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Problem: How do we power the economy with solar power at night?

Solution: Store the energy from the day in large batteries.

Problem: Modern lithium-ion batteries are far too expensive to store power for the grid.

Solution: Integrate the battery into the solar cell.

At least, that is what is being proposed in a recently published study by Prof Song Jin of the University of Wisconsin-Madison. For together with his research team, he has created a device that skips the step of making electricity, and instead stores the energy directly in the battery’s electrolyte.

This has been possible as the researchers used a ‘redox flow battery’. RFB’s are different because, as the online journal Science Daily explains, “Unlike lithium-ion batteries, which store energy in solid electrodes, the RFB stores chemical energy in liquid electrolyte.” By making this change, the team has been able to create a, “… single device that converts light energy into chemical energy by directly charging the liquid electrolyte. In the new device, standard silicon solar cells are mounted on the reaction chamber and energy converted by the cell immediately charges the water-based electrolyte, which is pumped out to a storage tank.”

The research team also claim that discharging the battery is very simple, with Prof Jin stating that, “We just connect a load to a different set of electrodes, pass the charged electrolyte through the device and the electricity flows out.”

Whilst the idea of attaching a redox flow battery to a solar cell is not new, indeed models are already available on the market, what is different here is, as Prof Jin explains, “We now have one device that harvests sunlight to liberate electrical charges and directly changes the oxidation-reduction state of the electrolyte on the surface of the cells. [By doing this] We are using a single device to convert solar energy and charge a battery. It’s essentially a solar battery, and we can size the RFB storage tank to store all the energy generated by the solar cells.”

The results have been published in the scientific journal Angewandte Chemie International Edition, where the researchers give detail to their discovery describing it as, “An integrated photoelectrochemical solar energy conversion and electrochemical storage device is developed by integrating regenerative silicon solar cells and 9,10-anthraquinone-2,7-disulfonic acid (AQDS)/1,2-benzoquinone-3,5-disulfonic acid (BQDS) RFBs. The device can be directly charged by solar light without external bias, and discharged like normal RFBs with an energy storage density of 1.15 Wh L⁻¹ and a solar-to-output electricity efficiency (SOEE) of 1.7 % over many cycles. The concept exploits a previously undeveloped design connecting two major energy technologies and promises a general approach for storing solar energy electrochemically with high theoretical storage capacity and efficiency.”

Whilst the new device has yet to be scaled up to an industrial scale, it theoretically seems a very possible option. As Prof Jin states that, “”The RFB is relatively cheap and you can build a device with as much storage as you need, which is why it is the most promising approach for grid-level electricity storage.” Jin continues to describe the devices many advantages, saying, “The solar cells directly charge the electrolyte, and so we’re doing two things at once, which makes for simplicity, cost reduction and potentially higher efficiency.”

Better still, the model used in the study contained no expensive rare metals, instead the tank that makes up the liquid electrolyte is filled with organic molecules. However, the team is continuing to search for, “electrolytes with larger voltage differential, which currently limits energy storage capacity.”

This discovery is very promising for the solar energy industry, as not only does open the door to improved solar cell efficiency, but also increases solar energy’s adaptability for use on the grid. Furthermore, as solar energy becomes a more widely used form of power generation, then it is possible that this device will become the standard battery for all future solar panel designs.

Photo credit: David Tenenbaum/UW-Madison

Coffee drinkers are causing a problem. What to do with the millions of tons of used coffee grounds that are created every year?

To date scientists have found numerous ways to make use of the smelly, damp, brown waste, discovering that they can be used as a fertiliser feedstock, that they can be mixed into animal feed, or can be used as an energy source for biofuels.

Recently adding to this list, chemists found out that in a powder form they could be used as a way to remove heavy metal ions (such as lead or mercury) from water.

Whilst this last method has a very practical goal in making water safer for human consumption, it also had an impractical side, in that an additional process was needed to separate the powder from the purified water. That problem has also now been solved, as a team from the Italian Institute of Technology in Genoa, has discovered a way to use the coffee grounds in a filter that greatly simplifies the process.

The researchers have published their results in the journal ACS Sustainable Chemistry & Engineering, where they describe the filter as a, “…bioelastomeric foam composed of 60 wt % of spent coffee powder and 40 wt % of silicone elastomer [that] uses the sugar leaching technique.” The findings continue to explain how the foam was, “…successful in the removal of Pb²⁺ and Hg²⁺ ions from water. [Whilst] The capability of the bioelastomeric foams to interact with Pb²⁺ and Hg²⁺ is not affected by the presence of other metal ions in water as tests in real wastewater demonstrate. [Furthermore] The fabricated foams can be used for the continuous filtration and removal of metal ions from water, demonstrating their versatility, in contrast to the sole coffee powder utilized so far, opening the way for the reutilization and valorization of this particular waste.”

The foam filter made with used coffee grounds removes heavy metal ions like lead and mercury from contaminated water.

As the online journal Science Daily reports, the results are very promising, as it states that, “In still water, the foam removed up to 99 percent of lead and mercury ions from water over 30 hours. [Whilst] In a more practical test in which lead-contaminated water flowed through the foam, it scrubbed the water of up to 67 percent of the lead ions.”

