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Nitrogen‐doped carbon materials play an important role in the electrolysis of water due to their low cost and high stability. The major roles of N‐doped carbon materials in water electrolysis are electrocatalysts or catalyst support for metal‐based catalysts. However, the evolution of structures and performances of N‐doped carbon catalysts/support during electrochemical hydrogen evolution reactions (HER) process has been seldom reported. Here, we found that the catalytic activities of N‐doped carbon were electrochemically activated during the in‐situ HER process. After electrochemical activation, the catalytic activities of the nitrogen‐doped carbon towards HER were drastically improved and even approached the state‐of‐the‐art Pt/C catalyst. The examination of activation conditions and correlation with the catalytical performances demonstrated that the emerged pyridine N‐oxide structure was responsible for the enhanced catalytic performances. The reconstruction of surface chemical structures near the active sites during activation results in the enhanced surface hydrophilicity, which in turn makes the active sites more accessible by the protons. As a result, the catalytic HER performances were drastically improved in the activated catalysts. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon-coated Fe3O4/reduced graphite oxide (NC@Fe3O4/rGO) nanocomposites with in situ polymerized melamine-formaldehyde resin (MFR) as the carbon sources were synthesized via the decomposition of MFR/Fe3O4/rGO nanocomposites. Fe3O4 NPs were embedded in the integrated carbon matrix composed of protective carbon layer and conductive rGO sheets offering excellent buffer effect. The NC@Fe3O4/rGO nanocomposites were tested as anode materials for lithium-ion batteries (LIBs) and displayed a large reversible specific capacity of above 900 mA h g−1 after 100 cycles at a current density of 50 mA g−1, high coulombic efficiency (~ 98%) with an initial coulombic efficiency of 86%. The high initial coulombic efficiency is critical for the practical application of the transition metal oxide–based anode materials. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) has drawn great attention in the field of lithium‐ion batteries (LIBs) due to its promising high theoretical capacity and abundance in nature. However, rapid capacity fading, low charge/discharge rate and low capacity exceedingly limit the application of bare Fe3O4 anode. Here, we report a facile and scalable method to construct multilayered reduced graphene oxide (rGO)/Fe3O4@polydopamine (PDA) hydrogel (rGO/Fe3O4@PDA hydrogel) for the anodes of LIBs. During the lithiation/delithiation processes, PDA and rGO can effectively inhibit the volume change and avoid structural pulverization. rGO backbone also provides sufficient electrical conductivity and a high specific surface area. The PDA layer suppresses the repetitive growth and thickening of solid‐electrolyte interphase (SEI), playing a role of artificial SEI. As a result, high capacity and superior cycle stability (1358 mAh g−1 after 300 cycle at 1 A g−1) as well as satisfying rate performance (around 600 mAh g−1 at 3 C), fast charge/discharge rate (712 mAh g−1 after 2000 cycles at 3 A g−1), high columbic efficiency and stable reverse reaction are achieved. Interestingly, capacity growth can be observed in the multilayered rGO/Fe3O4@PDA anode owing to the gradual activation of tight encapsulation by rGO sheets. This design concept and structural construction strategy are hopeful be extended to other systems for the next‐generation advanced LIBs. A multilayered hydrogel is fabricated by a facile and scalable method for the anodes of lithium‐ion batteries. A superior performance at a fast charge/discharge rate (712 mAh g−1 after 2000 cycles at 3 A g−1) and a capacity growth (1358 mAh g−1 after 300 cycles at 1 A g−1) can be observed in the multilayered rGO/Fe3O4@PDA anodes (rGO: reduced graphene oxide; PDA: polydopamine). [ABSTRACT FROM AUTHOR]

As a novel tissue engineering material and transistor, reduced graphite oxide (rGO) hydrogel is attracting more and more attention, and a stable and highly electrical conductive rGO hydrogel is the cornerstone for these applications. We controlled the structures of graphite oxides (GOs) with three different methods and the corresponding assembled rGO hydrogels were obtained using Vitamin C (VC) as the reducing agent and the stability and electrical resistance of the rGO hydrogel were studied. The results showed that the appropriate interlayer distance and grain size of GO prepared by two-step oxidation were beneficial for VC molecules to insert in the interspace between layers for the reduction. After reduction, the loose and tangled network structure was well assembled, which determines the stability and electrical conductivity of the resulted rGO hydrogel. [ABSTRACT FROM AUTHOR]

Abstract: Graphene oxide (GO) sheets are introduced to stabilize the shape of the most widely studied phase change material for thermal storage, polyethylene glycol (PEG) during the solid–liquid phase change process. In this composite, a maximum weight percentage of PEG as high as 96% without any leakage up to a temperature as high as 150°C, far above the melting temperature of PEG, has been achieved. Such a weight percentage of PEG is the highest value among PEG based shape-stabilized PCMs to the best of author׳s knowledge. The shape-stable PCM presents a high heat storage capacity of 142.8Jg−1 and excellent thermal reliability within at least 200 melting/freezing cycles. The thermal properties of the PEG/GO composite PCMs with various GO contents are also investigated. The present study provides a highly potential shape-stabilized composite PCM with a high content of PEG for thermal energy storage as well as a way to enhance the heat storage density of PEG based shape-stabilized PCM. [Copyright &y& Elsevier]

The "ion-dipole" interaction has been the most widely accepted mechanism for the direct formation of polar phases (β, γ) of poly(vinylidene fluoride) (PVDF), which have been widely used as transducers, actuators, and sensors. However, the type of charged ions is still controversial. In order to throw light upon this issue, two types of charged small organic molecules that are in different physical states (melt or solid) during the crystallization of PVDF were melt-blended with PVDF resin. Results revealed that only the incorporation of positive charged molecules can lead to the formation of polar phases. Additionally, it is interesting to find that during the crystallization of PVDF, molten positively charged molecules resulted in β-phase dominating, while solid positively charged molecules exclusively induced γ-phase. These results lead to the understanding that the induced formation of polar phases of PVDF is due to the "positive ion-CF2 dipole" interaction.