Wednesday, July 8, 2015

MIT develops Supercapacitors from Niobium Nanowire Yarns for wearable electronics

As reported by MIT News : Wearable electronic devices for health and fitness monitoring are a rapidly growing area of consumer electronics; one of their biggest limitations is the capacity of their tiny batteries to deliver enough power to transmit data. Now, researchers at MIT and in Canada have found a promising new approach to delivering the short but intense bursts of power needed by such small devices.

The key is a new approach to making supercapacitors — devices that can store and release electrical power in such bursts, which are needed for brief transmissions of data from wearable devices such as heart-rate monitors, computers, or smartphones, the researchers say. They may also be useful for other applications where high power is needed in small volumes, such as autonomous microrobots.

The new approach uses yarns, made from nanowires of the element niobium, as the electrodes in tiny supercapacitors (which are essentially pairs of electrically conducting fibers with an insulator between). The concept is described in a paper in the journal ACS Applied Materials and Interfaces by MIT professor of mechanical engineering Ian W. Hunter, doctoral student Seyed M. Mirvakili, and three others at the University of British Columbia.

Here below is the abstract for the publication or you can continue reading the story from MIT News.

High-Performance Supercapacitors from Niobium Nanowire Yarns

Seyed M. Mirvakili, Mehr Negar Mirvakili, Peter Englezos, John D. W. Madden, and Ian W. Hunter

ACS Appl. Mater. Interfaces, 2015, 7 (25), pp 13882–13888
DOI: 10.1021/acsami.5b02327

The large-ion-accessible surface area of carbon nanotubes (CNTs) and graphene sheets formed as yarns, forests, and films enables miniature high-performance supercapacitors with power densities exceeding those of electrolytics while achieving energy densities equaling those of batteries.1−7 Capacitance and energy density can be enhanced by depositing highly pseudocapacitive materials such as conductive polymers on them.3,8−15 Yarns formed from carbon nanotubes are proposed for use in wearable supercapacitors.3,16 In this work, we show that high power, energy density, and capacitance in yarn form are not unique to carbon materials, and we introduce niobium nanowires as an alternative. These yarns show higher capacitance and energy per volume and are stronger and 100 times more conductive than similarly spun carbon multiwalled nanotube (MWNT) and graphene yarns.6,17−22 The long niobium nanowires, formed by repeated extrusion and drawing,17 achieve device volumetric peak power and energy densities of 55 MW·m–3 (55 W·cm–3) and 25 MJ·m–3 (7 mWh·cm–3), 2 and 5 times higher than that for state-of-the-art CNT yarns, respectively.3 The capacitance per volume of Nb nanowire yarn is lower than the 158 MF·m–3 (158 F·cm–3) reported for carbon-based materials such as reduced graphene oxide (RGO) and CNT wet-spun yarns,5 but the peak power and energy densities are 200 and 2 times higher, respectively.5 Achieving high power in long yarns is made possible by the high conductivity of the metal, and achievement of high energy density is possible thanks to the high internal surface area. No additional metal backing is needed, unlike for CNT yarns and supercapacitors in general, saving substantial space. As the yarn is infiltrated with pseudocapacitive materials such as poly(3,4-ethylenedioxythiophene) (PEDOT), the energy density is further increased to 10 MJ·m–3 (2.8 mWh·cm–3). Similar to CNT yarns, niobium nanowire yarns are highly flexible and show potential for weaving into textiles and use in wearable devices.

No comments:

Post a Comment