But the journal continues by highlighting the most important part of the filter system, when it states that, “Because the coffee is immobilized, it is easy to handle and discard after use without any additional steps.”

Whilst the discovery has yet to undergo a full peer review, and so is some way off being applied industrially, the idea that coffee grounds are not simply for landfill may take away some of the bitter taste from your next cup. In fact, it is great to know that in the future, drinking coffee will improve your drinking water.

In recent weeks, actually in recent decades, the biofuel industry has come under pressure to prove that it is economically viable. Headlines such as “Biofuels ‘Irrational and worse than fossil fuels’” (BBC April 2013) and “Greens reconsider biofuels mandate” (Bloomberg July 2016) have come in a rush of negative stories as the biofuel industry strives to prove its value.

But a new wave of thinking is to turn the bulk waste of plant matter, lignin, (from the stalks, stems and dry, woody pulp from many crops) into a useful chemical feedstock.

Up until now the only way to get any value from this waste product was to burn it for heat or electricity production, but now a research team from Sandia National Laboratories has found a possible route to breaking open lignin so that it can be utilised for its chemical properties.

The study began as a way to make biofuels a more realistic solution to replace fossil fuels, but has since turned into a potential route for cheaper chemicals production. The researchers started by examining the biofuels business model, and realised that in many cases it simply wasn’t viable. Growing corn to produce ethanol is a highly technical and expensive process that uses a lot of land and requires months of growing to produce a product that, for the most part, will simply be burned.

The team then looked at the fossil fuel industry, and saw many similarities in its structure to the biofuel industry. Crude oil production is a highly technical and expensive process given that is extracted from miles underground (or even under oceans), it is expensive to refine and then often needs to be shipped (across continents) to its market, simply to be burned. The business model only really becomes effective once the specialty chemicals industry has extracted the useful feedstock from crude.

As the study’s principal investigator Seema Singh outlined, when she said, “Gasoline is a low-value, high-volume product. This is balanced by the high-value chemicals derived from about 6-10 percent of every barrel of oil.” Her team realised, that what the biofuels industry needs is a way to add value to its business model, and turning crop waste products into a chemical feedstock would definitely achieve that.

The discovery began with chemists wondering how to access the chemical properties of lignin, and as often happens, they found inspiration from nature. As Singh says, “We know that over a long period of time fungus and bacteria do eventually break down lignin. If we can understand this process, we can use what nature already knows for biofuel and chemical production from lignin.”

As the online journal Science Daily reports, “Since bacteria are easier to engineer for industrial production of desired chemicals, the researchers focused on bacteria. The best candidate was Sphingobium, or SYK-6, found in the lignin-rich waste stream from wood pulp production.

SYK-6 was extremely intriguing because it only feeds on lignin. Microbes generally live off sugar, which is much easier to break down and extract energy from. Imagine a choice between eating a corn kernel or a corn husk.”

Using a method called metabolic flux analysis, the team was able to follow the route of carbon from the feedstock, and find out how SYK-6 metabolises lignin. In doing so, “The Sandia team’s paper reports the method used to decipher the metabolic pathway of SYK-6.”

The researchers published their results in the scientific journal Proceedings of the National Academy of Science, where they explained the rationale behind their study as follows;

“In this study we combined the unique approaches of both chemical engineering and biology to gain a deeper understanding of the metabolism of a soil bacterium, Sphingobium sp. SYK-6, that enables it to survive on lignin-derived monomers and oligomers. Understanding the central metabolism of SYK-6 will enable researchers to redesign the metabolic pathways of Sphingobium sp. SYK-6 more effectively to provide a renewable route for the production of products currently sourced from petrochemicals.”

Sandia National Laboratories researchers Arul Varman, left, and Seema Singh.

However, this discovery is an unfinished story, as Patti Koning makes clear when she explains on the Sandia National Laboratory website how Singh and her team are already working on ways to genetically engineer SYK-6, in order to “…stop its metabolic process at a point when platform chemicals can be extracted from the lignin.” She also points out that, “Another path would be to splice the genes responsible for the important desired metabolic process in SYK-6 onto a strong industrial host like E. coli to create a chassis for desired fuels and chemicals. Platform chemicals, which can be used to derive valuable chemicals like muconic acid and adipic acid, are the goal.”

Ultimately the discovery opens a path that may turn plant waste into a chemical feedstock that could produce high-value products.

“Lignin is an untapped resource,” said Singh. “But as a basis for high-value chemicals, it is of immense value. Those high-value chemicals can be the basis for polyurethane, nylon, and other bioplastics. Decoding SYK-6 metabolic pathway is providing a roadmap for lignin valorization.”

While the science for industrial chemical production from lignin may still be a long way off, it is an amazing breakthrough to have found a way to turn waste plant matter into chemical feedstock. Given the impact that the chemical industry has on modern lives, how different would the world be if high-value chemicals were produced from the wheat stalks grown in Africa, or the corn husks of Peru?

Photo credit: Pacific Northwest National Laboratory

Photo credit: Dino Vournas

Main credit: Mike Belliveau