Iron decorated ultrathin cobaltous hydroxide nanoflakes with impressive electrochemical reactivity for aqueous Zn batteries

The main bottlenecks of current Co-based cathodes are their relatively low capacity and inferior reversibility. Here, we report Fe decorated cobaltous hydroxide (FCO) nanoflakes with vastly improved capacity and cycling stability via an efficient surface activation approach, which function as an advanced cathode for Co-Zn batteries. In comparison with the pristine cobaltous hydroxide (CO), the FCO sample owns higher electrochemical reactivity and a larger electrochemical surface area, endowing it with impressive electrochemical properties.

Well-defined hollow tube@sheets NiCo2S4 core-shell nanoarrays for ultrahigh capacitance supercapacitor

Reasonable design of electrodes with well-defined nanostructure is the central aspect in the practical application of high-performance supercapacitors. Herein, hollow tube@sheets NiCo₂S₄ core-shell nanoarrays are rationally constructed to the free-standing electrode by in situ growing ZIF-67 on Co-precursor nanorods array and sequentially performing anion-exchange (S^2-) and cation-exchange (Ni²⁺). The well-defined nanostructures can shorten the ion transport path in the charging-discharging process, increase the specific surface area and electrochemical active cites, which help in improving electrochemical performance. Therefore, the unique tube@sheets NiCo₂S₄ core-shell nanoarrays exhibit intriguing electrochemical performance and show excellent areal capacitance of 11.3 F cm^-2 (3227.94 F g^-1) at a current density of 2 mA cm^-2 (2 A g^-1). The assembled asymmetric supercapacitor device delivers a high energy density of 0.42 mW h cm^-2 at a power density of 2.1 mW cm^-2 and displays outstanding cyclic stability (90.2% retention after 5000 cycles). Consequently, the well-defined nanostructure engineering strategy is beneficial for designing active electrode materials for efficient energy storage devices.

Facile assembly of 2D Ni-based coordination polymer nanosheets as battery-type electrodes for high-performance supercapacitors

Large-scale Ni-based nano-sized coordination polymers (Ni-nCPs) are facilely constructed by a self-assembled approach at room temperature and atmosphere pressure. In this strategy, we use only the environmentally friendly solvents of water and ethanol, and the synthesis of 2D Ni-nCPs via a self-assembly route appears close to the "green chemistry" concept. In addition, the morphologies of the Ni-nCPs can be easily adjusted by the water/ethanol ratio. Owing to its unique 2D ultrathin nature and large specific surface area, Ni-nCPs-1 achieves a great number of channels for the transport of electrons and ions and electrochemically redox active sites for a faradaic reaction. Therefore, battery-type Ni-nCPs-1 electrodes have a bright prospect in energy storage, and can reach an outstanding specific capacitance value as high as 1066.9 F g^-1 at 1 A g^-1. Additionally, the asymmetric supercapacitor (Ni-nCPs-1//active carbon) displays a high energy density of 47.9 W h kg^-1 at a power density of 440 W kg^-1 and an excellent long-term cycle stability. This work may open up a new path in advanced electrode materials for efficient and real-time energy storge applications.

Controlled Preparation of Hollow and Porous Co9S8 Microplate Arrays for High-Performance Hybrid Supercapacitors

The design and controlled preparation of hollow and porous metal sulfide arrays are an important issue for electrochemical energy storage and conversion because of their unique structural merits including large surface areas, shortened diffusion paths, and rich reaction sites. Herein, a hollow and porous Co₉S₈ microplate array (MPA) was successfully fabricated by a facile self-sacrifice template strategy, which involved the uniform growth of a metal-organic framework microplate template on Ni foam (NF) and annealing in air, followed by an anion-exchange reaction with S^2- ions. The resulting Co₉S₈-MPA/NF as a binder-free electrode for a supercapacitor shows a high specific capacitance of 1852 F g^-1 (926 C g^-1) at 1 A g^-1 and an excellent cycling stability (86% retention after 5000 cycles at 20 A g^-1). Moreover, a hybrid supercapacitor (HSC) constructed with Co₉S₈-MPA/NF and activated carbon exhibits an outstanding energy density of 25.49 Wh kg^-1 at a high power density of 800 W kg^-1 and a long-term stability of 92% capacitance retention after 5000 cycles at 10 A g^-1. It is worth noting that the prepared all-solid-state HSC can light a red light-emitting diode for 2 min, proving to be a great practical application prospect. These excellent electrochemical behaviors show that this effective conversion strategy offers more possibilities for the development of high-performance energy storage metal sulfide materials.

Roll-to-roll printed high voltage supercapattery in lead-contaminated aqueous electrolyte

This work investigated the potential application of roll-to-roll printed PEDOT:PSS on an ITO/PET substrate using Pb2+ containing 0.1 M NaCl aqueous solution for a supercapattery. The PEDOT:PSS/ITO/PET electrode achieved 2.2 μAh cm-2 (46.5 mAh g-1) in 0.1 M NaCl and 10 μAh cm-2 (216.8 mAh g-1) in 2 mM Pb2+/0.1 M NaCl at a current density of 0.2 mA cm-2 (4.34 A g-1). The electrode also shows good cyclic performance that retains 63% of its initial capacitance after 1000 charge-discharge cycles. A device operating at a high voltage of 1.8 V was built using PEDOT:PSS/ITO/PET in aqueous electrolyte. The energy density of the symmetric PEDOT:PSS/ITO/PET device is 6.2 Wh kg-1 in 0.1 M NaCl and is improved to 11 Wh kg-1 in 3 mM Pb2+/0.1 M NaCl.

Metal–organic framework derived petal-like Co3O4@CoNi2S4 hybrid on carbon cloth with enhanced performance for supercapacitors

Starting from 2D Co-based metal-organic frameworks, novel petal-like core-shell Co₃O₄@CoNi₂S₄ nanowall arrays are synthesized on carbon cloth using a facile two-step method and investigated as promising electrode materials for supercapacitors.

MOF-assisted construction of a Co9S8@Ni3S2/ZnS microplate array with ultrahigh areal specific capacity for advanced supercapattery

Transition metal sulfides are important candidates of battery-type electrode materials for advanced supercapatteries due to their high electric conductivity and electrochemical activity. The Co9S8@Ni3S2/ZnS composite microplate array was prepared by a metal-organic framework-assisted strategy because the electrochemical properties of composite arrays are governed by the synergistic effects of their diverse structures and compositions. As a battery-type material, the Co9S8@Ni3S2/ZnS electrode expressed an ultrahigh areal specific capacity of 8192 C cm-2 at the current density of 2 mA cm-2, and excellent cycling stability of 79.7% capacitance retention after 4000 cycles. An assembled supercapattery device using the Co9S8@Ni3S2/ZnS microplate array as a positive electrode and active carbon as the negative electrode delivered a high energy density of 0.377 mW h cm-2 at a high power density of 1.517 mW cm-2, and outstanding retention of 95.2% after 5000 cycles. As a result, the obtained Co9S8@Ni3S2/ZnS shows potential for applications in high-performance supercapattery.