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Reverse electrodialysis using Nafion™ membranes to produce renewable energy

In the order to address the global need for renewable and clean energy sources, salinity-gradient energy harvested by reverse electrodialysis (RED) is attracting significant interest in recent years. In addition, brine solution coming from seawater desalination is currently considered as a waste; however thanks to its high salinity it can be exploited as a valuable resource to feed RED. RED is an engineered adaptation of nature’s osmotic energy production where ions flow pass the cell membrane in order to produce the universal biological currency ATP. This energy is also harvested by the RED technology.

Now, more than ever there is need for sustainable and environmentally friendly technological solutions in order to keep up with ever growing demand for clean water and energy. The traditional linear way “produce and throw away” does no longer serve the society anymore and the new approach of circular economy has take a place, where any waste can be considered as a valuable resource for another process. In this respect, reverse electrodialysis is a promising electromembrane-based technology to generate power from concentrated solutions by harvesting the Gibbs free energy of mixing the solutions with different salinity. In particular, brine solutions produced in desalination plants, which is currently considered as a waste, can be used as concentrated streams in RED stack.

Avci et al. of the University of Calabria, Italy, have recently published their solution for brine disposal using RED-stack. They have realized that in order to maximize generated power, the high permselectivity and ion conductivity of membrane components in RED are essential. Although Nafion™ membranes are among the most prominent commercial cation exchange membrane solutions for electrochemical applications, no study has been done in its utilization toward RED processes. This was the first reported RED stack using Nafion™ membranes.

A typical RED unit is similar to an electrodialysis (ED) unit, which is a commercialized technology. ED uses a feed solution and the electrical energy, while producing concentrate and dilute, separately. On the other side, RED uses concentrated and dilute solutions that are mixed together in a controlled manner in order to produce spontaneously electrical energy. In a RED stack, repeating cells comprised of alternating cation and anion exchange membranes that are selective for anions and cations. The salinity gradient over each ion exchange membrane creates a voltage difference which is the driving force for the process. The ion exchange membranes are one of the most important components of a RED stack.

The performance of Nafion™ membranes (Nafion™ 117 and Nafion™ 115) have been evaluated under a high salinity gradient conditions for the possible application in RED. In order to simulate the natural environments of RED operation, NaCl solution as well as multicomponent NaCl + MgCl2 have been tested.

Gross power density under high salinity gradient and the effect of Mg2+ on the efficiency in energy conversion have been evaluated in single cell RED using Nafion™ 117, Nafion™ 115, CMX and Fuji-CEM-80050 as cation exchange membranes. Two commercial cation exchange membranes – CMX and Fuji-CEM 80050, frequently used for RED applications, have served as benchmark.

The results show that under the condition of 0.5 M / 4.0 M NaCl solutions, the highest Pd,max was achieved using Nafion™ membrane. This result is attributed to their outstanding permselectivity compared to other CEMs. In the presence of Mg2+ ions, Pd,max reduction of 17 and 20% for Nafion™ 115 and Nafion™ 117 were recorded, respectively. Both membranes maintained their low resistance; however a loss in permselectivity was measured under this condition. Even though, it was reported that Nafion™ membranes outperformed other commercial membranes such as CMX and Fuji-CEM-80050 for RED application.

(Photo: Wikipedia)

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Accelerated deforestation in the EU

Forests are vital to our society. In the EU, forests make up around 38% of the total land area. They are important carbon sinks as they eliminate around 10% of EU greenhouse gases. Efforts to conserve them are a key part of EU climate targets. However, the increasing demand for forest products poses challenges for sustainable forest management.

According to a report recently published in the renowned science magazine Nature, the EU’s deforested area has increased by 49% and with it the loss of biomass (69%). This is due to large-scale deforestation, which reduces the continent’s carbon absorption capacity and accelerates climate change.

The analyzed a series of very detailed satellite data. The authors of the report show that deforestation occurred primarily on the Iberian Peninsula, the Baltic States, and Scandinavia. Deforestation of forest areas increased by 49% between 2016 and 2018. Satellite images also show that the average area of ​​harvested land across Europe has increased by 34 percent, with potential implications for biodiversity, soil erosion and water regulation.

