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Energy storage is ripe for reinvention

U of T engineers are at the forefront of that innovation

U of T engineers envision replacing these capacitors with more efficient ultracapacitors. (BigStock photo)

Pity the poor batteries, solar cells and capacitors. They’ve been huddled on the sidelines watching memory prices plummet, computing processing power skyrocket and computers shrink from the size of filing cabinets to the scale of nail files. Blame chemistry.

By and large, batteries, fuel cells, capacitors and solar panels have resisted the lure of Moore’s law, economies of scale and miniaturization. They’ve improved, sure, but not on the logarithmic scales of memory and processing power. Chemistry has constrained them to a more staid, linear kind of progress.

That’s because, in the end, energy storage devices are all dependent on simple electrochemical bonds. And, there’s only so much storage, energy and oomph you can coax out of anodes; cathodes; often leaky electrolytes and a delicate dosey doe of electrons.

“Battery chemistry, if you look at the lead acid battery, for example, hasn’t changed in 100 years. There’s a thermodynamic limit you just can’t go beyond,” explains materials science amd engineering associate professor Keryn Lian. “However, tremendous progress has been made on batteries, just like so much has been done to improve silicon.”

So, refining energy storage – that’s tricky.

Gnarly problems and engineering enigmas

And, try to quench the thirst of juice-hoarding gizmos while at the same time making sure the energy devices they use are produced, function and retire in sustainable ways? That’s a gnarly, complex problem that would vex Thomas Edison, Richard Feynman or Nikola Tesla on their best days.

But, it turns out that those are just the kind of enigmas that U of T Engineering researchers love to dive into, headlong.

Lian, for example, has plunged into the world of capacitors, more specifically, ultracapacitors – the new superheroes of the energy storage world.

Let’s step back. A capacitor, like a battery, stores energy. But a battery is like a big water tank with a small faucet – only a limited amount of energy can flow out. Capacitors, on the other hand, can store energy and send gushers of juice out in a sudden burst, sometimes dumping their charges in just milliseconds. To use another analogy, they’re sprinters, not marathoners.

But ultracapacitors can store more energy than regular capacitors: they’re like a capacitor-battery hybrid. Part of the ultracapacitor’s superpowers come from the surface area of the electrodes inside them.

It turns out, the more surface area electrodes have, the greater their charge capacity. Lian and her team are working with chemically modified carbon nanotubes, which have dramatically greater surface area than in regular capacitors. Ultracapacitors with these scads of micropores not only have greater storage capacity, they discharge much faster than regular batteries, and their charge cycle doesn’t deteriorate over time. Lian’s team is also experimenting with super-thin, non-leaky polymer electrolytes, which give ultracapacitor longer life cycles and greater energy efficiency.

Printing power

But capacitors, even ultracapacitors, aren’t solo players, especially when it comes to delivering sustainable, practical energy. Often they’re teamed up with batteries or solar cells, and that’s where chemical engineering professor Tim Bender comes in.

Bender and his team of researchers are developing inexpensive, organic solar cells with super vision. Most solar cells can convert only a very narrow slice of the light spectrum into electricity, from about near- ultraviolet up to what we see as green (about 800 nanometres). That’s as good as non-organics can get.

“In order to get silicon to absorb beyond 800 nanometres, you basically have to break the laws of science,” explains Bender. “It’s a fundamental materials limitation.”

However, Bender’s panels, which are made from organic crystals, suck in light up to 1,600 nanometres, and beyond. That’s because they’re “printed” from separate laminates of light-sensitive materials that combine to cover the waterfront, so to speak. Imagine them like the yellow, magenta and cyan inks in your inkjet printer combining to make black, with black here representing how little light escapes from Bender’s panels.

The design means that the same size of panel can generate far more electricity than standard solar cells and do it using recyclable, sustainable and organic materials. And do it more cheaply. “The silicon used in traditional solar cells is the same material that Intel, AMD and Apple compete for,” explained Bender.

That means market demand can push the price of silicon cells much higher than organic crystal ones. Plus, turning sand into silicon is a chemical and energy intensive process.

