Pseudocapacitive Charge Storage in Titanate–Reduced Graphene Oxide Nanocomposites

Abstract

Pseudocapacitance is an emerging charge-storage mechanism that allows materials to achieve both high energy and high power capabilities. One strategy to enable pseudocapacitance is to modulate material morphologies at the nanoscale because the specific surface area and pore structure are strongly related to charge-storage kinetics. In our study, two different sodium titanate (Na 2 Ti 3 O 7 ) morphologies, nanotubes and nanosheets, are prepared by efficient synthetic routes to examine the influence of surface nanostructures on both Li + and Na + charge storage properties in nonaqueous electrolytes. We confirm that the titanate nanotube structure provides higher surface area and pore volume compared to its nanosheet counterpart by using surface analysis techniques. Moreover, we incorporate reduced graphene oxide (rGO) to further improve the high-rate capability of the titanates. The nanotube-rGO nanocomposite exhibits superior electrochemical performance in terms of capacity (170 and 80 mAh g –1 in a Li + and Na + system, respectively) and rate capability, accompanied by a broad voltammetric response and sloping charge-discharge voltage profiles under galvanostatic mode. These electrochemical features resemble pseudocapacitive charge-storage and this mechanism is further verified by electrochemical kinetic analysis using current–scan rate dependence. This analysis allow us to determine that 80% of the stored charge at 1 mV s –1 arises from surface-limited processes for the titanate nanotube-rGO nanocomposite. This study demonstrates the importance of modulating surface structures, thereby enabling facile storage of ions to the electrochemically active sites of the material of interest. Figure 1