Abstract:Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH) networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH). When serving as electrode… Show more
“…Figure 2b shows the Raman spectrum for the Cu(OH) 2 /graphene composite. The Raman spectra exhibit three noticeable peaks at 1349 cm −1 , 1579 cm −1 , and 2715 cm −1 corresponding to the D-band, G-band, and 2D-band of graphene, respectively, which confirmed the existence of graphene [9]. Fig.…”
Section: Resultsmentioning
confidence: 93%
“…As illustrated in Fig. 1, the electrochemical synthesis process was implemented in a two-electrode cell system [9], where graphite foil acts as anode and Cu foam acts as cathode. In order to achieve in situ self-assembly of cypress leaf-like Cu(OH) 2 nanostructure/graphene nanosheets composite, the electrolyte is a mixed solution of 0.1 M (NH 4 ) 2 SO 4 (100 mL) and NH 3 ·H 2 O (3 mL).…”
Section: Methods Sectionmentioning
confidence: 99%
“…The ever depletion of fossil fuels and aggravation of environmental pollutions call for urgently exploring sustainable energy sources and developing energy storage technologies to meet application requirements of many electronic devices and hybrid vehicles in our modern society [1, 2]. As a promising energy storage device, supercapacitors (SCs) have attracted much attention in view of their small size, high power density, fast recharge ability, long lifespan and desirable operational safety [3–8] There are two classes of SCs, pseudocapacitors and electrical double layer capacitors (EDLCs), on the basis of energy storage mechanism [9]. Carbon material with many advantages of abundance, non-toxic, large surface area, good conductivity, excellent chemical durability, is a typical electrode material for double-layer capacitors (EDLCs), storing charge in the electric double-layer near electrolyte/electrode surface by electrostatic adsorption [10–16].…”
Transition metal hydroxides and graphene composite holds great promise to be the next generation of high performance electrode material for energy storage applications. Here we fabricate the cypress leaf-like Cu(OH)
2
nanostructure/graphene nanosheets composite through one-step in situ synthesis process, employed as a new type of electrode material for high efficiency electrochemical energy storage in supercapacitors. A solution-based two-electrode system is applied to synthesize Cu(OH)
2
/graphene hybrid nanostructure, where anodic graphene nanosheets firmly anchor cathodic Cu(OH)
2
nanostructure due to the electrostatic interaction. The in situ self-assembly of Cu(OH)
2
/graphene ensures good structural robustness and the cypress leaf-like Cu(OH)
2
nanostructure prompt to form the open and porous morphology. The hybrid structure would facilitate charge transport and effectively mitigate the volume changes during long-term charging/discharging cycles. As a consequence, the Cu(OH)
2
/graphene composite exhibits the highest capacitance of 317 mF/cm
2
at the current density of 1 mA/cm
2
and superior cyclic stability with no capacitance decay over 20,000 cycles and remarkable rate capability at increased current densities.
“…Figure 2b shows the Raman spectrum for the Cu(OH) 2 /graphene composite. The Raman spectra exhibit three noticeable peaks at 1349 cm −1 , 1579 cm −1 , and 2715 cm −1 corresponding to the D-band, G-band, and 2D-band of graphene, respectively, which confirmed the existence of graphene [9]. Fig.…”
Section: Resultsmentioning
confidence: 93%
“…As illustrated in Fig. 1, the electrochemical synthesis process was implemented in a two-electrode cell system [9], where graphite foil acts as anode and Cu foam acts as cathode. In order to achieve in situ self-assembly of cypress leaf-like Cu(OH) 2 nanostructure/graphene nanosheets composite, the electrolyte is a mixed solution of 0.1 M (NH 4 ) 2 SO 4 (100 mL) and NH 3 ·H 2 O (3 mL).…”
Section: Methods Sectionmentioning
confidence: 99%
“…The ever depletion of fossil fuels and aggravation of environmental pollutions call for urgently exploring sustainable energy sources and developing energy storage technologies to meet application requirements of many electronic devices and hybrid vehicles in our modern society [1, 2]. As a promising energy storage device, supercapacitors (SCs) have attracted much attention in view of their small size, high power density, fast recharge ability, long lifespan and desirable operational safety [3–8] There are two classes of SCs, pseudocapacitors and electrical double layer capacitors (EDLCs), on the basis of energy storage mechanism [9]. Carbon material with many advantages of abundance, non-toxic, large surface area, good conductivity, excellent chemical durability, is a typical electrode material for double-layer capacitors (EDLCs), storing charge in the electric double-layer near electrolyte/electrode surface by electrostatic adsorption [10–16].…”
Transition metal hydroxides and graphene composite holds great promise to be the next generation of high performance electrode material for energy storage applications. Here we fabricate the cypress leaf-like Cu(OH)
2
nanostructure/graphene nanosheets composite through one-step in situ synthesis process, employed as a new type of electrode material for high efficiency electrochemical energy storage in supercapacitors. A solution-based two-electrode system is applied to synthesize Cu(OH)
2
/graphene hybrid nanostructure, where anodic graphene nanosheets firmly anchor cathodic Cu(OH)
2
nanostructure due to the electrostatic interaction. The in situ self-assembly of Cu(OH)
2
/graphene ensures good structural robustness and the cypress leaf-like Cu(OH)
2
nanostructure prompt to form the open and porous morphology. The hybrid structure would facilitate charge transport and effectively mitigate the volume changes during long-term charging/discharging cycles. As a consequence, the Cu(OH)
2
/graphene composite exhibits the highest capacitance of 317 mF/cm
2
at the current density of 1 mA/cm
2
and superior cyclic stability with no capacitance decay over 20,000 cycles and remarkable rate capability at increased current densities.