The accelerating deforestation could thwart the EU’s strategy to combat climate change, which aims in particular to protect forests in the coming years, the experts warn in their study. For this reason, the increasing use of forests is challenging to maintain the existing balance between the demand for wood and the need to preserve these key ecosystems for the environment. Typically, industries such as bioenergy or the paper industry are the driving forces behind deforestation.

The greatest acceleration in deforestation was recorded in Sweden and Finland. In these two countries, more than 50% of the increase in deforestation in Europe has been recorded. Next in line are Spain, Poland, France, Latvia, Portugal and Estonia, which together account for six to 30% of the increase, the study said.

Experts suggest linking deforestation and carbon emissions in model calculations before setting new climate targets. The increase in forest harvest is the result of the recent expansion of global wood markets, as evidenced by economic indicators for forestry, timber bioenergy and international trade. If such a high forest harvest continues, the EU’s vision of forest-based mitigation after 2020 could be compromised. The additional carbon losses from forests would require additional emission reductions in other sectors to achieve climate neutrality.

At Frontis Energy, we find the competition between bioenergy and this important carbon sink particularly disturbing, as both are strategies to mitigate global warming.

(Photo: Picography / Pixabay)

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Light-driven process turns greenhouse gases into valuable products

Much research has been done in order to reduce the use of fossil petroleum products as fuels. In that respect syngas (synthetic gas) seems as a great opportunity for sustainable energy developments. Syngas is the mixture composed of hydrogen (H2) and carbon monoxide (CO) as its main components. It represents an important chemical feedstock used widely for industrial processes for generating chemicals and fuels:

Global use of syngas in industrial processes.

Syngas can be produced from methane (CH4) in a reforming reaction with water (H2O), oxygen (O2) or carbon dioxide (CO2). The process called methane dry reforming (MDR) can be combined with carbon dioxide:

CH4 + CO2 → 2 H2 + 2 CO

It is an environmentally friendly path, turning two greenhouse gases into a valuable chemical feedstock.

However, the MDR is process requires chemical catalysts and high temperatures in the range between 700 − 1,000°C. Usually, it suffers from coke deposition and, in consequence, catalyst deactivation.

Some chemists have recently demonstrated that light, and not heat, might be a more effective solution for this energy-hungry reaction.

The photocatalytic solution

A team of researchers at the Rice University in Houston, Texas, together with colleagues from Princeton University and the University of California have developed superior light-stimulated catalysts that can efficiently power MDR reactions without any heat input. This work has been published in the prestigious journal Nature Energy.

They have reported a highly efficient and coke-resistant plasmonic photocatalyst containing precisely one ruthenium (Ru) atom for every 99 copper (Cu) atoms. The isolated single-atom of Ru obtained on Cu antenna nanoparticles provides high catalytic activity for the MDR reaction. On the other side, Cu antennas allow strong light adsorption and under illumination and deliver hot electrons to ruthenium atoms. The researchers suggested that both, hot-carrier generation and single-atom structure are essential for excellent catalytic performance in terms of efficiency and coking resistance.

The optimal Cu-Ru ratio have been investigated in synthesized series of CuxRuy catalysts with varying molar ratios of plasmonic metal (Cu) and catalytic metal (Ru), where x,y are atomic percentage of Cu and Ru. Overall, the Cu19.8Ru0.2 was the most promising composition in terms of selectivity, stability and activity. In comparison to pure Cu nanoparticles, the Cu19.8Ru0.2 mix exhibits increased photocatalytic reaction rates (approx. 5.5 times higher) and improved stability with its performance maintained over 20 h period. Calculations showed that isolated Ru-atoms on Cu lower the activation barrier for the methane dehydrogenation step in comparison to pure Cu without promoting undesired coke formation.

In addition, the research has been supported by different methods (CO-DRIFTS with DFT) in order to unravel and prove single-atom Ru structures on Cu nanoparticles occurring in Cu19.9Ru0.1 and Cu19.8Ru0.2 compositions.

