2D materials sandwich promises high energy density flexible supercaps

July 04, 2017 // By Julien Happich
Using a simple and highly scalable fabrication technique, a team of Chinese researchers has combined the exceptional mechanical and electrical properties of Phosphorene and Graphene nanosheets to create a novel type of Micro SuperCapacitors (PG-MSC).

Close-up of the dry transferred PG hybrid
film onto the PET substrate.

In their paper "One-Step Device Fabrication of Phosphorene and Graphene Interdigital MicroSupercapacitors with High Energy Density" published in the ACS Nano journal, the researchers explain their manufacturing process, starting with stable inks of electromechanically exfoliated graphene and phosphorene successively filtered/deposited through a customized interdigitated mask onto a PTFE membrane and then transferred onto a PET foil. A ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate or BMIMPF6) is then drop cast onto the pattern.

Analysing their devices under Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), the scientists observed the compact layered structure of the Phosphorene-Graphene (PG) film, in which relatively small phosphorene nanosheets are uniformly incorporated into the interlayer of large graphene nanosheets, showing the excellent structural integration of the two materials.

They also report for this phosphorene-incorporated graphene (PG) film a high electrical conductivity of 319 S cm−1, an order of magnitude higher than what literature reports for graphene/polymer hybrid films (21−40 S cm−1), guaranteeing both high electron transport and fast ionic transport.

Working in ionic liquid, the finalized Micro SuperCapacitors were characterized with an areal capacitance of 9.8mF cm−2, a volumetric capacitance of 37.0 F cm−3, and an energy density of 11.6mWh cm−3, over twice higher than that of most nanocarbon-based MSCs according to the paper. Thanks to the ionic liquid used, the devices supported high operating voltage (3V) while avoiding the oxidation of phosphorene and exhibiting a high thermal stability (up to 200°C).