EES Blog

Scientists in the US have taken the first steps towards designing a flexible and lightweight fabric that can act as a power supply for smart garments.

Electronic textiles, or ‘smart’ textiles, are fabrics that have built-in functions such as sensing, data storage and communication. But as with all electronics, they require a power source. Conventional batteries are too bulky to wear, so a power source that can be combined and integrated into the garment is highly desirable.

Previous attempts to make wearable energy storage devices involved the use of nonwoven materials not usually used in clothes and expensive active materials like carbon nanotubes and nanowires.

Yury Gogotsi and colleagues at Drexel University, Philadelphia, have taken everyday fabrics like woven cotton and polyester materials and impregnated them with porous carbon powders, taking advantage of the natural porous nature of these materials. Using common techniques like screen printing, ink-jet printing and dip-coating, textile electrodes can be made on a large scale without the expense of new processes needing to be designed.

A battery can be integrated into a garment by impregnating woven cotton and polyester fabrics with porous carbon

‘Our work makes a significant advancement in this area as our electrodes can store 400-700 times the energy per area of previously reported literature while also being flexible, non-toxic and has great potential to be integrated into textiles and clothing,’  says Gogotsi.   

The woven and knitted fabrics have empty space between individual fibres and between yarns, and it is into these spaces that the carbon powders are inserted, allowing ion transfer. The team were able to achieve higher mass loadings and capacitance levels on comparison with previous techniques.  

‘The relatively simple approach to engender conductivity to textile substrates has broad impact,’ comments Tushar Ghosh, a specialist in textile engineering from North Carolina State University, US. ‘The work contributes to the body of knowledge necessary for energy harvesting and storage in textiles of the future.’   

Although more work is needed to get a finished product, the hope is to develop this technology into a number of smart garment devices that can be used in a variety of fields such as healthcare, the army and even aerospace exploration. 

Rebecca Brodie   

Read the paper from Energy & Environmental Science:

Carbon coated textiles for flexible energy storage
Kristy Jost, Carlos R. Perez, John K. McDonough, Volker Presser, Min Heon, Genevieve Dion and Yury Gogotsi
Energy Environ. Sci., 2011
DOI: 10.1039/c1ee02421c

An energy scavenger device that can convert both solar energy and movement energy into electricity to power portable electronics has been made by scientists from Korea and the US. The device could find its way into your home in the future as it’s flexible enough to be attached to clothes, bags, curtains or flags, say the researchers.

Sang-Woo Kim from Sungkyunkwan University in Suwon and colleagues made the device from piezoelectric zinc oxide and an organic solar cell so that electrical energy can be provided either by sunlight or wind or body movement, depending on which source is available at the time.

It’s been believed that solar energy is sufficient for powering portable electronics because it has a high efficiency, but many mobile electronics are operated indoors in areas with dim lighting. In such cases, the power that can be harvested drops by two to three orders of magnitude, say the researchers, and harvesting energy from other sources becomes viable. 

The device can be incorporated into flags to harvest both movement and solar energy

So far, attempts to make multi-type energy devices have been plagued by cross-talk problems, in which energy transfer between adjacent conductors occurs, causing a drop in efficiency. Kim’s device gets around this problem. The team made a cathode from an indium tin oxide coated polymer. They coated this with a layer of zinc oxide nanorods – the parts that are activated by movement. Another polymer layer – the part that’s activated by light – was added between the nanorods. The rods have a dual role because they also transport electrons generated by the solar cell.

In tests, the device gave outputs of tens of millivolts to 120 millivolts when using solar energy and tens of millivolts to 150 millivolts when using piezoelectric energy.

‘Materials chemistry can provide integrated solutions to energy harvesting and regeneration via new developments, especially in the area of smart and multifunctional systems. This work presents one such development via the fusion of photovoltaic and piezoelectric hybrid materials,’ says Elias Siores, an expert in piezoelectric materials from the University of Bolton, UK. ‘Such systems will pave the way forward in enhancing effectiveness and efficiency in energy conversion systems.’