The comparison between thermocatalytic and photocatalytic activity at the same surface for MDR has also been demonstrated. The thermocatalytic reaction rate at 726°C (approx. 60 µmol CH4 / g / s) was less than 25% of photocatalytic reaction rate under white-light illumination with no external heat (approx. 275 µmol CH4 / g / s). This enhancement in the activity is attributed to the hot-carrier generated mechanism which is predominant in the photocatalytic MDR. The role of the hot-carrier is an increase in C−H activation rates on Ru as well as improved H2 desorption.

The scientists also reported the catalyst achieving a turnover frequency of 34 mol H2  / mol Ru / s and photocatalytic stability of 50 h under focused white light illumination (19.2 W / cm2) with no external heat.

As the synthesized photocatalysts is primarily based on Cu which is an abundant element, this approach provides a promising, sustainable catalyst operating at low-temperatures for MDR. This allows cheaper syngas production at higher rates, bringing us closer to a clean burning carbon fuel.

(Photo: Wikipedia)

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Promising hydrophilic membranes with fast and selective ion transport for energy devices

In addition to well-established Nafion™ membranes which are currently the best trade-off between high-performance and cost in proton exchange fuel cells (PEM), methanol fuel cells, electrolysis cells etc. As our energy resources are diversifying, there is a growing demand for efficient and selective ion-transport membranes for energy storage devices such as flow batteries.

A Sumitomo Electric flow battery for energy storage of a solar PV plant. (Photo: Sumitomo Electric Co.)

Redox flow batteries – the energy storage breakthrough

The high demand for a reliable and cost-effective energy storage systems is reflected in the increased diversity of technologies for energy storage. Among different electrochemical storage systems, one of the most promising candidates are redox-flow batteries (RFBs). They could meet large-scale energy storage requirements scoring in high efficiency, low scale-up cost, long charge/discharge cycle life, and independent energy storage and power generation capacity.

Since this technology is still young, the development of commercially and economically viable systems demands:

  • improvement of the core components e.g. membranes with special properties,
  • improvement of energy efficiency
  • reduction in overall cost system.

Meeting demands for redox flow batteries

Two research teams in the United Kingdom, one from Imperial College and the other from the University of Cambridge, pursued a new approach to design the next generation of microporous membrane materials for the redox-flow batteries. They recently published their data in the well renown journal Nature Materials. Well-defined narrow microporous channels together with hydrophilic functionality of the membranes enable fast transport of salt ions and high selectivity towards small organic molecules. The new membrane architecture is particularly valuable for aqueous organic flow batteries enabling high energy efficiency and high capacity retention. Importantly, the membranes have been prepared using roll-to-roll technology and mesoporous polyacrylonitrile low-cost support. Hence, these innovative membranes could be cost effective.

As the authors reported, the challenge for the new generation RFBs is development of low-cost hydrocarbon-based polymer membranes that features precise selectivity between ions and organic redox-active molecules. In addition, ion transport in these membranes depends on a formation of the interconnected water channels via microphase separation, which is considered a complex and difficult-to-control process on molecular level.

The new synthesis concept of ion-selective membranes is based on hydrophilic polymers of intrinsic microporosity (PIMs) that enable fast ion transport and high molecular selectivity. The structural diversity of PIMs can be controlled by monomer choice, polymerization reaction and post-synthetic modification, which further optimize these membranes for RFBs.

Two types of hydrophilic PIM have been developed and tested: PIMs derived from Tröger’s base and dibenzodioxin-based PIMs with hydrophilic and ionizable amidoxime groups.

The authors consider their approach innovative because of

  1. The application of PIMs to obtain rigid and contorted polymer chains resulting in sub-nanometre-sized cavities in microporous membranes;
  2. The introduction of hydrophilic functional groups forming interconnected water channels to optimize hydrophilicity and ion conductivity;
  3. The processing of the solution to produce a membrane of submicrometre thickness. This further reduces ion transport resistance and membrane production costs.

