Hierarchical graphene-based composite consisting of graphene sheets intercalated by MnO2-coated carbon nanotubes (MnC) was prepared for high-performance supercapacitor electrode. The highly ...negatively charged graphene oxides reduced by urea (RGO) and the positively charged MnC functionalized with poly(diallyldimethylammonium chloride) created a strong electrostatic interaction, forming a hierarchical nanostructure. The elelctrocapacitive behaviors of MnC/RGO (MnC-G) were systematically investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 193 F/g was achieved for the MnC-G composite with 37% RGO, which was almost 3-fold higher than 69 F/g of carbon nanotubes/RGO and 2-fold higher than 89 F/g of MnO2/RGO composite. Moreover, an excellent rate performance, a good capacitance retention (∼70%) and a superior Coulombic efficiency (94–96%) were also observed during the continuous 1300 cycles of galvanostatic charge–discharge.
A method for preparing three-dimensional (3D) carbon-based architectures consisting of mesoporous carbon spheres intercalated between graphene sheets is demonstrated in this paper. Colloidally ...dispersed negatively charged graphene oxide (GO) sheets strongly interacted with positively charged mesoporous silica spheres (MSS) to form a MSS-GO composite. The MSS were then used as template for replicating mesoporous carbon spheres (MCS) via a chemical vapor deposition process, during which the GO sheets were reduced to reduced graphene oxide (RGO). Removal of the silica spheres left behind a 3D hierarchical porous carbon architecture with slightly crumpled graphene sheets intercalated with MCS. The 3D carbon structure contained a low amount of oxygen (3.2% of atomic ratio of O/C) than a RGO sample (10.1%), which was prepared by using the chemical reduction method with hydrazine as the reducing agent. Thermal annealing of the 3D carbon structure in ammonia atmosphere further reduced the O/C atomic ratio to 1.6%. The capacitive performance of the samples as supercapacitor electrodes was investigated using the cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. The 3D carbon structure showed a substantially lower equivalent series resistance and a higher power capability than the RGO electrode. In addition, the 3D carbon electrode exhibited an excellent electrochemical cyclability with 94% capacitance retention after 1000 cycles of galvanostatic charge-discharge. The method demonstrated in this work opens up a new route to the preparation of 3D graphene-based architectures for supercapacitor applications.
We present a facile yet effective two-step activation method to prepare a hierarchically porous carbon with natural shiitake mushroom as the starting materials. The first step involves the activation ...of shiitake mushroom with H3PO4, while the second step is to further activate the product with KOH. The resulting carbon is comprised of abundant micro-, mesopores and interconnected macropores that has a specific surface area up to 2988m2g−1 and pore volume of 1.76cm3g−1. With the unique porous nature, the carbon exhibited a specific capacitance of 306 and 149Fg−1 in aqueous and organic electrolyte, respectively. Moreover, this carbon also shows a high capacitance retention of 77% at large current density of 30Ag−1 and exhibited an outstanding cycling stability with 95.7% capacitance preservation after 15,000 cycles in 6M KOH electrolyte. The far superior performance as compared with those of the commercially most used activated carbon RP20 in both aqueous and non-aqueous electrolyte demonstrates its great potential as high-performance supercapacitor electrode. The two-step method developed herein also represents a very attractive approach for scalable production of various functional carbon materials using diverse biomasses as starting materials.
Hollow carbon spheres (HCS) with specific surface areas as high as 2239 m2/g were prepared by chemical vapor deposition with ferrocene as the carbon precursor and colloidal silica spheres as the ...template. Chemical oxidative polymerization of aniline in the presence of the HCS yielded composite materials with a layer of polyaniline (PANI) deposited on the external surface of the HCS. The electrocapacitive properties of the composite materials (HCS-PANI) with different PANI contents were evaluated using cyclic voltammetry, galvanostatic charge−discharge, and electrochemical impedance spectroscopy techniques. Results showed that the specific capacitances of the HCS before and after PANI coating were, respectively, 268 and 525 F/g in an aqueous H2SO4 electrolyte, which is almost doubly enhanced. A maximum energy density of 17.2 Wh/kg was achieved for the HCS-PANI electrode at a discharge current density of 0.1 A/g. However, the energy density of the HCS-PANI electrodes with higher PANI contents (>65 wt %) declined quickly as the power density increased. An asymmetric supercapacitor using the composite material as the positive electrode and HCS as the negative electrode showed good electrochemical stability, with 73% of the capacitance, 75% of the energy density, and almost 100% of the power density being retained after 1000 cycles at a current density of 1.0 A/g.
By using three-dimensional (3D) tubular molybdenum disulfide (MoS2) as both an active material in electrochemical reaction and a framework to provide more paths for insertion and extraction of ions, ...PANI nanowire arrays with a diameter of 10–20 nm can be controllably grown on both the external and internal surface of 3D tubular MoS2 by in situ oxidative polymerization of aniline monomers and 3D tubular MoS2/PANI hybrid materials with different amounts of PANI are prepared. A controllable growth of PANI nanowire arrays on the tubular MoS2 surface provides an opportunity to optimize the capacitive performance of the obtained electrodes. When the loading amount of PANI is 60%, the obtained MoS2/PANI-60 hybrid electrode not only shows a high specific capacitance of 552 F/g at a current density of 0.5 A/g, but also gives excellent rate capability of 82% from 0.5 to 30 A/g. The remarkable rate performance can be mainly attributed to the architecture with synergistic effect between 3D tubular MoS2 and PANI nanowire arrays. Moreover, the MoS2/PANI-60 based symmetric supercapacitor also exhibits the excellent rate performance and good cycling stability. The specific capacitance based on the total mass of the two electrodes is 124 F/g at a current density of 1 A/g and 79% of its initial capacitance is remained after 6000 cycles. The 3D tubular structure provides a good and favorable method for improving the capacitance retention of PANI electrode.
