3D core–shell nanostructures of few-layer NiFe LDH nanosheets grown on Cu nanowires are fabricated toward highly efficient overall water splitting.

Transition metal carbide nanocrystalline M3C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M3C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec(-1) for Fe3C-GNRs, Co3C-GNRs, and Ni3C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M3C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm(-2) at an overpotential of 200 mV, low onset overpotential of 32, 41, and 35 mV, small Tafel slope of 46, 57, and 54 mV dec(-1) for Fe3C-GNRs, Co3C-GNRs, and Ni3C-GNRs, respectively, as well as an excellent stability in acidic media.

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As the cylindrical sp2-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π–π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry.

We report that gold thermally deposited onto n-layer graphenes interacts differently with these substrates depending on the number layer, indicating the different surface properties of graphenes. This results in thickness-dependent morphologies of gold on n-layer graphenes, which can be used to identify and distinguish graphenes with high throughput and spatial resolution. This technique may play an important role in checking if n-layer graphenes are mixed with different layer numbers of graphene with a smaller size, which cannot be found by Raman spectra. The possible mechanisms for these observations are discussed.

Until now, supercapacitors have been optimized in many ways to solve the abovementioned two main issues, such as the modification of existing materials, [5,6] the discovery of new materials, [7][8][9] the exploration of electrolytes, [10][11][12] the assembly of full supercapacitors, [13] the optimization of the voltage window etc. [14,15] Specifically, from the perspective of material development, RuO 2 is regarded as an ideal supercapacitor electrode material due to its high specific capacitance, but its high cost limits its practical application. [16,17] Thus, other nonnoble pseudocapacitive materials (for example, MnO 2 , [18] Fe 2 O 3 , [19] MoO 3 , [20] Nb 2 O 5 , [21] and VN [22] ) have attracted much attention. However, the poor electronic conductivity of most pseudocapacitor materials lead to their higher electrode resistances and lower power densities compared with those of EDLCs (Electrical Double Layer Capacitors) and electrolytic capacitors. [23] Very recently, 2D materials with high capacitances, such as MXenes, have been reported, but their main drawbacks are their complex synthetic processes and the use of highly toxic hydrofluoric acid (HF). [7,9] With regard to electrolytes, most researchers prefer aqueous electrolytes for their higher ionic concentration, lower resistance, lower cost, and better environmental-friendliness compared to those of organic electrolytes. [13,24,25] However, the limited potential window of aqueous supercapacitors, owing to the theoretical water splitting potential window of 1.23 V, is a challenge. To widen the potential window, supercapacitor electrodes must always be assembled into supercapacitor systems or so-called full supercapacitors, including symmetric supercapacitors, asymmetric supercapacitors, and hybrid supercapacitors. [4,5,13] To further enhance the voltage window of a single electrode or full supercapacitor, some methods have been adopted, including surface charge optimization, [14] electrode material modification, [15,26] electrolyte exploration, [5,10,24,27] and unique full supercapacitor system assemblies. [4,5,13] Although the above strategies have resulted in great progress for supercapacitors over the past few decades, the application of supercapacitors is still limited. Acquiring excellent performance while using simple methods is still a challenge. Thus, new strategies for the further development of supercapacitors are urgently needed. Herein, we propose a new view of the supercapacitor called the "integrated supercapacitor." As shown in the "supercapacitor tree" (Figure 1a), the integrated supercapacitor is a powerful strategy for integrating the traditional concepts of positive electrodes, negative electrodes, symmetric Charging times ranging from seconds to minutes with high power densities can be achieved by electrochemical capacitors in principle. Over the past few decades, the performance of supercapacitors has been greatly improved by the utilization of new materials, preparation of unique nanostructures, investigation of electrolytes, and ...

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Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC-CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η10 (the overpotential for driving a current of 10 mA cm(-2)) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec(-1) in acid solution, and η10 of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec(-1) in alkaline media, respectively. Electrochemical stability test further confirms the long-term operation of the catalyst in both acidic and alkaline media.