Tungsten nitride incorporated graphene fibers for wearable supercapacitors

Abstract

Graphene-based fibers attract much scientific interest as electrode materials for wearable energy storage devices such as supercapacitors owing the high conductivity of graphene and the mechanical flexibility associated with the fiber shape. However, due to restacking of graphene sheets in graphene fibers, the SSA of graphene is severely reduced. As graphene fibers store charge only through the double layer mechanism, the energy density obtained by them is much lower. Addition of pseudo-capacitive materials such as Transition Metal Oxides (TMOs) or Conducting Polymers (C.Ps) is the usual solution to achieve a higher energy density. However, the low conductivity of TMOs and the structural stability issues of C.P/graphene hybrids limit the rate capability and long cycle life of the fiber supercapacitor. In this work, we employ tungsten nitride (WN), a transition metal nitride (TMN) which are chemically stable compounds and intrinsically provide both high capacitance and high conductivity, to make a hybrid with graphene fiber and compare its performance with tungsten oxide ($WO_3$)-graphene hybrid fiber. We observed that the electrical conductivity and electrochemical performance of the tungsten nitride- graphene hybrid fiber is much higher than the corresponding $WO_3$-graphene hybrid fiber. We can infer that TMNs can prove to be very beneficial when mixed with graphene compared to TMOs for flexible energy storage device applications.