The research group at Department of Physics, IIT Guwahati led by Uday Narayan Maiti, in collaboration with Prof. Subhradip Ghosh, IIT Guwahati and N. Padma of Physics group, Bhabha Atomic Research Centre (BARC), Mumbai, under BRNS (Board of Research in Nuclear Science) project has developed a new soft hybrid material, known as a hydrogel, to increase the energy storage performance of supercapacitor devices.

A hydrogel is a porous framework of interconnected materials, in which water remains stably locked within the pores. As a building block of the hydrogel, they have chosen two different kinds of nanosheets, namely graphene and MXene, which store charge via two different mechanisms.

In Supercapacitors two electrodes (anode and cathode), made of suitable materials, are immersed within electrolyte solution, and energy is stored by charge accumulation on the electrode surfaces. Atomic-thin sheet-like materials, known as nanosheets, are considered the best choice for supercapacitor electrodes as they can offer a large area to store charge. However, integrating microscopic ultra-small nanosheets into a usable macroscopic scale is highly challenging.

They have developed the hydrogels electrodes by a simple room-temperature process in which graphene and MXene spontaneously assemble themselves over a metal plate within a water medium. This unique structure can avoid the restacking challenge associated with charge-storing nanosheets. Graphene, a single-atom thin carbon sheet, stores charge on its surface via physical adsorption, known as electrical double layer mechanism (EDLC). Whereas, MXene, nanosheets of titanium carbide, stores charge via both EDLC and chemical reaction on its surface, known as pseudo-capacitance

Researchers at IIT Guwahati showed that their supercapacitors based on MXene-graphene hydrogels can be repeatedly charged and discharged over 10000 times, with only minimal performance degradation. Such durability is much better than the conventional batteries that typically wear out within 300-500 charging-discharging cycles. The supercapacitor devices developed in the lab can be charged in seconds to their full capacity. It can store energy as high as 30 Wh per kilogram of the materials, which is one of the best values reported to date in MXene based system. Importantly, these supercapacitors can deliver energy at a very fast rate when required, which is presented in terms of power density. They have achieved the highest power density 1.13 kW per kg of electrode material which is almost twice the power offered by current Li-ion batteries. Their hydrogel devices can be engineered to be compact enough to fit the extremely tight spaces of modern portable electronics, which is gaining increasing popularity among the masses. 

The results of these breakthrough work in MXene based supercapacitor technologies were published in 'Electrochimica Acta' and 'Carbon' recently.