“…E, Schematic illustration of the deposition of electrochemically exfoliated graphene nanosheets on a 3D porous Ni foam electrode. Reproduced with permission from Ma et al, Copyright 2016, RSC. F, Preparation of graphene‐2D material composites by simultaneous electrochemical exfoliation and assembly in a single‐compartment electrochemical cell.…”
Section: Graphene Composite Synthesis By Electrochemical Exfoliationmentioning
confidence: 99%
“…Exfoliated graphene nanosheets from graphite electrodes would attach on the surface of porous counter electrodes forming 3D porous composites. For example, Ma et al presented a one‐step synthesis of a Ni(OH) 2 /graphene composite via synchronous anodic exfoliation of a graphite electrode and deposition of graphene nanosheets on a 3D porous cathode. As shown in Figure E, Ni(OH) 2 was formed on the surface of 3D nickel foam, while electrochemically exfoliated graphene nanosheets were assembled on the surface of Ni(OH) 2 .…”
Section: Graphene Composite Synthesis By Electrochemical Exfoliationmentioning
Synthesis of structurally controlled graphene materials is critical for realizing their practical applications. The electrochemical exfoliation of graphite has emerged as a simple method to produce graphene materials. This review examines research progress in the last 5 years, from 2015 to 2019. Graphene material synthesis methods generally have a trade‐off between increasing production yield and achieving better material property control. The synthesis conditions for synthesizing pristine graphene, graphene oxide (GO), and graphene composites are significantly different. Thus, in this review, we first discuss synthesis methods for graphene materials with high C/O ratios from four aspects: graphite electrodes, equipment engineering, electrolytes, and additional reduction methods. Next, we survey synthesis methods for GO and examine how the pretreatment of the graphite electrodes, electrolytes, and operation parameters, such as applied voltages, electrolyte temperatures, and mechanical forces, affect the quality of GO. Further, we summarize electrochemical exfoliation methods used to dope graphene materials, introduce covalent functional groups, incorporate various nanoparticles, and assembly of graphene architectures. For all synthesis methods, we compare the properties of resulting graphene materials such as C/O ratios, lateral size, layer numbers, and quality characterized by Raman spectroscopy. Lastly, we propose our perspectives on further research. We hope this review stimulates more studies to realize the on‐demand production of graphene materials with desired properties using electrochemical exfoliation methods.
Lithium‐rich, Mn‐based layered oxides Li2MnO3‐LiMO2 (M=Ni, Co) have been considered as promising cathode candidates owing to their high capacity. However, the resources shortage and high price of cobalt make it imperious to substitute cobalt with other high‐abundance elements. Here, we synthesized a low‐cost, cobalt‐free, Fe‐substituted oxide material, Li(Li0.16Ni0.19Fe0.18Mn0.46)O2. It exhibited a high reversible capacity of 169.2 mAh g−1 after 100 cycles and maintained an extraordinarily high discharge potential during cycling. X‐ray photoelectron spectroscopy and DFT calculations revealed that super iron FeIV exists in the delithiated state, and oxygen participates in the redox reaction in addition to the Ni2+/Ni4+ and Fe3+/Fe4+ redox couples. The anionic oxidation preferentially occurred on oxygen with a Li−O−Li configuration and with oxidized Fe and Ni coordination.
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