In this paper, a hierarchical NiCo2S4@polypyrrole core-shell heterostructure nanotube array on Ni foam (NiCo2S4@PPy/NF) was successfully developed as a bind-free electrode for supercapacitors. NiCo2S4@PPy-50/NF obtained under 50 s PPy electrodeposition shows a low charge-transfer resistance (0.31 Ω) and a high area specific capacitance of 9.781 F/cm(2) at a current density of 5 mA/cm(2), which is two times higher than that of pristine NiCo2S4/NF (4.255 F/cm(2)). Furthermore, an asymmetric supercapacitor was assembled using NiCo2S4@PPy-50/NF as positive electrode and activated carbon (AC) as negative electrode. The resulting NiCo2S4@PPy-50/NF//AC device exhibits a high energy density of 34.62 Wh/kg at a power density of 120.19 W/kg with good cycling performance (80.64% of the initial capacitance retention at 50 mA/cm(2) over 2500 cycles). The superior electrochemical performance can be attributed to the combined contribution of both component and unique core-shell heterostructure. The results demonstrate that the NiCo2S4@PPy-50 core-shell heterostructure nanotube array is promising as electrode material for supercapacitors in energy storage.

High-performance supercapacitors require the design and development of electrode materials with high conductivity and a large electrolyte-accessible surface area. Here, the use of a conductive NiCoP nanoarray on nickel foam (NiCoP/NF) as a superior pseudocapacitor electrode is demonstrated. This 3D electrode exhibits high areal capacitances of 9.2 and 5.97 F cm at current densities of 2 and 50 mA cm , respectively, with good rate capability and cycling stability. The asymmetric supercapacitor (ASC) device assembled using NiCoP/NF as positive electrode and active carbon as negative electrode delivers a high energy density of 1.16 mWh cm at a power density of 1.6 mW cm with 72 % retention of its initial specific capacitance after 2000 cycles at 50 mA cm . The practical use is further demonstrated with two such ASC devices in series to light six LED indicators and also to drive an alkaline water electro- lyzer using NiCoP/NF as both cathode and anode for hydrogen production.

In this work, γ-MnS/reduced graphene oxide composites (γ-MnS/rGO) were prepared using a facile one-pot hydrothermal method. As an electrode material for supercapacitors, the γ-MnS/rGO-60 composite obtained under dosages of graphene oxide  was 60 mg and exhibited an enhanced specific capacitance of 547.6 F g at a current density of 1 A g, and outstanding rate capability (65% capacitance retention at 20 A g), with superior cycling stability and electrochemical reversibility. An asymmetric supercapacitor assembled from γ-MnS/rGO-60 composite and rGO (γ-MnS/rGO-60//rGO) showed a voltage window of 0-1.6 V and delivered a high energy density of 23.1 W h kg at a power density of 798.8 W kg, and 15.9 W h kg at 4.5 kW kg. Moreover, two such 1.0 × 1.0 cm devices connected together in series easily light up a group of LED lights, showing its potential practical application as an attractive energy storage device.

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The development of Earth-abundant low-cost catalyst materials for effective water oxidation is of critical importance for electrochemical hydrogen production. The first use of hydrothermally in situ grown cobalt carbonate hydroxide hydrate nanowires array on carbon cloth as an effective catalyst electrode for water oxidation in alkaline electrolytes is described. This three-dimensional electrode shows high catalytic activity with the need of overpotential of 323 mV to drive 10 mA cm −2 , and its activity can be retained for at least 40 h.