Hybridized Graphene for Supercapacitors: Beyond the Limitation of Pure Graphene

Qin

Batmunkh

et al. 2021

JOM

In this work, we present a facile yet effective method to prepare boron-doped, highly reduced electrochemical graphene oxide (B-rEGO) using electrochemical oxidation coupled with high-temperature thermal reduction. We first fabricated EGO from natural graphite powder in different concentrations of sulfuric acid electrolytes in a packed-bed reactor and found that the 12 M acid could produce EGO with the highest level of oxidation. To introduce heteroatom doping (non-metallic boron), sufficient boric acid was added to the sulfuric acid electrolyte for electrochemical reactions whereby the boron-doped graphene precursor could be formed, namely tetraborate anion intercalated EGO compounds, and it could transform into B-rEGO by annealing at 900°C for 3 h under Ar gas. We found that the B-rEGO was highly defective as well as effectively deoxygenated and contained 0.21 at.% of boron. The as-prepared B-rEGO is used as an active material in sodium ion battery anodes, delivering a good capacity of 129.59 mAh g À1 at the current density of 100 mA g À1 and long-term cyclic stability which could retain 100.20 mA g À1 after 800 cycles at 500 mA g À1 .

“…To synthesize EGO, we used the apparatus and method as described comprehensively in our previous work. 19 The electrochemical glass tubular reactor is shown in Fig. 1a.…”

Section: Synthesis Of Ego and Regomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Facile Synthesis of Boron-Doped Reduced Electrochemical Graphene Oxide for Sodium Ion Battery Anode

Qin

Batmunkh

et al. 2021

JOM

“…Among carbon-based electrodes, although graphene has been considered one of the most promising electrode materials with remarkable conductivity and high theoretical surface area, the theoretical limit of the specific capacitance is 550 F g −1 . [5][6][7][8][9] Therefore, different strategies have been applied to improve the capacitance of carbon-based electrodes, among which a promising approach is to introduce pseudocapacitance by adding manganese oxides (MnO x ) due to their high theoretical capacitances and their earth-abundant and nontoxic nature.…”

Section: Introductionmentioning

confidence: 99%

Flash‐Induced Ultrafast Production of Graphene/MnO with Extraordinary Supercapacitance

Yang

et al. 2021

Small Methods

Self Cite

MnO 2 ) electrodes (1110 F g −1 ), [10,11] which indicates its potential to further improve the capacitance of carbon-based electrodes. In 2013, Liao et al. [10] proposed the fabrication of vertically-aligned graphene@MnO nanosheets as high-performance SC electrodes through a hydrothermal process, and increased the specific capacitance of electrode to 790 F g −1 . Later, other fabrication approaches such as carbon-coating of self-assembly of MnO nanoparticles, direct electrospinning on carbon nanofibers, and thermal plasma deposition of MnO onto porous carbon materials have also been investigated to synthesize MnO/carbon electrodes. [11][12][13] However, although nano-MnO has been synthesized and deposited in carbon-based electrodes, the process is relatively complicated and usually requires multiple steps. This is because nano-MnO suffers from agglomeration of the particles during the synthesis process, which leads to loss of surface active sites and thus a decrease in electrochemical activity. As a result, the reported capacitances of MnO/carbon electrodes are generally less than 800 F g −1 , which are far below the theoretical limit of MnO (only approximately 60% is achieved). Therefore, it remains challenging to well anchor the MnO homogeneously onto carbon networks through a facile and simple process to produce high capacitance SC electrodes.Flash reduction is considered as one promising solution to the production of graphene/MnO electrodes in a green and facile manner. The irradiation of intensive flash light pulse triggers fierce reduction and exfoliation of graphene oxide (GO) films due to efficient photothermal effect, leaving highly conductive and porous flash reduced graphene oxide (frGO) electrodes with excellent electrochemical performances. [14][15][16][17] Large amount of gases such as carbon monoxide (CO), carbon dioxide (CO 2 ), water vapor (H 2 O), and hydrogen (H 2 ) are released from the reduction of GO, coupled with instant temperature rise within GO films after flash irradiation, which provides an ideal environment for the reduction of MnO 2 to MnO. [18,19] In this paper, we report, for the first time, a green and simple co-reduction method for producing high-performance graphene/MnO electrodes via ultrafast flash reduction process within several milliseconds. We tailor the reducing gases (CO and H 2 ) generated from flash reduction of GO to fully transform the pre-deposited MnO 2 nano-needles into MnO without agglomeration simultaneously during the production of high-quality porous graphene materials. Through rational control the feeding ratio guided by simulation studies, optimal Production of high-capacitance electrodes beyond the theoretical limit of 550 F g −1 of pure graphene materials is highly desired for energy storage applications, yet remains an open challenge, especially with a facile and simple process. By rational design of reaction condition guided by theoretical analysis, the ultrafast (within millisecond) fabrication of highperformance graphene/MnO electrodes via a low-cost ...

“…However, the zigzag network and overlarge pore size make the porous structures unsuitable for maximizing spatial charge storage. The onion-like, edge-oriented, or other particles with a large external surface and edge area can provide additional ion adsorption/desorption sites, enlarging the capacitance at the high-frequency region 7,18,[31][32][33] . Nevertheless, it always requires another scaffold to support these nanosized particles, leading to a critical influence on the high-frequency response.…”

Section: Introductionmentioning

confidence: 99%

Vertical Graphene Arrays for AC Line-Filtering Capacitors

Wen

Chen

et al. 2021

Preprint

High-frequency responsive electrochemical capacitor (EC), which can convert alternating current (AC) in the circuit to direct current (DC), is an ideal filtering capacitor with lightweight superiority to replace the bulky aluminum electrolytic capacitor (AEC). However, current electrodes are difficult to achieve high energy density and high-frequency response properties simultaneously, primarily due to the electrode structure dilemmas of maximizing the electrode area or accelerating the ion transport. Herein, strictly vertical graphene arrays (SVGAs) directly prepared by electric-field-assisted plasma enhanced chemical vapor deposition have been successfully designed as the main electrode material of ECs to ensure the ions rapidly adsorb/desorb within the richly available surface spaces. The SVGAs exhibit an excellent specific areal capacitance of 1.72 mF‧cm− 2 at Φ120 = 80.6° even after 500,000 cycles in the aqueous ECs, which is far better than that of most quasi-vertical electrodes and carbon-related materials. Impressively, the output voltage could also be improved to 2.5 V when using the organic electrolyte, and an ultra-high energy density of 4.75 mF‧V2‧cm− 2 at Φ120 = 80.6° can also be handily achieved. Moreover, both aqueous and organic ECs-SVGAs can well smooth arbitrary AC waveforms into DC signals, indicating that ECs-SVGAs have colossal potentials to replace outmoded AECs.