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Metal organic frameworks (MOFs) are considered as very promising positive electrode materials for supercapacitors. To achieve good electrochemical performance, in this work, we report a mixed-ligand approach to prepare modified Ni-MOF by using trimesic acid (BTC) as the modulator to partially replace the terephthalic acid (PTA) ligands. The introduction of BTC can induce the formation of nanosheets with inserted albizia flower-like spheres, where the nanowires on the albizia flower-like spheres can provide rich redox reaction sites and the “spacer” spheres between the layers can hinder the aggregation of the 2D nanosheets to provide fast transport pathways. Moreover, adsorption simulation shows that the adsorption energy of OH− on the mixed organic ligands is increased after introducing the BTC ligands, which may improve the reversible redox reaction kinetics in the electrode materials. The as-obtained albizia flower-like spheres@nanosheets structured Ni-MOF with the optimized amount of BTC exhibits a high capacitance of 920 F g−1 at 1 A g−1, good rate capability of 61% at 20 A g−1, and an excellent cycling stability in 6 M KOH electrolyte. This work may provide helpful guidance for controlling the structure and surface property of MOFs to improve the electrochemical performance for supercapacitors.

A novel 1D/2D hybrid design is reported for synthesizing a high performance NiCo-hydroxide nanowires/reduced graphene oxide (NiCo-NWs/G) composite. The oxygen-containing groups on the graphene oxide surface can act as anchoring sites for uniformly adsorbing the metal seeds, leading to the dispersed formation of thin NiCo-NWs on the graphene surface. The existence of graphene in NiCo-NWs/G can provide a conductive network to boost the faradaic reactions. In addition, the bimetallic NiCo-NWs possess rich redox reaction sites and the thin nanowire structure ensures that electrons can move rapidly from the reaction sites to the current collectors. Owing to the synergic effects of 1D NiCo-NWs and 2D graphene, the developed NiCo-NWs/G electrode exhibits an excellent performance of 1449 F g−1 at a current density of 1 A g−1, a high rate capability of 61% at 20 A g−1, and a good cycling stability in 6 M KOH electrolyte. Moreover, the asymmetric supercapacitor with NiCo-NWs/G as a positive electrode and active carbon as a negative electrode delivers a high energy density of 42.1 W h kg−1 at a power density of 0.8 kW kg−1. This work may pave a promising new way for the development of 1D/2D composites based on pseudocapacitive hydroxides and carbon materials for high-performance asymmetric supercapacitors.

Pd nanocatalysts were successfully synthesized by the ethylene glycol reduction method using graphene as supports and applied to the selective hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN). The results indicate that the low transfer resistance and strong metal-support interactions between RGO and Pd nanoparticles of Pd/RGO can efficiently improve the selectively. The low transfer resistance can shorten the stay time of the product molecule o-chloroaniline (o-CAN) on the surface of the catalyst sites and then reduce the dechlorination side-reaction of o-CAN. The strong metal-support interactions can lead to the electron-deficient state of the Pd nanoparticles which weakened the extent of electron feedback from the Pd nanoparticles to the aromatic ring and suppressed the hydrodechlorination of o-CAN. Moreover, the selectivity can be further improved for the hydrogenation of o-CNB after grafting sodium polystyrenesulfonate on the Pd/RGO to cover the low-coordinated surface Pd atoms.

Lithium sulfur (Li-S) battery is considered as one of promising energy-storage devices owing to its high energy density and low cost. However, it is still a great challenge to explore stable sulfur cathode with high sulfur loading and good cycling performance. Herein, we report a facile method to prepare N,S co-doped hierarchical pore structured carbon foam @porous carbon (CF@N-SPC) through a carbonation process from resin aerogel coated melamine foam with thiourea as the source for N and S codoping. The close combination of a carbon interconnected skeleton and the resin aerogel derived carbon forms the hierarchical pore structure that improves the electron and ion transport. The prepared CF@N-SPC can be used as a freestanding cathode without a conductive additive and a binder. Due to the synergistic effect of the hierarchical pore structure and N, S codoping, the sulfur loading in the carbon foam-based cathode can reach up to 10.6 mg cm−2. Owing to these unique merits, the CF@N-SPC/S cathode exhibits high capacity and good cycling performance: it yields a discharge capacity of 1212 mA h g−1 at 0.1 C with 4.0 mg cm−2 sulfur loading; it also exhibits a good discharge capacity of 668 mA h g−1 at 0.5 C when the sulfur loading increases to 10.6 mg cm−2, capacity retained by 72% in 200 cycles; it experiences a very small capacity decay rate of 0.05% per cycle in 700 cycles at 1 C. Our rational design and facile synthesis of the carbon foam-based freestanding cathode is promising and applicable for development of high performance Li-S batteries.

Here we report a facile and mild synthesis of the sulfonated graphene (PSS-RGO) catalysts by in situ polymerization of sodium p-styrenesulfonate. Graphene sheets can be used as the flat backbones to graft abundant sulfonate groups on both sides. The PSS-RGO catalysts were characterized by 1H Nuclear Magnetic Resonance (1H NMR), energy dispersive spectrometer, Raman spectroscopy, X-ray photoelectron spectroscopy, and so on. The catalytic properties of the PSS-RGO catalysts for the hydrolysis of ethyl acetate and the esterification of acetic acid with ethanol were evaluated, showing that the as-made PSS-RGO catalysts were active for both probe reactions. The possible deactivation mechanism involved in the surface catalysis of the graphene-based acid catalysts has been addressed.