Ionic conductivity has been evaluated by the real-time experimental observations of water and ion uptake. The results suggest that water adsorption in the confined three-dimensional interconnected micropores leads to the formation of water-facilitated ionic channels, enabling fast transport of water and ions.

The selective ionic and molecular transport in PIM membranes was analyzed using concentration-driven dialysis diffusion tests. It was confirmed that new design of membranes effectively block large redox active molecules while enabling fast ion transport, which is crucial for the operation of organic RFBs.

In addition, long-term chemical stability, good electrochemical, thermal stability and good mechanical strength of the hydrophilic PIM membranes have been demonstrated.

Finally, it has been reported that the performance and stability tests of RFBs based on the new membranes, as well as of ion permeation rate and selectivity, are comparable to the performances based on a Nafion™ membranes as benchmark.

(Mima Varničić, 2020, photo: Wikipedia)

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High-performance biomass molecule for better Diesel fuel

In our previous blog posts we have discussed resource recovery from waste related to the wastewater treatment and showed improved and enforced regulations have a positive impact on water quality and public health. Now we show that clever catalytic processes can be used to extract valuable commodities from waste agricultural products.

Low-cost waste biomass can serves as renewable source to produce a sustainable alternative to fossil carbon resources in order to meet the need for the environmentally friendly energy. For example, the C2 and C4 ethers derived from carboxylic acids obtained from biomass are promising fuel candidates. It has been reported, that when using ethers biofuel parameters such as ignition quality and sooting have significantly improved compared to commercial petrodiesel (>86% yield sooting index reduction). Ignition quality (cetane number) was improved by more than 56%.

The scientists from National Renewable Energy Laboratory, together with their colleagues from Yale University, Argonne National Laboratory, and Oak Ridge National Laboratory are working on a joint project with the goal of co-optimization of fuels and engines. The research focuses on improving fuel economy and vehicle performance while at the same time reducing emissions through identification of blendstock derived from biomass.

In their recent article, published in the renown journal PNAS, a novel molecule, 4-butoxyheptane, has been isolated in a high-yielding catalytic process from lignocellulosic biomass. Due to its high oxygen content, this advantageous blendstock can improve the performance of diesel fuel by reducing the intrinsic sooting tendency of the fuel upon burning.

The research team has reported a “fuel-property-first” approach in order to accelerate the development process of producing suitable oxygenate diesel blendstocks.

This rational approach is based on following steps:

  1. Fuel Property Characterization – includes mapping and identification of accessible oxygenates products; predicting fuel properties of those products a priori by computationally screening
  2. Production process – development of the conversion pathway starting from biomass. Includes continuous, solvent-free synthesis process based on a metal/acid catalyst on a liter-scale production of the chosen compound
  3. Testing and analysis – with the goal to validate and compare fuel property measurements against predictions

Fuel properties of target oxygenates that have been investigated are related to the health- and safety- aspects such as flash point, biodegradation potential, and toxicity/water solubility, as well as market and environmental aspects such as ignition quality (cetane number), viscosity, lower heating value and sooting potential reduction with oxygenated blendstocks. As a result, 4-butoxyheptane, looked as the most promising molecule to blend with and improve traditional diesel. It has been shown, that the fuel property measurements largely agreed with predictive estimations, validating accuracy of the a priori approach for blendstock selection.

The mixture at 20-30% blend of 4-butoxyheptane molecule into diesel fuel has been suggested as favorable. The improvement in autoignition quality as well as significant reduction of yield sooting index from 215 to 173 (20% reduction) demonstrates that the incorporation of this molecule could improve diesel emission properties without sacrificing performance. In terms of flammability, toxicity, and storage stability, the oxygenate fuel has been evaluated to be at low-risk.

Life-cycle analysis show that this mixture could be cost-competitive and have the potential in significant greenhouse gas reductions (by 50 to 271%) in comparison to petrodiesel.

As research is a perpetual process, more of it is necessary and should include testing of the bioblendstock in an actual engine and production of the biofuel in an integrated process directly from biomass.

