Blog

Perovskite oxides have for a number of years promised to be a breakthrough material in many fields in industrial chemistry. They have the potential to be applied in improved solar thermochemical fuel production, to create non-volatile memory chips for computers, and they also hold the key to extending the life of fuel cell electrodes.

However, this class of oxide materials has always had the drawback of being relatively unstable over time, and it is this instability that is preventing its further development.

Now however, a breakthrough has been made by a team at MiT which promises to drastically improve their performance and, as the MiT news website reports, will make them “…promising candidates to serve as electrodes in energy-conversion devices such as fuel cells and electrolyzers.”

The MiT team is already well-known in the industry for its 2013 work on improving fuel cells via a ‘superlattice’ that increased oxygen reactions, as reported here, and now seem to have solved another fuel cell challenge.

When discussing her team’s discovery, Bilge Yildiz, Associate Professor of Materials Science and Engineering at MiT, explained how surfaces exposed to water or gas at high temperatures (such as those inside fuel cells and electrolyzers) “suffer from degradation because of chemical segregation and phase separation. We, as well as others in the field, have discovered in the past several years that the surfaces of these perovskites get covered up by a strontium-oxide related layer, and this layer is insulating against oxygen reduction and oxygen evolution reactions, which are critical for the performance of fuel cells, electrolyzers, and thermochemical fuel production. This layer on the electrode surface is detrimental to the efficiency and durability of the device, causing the surface reactions to slow down by more than an order of magnitude.”

Publishing their results in Nature Communications, the team state that, “[reducing the concentration of positively charged oxygen vacancies on the surface] improves the oxygen surface exchange kinetics and stability significantly, albeit contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O₂ molecules.”

As the online journal Phys.org reports, “The team’s analysis shows that there is a sweet spot in the addition of more oxidizable elements to the surface, both in terms of the composition and the concentration. In these initial experiments, they tried several different elements to provide the protective effect. The improvement increases up to a certain concentration, and then adding more of the surface additives starts to make things worse again. So for any given material, there will be an optimum amount that should be added, they found. Using hafnium, the new treatment has been shown to reduce the rate of degradation, and increase by 30 times the rate of oxygen exchange reactions at the surface.”

However, the chemical market for hafnium is unlikely to change overnight, as, “the surface treatment amounts to no more than a single atomic layer over the bulk material.”

Instead, what is significant about the discovery is that it opens up the possibility for other developments with perovskite oxides that could dramatically change the way we use fuel cells.

As John Kilner, a professor of energy materials at Imperial College, London, said when commenting on the work, “The observations could be used to produce more robust fuel cells with lower degradation rates, which at the moment is a major target for solid oxide fuel cell developers.”

Whilst William Chueh, an Assistant Professor of Materials Science and Engineering at Stanford University, also saw the importance of the research, noting that, “In this work, Yildiz and co-workers identified a new way to substantially improve the stability of cobalt-based electrocatalysts simply by adding a small amount of dopants on the surface.”

If Yildiz and her team have really found a method to prevent the degradation of perovskite oxides by adding a simple atomic layer coating, then they will not just have changed the fuel cell industry, but may have opened the door to a whole range of improvements across numerous industries. But for now the key impact will most likely be in fuel cell technology. As Chueh makes clear when stating, “The most promising application of this work is to substantially improve the stability of solid-oxide fuel cells. This is the key issue that controls the cost, and limits the widespread adoption of this technology.”

Now that the issue of cost has been mostly resolved, the industry is wondering who will be first to make use of this breakthrough by bring product to market.

Photo credit: Felice Frankel

Mankind is using more and more rare earth minerals. As consumer society spreads to the developing world, demand for the minute quantities of irreplaceable metals and minerals that are used in the manufacture of so much of the modern world is growing daily. For example the growing use of Scandium for aerospace components, or the increased need for Lanthanum in electronic devices.

But now it seems that an industrial accident in North Carolina may have shown the way to a new source.

In February 2014 a break in a storm water pipe was discovered at Duke Energy’s retired coal fired power station at the small town of Eden in North Carolina. As the News Observer reported, despite the company’s efforts to stop the flow, as much as 80,000 tons of toxic coal ash went into the Dan River poisoning water supplies and causing untold damage to local wildlife.

A year later, Duke Energy (America’s largest energy producer) admitted that some seepage was still occurring, including from other sites, and the flow of coal ash into the river had not entirely been stopped.

As a result of the spill (the third largest of its kind in US history) Duke Energy was taken to court, and as CBS news reported, “…pleaded guilty to nine violations of the federal Clean Water Act and will pay $102 million in fines and restitution.” The report continues by stating that, “Duke was also sentenced to five years’ probation.” And so, “the company will be monitored for compliance.”

Naturally the case attracted huge attention from mainstream media, environmental lobbyists and the energy industry. But the scientific community was also brought in, by all parties, to investigate the full impact of the spill.

One such study was conducted by the highly regarded Gillings School of Public Health, and was co-funded by “state and federal regulatory agencies to help answer important questions about the type and amounts of toxic chemicals present in the coal ash, enabling regulators to better assess potential risks to communities along the river.”

As the lead researcher Dr. Damian Shea, Professor at the Department of Biological Sciences at North Carolina State University noted, ““There are a number of potentially hazardous chemicals contained in coal ash, primarily toxic metals such as arsenic and selenium. Cancer-causing chemicals called polycyclic aromatic hydrocarbons, or PAHs, may also be present at lower levels.”