Nitrogen-doped hollow carbon materials have been facilely fabricated via the simple carbonization process by using ZIF-8 polyhedrons coated with polydopamine (PDA). ZIF-8 polyhedrons can be used as sacrificial templates for the hollow structures and both ZIF-8 polyhedrons and PDA can be used as carbon and nitrogen sources. Due to the synergistic effect of the hierarchical pore structure and high level N doping, the nitrogen-doped hollow carbon materials can serve as ideal electrode materials for supercapacitors, exhibiting an enhanced specific capacitance of 253 F g−1 at a current density of 0.2 A g−1 and excellent rate capability with a capacitance retention of 70% at a high current density of 20 A g−1. Moreover, ZIF-8@PDA-C also shows excellent electrochemical stability with 93% capacitance retention over 10 000 cycles. This will also provide a new strategy for configuring nitrogen-doped hollow carbon electrode materials for supercapacitors and other carbon-based energy storage devices.

Two-dimensional (2D) N,S co-doped porous carbon nanosheets are prepared in the presence of graphene oxide (GO) from expired wheat flour. It is found that GO can effectively direct the morphologies of the activated products, resulting in unique 2D structures. The as-obtained 2D N,S co-doped porous carbon nanosheets as electrodes for supercapacitors exhibit a high specific capacitance of 291 F g−1 at a current density of 0.5 A g−1 and good rate capability with a capacitance retention of 70% at a high current density of 30 A g−1. The 2D N,S co-doped porous carbon nanosheet electrodes also exhibit good cycling performance, possessing a high capacitance retention of over 93% after 5000 charge–discharge cycles at a current density of 5 A g−1. Experimental and theoretical results reveal that the synergistic effect of the N and S species can improve the electrochemical performance. The peculiar 2D structural characteristics featuring a short ion transport distance and abundant porous channels also can increase the specific capacitance.

Two-dimensional (2D) nitrogen-containing porous carbon nanosheets are prepared in the presence of graphene oxide (GO) as a structure-directing agent by a simple yet facile hydrothermal method. It is found that GO can effectively tune the morphologies of the hydrothermal carbonaceous products, resulting in the unique 2D structures. The as-obtained 2D nitrogen-containing porous carbon nanosheets as electrodes for supercapacitors exhibit a high specific capacitance of 301.6 F g−1 at a current density of 0.5 A g−1 and superior rate capability with a capacitance retention of 70.5% at a high current density of 20 A g−1. The 2D nitrogen-containing porous carbon nanosheet electrodes also exhibit good cycling performance, possessing a high capacitance retention of over 92.3% after 5000 charge–discharge cycles at a current density of 5 A g−1. Such superior electrochemical performance of the 2D nitrogen-containing porous carbon nanosheets could be attributed to the high pseudocapacitive effect of the nitrogen-containing species and the peculiar structural characteristics featuring a short ion transport distance and abundant porous channels.

Ultrathin 2D nitrogen-doped carbon nanosheets with a thickness of about 5 nm have been facilely synthesized from potato starch by using graphene oxides (GO) as the structure-directing agent. The pore structures and surface properties can be feasibly and rationally tailored by addition of a certain amount of GO in the precursor. The addition of GO to the potato starch can increase the surface areas and the pyridinic-N and pyrrolic-N ratios of the as-prepared 2D carbon nanosheets. The as-obtained ultrathin nitrogen-doped carbon nanosheets with the optimized amount of GO in potato starch (3 wt%) possess a unique 2D structure, a high N content, and high ratios of pyridinic-N and pyrrolic-N, exhibiting a high capacitance of 301 F g−1 at 0.5 A g−1, superior rate capability of 81% at 50 A g−1, and good cycling stability in 6 M KOH electrolyte. Experimental and theoretical results show that high pyridinic-N and pyrrolic-N ratios in the NCNSs are beneficial for improving the electrochemical performance. This work may provide helpful guidance for understanding the effect of the addition of GO to biomass precursors on the electrochemical performance of the 2D nitrogen-doped carbon electrodes for supercapacitors.

Nitrogen-containing groups functionalized graphene has been synthesized via the reaction of graphene oxide with 1, 8-diazoicyclo (5, 4, 0) undecene-7, trimethylamine (DBU) through epoxide-ring-open reaction without high temperatures. Samples were analyzed by x-ray diffraction spectroscopy, Raman, N2 adsorption-desorption, transmission electron microscope, galvanostatic charge/discharge, and cyclic voltammetrys. Results show that the amount of added DBU has great influence on the structure and properties of the resultant graphene. The DBU modified graphene with appropriate N content and low charge transfer resistance exhibits 190 F g−1 at 5 mV s−1 in 6 M KOH aqueous solution. This will also provide a new strategy for configuring nitrogen-containing groups functionalized graphene electrode materials for supercapacitors and other energy storage devices.