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• CoNi-LDH with a hierarchical hollow cage structure has been synthesized. • Two-step water-assisted coprecipitation method is utilized at room temperature. • The synergic effect of nickel nitrate adsorption on bimetallic CoNi-ZIF is optimized. • The assembled ASC supercapacitor device delivers excellent energy density, power density and cyclic stability. Single imidazolate framework-67 (ZIF-67) is commonly used as a template to prepare layered double hydroxides (LDHs) with specific morphology to improve the performance of materials. Herein, the Co2+ ion in ZIF-67 is partially substituted by Ni2+ to obtain the dodecahedron bimetallic imidazolate framework (CoNi-ZIF). Subsequently, using bimetallic CoNi-ZIF as the sacrificial template, CoNi-LDH hierarchical hollow cage structures with wrinkled nanosheet arrays are synthesized at room temperature and in aqueous solution by an inexpensive and environment friendly surfactant-free approach. The optimized etched CoNi-LDH4 has a maximum specific capacitance of 1877 F g−1 at a current density of 1 A g−1, and cycling stability of 99.89% after 5000 cycles, which is significantly better than that of ZIF-67 derived CoNi-LDH67 (1357 F g−1 at 1 A g−1, cycling stability of 73.35%). The asymmetric supercapacitor with CoNi-LDH4 as a cathode and activated carbon (AC) as anode has an energy density of 49.3 Wh kg−1 at 750 W kg−1 power output and stable cycling performance (capacity retention of 92.13% after 5000 cycles). This study shows the prospect of bimetallic CoNi-ZIF derived LDHs nanostructures prepared at room temperature and in aqueous solution to improve the performance and stability of supercapacitors. [ABSTRACT FROM AUTHOR]

The integration of two transition metals with carbon materials provides a great potential to boost the catalytic and electrochemical properties of supercapacitor. However, a scalable fabrication of such composite materials remains a challenge. Here, ternary composites of NiS–NiCo 2 O 4 @C nanosheets were derived from nickel and cobalt oleate using Na 2 SO 4 as both hard template and sulfur source. The NiS–NiCo 2 O 4 @C composites were then tested as catalysts toward rapid reduction of 4-nitrophenol (4-NP) and as electrode materials for supercapacitors. It was found that the catalytic and electrochemical properties of the composites were tuned by adjusting the ratios of Co to Ni and annealing temperature. The optimized composite showed the highest reduction rate constant for 4-NP reduction (1.78 min−1). In addition, this composite has also shown high specific capacitance of 1411 F g−1 at 1 A g−1and 99.5% capacity retention after 2000 continuous charge-discharge cycles at a current density of 3 A g−1, which is much higher than their respective monometallic Co and Ni composites. Furthermore, the ASC device (CN14//AC) achieved a high energy density of 37.2 W h kg−1 at a power density of 799.9 W kg−1, and a good cycling performance of retention(89%) after 5000 cycles. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract The NA-LDH-OA-2//AC ASC device deliver a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1, and good cycling performance. Highlights • The NA-LDH-OA ultrathin nanosheets were synthesized by two-phase solvothermal method. • Excellent cycling stability of 94.5% capacitance retention after 5000 cycles. • The asymmetric supercapacitor achieved a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1. Abstract Using sodium oleate as surfactant and intercalating agent, a regulated Ni-Al layered double hydroxide (NA-LDH-OA) nanosheets with a high interlayer space were prepared by two-phase method combined with a short reflux process and mild solvothermal reaction. In the process of electrochemical reaction, the electron transport is accelerated by the higher base spacing of the NA-LDH-OA ultrathin nanosheets. The as-prepared material exhibited a high specific capacity (1.040 C cm−2 at a current density of 1.68 mA cm−2) and good cycling performance (capacity retention of 88.25% after 2000 cycles) in a three-electrode system. Moreover, an aqueous asymmetric supercapacitor (ASC) was assembled using the synthesized NA-LDH-OA nanosheets as the positive electrode and activated carbon (AC) as the negative electrode. The aqueous ASC device (NA-LDH-OA-2//AC) achieved a high energy density of 40.26 Wh kg−1 at a power density of 943 W kg−1, and a good cycling performance of 94.5% retention after 5000 cycles. These results demonstrated that the NA-LDH-OA nanosheets possess the potential for upcoming energy storage devices. [ABSTRACT FROM AUTHOR]

