Fast Activation of Graphene with a Highly Distorted Surface and Its Role in Improved Aqueous Electrochemical Capacitors

Abstract

In graphene-based materials, the energy storage capacity is usually improved by rich porous structures with extremely high surface areas. By utilizing surface corrugations, this work shows an alternative strategy to activate graphene materials for large capacitance. We demonstrate how to simply fabricate such activated graphene and how these surface structures helped to realize considerable specific capacitance (e.g., electrode capacitance of ∼340 F g–1 at 5 mV s–1 and a device capacitance of ∼343 F g–1 at 1.7 A g–1) and power performance (e.g., power density of 50 and 2500 W kg–1 at an energy density of ∼10.7 and 1.53 Wh kg–1, respectively) in an aqueous system that are comparable to and even better than those of highly activated graphene materials with ultrahigh surface areas. This work demonstrates a path to enhance the capacity of carbon-based materials, which could be developed and combined with other systems for various improved energy storage applications.

Lattice Distortion and H‐passivation in Pure Carbon Electrocatalysts for Efficient and Stable Two‐electron Oxygen Reduction to H2O2

“…Therefore, DFT simulations and more experiments were explored to further clarify the 2e − ORR activation of M–CC associating with these newly formed distorted lattices and H‐passivation. According to TEM characterizations (Figure 1c,d, Figure S3j,i–p), different lattice distortion extents ( R%, R =100× ( L 0 ‐L )/ L 0 =15, 20, 25, 30, 35, 40, 45 ) were applied to simulate the structure, where L 0 and L are the lattice constant of pure and distorted graphene layer, respectively (Figure S7a, similar to our previous report) [19i] . The pure graphene and distorted lattice without the H‐passivation cannot activate the O−O bond (Figure S7a).…”

Understanding and Optimizing Capacitance Performance in Reduced Graphene‐Oxide Based Supercapacitors

“…Notably, for instance, as-synthesized GO has been subjected to prolonged ultrasonication to achieve an exfoliated GO suspension; then, further processed by hydro-/solvo-thermal curing, vacuum filtration or cast into templates of mesostructured foams followed by reduction either with chemical and/or thermal routes (see details in Table S1, Supporting Information). Nevertheless, the high capacitance values of 280±20 to 340±10 F g −1 at 0.5 A g −1 in EG samples in this work are higher than most of the RGO based structures in the literature and superior to direct solidstate thermal-/microwave-shock exfoliated and plasma reduced graphene counterparts, [28,29,51,[57][58][59][60][61][62][63][64][65][66][67] which typically show capacitance of <250 F g −1 (Figure S9, Supporting Information). Such an improvement of up to 40% suggests that despite using similar techniques, our optimized synthesis and processing conditions can lead to significant enhancement in their final device performance.…”

Structure‐guided Capacitance Relationships in Oxidized Graphene Porous Materials Based Supercapacitors

“…For example, the exfoliated graphene or RGO materials produced under plasma and laser/light irradiated conditions in literature show capacitance values between 30 to 300 F g À1 , and a significant drop in capacitance is often observed with further graphitization of the samples under high temperature, anything over 400 °C (Table S1, Supporting Information). [2,29,33,38,39,[45][46][47][48][49][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] To understand such a significant variation in capacitance between RGO materials of mildly reduced and highly graphitized nature, four sets of RGO samples are further produced with varied reduction/graphitization degrees. In this case, thermal annealing is performed on low, medium and high porosity representative samples of EG 1 , EG 3 , EG 4 and EG 6 at different temperatures of 400, 600, 800, 1000 and 1100 °C and resultant graphitized EG samples are named as GEG X-T (T is annealing temperature).…”

“…For example, the exfoliated graphene or RGO materials produced under plasma and laser/light irradiated conditions in literature show capacitance values between 30 to 300 F g −1 , and a significant drop in capacitance is often observed with further graphitization of the samples under high temperature, anything over 400 °C (Table S1, Supporting Information). [ 2,29,33,38,39,45–49,51–67 ]…”

“…2023, 6, e12637 example, RGOs further reduced under elevated temperatures of over 400 °C have been shown to yield much lower capacitance values of below 150 F g À1 relative to more than 200 F g À1 for mildly reduced RGOs. [6,13,16,20,22,29,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] In this case, the capacitance variation is linked to reduction (i.e., inherent oxygen functional groups of RGO) levels as well as accessible graphene layer networks of different porosity, conductivity and density. However, in all these analysis scenarios, there is no clear-cut understanding of the overall capacitance variation against key structural parameters of either 1) oxygen functional concentration linked pseudo-capacitance and 2) surface area promoted EDLC.…”