Elinor Richards

Read the paper from Energy & Environmental Science:

Control of naturally coupled piezoelectric and photovoltaic properties for multi-type energy scavengers
Dukhyun Choi, Keun Young Lee, Mi-Jin Jin, Soo-Ghang Ihn, Sungyoung Yun, Xavier Bulliard, Woong Choi, Sang Yoon Lee, Sang-Woo Kim, Jae-Young Choi, Jong Min Kim and Zhong Lin Wang
Energy Environ. Sci., 2011
DOI: 10.1039/c1ee02080c

Limestone batteries could be the key to transporting energy across huge distances, according to chemists in Germany. The idea, which would be used to take solar energy harnessed in the African desert to cities in Europe, might be more efficient than power lines, and could even sequester carbon dioxide emitted by fossil fuel plants.

Researchers exploring greener ways to generate electricity have often looked to the deserts, where enough sunlight falls in six hours to power the world for an entire year. DESERTEC, developed by European scientists, economists and politicians, offers one way to tap this resource. In this concept, power plants would be located in northern Africa that concentrate the sun’s rays onto oil, which would boil water into steam to drive turbines. The electricity generated by these turbines would then be transported thousands of kilometres to cities in Europe via high-voltage, direct-current (HVDC) power lines.

HVDC lines can be more efficient than normal alternating-current lines, because they operate at less current and, therefore, suffer less resistance. But over 3000km, HVDC lines are still expected to lose 10 per cent of their power, dragging down the overall efficiency of the DESERTEC concept from 12 per cent to 10.8 per cent.

Now, Benjamin Müller and colleagues at the University of Erlangen, under the auspices of the Energy Campus Nuremberg research platform, have come up with an idea that could ameliorate this loss, and at the same time cut some of the CO₂ produced by fossil fuel plants. Rather than generate electricity at the African solar concentrators, says Müller’s group, engineers should direct the sunlight to reactors filled with limestone (CaCO₃). At around 1000°C, the limestone would convert to quicklime (CaO) and CO₂, which could be converted using other solar energy and hydrogen into useful fuel such as methane. Meanwhile, the lime could be transported over land and sea to European cities where, upon heating to 650°C in the presence of CO₂ from local fossil fuel plants, it would reconvert to limestone with a massive release of heat. This heat would then boil water into steam to drive turbines, generating electricity on-site.

 The Erlangen researchers estimate that, overall, their method would keep the DESERTEC efficiency at 12 per cent. What’s more, they calculate that the extra CO₂ sucked up at fossil fuel plants could reduce the total CO₂ output of Germany alone by up to 50 per cent.

‘The idea is sound, intriguing and is worthy of detailed investigation [because] it challenges existing thinking,’ says Magdi Ragheb, an engineer at the University of Illinois at Urbana-Champaign, US, who has studied the DESERTEC concept. However, Ragheb points out potential problems, such as the transport of solids. ‘Liquids such as petroleum are easy to handle as they can be pumped; solids are more difficult to handle,’ he adds.

Other environmental experts agree that the idea may suffer practical hurdles. ‘It was the first time I had seen this idea, so from that perspective it’s intriguing,’ says Sally Benson, an expert in carbon dioxide sequestration at Stanford University in California, US. ‘[But] you’ve got all this solid you need to react very quickly…you’d need to have it very finely ground, so now all the material handling becomes a big issue.’

Müller’s group itself points out another practical drawback – that, over time, the limestone’s crystal structure would change, so engineers wouldn’t be able to convert 100 per cent of it to lime. ‘Artificially synthesised materials [would instead be] the best option to achieve a high degree of conversion,’ says Müller. ‘But addressing this problem is a big issue in research at the moment.’ However, he adds that his group is exploring other candidates besides limestone for chemical storage.

‘The [idea] sounds interesting,’ says Michael Straub, a spokesperson for the DESERTEC Foundation. ‘But as we have just a few years left to slow down global warming, we are actually focusing on technologies that are available today. As the worldwide implementation of DESERTEC will take decades, this technology might be an option for future [solar concentrator] plants.’

Jon Cartwright

Read the paper from Energy & Environmental Science:

A new concept for the global distribution of solar energy: energy carrying compounds
B. Müller, W. Arlt and P. Wasserscheid, Energy Environ. Sci., 2011
DOI: 10.1039/c1ee01595h