Laser‐Assisted Lattice Recovery of Graphene by Carbon Nanodot Incorporation

Abstract

Producing highly oriented graphene is a major challenge that constrains graphene from fulfilling its full potential in technological applications. The exciting properties of graphene are impeded in practical bulk materials due to lattice imperfections that hinder charge mobility. A simple method to improve the structural integrity of graphene by utilizing laser irradiation on a composite of carbon nanodots (CNDs) and 3D graphene is presented. The CNDs attach themselves to defect sites in the graphene sheets and, upon laser‐assisted reduction, patch defects in the carbon lattice. Spectroscopic experiments reveal graphitic structural recovery of up to 43% and electrical conductivity four times larger than the original graphene. The composites are tested as electrodes in electrochemical capacitors and demonstrate extremely fast RC time constant as low as 0.57 ms. Due to their low defect concentrations, the reduced graphene oxide‐carbon nanodot (rGO‐CND) composites frequency response is sufficiently fast to operate as AC line filters, potentially replacing today's electrolytic capacitors. Using this methodology, demonstrated is a novel line filter with one of the fastest capacitive responses ever reported, and an aerial capacitance of 68.8 mF cm−2. This result emphasizes the decisive role of structural integrity for optimizing graphene in electronic applications.

History and Perspectives on Ultrafast Supercapacitors for AC Line Filtering

“…The carbon composite electrodes for the high‐frequency SCs were developed mostly with the graphene electrodes. [ 102–104 ] Since the graphene has advantages such as high electrical conductivity, a large specific surface area, and a 2D layered structure, it can serve as an excellent template for carbon composite materials, leading to synergistic effects. The graphene/amorphous carbon composite was synthesized by using Ni foil via ambient‐pressure CVD.…”

“…The rGO/CNT‐composite‐based SC was tested with an ionic liquid, 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMImBF 4 ), exhibiting the moderate frequency response with an impedance phase angle of −64.4° at 120 Hz, a relaxation time constant of 2.08 ms, and a wide voltage window of 4 V. A reduced graphene oxide/carbon nanodot (rGO/CND) composite was synthesized by the laser‐assisted graphitization process. [ 104 ] The laser‐induced thermal reaction ablated the defective carbon fragments into the plasma and formed CC bonds among the neighboring carbons of the CND and rGO. The integrated merging of the reduced CND with rGO formed a continuous 3D extension of the graphene substrate patched by the CNDs.…”

“…The carbon composite electrodes for the high-frequency SCs were developed mostly with the graphene electrodes. [102][103][104] Since the graphene has advantages such as high electrical conductivity, a large specific surface area, and a 2D layered [87] Copyright 2013, Royal Society of Chemistry. (b-d) Reproduced with permission.…”

“…However, they have been frequently adopted in high-frequency SCs owing to their less corrosive nature and wider ESW compared to both alkaline and acid electrolytes. [22,31,46,47,49,[51][52][53]104] Owing to the less corrosive nature of the neutral electrolytes, a wide range of current collectors or/and electrode materials, particularly the ones that are highly unstable to basic or acidic environments, were explored. [51,53] On the other hand, while alkaline and acidic electrolytes have ESWs of approximately 1 V, neutral electrolytes exhibit wider ESW (e.g., ≈1.8 V) due to large overpotentials against water electrolysis.…”

Graphene's Role in Emerging Trends of Capacitive Energy Storage

“…Building on this, we have shown that CNDs also serve to patch defects in laser-reduced GO resulting in higher surface areas and conductivities. [52,53] The addition of CNDs leads to a 130% increase in the active surface area. Compared to laser-reduced GO, the electrical conductivity grows by about ten times.…”