Binder-free, nano-sized needlelike MnO2-submillimeter-sized reduced graphene oxide (nMnO2-srGO) hybrid films with abundant porous structures were fabricated through electrophoretic deposition and subsequent thermal annealing at 500 °C for 2 h. The as-prepared hybrid films exhibit a unique hierarchical morphology, in which nMnO2 with a diameter of 20—50 nm and a length of 300—500 nm is randomly anchored on both sides of srGO. When evaluated as binder-free anodes for lithium-ion half-cell, the nMnO2-srGO composites with a content of 76.9 wt% MnO2 deliver a high capacity of approximately 1652.2 mA•h•g−1 at a current density of 0.1 A•g−1 after 200 cycles. The high capacity remains at 616.8 mA•h•g−1 (ca. 65.1% capacity retention) at a current density as high as 4 A•g−1. The excellent electrochemical performance indicates that the nMnO2-srGO hybrid films could be a promising anode material for lithium ion batteries (LIBs).

A hierarchical graphene/polyaniline hollow microspheres with sandwich structure (GCS@PANI@RGO) have been successfully synthesized by the in situ polymerization of PANI on the surface of graphene carbon sphere (GCS) and then the electrostatic self-assembly of graphene oxide and reduction without etching templates. The morphologies and microstructures of the microspheres were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and nitrogen adsorption measurements. The results show that the GCS@PANI@RGO composites demonstrate desirably hierarchical hollow microspheres with sandwich structure and the strong interactions such as electrostatic interactions, hydrogen bonding and π–π interactions existed between the layers in hierarchical hollow microspheres. The electrochemical behaviors of GCS@PANI@RGO as electrode were investigated by cyclic voltammograms, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The GCS@PANI-8@RGO showed a high specific capacitance of 446.19 F g−1 at the scanning rate of 5 mV s−1 in 1 M H2SO4 solution, and exhibit an outstanding long-term cycling stability with capacitance retentions of 93.4% after 1000 charging–discharging cycles at a current density of 2 A g−1 and even 88.7% after 5000 cycles. The excellent electrochemical performance can be ascribed to the novel sandwiched hollow structure, and the synergic effect of the three components of GCS, PANI and RGO, which greatly enhance the electrical conductivity, promote the utilization of active materials and improve the structural stability. Therefore, such novel hierarchical hollow materials could be considered as quite suitable and promising electrodes for high-performance supercapacitors.

Graphene oxide/resorcinol–formaldehyde microsphere (GORFM) was synthesised by a simple-inverse suspension polymerisation under ambient pressure drying and the graphene composite microsphere (GCM) was obtained by carbonisation in a nitrogen atmosphere. The morphologies and microstructures of GORFM and GCM samples were characterised by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface area analysis. The results showed that the diameters of GORFM were controlled in the range of 5–10 μm with perfect sphericity. The inner layer of GORFM was composed of resorcinol–formaldehyde (RF) particles, and the outer layer was the wrinkled GO sheets intercalated with RF through chemical and physical interactions. The GCM-1.5 sample achieved the highest specific surface area of 1128 m2/g and the mesopore area was 699 m2/g. The electrochemical behaviours of GCM as an electrode were investigated by cyclic voltammograms, electrochemical impedance spectroscopy and capacitive deionisation (CDI). The specific capacitance and electrosorption capacity of GCM-1.5 was 290.2 F/g and 33.52 mg/g, respectively. The current efficiencies were in the range of 77.75–81.41%. These results implied that GCM had a potential application in CDI due to its low-cost and high performance.

A new nitrogen rich porous graphene-cross-linked melamine formaldehyde carbon cryogel (GCMFCC) was successfully prepared by a sol-gel poly condensation reaction catalyzed by Na2CO3; it was subsequently converted to a cryogel by freeze-drying. The melamine formaldehyde carbon cryogel (MFCC) and GCMFCC-x were synthesized and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM). XPS and BET analysis showed that the as- prepared GCMFCC-5% cryogel had a highest nitrogen content of 14.29% with surface area of 261.33 m2/g and unimodal meso-pore volume of 0.36 cm3/g. The electrochemical behavior of MFCC and GCMFCC-x samples was investigated by cyclic voltammetry and charge/discharge cycles. GCMFCC-5% achieved highest capacitance of 313.24 F/g. Hence, GCMFCC is a promising electric double-layer capacitor material with low production costs and the ability to avoid supercritical drying.

A new method of synthesizing hybrid organic and carbon xerogel using graphene oxide as the cross-linking agent in the polycondensation of phenol and formaldehyde is presented. The organic xerogel is dried under ambient conditions, and the graphene cross-linked phenol–formaldehyde hybrid carbon xerogel (GCPFCX) is obtained through carbonization. Mechanically strong graphene oxide (GO) increases gel skeleton strength, giving organic xerogel very low drying shrinkage, low density and high mechanical property. The GCPFCX exhibits a layered structure, indicating a change in the gel structure resulting from the addition of GO. The PF molecular chains possibly grow along the GO surface because of strong interactions between the two compounds.