But a further study conducted at the Nicholas School of the Environment at Duke University began to find that large amounts of rare earth minerals (or rare earth elements; REE) were also present. They compared deposits from all over America and found that coal ash from the Appalachian Mountains had the highest concentrations.

Furthermore, the report noted that the REE content was often higher in the coal ash that in standard sourcing ores, stating, “The fraction of critical REEs (Nd, Eu, Tb, Dy, Y, and Er) in the fly ashes was 34–38% of the total and considerably higher than in conventional ores (typically less than 15%).”

However, the question remains as to whether or not the minerals are recoverable, as the report concludes by saying, “Overall, this study shows that coal fly ash production could provide a substantial domestic supply of REEs, but the feasibility of recovery depends on the development of extraction technologies that could be tailored to the major mineral content and origins of the feed coal for the ash.”

For this reason, the research continued by focusing on the feasibilty of recovery, as research team member Prof. Heileen Hsu-Kim states, “For any future venture to begin an extraction program, the recovery method will need to be tailored to the specific chemistry of the coal ash being used.”

One extraction method, as the journal Phys.org reports, was that, “The Duke researchers tried ‘roasting’ the coal ash with an alkali agent before dissolving it with nitric acid. [And found that] Even though the process hadn’t been optimized for recovery purposes, the tests showed a marked improvement in extraction efficiency.”

Whilst the research has yet to draw a full conclusion on the practicality of REE recovery, it is already known that in China, Lithium is being extracted from coal (you can read more about that here), so the idea of extracting from coal ash is far from science fiction.

Given the planets need for rare earth minerals and the energy industry’s desire to make use of what is currently a toxic waste, it seems only a matter of time before an economic method of extraction is developed.

As Hsu-Kim notes, “The Department of Energy is investing $20 million into research on extraction technologies for coal wastes, as there is literally billions of dollars’ worth of rare earth elements contained in our nation’s coal ash. [For now] The reagents we used are probably too expensive to use on an industrial scale, but there are many similar chemicals. The trick will be exploring our options and developing technologies to drive the costs down. That way we can tap into this vast resource that is currently just sitting around in disposal ponds.”

When and how the extraction method will be found remains to be seen, but it is sure to have a major impact on chemical trading markets. Turning waste into a much needed resource looks like a win/win situation for everyone. Or will some rare earth mineral traders lose out?

Photo Credit 3: Heileen Hsu-Kim, Duke University.

Photo Credit 2: Heileen Hsu-Kim, Duke University. The Roxboro Steam Station, a four-unit, 2,422-megawatt coal-fired Duke Energy plant in Semora, N.C., is one of the largest power plants in the United States. It began operation in 1966, with additions in 1973 and 1980.

Photo Credit 1: http://www.southeastcoalash.org/

Throughout history, man has marveled at the beauty of nature’s colours, including those in beetles, butterfly wings and opals. Until now, creating manmade substances with such refractive colour intensity has not been possible. This is because these magnificent colours are not pigment based, but instead reflect light brilliantly through the systematic ordering of their microstructures.

Recently though, a team led by the University of Cambridge invented a method called Bend-Induced-Oscillatory-Shearing (BIOS), that makes it possible to manufacture “hundreds of metres of these materials, known as ‘polymer opals’ (PO), on a roll-to-roll process.”

“Finding a way to coax objects a billionth of a metre across into perfect formation over kilometre scales is a miracle,” said Professor Jeremy Baumberg, the paper’s senior author. “But spheres are only the first step, as it should be applicable to more complex architectures on tiny scales.”

As the online journal Phys.org reports, “In order to make polymer opals in large quantities, the team first needed to understand their internal structure so that it could be replicated. Using a variety of techniques, including electron microscopy, x-ray scattering, rheology and optical spectroscopy, the researchers were able to see the three-dimensional position of the spheres within the material, measure how the spheres slide past each other, and how the colours change.”

The research team, which has published its results in the journal Nature Communications, is optimistic about the potential for this discovery, stating that, “In addition to a clear demonstration of large-scale assembly using this BIOS method, our work provides the first experimental determination of the detailed PO structure, and new physical insights into the microscopic mechanisms behind crystallization of this rheologically unique system. The general principles underpinning BIOS can thus be applied in many ways including ordering of widely varying nanoparticle sizes, and even mixtures with polydispersity exceeding 20% which are normally impossible to order. For instance, anisotropic nanoparticles should have even further improved degrees of ordering, delivering a range of nematic phases in flexible films. This may be particularly interesting in the case of cellulose nanorods, which are known to produce intense structural colours but take days to form chiral nematic phases. The shearing of nanoparticle systems in this fashion also acts to segregate nano components into stacks of ordered two-dimensional layers, opening up many new possible architectures. ”

Looking to the future, the University’s commercial arm has received 100’s of enquiries from chemical companies interested in the new material, such that a spin-out company called Phomera Technologies, has been founded.

As well as studying ways to fully industrialize the process or in how to amend production to meet specific commercial needs, the company is hoping to monetize the venture further with a view to using the product in heat reflective coatings for buildings, smart clothing and footwear, or for packaging applications and banknote security features.

Beyond the money, much of the scientific community is simply happy to have met a challenge set by nature. As PhD student Qibin Zhao, the paper’s lead author said, “It’s wonderful to finally understand the secrets of these attractive films.”

Photo Credit: Nick Saffell/University of Cambridge

Photo Credit: Mike McDowell/birdigiscoper.cz