Anode performance has been regarded as a crucial factor determining long-term stability and electricity generation of microbial fuel cells (MFCs), which restricts by the difficult extracellular electron transfer (EET) on the microbe/anode interface. Herein, inspired by biological enzyme systems, this study synthesized the biomimetic nanozymes with Fe-N-S-C active sites as the anode materials of MFCs, which was similar to the hemes of c-type cytochromes (c-Cyts) for boosting EET process. As excepted, an obviously faster start-up and a much higher power density were achieved by the MFCs equipped with Fe-N-S-C nanozymes (startup time, 3.5 d; power density, 2366 ± 34 mW m−2) than that based on traditional carbon cloth (startup time, 5.6 d; power density, 1009 ± 26 mW m−2). Such unique features of Fe-N-S-C nanozymes anode not only greatly favored the bacterial adhesion and the electroactive bacteria enrichment on the anode surface, but also efficiently facilitated the EET process between the electroactive bacteria and anode surface. This study provided a feasible strategy for designing the novel MFC anode materials from the perspective of bionic enzyme. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new method for preparation of HA-K by alkali quenching of sludge was proposed. • Chlorination roasting and quenching can control the pore structure of carbon. • The specific capacitance of the prepared N, O porous carbon is 395F g−1. • This study provides a new idea for the harmless and resource utilization of sludge. Municipal sludge (MS) pyrolysis is often used to produce carbon materials for supercapacitors, however, the conventional heating process limits the improvement of its performance. In this paper, a facile method for the preparation of potassium humate (HA-K) by co-pyrolysis of MS and alkali was proposed for the first time, and then it was mixed with sodium chloride for roasting and quenching to obtain high performance HA-K carbon materials for supercapacitors. Compared with the electrode without chlorination roast quenching, the sample of HA-K-650-M−Q (the sample calcined at 650°C and quenched at 200°C) exhibited higher specific capacitance (395F g−1 at 1 A g−1) and enhanced energy density (32.28 Wh kg−1 at a power density of 2805 W kg−1). After 10,000 cycles at 10 A g−1, the capacitance retention rate reached 87%. This remarkable performance is due to its proper N- and O- self-doping and hierarchical porous geometry, which fundamentally promotes mass and charge transfer in the reaction. Therefore, this study provides a feasible method to solve the problem of sludge value-added and design suitable for the practical application of carbon materials. [ABSTRACT FROM AUTHOR]

• A facile method of directly converting electroplating sludge into nickel-based energy storage composites. • The unique embedded multilevel nanostructure improves the effective reaction of active substances with electrolyte. • Fe-Al co-doped α-Ni(OH) 2 and Ni(HCO 3) 2 composites show high specific capacitance and good cycling stability. The recovery of heavy metals from electroplating sludge is an important technology, which can not only reduce environmental pollution, but also serve as a secondary source of metals. However, the current techniques are either non-selective or difficult to operate, which limits its applications in recovery technologies. Herein, based on the existence of multiple metal ions in electroplating sludge, Fe and Al co-doped ultrathin α-Ni(OH) 2 nanosheets embedded in Ni(HCO 3) 2 nanowire assembly spheres were prepared by adjusting the ratio of urea under hydrothermal condition. Under the optimum conditions, the recovery of Ni, Fe, and Al are 92.58%, 81.52%, and 61.19% respectively. In addition, at the current density of 1 A g−1, the specific capacitance of the spherical composite electrode is as high as 495.6 C g−1, and the retention rate of the initial capacity is 55.58% after 3500 cycles in 6 M KOH electrolyte, showing good cycling stability. Furthermore, the ASC device (NN-4//AC) achieved a high energy density of 30.27 Wh kg−1 at a power density of 0.37 kW kg−1. A new method for converting electroplating sludge into nickel-based energy storage materials was developed, which provided a new strategy and idea for the harmless and resourceful treatment of electroplating sludge. [ABSTRACT FROM AUTHOR]

• NiCo-LDH with a three-dimensional (3D) hierarchical hexagonal flower-like structure is synthesized. • Binary additives H 2 tfbdc and HMT are used to tune morphology and deliver large interlayer spacing of 9.3 d(Å). • The synergic effect of hydrothermal heating temperature and time is optimized. • The assembled ASC supercapacitor device exhibits excellent energy density and power density. Dodecahedral imidazolium framework-67 (ZIF-67) is synthesized in aqueous solution and used as a sacrificial template for the synthesis of uniform three-dimensional (3-D) hierarchical hexagonal flower-like nickel–cobalt layered double hydroxides (NiCo-LDH) by facile hydrothermal treatment. TEM and SEM results reveal that each microflower is composed of abundant two-dimensional (2D) ultrathin wrinkled nanosheets. The induction of 2,3,5,6-terafluroterephthalic acid (H 2 tfbdc) and hexamethylenetetramine (HMT) as an additive along with nickel nitrate hexahydrate plays a vital role to tune uniform hierarchical morphology and augmented electrochemical performance. The supercapacitor performance results show that (NiCo-LDH)S HH electrode has the best supercapacitor performance when it is used as a pseudo-capacitor. The maximum specific capacitance is 1765 F g−1 at the current density of 1 A g−1 with stable cycling performance. An asymmetric supercapacitor device assembled using (NiCo-LDH)S HH as the positive and activated carbon (AC) as the negative electrode attains a high energy density of 53.31 Wh kg−1 at a power density of 749.7 W kg−1 with 84.3% capacitance retention after 6000 cycles. This work provides a novel route for the design and synthesis of two-component hydrotalcite with 2D nanosheets having a large interlayer spacing of 9.3 d(Å) and its potential application in electrochemical energy storage. [ABSTRACT FROM AUTHOR]