(Mima Varničić, 2020, photo: Pixabay)

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Global wastewater resources estimated

In our last post on water quality in China, we pointed out a study that shows how improved wastewater treatment has a positive effect on the environment and ultimately on public health. However, wastewater treatment requires sophisticated and costly infrastructure. This is not available everywhere. However, extracting resources from wastewater can offset some of the costs incurred by plant construction and operation. The question is how much of a resource is wastewater.

A recent study published in the journal Natural Resources Forum tries to answer that question. It is the first to estimate how much wastewater all cities on Earth produce each year. The amount is enormous, as the authors say. There are currently 380 billion cubic meters of wastewater per year worldwide. The authors omitted only 5% of urban areas by population.

The most important resources in wastewater are energy, nutrients like nitrogen, potassium and phosphorus, and the water itself. In municipal wastewater treatment plants they come from human excretions. In industry and agriculture they are remnants of the production process. The team calculated how much of the nutrient resources in the municipal wastewater is likely to end up in the global wastewater stream. The researchers come to a total number of 26 million tons per year. That is almost eighty times the weight of the Empire State Building in New York.

If one would recover the entire nitrogen, phosphorus and potassium load, one could theoretically cover 13% of the global fertilizer requirement. The team assumed that the wastewater volume will likely continue to increase, because the world’s population, urbanization and living standards are also increasing. They further estimate that in 2050 there will be almost 50% more wastewater than in 2015. It will be necessary to treat as much as possible and to make greater use of the nutrients in that wastewater! As we pointed out in our previous post, wastewater is more and more causing environmental and public health problems.

There is also energy in wastewater. Wastewater treatment plants industrialized countries have been using them in the form of biogas for a long time. Most wastewater treatment plants ferment sewage sludge in large anaerobic digesters and use them to produce methane. As a result, some plants are now energy self-sufficient.

The authors calculated the energy potential that lies hidden in the wastewater of all cities worldwide. In principle, the energy is sufficient to supply 500 to 600 million average consumers with electricity. The only problems are: wastewater treatment and energy technology are expensive, and therefore hardly used in non-industrialized countries. According to the scientists, this will change. Occasionally, this is already happening.

Singapore is a prominent example. Wastewater is treated there so intensively that it is fed back into the normal water network. In Jordan, the wastewater from the cities of Amman and Zerqa goes to the municipal wastewater treatment plant by gravitation. There, small turbines are installed in the canals, which have been supplying energy ever since their construction. Such projects send out a signals that resource recovery is possible and make wastewater treatment more efficient and less costly.

The Frontis technology is based on microbial electrolysis which combines many of the steps in wastewater treatment plants in one single reactor, recovering nutrients as well as energy.

(Photo: Wikipedia)

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China has improved inland surface water quality

During the last decades, China has achieved rapid development in technology and economics, however at a huge environmental cost. The deterioration of inland surface water quality is considered one of the most serious environmental threats to ecosystem and ultimately public health.

Since 2001, China made major efforts to tighten the application of environmental rules in order to stop water pollution emitted by cities, farm and industry. According to the government’s “10th National Five-Year Plan”, large investments were made for pollution control and wastewater discharge regulation systems.

Small research studies showed that with this campaign, Chinese’s lakes and rivers got cleaner. Since then water quality has improved significantly − however, other parts of country still have problems with polluted water.

Now, a team of researchers of the at the Chinese Academy of Sciences in Beijing, has published one of the most comprehensive national investigation of China’s surface water quality in the renown journal Science. The researchers investigated all regions of the country to learn how surface water responds to multiple driving forces over time and space. Their report covers the assessment of water quality by means of three parameters: dissolved oxygen level (DO), chemical oxygen demand (COD) and ammonium nitrogen (N) in inland surface waters. They performed monthly site-level measurements at major Chinese rivers and lakes across the country between 2003 and 2017.

Due to regional variations in China’s inland water quality as well as the dynamics in multiple anthropogenic pollution sources, such studies are crucially important to identify the necessary regulation measures and water quality improvement policies adapted to ecosystem sustainability at all diverse country regions.

