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A simple hard template method and hydrothermal process have been employed to fabricate a self-standing hierarchical porous MnO 2 /graphene film. Thus-constructed electrode materials for binder-free supercapacitors exhibit a high specific capacitance of 266.3 F g −1 at the density of 0.2 A g −1 . Moreover, the two-electrode device demonstrates an excellent rate capability and cycling stability with capacitance retention of 85.1% after 2000 charge–discharge cycles at a current density of 1 A g −1 . The porous nanostructured design can effectively improve the specific surface areas and account for the shorter relaxation time for the electrodes, resulting in a high electrochemical performance. [ABSTRACT FROM AUTHOR]

A CoO/3D graphene composite synthesized via hydrothermal method was used as an anode material for Li-ion batteries. X-ray diffraction, scanning electron microscopy, thermogravimetry, energy-dispersive X-ray spectroscopy, transmission electron microscope, cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge measurement were conducted to evaluate the physical and electrochemical properties of the CoO/3D graphene composite. Results showed that the composite delivered high rate capacities of 1481.1, 657.7, 472.5, 423.8, and 391.2 mAh g −1 , at 50, 100, 200, 300, 400, and 500 mA g −1 , respectively. The capacity after 100 cycles was 860 mAh g −1 at 50 mA g −1 , thereby indicating excellent cycle stability. The excellent electrochemical performance was ascribed to 3D graphene sheets that were formed in the composite structure. [ABSTRACT FROM AUTHOR]

Abstract The development of high-performance noble metal-free electrochemical catalyst for effective water splitting is a key factor to achieve low-cost and sustainable renewable energy production. Herein, for the first time, highly dispersed cobalt nanoparticles decorated uniform nitrogen doped graphene (CoNPs-N-GR) was design synthesized. In the preparation procedure, graphene oxide (GO) was employed as supporting material, polydopamine as nitrogen source, location reagent as well as connecting agent for uploading cobalt metal ion, and then cobalt metal-organic frameworks (ZIF-67) in situ grew on GO. During the calcining process, GO reduction, nitrogen doping and cobalt nanoparticles forming were finished in one step. Scanning electron microscopy (SEM) images, transmission electron microscopy (TEM), energy-dispersive X-ray (EDS), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) were applied to characterize the as-prepared CoNPs-N-GR. Moreover, owing to the presence of dopamine, high dispersed cobalt nanoparticles were obtained, leading to high electrocatalytic activity of CoNPs-N-GR for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. HER reaches 10 mA cm−2 at the over-potential of 0.453 V with a Tafel slope of 67 mV dec−1. OER reaches 10 mA cm−2 at the over-potential of 1.63 V with a Tafel slope of 65 mV dec−1. And the as-prepared CoNPs-N-GR shows excellent durability in the long-term stability for HER and OER. Graphical abstract Image 1 Highlights • Highly dispersed CoNPs decorated uniform nitrogen doped graphene was prepared. • Polydopamine as nitrogen source, location reagent as well as connecting agent. • In situ grow of cobalt metal-organic frameworks (ZIF-67) as cobalt precursor. • High electrocatalytic performance for both HER and OER in alkaline media. [ABSTRACT FROM AUTHOR]

Abstract: Bimetallic palladium–silver nanoparticles (NPs) supported on reduced oxide graphene (RGO) with different Pd/Ag ratios (Pd–Ag/RGO) were prepared by an easy green method which did not use any additional reducing agents or a dispersing agent. During the process, simultaneous redox reactions between AgNO3, K2PdCl4 and graphene oxide (GO) led to bimetallic Pd–Ag NPs. The morphology and composition of the Pd–Ag/RGO were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis and Raman spectroscopy. Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical activities and stabilities of these Pd–Ag/RGO catalysts for the electro-oxidation of methanol and ethanol in alkaline media. Among the different Pd/Ag ratios, the Pd–Ag (1:1)/RGO had the best catalytic activities and stability. So it is a promising catalyst for direct alcohol fuel cell applications. [Copyright &y& Elsevier]