Extremely large magnetoresistance in few-layer graphene/boron–nitride heterostructures

Extremely large magnetoresistance in few-layer graphene/boron–nitride heterostructures

 Kalon Gopinadhan, Young Jun Shin, Rashid Jalil, Thirumalai Venkatesan, Andre K. Geim, Antonio H. Castro Neto & Hyunsoo Yan

 Nature Communications 6, Article number: 8337 doi:10.1038/ncomms9337

Received 19 December 2014 Accepted 11 August 2015 Published 21 September 2015

Researchers from the prestigious National University of Singapore (NUS) have successfully invented a new hybrid magnetic sensor, more sensitive than most commercially available sensors to date.

Understanding magnetoresistance, the change in electrical resistance under an external magnetic field, at the atomic level is of great interest both fundamentally and technologically. Graphene and other two-dimensional layered materials provide an unprecedented opportunity to explore magnetoresistance at its nascent stage of structural formation. Here we report an extremely large local magnetoresistance of~2,000% at 400 K and a non-local magnetoresistance of >90,000% in an applied magnetic field of 9 T at 300 K in few-layer graphene/boron–nitride heterostructures. The local magnetoresistance is understood to arise from large differential transport parameters, such as the carrier mobility, across various layers of few-layer graphene upon a normal magnetic field, whereas the non-local magnetoresistance is due to the magnetic field induced Ettingshausen–Nernst effect. Non-local magnetoresistance suggests the possibility of a graphene-based gate tunable thermal switch. In addition, our results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications.

Supercharging a 3-D Hybrid Supercapacitor with Graphene

By combining sheets of graphene with a traditional battery material, scientists have created hybrid supercapacitors that can store as much charge as lead acid batteries but can be recharged in seconds compared with hours for conventional batteries.

Now researchers at the University of California, Los Angeles, have developed a hybrid supercapacitor that is based on graphene, which is made of single layers of carbon atoms. Graphene is flexible, transparent, strong and electrically and thermally conductive, qualities that have led to research worldwide into whether the material could find use in advanced circuitry and other devices.
The scientists combined graphene with manganese dioxide, which is widely used in alkaline batteries and is both abundant and environmentally friendly. The manganese dioxide formed microscopic flowers made of flakes only 10 to 20 nanometers thick. The supercapacitors also incorporated electrolytes that can operate at high voltages.

Significance

Batteries run just about everything portable in our lives such as smartphones, tablets, computers, etc. Although we have become accustomed to the rapid improvement of portable electronics, the slow development of batteries is holding back technological progress. Thus, it is imperative to develop new energy storage devices that are compact, reliable, and energy dense, charge quickly, and possess both long cycle life and calendar life. Here, we developed hybrid supercapacitors that can store as much charge as a lead acid battery, yet they can be recharged in seconds compared with hours for conventional batteries.

Abstract

Supercapacitors now play an important role in the progress of hybrid and electric vehicles, consumer electronics, and military and space applications. There is a growing demand in developing hybrid supercapacitor systems to overcome the energy density limitations of the current generation of carbon-based supercapacitors. Here, we demonstrate 3D high-performance hybrid supercapacitors and microsupercapacitors based on graphene and MnO₂ by rationally designing the electrode microstructure and combining active materials with electrolytes that operate at high voltages. This results in hybrid electrodes with ultrahigh volumetric capacitance of over 1,100 F/cm³. This corresponds to a specific capacitance of the constituent MnO₂ of 1,145 F/g, which is close to the theoretical value of 1,380 F/g. The energy density of the full device varies between 22 and 42 Wh/l depending on the device configuration, which is superior to those of commercially available double-layer supercapacitors, pseudocapacitors, lithium-ion capacitors, and hybrid supercapacitors tested under the same conditions and is comparable to that of lead acid batteries. These hybrid supercapacitors use aqueous electrolytes and are assembled in air without the need for expensive “dry rooms” required for building today’s supercapacitors. Furthermore, we demonstrate a simple technique for the fabrication of supercapacitor arrays for high-voltage applications. These arrays can be integrated with solar cells for efficient energy harvesting and storage systems

IEEESpectrum 2015