A new synthesis route based on polycondensation of phenol and formaldehyde cross-linked by graphene oxide (GO) was developed. Wet gel after gelation was converted into an organic xerogel by ambient pressure drying to obtain GO-cross-linked phenol–formaldehyde (PF) organic xerogels (GOCPFOX). Graphene-cross-linked PF carbon xerogels (GCPFCX) were produced by carbonization. The morphology and chemical structure of GOCPFOX and GCPFCX were analyzed. The electrochemical behavior of GCPFCX as an electrode material in electric double-layer capacitors (EDLCs) was investigated. Results show that the high mechanical strength of GO increased the gel skeleton strength; thus, organic xerogels exhibit very low drying shrinkage. Scanning electron micrographs indicated that addition of GO altered the gel structure. Thus, when GO was added into the PF solution, the PF molecular chains were anchored on the surface of GO by chemical and physical interaction. The GCPFCX-10 sample achieved the highest specific surface area, mesoporous volume, and specific capacity with 378 m2/g, 0.56 cm3/g, and 116 F/g, respectively. Hence, GCPFCX is a potential material for EDLCs owing to its low production cost and ability to avoid supercritical drying.

In this paper, 2,2′-dichlorohydrazobenzene was synthesized by the electrochemical reduction of o-chloronitrobenzene using the ion-exchange membrane method. The effects of different catalysts (litharge, lead tetroxide, and lead nitrate) on the synthesis were investigated. The influence of different catalyst loading approaches on the electrochemical reduction were also examined. The structure and surface morphology of the catalysts were characterized by X-ray diffraction and scanning electron microscopy. Catalyst activity was examined by dynamic potential analyses and cyclic voltammetry. Litharge was found to induce the greatest improvement in the electrolysis reaction rate and also decreases the reaction time. Coating the catalyst on the cathode helps enhance the product yield. The possible reaction mechanism was studied, and the catalyst was found to play a key role in transforming raw substances into intermediates. However, there is little effect on intermediate product transformation into the desired product.Highlights► 2,2′-dichlorohydrazobenzene was synthesized by electrochemical reduction. ► The ion-exchange membrane method was used in synthesis. ► The main active substance in the electrochemical reduction is litharge. ► Coating the catalyst on the cathode can improve the product yield. ► A possible reaction mechanism is proposed.

TiO2-doped carbon aerogels (CAs) were synthesized by sol–gel polymerization of a mixture of resorcinol, formaldehyde and tetrabutyl orthotitanate, followed by gelation and supercritical drying and carbonization in N2 gas atmosphere. The morphology of these TiO2-doped CAs was characterized by transmission electron microscopy. X-ray diffraction and Brunauer–Emmett–Teller methods were employed to determine the microstructure and surface characteristics of samples. It was found that the doped TiO2 had no significant effect on the surface area of the samples, whereas the pore and mesopore volumes were increased by the addition of TiO2. The TiO2 particles were kept still as anatase in samples carbonized at 900 °C, and did not transform into rutile on heating. Electrochemical performance of the samples as electrode materials was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge/discharge measurements. The results showed that the specific capacitance of CA electrodes had been improved by TiO2 doping, and the samples with wider pore diameters have higher capacitance values.

•The cross-linked quaternised polyvinyl alcohol membrane was synthesized.•The effects of cross-linking degree on the membrane were investigated.•The membrane as anion exchange membrane was combined with activated carbon.•The compressed membrane electrode was compared with coated membrane electrode.•The kinetics of electrosorption to electrode followed the pseudo-first-order model.A cross-linked quaternised polyvinyl alcohol (QPVA) membrane, modified with glycidyltrimethylammonium chloride and glutaraldehyde, was used as an anion exchange membrane for membrane capacitive deionization (MCDI). The microstructure and properties of the membrane were characterized by elemental analysis, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The electrochemical influences of QPVA on activated carbon electrode were examined by cyclic voltammetry and electrochemical impedance spectroscopy. And electrosorption performance of the composite electrode was investigated by NaCl capacitive deionization test. The results showed that the structure order degree, ion exchange capacity and moisture content of QPVA decreased with an increasing degree of cross-linking. Accompanied by lower electric resistance, the carbon electrode with a compressed membrane exhibited a higher specific capacitance (180 F/g) than the coated membrane (155 F/g). The cross-linked QPVA membrane (0.8 mL 5 wt.% glutaraldehyde solution and 0.5 g QPVA) was compressed onto an active carbon (AC) electrode and provided the optimum conditions of deionization with the adsorption capacity of 15.6 mg/g, and the adsorption kinetics of NaCl onto the composite electrodes was affirmed by Lagergren's pseudo-first-order model.