The results show that during the past 15 years, annual mean pollution concentration has declined across the country at significant linear rates or was maintained at acceptable levels. Consequently, the annual percentage of water quality have increased by 1.77% for COD, 1.83% for N and 1.45% for DO per year. While China has not yet implemented environmental water standards, the study shows that China’s water quality is improving nonetheless.

The best news is that the notoriously high pollution levels have declined as cities and industry have worked to clean up and reduce their discharges. According to the authors, the most visible alleviation was noticed in northern China, while in the western region of the country water quality remained at their low pollution level throughout the observation period. The reason is likely that pollution is caused by human activity, of which there is less in those parts of the country.

Despite large efforts toward decreased pollution discharges, urban areas are still considered as the major pollution centers. These areas face additional pressure due to the constant migration and fast urbanization of the rural regions. Especially in northern China, with high-density human activity and exploding urbanization, achieving and maintaining a clean environment is a permanent struggle.

To further reduce pollution and improve water quality, the authors recommend that future activities focus on water management systems and the water pollution control. For both, the central government issued guidelines to control and improve water use and pollution discharge at regional and national levels for 2020 and 2030.

At Frontis Energy, we certainly support activities in China that help improving the countries water quality and public health. The Frontis technology gives its user an incentive to to clean wastewater before discharge by extracting its energy. Our patent pending solutions are based on microbial electrolysis which helps to extract energy from wastewater and apply in particular to China.

Mima Varničić, 2020

(Photo: Gil Dekel / Pixabay)

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Future challenges for wind energy

Many people believe that there is no need for improvement because wind turbines have been working for decades. Wind energy has the potential to be one of the world’s cheapest energy sources. In a recent article in the Science magazine, major challenges have been addressed to drive innovation in wind energy. Essentially three directions were identified:

  1. The better use of wind currents
  2. Structural and system dynamics of wind turbines
  3. Grid reliability of wind power

In order to make better use of wind currents, the air mass dynamics and its interactions with land and turbines must be understood. Our knowledge of wind currents in complex terrain and under different atmospheric conditions is very limited. We have to model these conditions more precisely so that the operation of large wind turbines becomes more productive and cheaper.

To gain more energy, wind turbines have grown in size. For example, when wind turbines share larger size areas with other wind turbines, the flow changes increasingly.

As the height of wind turbines increases, we need to understand the dynamics of the wind at these heights. The use of simplified physical models has allowed wind turbines to be installed and their performance to be predicted across a variety of terrain types. The next challenge is to model these different conditions so that wind turbines are optimized in order to be inexpensive and controllable, and installed in the right place.

The second essential direction is better understanding and research of the wind turbine structure and system dynamics . Today, wind turbines are the largest flexible, rotating machines in the world. The bucket lengths routinely exceed 80 meters. Their towers protrude well over 100 meters. To illustrate this, three Airbus A380s can fit in the area of ​​one wind turbine. In order to work under increasing structural loads, these systems are getting bigger and heavier which requires new materials and manufacturing processes. This is necessary due to the fact that scalability, transport, structural integrity and recycling of the used materials reach their limits.

In addition, the interface between turbine and atmospheric dynamics raises several important research questions. Many simplified assumptions on which previous wind turbines are based, no longer apply. The challenge is not only to understand the atmosphere, but also to find out which factors are decisive for the efficiency of power generation as well as for the structural security.

Our current power grid as third essential direction is not designed for the operation of large additional wind resources. Therefore, the gird will need has to be fundamentally different then as today. A high increase in variable wind and solar power is expected. In order to maintain functional, efficient and reliable network, these power generators must be predictable and controllable. Renewable electricity generators must also be able to provide not only electricity but also stabilizing grid services. The path to the future requires integrated systems research at the interfaces between atmospheric physics, wind turbine dynamics, plant control and network operation. This also includes new energy storage solutions such as power-to-gas.

Wind turbines and their electricity storage can provide important network services such as frequency control, ramp control and voltage regulation. Innovative control could use the properties of wind turbines to optimize the energy production of the system and at the same time provide these essential services. For example, modern data processing technologies can deliver large amounts of data for sensors, which can be then applied to the entire system. This can improve energy recording, which in return can significantly reduce operating costs. The path to realize these demands requires extensive research at the interfaces of atmospheric flow modeling, individual turbine dynamics and wind turbine control with the operation of larger electrical systems.

