Self-assembled three-dimensional macroscopic graphene/MXene-based hydrogel as electrode for supercapacitor

Luojiang Zhang,Siu Wing Or

doi:10.1063/5.0015426

Abstract

Hydrogels with unique three-dimensional (3D) macroscopic porous architectures are attractive electrode materials for supercapacitors because of their superior electrolyte permeabilities and rapid electron/ion transports. In this letter, a cylindrical-type 3D macroscopic graphene/MXene-based hydrogel (GMH) is prepared by self-assembling laminar-structured graphene oxide (GO) and MXene (Ti3C2) nanosheets via a facile one-step hydrothermal method under the existence of ammonia water and hydrazine hydrate. GO is found to self-converge into a 3D macroscopic porous graphene framework during the hydrothermal process, while Ti3C2 nanosheets are able to prevent the graphene nanosheets from self-restacking. The as-prepared GMH shows a larger specific surface area of 161.1 m2 g−1 and a higher pore volume of 0.5 cm3 g−1 in comparison with the pure graphene hydrogel. A symmetric supercapacitor utilizing GMH as electrodes exhibits high energy densities of 9.3 Wh kg−1 and 5.7 Wh kg−1 at different power densities of 500 W kg−1 and 5000 W kg−1, respectively, as well as an outstanding long-term cycle stability with no loss in capacitance in excess of 10 000 continuous charge–discharge cycles. The strategy of preparation of a 3D macroscopic GMH is expected to realize promising high-performance hydrogel electrodes based on graphene and MXene for electrochemical energy storages.

Highlights

The high ion transport and electronic conductivity, together with the large specific surface area of electrode materials, form the vital factors to realize high electrochemical performance for SCs as they can facilitate the storage of more energy via the electric double layer or electrochemical reactions occurring at the electrode/electrolyte interface
Research in electroactive materials with three-dimensional (3D) hierarchical porous structures has attracted significant attention as the macropores afford ion accessibility to active surface while micro- and mesopores contribute to high specific surface area. 3D macroscopic hydrogels with cross-linked networks imbibing water and swelling are candidates for emerging electrode materials owing to their controllable hierarchical porous structures and attractive mechanical properties
We have developed a facile strategy for the synthesis of a high performance energetically stable 3D macroscopic graphene/MXene-based hydrogel (GMH)

Summary

INTRODUCTION

Supercapacitors (SCs), as an important member in various energy conversion and storage systems, have been useful in many challenging applications requiring enough power for a relatively short time or numerous rapid charge–discharge cycles. Much effort has been put on improving the energy density of SCs without sacrificing the power density or cycle stability. The high ion transport and electronic conductivity, together with the large specific surface area of electrode materials, form the vital factors to realize high electrochemical performance for SCs as they can facilitate the storage of more energy via the electric double layer or electrochemical reactions occurring at the electrode/electrolyte interface. With these in mind, research in electroactive materials with three-dimensional (3D) hierarchical porous structures has attracted significant attention as the macropores afford ion accessibility to active surface while micro- and mesopores contribute to high specific surface area. 3D macroscopic hydrogels with cross-linked networks imbibing water and swelling are candidates for emerging electrode materials owing to their controllable hierarchical porous structures and attractive mechanical properties.. A burgeoning family of nanosheets with graphene-like 2D morphology, transition metal nitrides and carbides (MXenes) with a general formula of Mn+1XnTx (M, as early transition metal; X, carbon or nitrogen element; T, surface functional groups such as −−F, −−O, and −−OH; and n = 1, 2, 3), have been studied as promising electrode materials for SCs owing to their high electrical conductivity and superior surface hydrophilicity.. A burgeoning family of nanosheets with graphene-like 2D morphology, transition metal nitrides and carbides (MXenes) with a general formula of Mn+1XnTx (M, as early transition metal; X, carbon or nitrogen element; T, surface functional groups such as −−F, −−O, and −−OH; and n = 1, 2, 3), have been studied as promising electrode materials for SCs owing to their high electrical conductivity and superior surface hydrophilicity.12–14 Such novel materials can be achieved by chemical etching out of the “A” element (mostly 13- or 14A-group) from the MAX phases with formula Mn+1AXn.. The assembled symmetric SC based on GMH electrodes demonstrates a high energy density of 9.3 Wh kg−1 at a power density of 500 W kg−1 and an outstanding long-term cycle stability over 10 000 continuous charge–discharge cycles

Preparation of Ti3C2 suspension

Characterization

Electrochemical measurements

RESULTS AND DISCUSSION

CONCLUSION