The downside of Bender’s organic solar cells, right now, is that they are far less efficient in converting light to electricity – about 6 per cent to traditional solar cells’ 30-43 per cent. But, if you have enough surface area (say your rooftop), it makes practical sense to use organics.

Bender imagines that in five years BlackBerries, iPhones and other smartphones will sport trickle- charging organic crystal solar cells – and the greater range of organics means those devices could charge in the light of a lecture hall, not just direct sunlight.

In a decade, he hopes you’ll be able to walk into RONA or Home Depot and pick up a roll of organic cells and do your house with them. And, he imagines a time when offset printers, like the ones used to produce daily newspapers, will also be able to print organic cells. “Any community or country that has access to an offset printer could produce organic cells in large quantities,” he explained.

Electrical and computer Engineering Professor Ted Sargent also has his sights set on solar. But he thinks big sustainable solutions come in small packages – really small. So small you can measure them using two-dozen atoms as a yardstick.

That’s because Sargent and his team, funded in part by an investment from the King Abdullah University of Science and Technology (KAUST), are tackling sustainability solutions one nanoparticle at a time. He thinks custom nanomaterials can produce paintable solar cells that could turn any surface, even any fabric into a sustainable energy generator.

It turns out that nanoparticles can not only be laid down like paint, but are versatile as well. Build them right, from the atom up, and you have a flexible, wide-spectrum photovoltaic cell. You can even turn them into miniature ray guns. “We can paint these semiconductor particles right onto the chip,” explained Sargent, who also holds the Canada Research Chair in Nanotechnology, “and then turn the dried paint into a laser.”

Configured a little differently, the nanoparticle matrix could even unclog Internet bottlenecks because nanoparticle-based routers don’t have to convert fibre-optic signals to much slower electrical current and then back to light.

And the best part? According to Dr. Luke Brzozowski, director of the photovoltaics research program in Sargent’s group, nanomaterials use “bottom up,” or chemically synthesized fabrication that’s not only cheaper than traditional methods, it also takes less energy and will result in higher efficiency devices.

Look for devices using Sargent’s group’s “paint” to cover your world in five years or less. Some devices are being geared up for launch through the U of T spin-off company, InVisage Technologies.

Meanwhile Xagenic, another spin-off, is commercializing research Sargent’s team collaborated on with Professor Shana Kelley, of Pharmacy, Medicine and Institute of Biomaterials & Biomedical Engineering (IBBME), on nanobiosensors. So, maybe someday sustainability will only be skin deep – and that’s a good thing.

Fuel for Thought

Mechanical and industrial engineering assistant professor Aimy Bazylak would like to utilize energy from hydrogen – the same element that fuels the sun.

While batteries are closed systems, fuel cells rely on a fuel supply (often hydrogen) that maintains, along with a catalyst, the chemical reaction that produces electricity while producing only water and heat as waste products.
Hydrogen fuel cells for cars are the most high profile of fuel cells but there are many other types and applications, said Bazylak.

“Right now, the public has a huge interest in hydrogen fuel cell vehicles. Purely battery- powered cars are also in the spotlight right now, but, in the long run, car companies see hydrogen fuel cells running together with batteries as the ultimate solution. Purely battery- powered cars have limited range, so they will not be the silver bullet,” she explained.

Bazylak and her team are also interested in microfluidic fuel cells, so small (100 microns) that dozens of the high-density cells could fit in a container the size of a loonie. She imagines that these tiny cells, which could power portable electronics like cellphones and laptops, may become widely adopted before hydrogen fuel cell cars hit the road.

“Like other kinds of sustainable storage devices, fuel cells are just one part of a sustainable energy future,” says Bazylak. “In a portable energy system, fuel cells could provide the base power. Batteries could provide top-up, f luctuating power and ultracapacitors are there for very fast changes and power bursts, which are necessary when you turn on a device.” It’s a future where all the sustainable devices are in it together. “There is no one winner. You need everyone.

This article is excerpted from Skule Matters.