Advances in science are essential to drive innovation, cut costs and achieve smooth integration into the power grid. In addition, environmental factors must also be taken into account when expanding wind energy. In order to be successful, the expansion of wind energy use must be done responsibly in order to minimize the destruction of the landscape. Investments in science and interdisciplinary research in these areas will certainly help to find acceptable solutions for everyone involved.

Such projects include studies that characterize and understand the effects of the wind on wildlife. Scientific research, which enables innovations and the development of inexpensive technologies to investigate the effects of wild animals on wind turbines on the land and off the coast, is currently being intensively pursued. To do this, it must be understood how wind energy can be placed in such a way that the local effects are minimized and at the same time there is an economic benefit for the affected communities.

These major challenges in wind research complement each other. The characterization of the operating zone of wind turbines in the atmosphere will be of crucial importance for the development of the next generation of even larger, more economical wind turbines. Understanding both, the dynamic control of the plants and the prediction of the type of atmospheric inflow enable better control.

As an innovative company, Frontis Energy supports the transition to CO2-neutral energy generation.

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Turbocharged lithium batteries at high temperatures

One of the biggest hurdles for the electrification of road traffic is the long charging time for lithium batteries in electric vehicles. A recent research report has now shown that charging time can be reduced to 10 minutes while the battery is being heated.

A lithium battery can power a 320-kilometer trip after only 10 minutes of charging − provided that its temperature is higher than 60 °C while charging.

Lithium batteries that use lithium ions to generate electricity are slowly charged at room temperature. It takes more than three hours to charge, as opposed to three minutes to tank a car.

A critical barrier to rapid charging is the lithium plating, which normally occurs at high charging rates and drastically affects the life and safety of the batteries. Researchers at Pennsylvania State University in University Park are introducing an asymmetrical temperature modulation method that charges a lithium battery at an elevated temperature of 60 °C.

High-speed charging typically encourages lithium to coat one of the battery electrodes (lithium plating). This will block the flow of energy and eventually make the battery unusable. To prevent lithium deposits on the anodes, the researchers limited the exposure time at 60 °C to only ~10 minutes per cycle.

The researchers used industrially available materials and minimized the capacity loss at 500 cycles to 20%. A battery charged at room temperature could only be charged quickly for 60 cycles before its electrode was plated.

The asymmetrical temperature between charging and discharging opens up a new way to improve the ion transport during charging and at the same time achieve a long service life.

For many decades it was generally believed that lithium batteries should not be operated at high temperatures due to accelerated material degradation. Contrary to this conventional wisdom, the researchers introduced a rapid charging process that charges a cell at 60 °C and discharges the cell at a cool temperature. In addition, charging at 60 °C reduces the battery cooling requirement by more than 12 times.

In battery applications, the discharge profiles depend on the end user, while the charging protocol is determined by the manufacturer and can therefore be specially designed and controlled. The quick-charging process presented here opens up a new way of designing electrochemical energy systems that can achieve high performance and a long service life at the same time.

At Frontis Energy we also think that the new simple charging process is a promising method. We are looking forward to the market launch of this new rapid charging method.

(Photo: iStock)

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Bioelectrically engineered fuel produced by yeasts

Yeasts such as Saccharomyces cerevisiae are, as the name suggests, used for large scale production of beer and other alcoholic beverages. Their high salt and ethanol tolerance not only makes them useful for the production of beverages, but also suitable for the production of combustion fuels at high alcohol concentrations. Besides ethanol, long-chain fusel alcohols are of high interest for biofuel production as well. Bioethanol is already mixed with gasoline and thus improves the CO2 balance of internal combustion engines. This liquid biofuel is made from either starch or lignocellulose. The production and use of bioethanol supports local economies, reduces CO2 emissions and promotes self-sufficiency. The latter is especially important for resource-depleted landlocked countries.

