Preventing Graphene from Restacking via Bioinspired Chemical Inserts: Toward a Superior 2D Micro-supercapacitor Electrode

Abstract

Graphene-based composites are promising materials for supercapacitors due to the high specific surface area and electrical conductivity of graphene. Reduction of graphene oxide (GO) is a practical approach to obtain graphene-like material but it suffers from the re-stacking of the graphene sheets. Herein, a two-dimensional composite electrode based on electrochemically reduced GO (ERGO) and polydopamine (PDA) is reported where the PDA is used as a "bioinspired chemical insert" to tackle with the restacking issue of graphene layers. This green and facile electrochemical fabrication method starts from the electro-reduction of GO followed by the electro-oxidation of dopamine (DA), present in the same electrolyte, by a simple switch between a cathodic to an anodic potential. The optimized ERGO-PDA composite electrode possesses combined features of excellent capacitive behavior, with a relaxation time (0) of 0.88 s, high gravimetric and volumetric capacitances (178 F•g -1 and 297 F•cm -3 , respectively, at 10 mV•s -1 ) and finally an excellent cycling stability at 100 to 2000 mV•s -1 , at least for 30000 cycles. DA electropolymerization yield monitored by quartz crystal microbalance and X-ray diffraction measurements demonstrate that PDA is formed between the graphene sheets which prevents the sheets from restacking and facilitate species diffusion inside the composite leading to a volumetric energy density of 8.6 mWh•cm -3 for a power density of 7.8 W•cm -3 . Additionally, the electrochemical quartz crystal microbalance demonstrates a dominant cationic charge compensation and a very efficient interfacial transfer characteristics since a totally reversible mass response during charge/discharge was observed for the optimized ERGO-PDA electrode.

Interface Properties of 2D Graphene–Polydopamine Composite Electrodes in Protic Ionic Liquid-Based Electrolytes Explored by Advanced Electrogravimetry

“…The relative concentration increase of the hydrated sodium cation is more significant and its transfer kinetics is almost twice faster in ERGO-PDA than in ERGO (Figure e,f). This is consistent with the higher d -spacing between the graphene sheets and the better rate capability of the ERGO-PDA electrode compared with the ERGO, which was reported in our previous work …”

“…In the PIL–water binary mixture, the composite electrode can deliver an energy density of 16.3 mWh·cm –3 at a scan rate of 10 mV·s –1 , which is almost twice higher than what the same electrode can achieve in the pristine aqueous electrolyte (8.7 mWh·cm –3 ) at the same scan rate. Even at a high cycling rate (1 V·s –1 ), the ERGO-PDA electrode can still deliver an energy density of 6.1 mWh·cm –3 , which is comparable to or higher than most of the recent reports on EDLC electrodes tested in the aqueous electrolyte evaluated under similar discharge rates. ,, According to the equation used for energy density calculation (eq ), this significant improvement of the energy density can be explained by the larger potential window in the [Pyr + ]­[HSO 4 – ]–water binary mixture (60/40 wt %): 1.2 V versus only 0.9 V in 0.5 M Na 2 SO 4 (pH = 2), which is more evidently seen in the CV curves presented in Figure , , and S5. This behavior is fully in line with the electrogravimetric results, which reveal that the water molecules are not implied in the interfacial electrochemical processes when PIL is present in the electrolyte.…”

“…ERGO and ERGO-PDA electrodes were synthesized according to the procedure reported in our previous work . Briefly, about 6 μL of a GO suspension was drop-cast on a gold electrode (0.2 cm 2 ) of a quartz resonator (9 MHz, AWSensors, Spain).…”

“…Due to the high relevance of the classical EQCM and ac -electrogravimetry for interface characterization, herein, they were exploited to address the interface behavior of our previously optimized two-dimensional (2D) graphene–polydopamine (ERGO-PDA) composite electrodes . Regarding the electrolytes, we were particularly interested in protic ionic liquid (PIL) electrolytes (presence of labile hydrogens) over aprotic ionic liquids (AILs) (absence of labile hydrogens).…”

Ion Dynamics at the Carbon Electrode/Electrolyte Interface: Influence of Carbon Nanotubes Types

“…In supercapacitors, the charge storage is based on a reversible adsorption of electrolyte ions towards the surface of electrodes [ 3 , 4 , 5 , 6 , 7 , 8 ]. Therefore, the selection of the electrode materials is important due to a certain number of parameters such as: specific surface area, porosity, structure, electrical conductivity, surface wettability, and electrochemical stability to improve the performance of electrodes [ 2 , 9 , 10 , 11 , 12 ].…”