An artificial photocatalyst, Pt–PdS/CdS with the Pt and PdS, respectively acting as reduction and oxidation cocatalysts, can achieve quantum efficiency up to 93% in photocatalytic H
2 production from ...Na
2S–Na
2SO
3 aqueous solution under visible light irradiation.
To efficiently convert solar energy into chemical energy by artificial photosynthesis, we need to develop visible-light-responsive photocatalysts with a high quantum efficiency (QE). Here we report that an artificial photocatalyst (Pt–PdS/CdS) can achieve a QE up to 93% in photocatalytic H
2 production in the presence of sacrificial reagents under visible light irradiation, and is very stable under the photocatalytic reaction conditions. The extremely high QE could be achieved by loading as low as 0.30
wt% of Pt and 0.13
wt% of PdS as cocatalysts on CdS.
Grain boundaries (GBs) significantly affect the electrical, optical, magnetic, and mechanical properties of 2D materials. An anisotropic 2D material like ReS2 provides unprecedented opportunities to ...explore novel GB properties, since the reduced lattice symmetry offers greater degrees of freedom to build new GB structures. Here the atomic structure and formation mechanism of unusual multidomain and diverse GB structures in the vapor phase synthesized ReS2 atomic layers are reported. Using high‐resolution electron microscopy, two major categories of GBs are observed in each ReS2 domain, namely, the joint GB including three structures, and the GBs formed from a reconstruction of Re4‐chains including seven different structures. Based on the experimental observations, a novel “nanoassembly growth model” is proposed to elucidate the growth process of ReS2, where three types of Re4‐chain reconstruction give rise to a multidomain structure. Moreover, it is shown that by controlling the thermodynamics of the growth process, the structure and density of GB in the ReS2 domain can be tailored. First‐principles calculations point to interesting new properties resulting from such GBs, such as a new electron state or ferromagnetism, which are highly sought after in the construction of novel 2D devices.
Nanoassembly growth model of low‐symmetry 2D materials is revealed to understand the formation mechanism of grain boundary and subdomain in CVD‐grown 1T′ ReS2. The controlled construct of diverse grain boundary structures combined with their novel properties will open up new prospects for the grain boundary‐mediated engineering of material properties and applications.
This work reports a facile method to prepare N-doped carbon sheets that are uniformly coated on the surface of CoNiO2@activated textile carbon (CS-CoNi@aTC). We used easily polymerized dopamine as ...the carbon precursor and hierarchical NiCo-LDH nanosheets grown on activated textile carbon as the flexible substrate. The subsequent thermal annealing treatment at 400 °C in a nitrogen atmosphere converts polydopamine into amorphous N-doped carbon and simultaneously decomposes the NiCo-LDH into CoNiO2. Both the thickness and mass loading of carbon sheets can be facilely controlled by changing the concentration of dopamine. Besides enhancing the areal capacitance of aTC by adding pseudocapacitance, these carbon sheets also significantly enhance the cycling stability of CoNiO2 through reinforcing the interfacial coupling of CoNiO2 nanosheets and carbon fibers. Acid etching of CoNiO2 leaves behind vertical carbon sheets connected on the aTC substrate (CS@aTC). An aqueous asymmetric supercapacitor (ASC) built with CS-CoNi@aTC and CS@aTC can exhibit remarkable cycling stability with 93% capacitance retention and 100% coulombic efficiency after continuous charging–discharging for 45 000 cycles. An assembled solid-state ASC delivers an areal capacitance of 284 mF cm−2 and a maximum volumetric energy density of 1.4 mW h cm−3 while exhibiting good flexibility and mechanical robustness.
Ruthenium oxide/graphene (RuO2/GR) hybrid materials for high performance electrochemical capacitor have been prepared by a solution-phase assembly technology between RuO2 nanosheets and GR nanosheets ...at room temperature. The high dispersion of RuO2 and GR nanosheets maintains a high structural stability for the hybrid material, and causes an obvious synergistic effect between the RuO2 and GR nanosheets. A specific capacitance of 479 F g-1 has been obtained for the hybrid material with RuO2 mass content of 40% (abbreviated as RuGR46), and a high specific capacitance of 998 F g-1 obtained for RuO2 in the electrode. The utilization of RuO2 in the RuGR46 hybrid material increases by adding GR, and the capacitance of RuGR46 is quite comparable to that of the pristine RuO2.xH2O while 60 wt% of RuO2 can be saved. A symmetrical electrochemical capacitor based on the RuGR46 electrode is assembled with 0.5 mol L-1 H2SO4 solution as the electrolyte in a voltage of 0-1.2 V. It can give a high energy density of 20.28 Wh kg-1 at a power density of 600 W kg-1. Moreover, it presents a high power density (14.03 Wh kg-1 at 12 kW kg-1) and excellent cycle performance.
