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Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe2O4) - based composite (NiFe2O4-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe2O4 from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe2O4 possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe2O4-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g−1) and superb durability. Simultaneously, the asymmetrical device based on NiFe2O4-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg−1). Moreover, NiFe2O4-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm−2, the wide linear range of 3.500 × 10−5 − 4.525 × 10−3 M, and the detection limit of 12.94 × 10−6 M with a signal to noise ratio of 3. Consequently, the NiFe2O4-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

In this account, elm seeds are employed to prepare oxygen enriched porous carbon materials with three-dimensional honeycomb-like structure (HLPC). The HLPC demonstrates favorable specific capacitance of 501 F/g at 1 A/g. Moreover, the assembled HLPC//HLPC symmetrical device delivers 18.6 Wh/kg at 1310 W/kg and maintains 8.36 Wh/kg at 13090 W/kg, which is regarded as competitive electrode compared with the previously reported biomass carbon-based materials. The outstanding performance is attributed to exceptional oxygen content, which could significantly enhance the overall capacitance and improve the wettability of the electrode. This work holds great potential to realize high-efficient, eco-friendly and industrial-grade production of biomass-derived carbon materials for advanced energy storage applications.

Intense efforts have been made to design and prepare hierarchical porous electrode materials because of high specific surface area and fast ions transport. In this work, a facile strategy for the polyvinyl pyrrolidone (PVP)-induced assembly of two-dimensional NiCo-LDHs nanosheets into three-dimensional flower-like microspheres is developed. The multilevel NiCo-LDHs microspheres possess high specific surface area and sufficient porosity. Electrochemical analysis manifests that the multilevel NiCo-LDHs is rather outstanding, which shows a comparatively high specific capacity of 622 C/g at 1 A/g, favorable rate performance and excellent long-term stability. Moreover, an optimized asymmetrical supercapacitor using flower-like NiCo-LDHs as positive electrode yields a maximum energy density of 63.4 Wh/kg at 934 W/kg. This work draws a promising way for the assembly of multidimensional configurations with immense prospect in energy-storage fields.

Constructing the porous graphitic carbon materials based on the renewable biomass-derived raw materials has raised widely attention in recent years. Herein, this work proposes a cost-effective and eco-friendly approach for fabricating the highly graphitic porous carbon (HGPC) materials using leaves of viburnum sargenti for the first time. The as-prepared carbon sample exhibits a moderate specific surface area of 762.3 m2/g, a high oxygen content of 16.75 at.%, which could contribute additional pseudocapacitance during electrochemical reaction process. And the doping of nitrogen atom (0.53 at.%) could availably improve the conductivity. Consequently, the HGPC electrode delivers an excellent specific capacitance of 612.8 F/g at 0.5 A/g and a remarkable cycling stability with 96.02% capacitance retention over 10,000 cycles. Additionally, the assembled HGPC//HGPC symmetric supercapacitor presents an ultrahigh energy density of 25.6 Wh/kg at the power density of 450 W/kg. This facile technique holds great promise to offer an effective and universal methodology for fabricating renewable biomass-derived carbon materials for high-performance supercapacitors.

Nickel cobalt selenides derived from metal organic framework have allured a lot of attention in energy storage areas. Herein, Nickel cobalt selenides (H-Ni-Co-Se) nanoarrays with hollow structure from pentagon-like Ni/Co-ZIF are successfully assembled on Ni-foam by employing sequential chemical etching and selenylation strategy. The hollow configuration grown on Ni-foam could offer rich electroactive region, shorten charge/ion diffusion length and enhance mass/electrons transfer. The as-prepared H-Ni-Co-Se delivers a favorable specific capacitance of 1175 F/g at 1 A/g, fast charge/discharge rate and excellent long-term stability. This versatile strategy can be extended to construct other transition metal compounds with outstanding electrochemical performance.