testing various solvents and binders, researchers in Wang’s lab at UC San Diego were able to find an ink formulation that makes AgO viable for printing . As a result, the battery can be printed in only a few seconds once the inks are prepared. It is dry and ready to use in just minutes. The battery could also be printed in a roll-to-roll process, which would increase the speed and make manufacturing scalable.

The batteries are printed onto a polymer film that is chemically stable, elastic and has a high melting point (about 200° C or 400° Fahrenheit) that can be heat sealed. Current collectors, the zinc anode, the AgO cathode and their corresponding separators each constitute a stacked screen-printed layer.

The team is already at work on the next generation of the battery, aiming for cheaper, faster charging devices with even lower impedance that would be used in 5G devices and soft robotics that require high power and customizable and flexible form factors.

This looks like a chemistry is a system that could compete with Lithium ion. This new version might have what is needed to depressurize the Lithium ion battery market. On the other hand, the team is making really big claims. If all aspects can scale up and compete economically consumers might see a worthy choice to the domination of Lithium ion. Just remember, silver is a precious metal; they used to make real money with it.

Lancaster University researchers are studying a crystalline material and discovered it has properties that allow it to capture heat energy from the sun. The energy can be stored for several months at room temperature, and it can be released on demand in the form of heat. With further development, these kinds of materials could offer exciting potential as a way of capturing solar energy during the summer months, and storing it for use in winter when less solar energy is available.

Image Credit: Lancaster University. Click image for the largest view.

As we move away from fossil fuels and shift to renewable energy, the need for new ways to capture and store energy becomes increasingly important.

The team’s research paper has been published in the journal Chemistry of Materials.

This would prove invaluable for applications such as heating systems in off-grid systems or remote locations, or as an environmentally-friendly supplement to conventional heating in houses and offices. It could potentially also be produced as a thin coating and applied to the surface of buildings, or used on the windscreens of cars where the stored heat could be used to de-ice the glass in freezing winter mornings.

The material is based on a type of ‘metal-organic framework’ (MOF). These consist of a network of metal ions linked by carbon-based molecules to form 3-D structures. A key property of MOFs is that they are porous, meaning that they can form composite materials by hosting other small molecules within their structures.

The Lancaster research team set out to discover if a MOF composite, previously prepared by a separate research team at Kyoto University in Japan and known as ‘DMOF1’, can be used to store energy – something not previously researched.

The MOF pores were loaded with molecules of azobenzene – a compound that strongly absorbs light. These molecules act as photoswitches, which are a type of ‘molecular machine’ that can change shape when an external stimulus, such as light or heat, is applied.

In tests, the researchers exposed the material to UV light, which causes the azobenzene molecules to change shape to a strained configuration inside the MOF pores. This process stores the energy in a similar way to the potential energy of a bent spring. Importantly, the narrow MOF pores trap the azobenzene molecules in their strained shape, meaning that the potential energy can be stored for long periods of time at room temperature.

The energy is released again when external heat is applied as a trigger to ‘switch’ its state, and this release can be very quick – a bit like a spring snapping back straight. This provides a heat boost which could be used to warm other materials of devices.

Further tests showed the material was able to store the energy for at least four months. This is an exciting aspect of the discovery as many light-responsive materials switch back within hours or a few days. The long duration of the stored energy opens up possibilities for cross-seasonal storage.

The concept of storing solar energy in photoswitches has been studied before, but most previous examples have required the photoswitches to be in a liquid. Because the MOF composite is a solid, and not a liquid fuel, it is chemically stable and easily contained. This makes it much easier to develop into coatings or standalone devices.

Dr. John Griffin, Senior Lecturer in Materials Chemistry at Lancaster University and joint Principal Investigator of the study, said, “The material functions a bit like phase change materials, which are used to supply heat in hand warmers. However, while hand warmers need to be heated in order to recharge them, the nice thing about this material is that it captures “free” energy directly from the sun. It also has no moving or electronic parts and so there are no losses involved in the storage and release of the solar energy. We hope that with further development we will be able to make other materials which store even more energy.”

These proof-of-concept findings open up new avenues of research to see what other porous materials might have good energy storage properties using the concept of confined photoswitches.

Joint investigator Dr. Nathan Halcovitch added: “Our approach means that there are a number of ways to try to optimise these materials either by changing the photoswitch itself, or the porous host framework.”

Other potential applications for crystalline materials containing photoswitch molecules include data storage – the well-defined arrangement of photoswitches in the crystal structure means that they could in principle be switched one-by-one using a precise light source and therefore store data like on a CD or DVD, but at a molecular level. They also have potential for drug delivery – drugs could be locked inside a material using photoswitches and then released on demand inside the body using a light or heat trigger.

Although the results were promising for this material’s ability to store energy for long periods of time, its energy density was modest. Next steps are to research other MOF structures as well as alternative types of crystalline materials with greater energy storage potential.

Its rare to see a new research field appear. This one is especially welcome and comes as quite a surprise as the span is already four months, with an estimated energy storage half-life of 4.5 years. While the density might be ‘modest’ the press release isn’t saying what the difference is between a heat charging value and the recovery value by mass.

That it works at all is the news. And significant news at that. What this new technology will become is anyone’s guess for now – and that is what makes it so interesting and exciting.