In order to efficiently produce ethanol and other alcohols from lignocellulose hydrolysates, yeasts must use both glucose and pentoses such as xylose and arabinose. This is because biomass is rich in both lignocellulose and thus glucose and xylose. However, this is also the main disadvantage of using Saccharomyces cerevisiae because it does not ferment xylose. Consequently, the identification of another yeast strains capable of fermenting both these sugars could solve the problem. Highly efficient yeasts can be grown in co-cultures with other yeasts capable of lignocellulose fermentation for ethanol production. Such a yeast is, for example, Wickerhamomyces anomalous.

To further improve ethanol production, bioelectric fermentation technology supporting traditional fermentation can be used. The microbial metabolism can thus be controlled electrochemically. There are many benefits of this technology. The fermentation process becomes more selective due to the application of an electrochemical potential. This, in turn, increases the efficiency of sugar utilization. In addition, the use of additives to control the redox equilibrium and the pH is minimized. Ultimately cell growth can be stimulated, further increasing alcohol production.

Such bioelectric reactors are galvanic cells. The electrodes used in such a bioelectric reactor may act as electron acceptors (anodes) or source (cathodes). Such electrochemical changes affect the metabolism and cell regulation as well as the interactions between the yeasts used. Now, a research group from Nepal (a resource-depleted landlocked country) has used new yeast strains of Saccharomyces cerevisiae and Wickerhamomyces anomalous in a bioelectric fermenter to improve ethanol production from biomass. The results were published in the journal Frontiers in Energy Research.

For their study, the researchers chose Saccharomyces cerevisiae and Wickerhamomyces anomalus as both are good ethanol producers. The latter is to be able to convert xylose to ethanol. After the researchers applied a voltage to the bioelectrical system, ethanol production doubled. Both yeasts formed a biofilm on the electrodes, making the system ideal for use as a flow-through system because the microorganisms are not washed out.

Saccharomyces cerevisiae cells in a brightfield microscopic image of 600-fold magnification (Foto: Amanda Luraschi)

The researchers speculated that the increased ethanol production was due to the better conversion of pyruvate to ethanol − the yeast’s central metabolic mechanism. The researchers attributed this to accelerated redox reactions at the anode and cathode. The applied external voltage polarized the ions present in the cytosol, thus facilitating the electron transfer from the cathode. This and the accelerated glucose oxidation probably led to increased ethanol production.

Normally, pyruvate is converted into ethanol in fermentation yeast. External voltage input can control the kinetics of glucose metabolism in Saccharomyces cerevisiae under both aerobic and anaerobic conditions. Intracellular and transplasmembrane electron transfer systems play an important role in electron transport across the cell membrane. The electron transfer system consists of cytochromes and various redox enzymes, which confer redox activity to the membrane at certain sites.

The authors also found that an increased salt concentration improved conductivity and therefore ethanol production. The increased ethanol production from lignocellulosic biomass may have been also be due to the presence of various natural compounds that promoted yeast growth. When the cellulose acetate membrane was replaced by a Nafion™ membrane, ethanol production also increased. This was perhaps due to improved transport of xylose through the Nafion™ membrane as well as the decrease of the internal resistance. A further increase of ethanol production was observed when the bioelectrical reactor was operated with fine platinum particles coated on the platinum anode and neutral red deposited on the graphite cathode.

Several yeast cultures from left to right: Saccharomyces cerevisiae, Candida utilis, Aureobasidium pullulans, Trichosporum cutaneum, Saccharomycopsis capsularis, Saccharomycopsis lipolytica, Hanseniaspora guilliermondii, Hansenula capsulata, Saccharomyces carlsbergensis, Saccharomyces rouxii, Rhodotorula rubra, Phaffia rhodozyba, Cryptococcus laurentii, Metschnikowia pulcherrima, Rhodotorula pallida

At Frontis Energy, we think that the present study is promising. However, long-chain fusel alcohols should be considered in the future as they are less volatile and better compatible with current internal combustion engines. These can also be easily converted into the corresponding long-chain hydrocarbons.