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Unique two-dimensional (2D) porous nanosheets with overwhelmingly rich channels and large specific surface area exhibit superior electrochemical capacitance performance, as compared to the conventional zero- and one-dimensional counterparts. As ternary transition metal sulfides (TMSs) are well recognized for their high electrochemical activity and capacity, and the replacement of oxygen with sulfur may result in high stability and flexible properties of the nanomaterials, as compared to transition metal oxides, herein we report the synthesis of 2D porous nanosheet arrays of ZnxCo1-xS (x = 0, 0.25, 0.5, 0.75, and 1) via a facile hydrothermal process. Due to the synergistic effect of the metal components and a unique 2D porous structure, the Zn0.5Co0.5S electrode was found to stand out as the best among the series, with a high specific capacity of 614 C g−1 at 1 A g−1 and excellent cycle retention rate of 90 % over 10, 000 cycles at 10 A g−1. Notably, a supercapattery based on a Zn0.5Co0.5S positive electrode and an activated carbon (AC) negative electrode (Zn0.5Co0.5S//AC) was found to display a 1.6 V voltage window, a 61 mA h g−1 specific capacity at 1 A g−1, a 49 Wh kg–1 energy density at 957 W kg–1 power density, and excellent cycling performance (88 % over 10, 000 cycles), suggesting tremendous potential of Zn0.5Co0.5S in the development of high-performance supercapattery devices.

In order to meet the increasing demand for electric energy, it is of great significance to develop high-performance electrochemical energy storage materials. Cobalt/nickel-based tungstates (MWO4, M ​= ​Co, Ni and Co–Ni) show much higher electrical conductivity than pure oxides. However, due to their relatively low capacity and poor cycle stability, their potential as electrode materials for high-performance supercapatteries is limited to a great extent. In this paper, we reported the successful synthesis of bimetallic two-dimensional (2D) Co–Ni tungstates thin sheets assembled by nanosheets through a substrate-free hydrothermal method. The ratio of Co/Ni was optimized to 1:1 and the as-obtained Co0.5Ni0.5WO4 (CNWO) electrode exhibited a high specific capacity of 626.4 ​C ​g−1 ​at 1 ​A ​g−1 and high cyclic stability (105.3% capacity maintained over 10,000 cycles at 10 ​A ​g−1) in a three-electrode system, which is attributed to the synergistic effect of 2D/3D porous architecture and bimetallic composition of CNWO. An alkaline hybrid supercapattery (CNWO//activated carbon(AC)) with CNWO as the positive electrode and AC as the negative one showed the maximum specific energy of 42.2 ​Wh·kg−1 ​at the specific power of 1047.7 ​W ​kg−1 with a long cycle life (93.5% capacity retention after 15,000 cycles at 10 ​A ​g−1). The rational design of CNWO could pave the way for the preparation of bimetallic oxides with significantly improved electrochemical property.

Layered metal hydroxide salts (LHSs) have recently gained extensive interests as an efficient electrode material for supercapacitors (SCs). Herein, we report, for the first time ever, the synthesis of a cobalt-nickel layered hybrid organic-inorganic LHS that was intercalated with benzoate anions (B-CoNi-LHSs) and observe a high performance as electrode materials for hybrid supercapacitors (HSCs). B-CoNi-LHSs were synthesized by using a co-precipitation method, where sodium benzoate was added dropwise to cobalt and nickel salt solution, without the addition of any organic solvent or surfactant. Due to the intercalation of anions and synergistic interactions of the multi-metallic components, the B-CoNi-LHSs electrode showed a high specific capacity of 570 C g−1 (specific capacitance of 1267 F·g−1) at 1 A g−1, excellent rate performance (65% from 1 to 10 A g−1) and outstanding cycling performance (81.09% over 8000 cycles), in comparison to the mono-metallic counterparts. An HSC device, assembled by using B-CoNi-LHSs as the positive electrode and activated carbon (AC) as the negative one, exhibited a power density of 780 W kg−1 at the energy density of 31.7 Wh kg−1, and 8543 W kg−1 at 18.1 Wh kg−1. Results from this study show that the organic-inorganic hybrids of layered dual-metal hydroxides intercalated with benzoate anions may be a viable candidate as electrode materials for high-performance SCs.

Tailoring the composition and nanostructure of transition metal compounds is critical for electrochemical energy storage materials. Transition metal oxalates, which are formed by oxalic acid (OA) with transition metals, have been regarded as potential battery-type electrode material for high-performance supercapatteries due to their excellent electrochemical stability, low cost, and adjustable pore sizes, yet still limited by their low conductivity. Herein, we report a facile way for fabricating trimetal oxalates with three-dimensional (3D) architecture assembled by interwoven nanosheets by a succinct-operated hydrothermal method. Benefiting from both unique 3D porous structures and the synergistic interactions of trimetal oxalates, the developed Mn0.4Ni0.1Co-OA shows a considerably high specific capacity (1141.6 C g−1) and ultralong cyclic life (85% capacity retention over 10,000 cycles). Additionally, the supercapattery assembled with the Mn0.4Ni0.1Co-OA electrode and the activated carbon (AC) electrode displays a maximum energy density of 32.2 Wh kg−1 at the power density of 770.2 W kg−1 and outstanding cycle life (retention rate of 88.1% after 15,000 cycles). The results presented in this work that the rational design of the composition and structure of oxalates can provide a new idea for the preparation of high-performance energy storage materials.