Search

Transition metal compounds containing nickel and copper have been investigated as electrode materials for energy storage. (Ni,Cu)(OH)2CO3 and α-Ni(OH)2 with different Ni/Cu ratios are synthesized by a simple hydrothermal method. All the samples show the similar dandelion-like morphology. It is demonstrated that the mole ratio of Ni to Cu is a key factor to influence the phase and electrochemical performances of the products. Carbonate anions will be intercalated into nickel copper layered double hydroxides with a hydrotalcite structure when the sample is nickel-rich, which will lead to much better electrochemical properties compared with the copper-rich samples with crystalline (Ni,Cu)(OH)2CO3 structure. Among all the materials, sample (Ni0.89Cu0.11)2(OH)2CO3 can deliver the highest specific capacitance of 1017.3 F g−1 at 1 A g−1 and retain 68.5% of the original value after 4000 cycles at 5 A g−1. Meanwhile, an asymmetric capacitor which is assembled by using the optimized material as a positive electrode and activated carbon as a negative electrode exhibits a high energy density of 38.56 Wh kg−1 at a power density of 850.01 W kg−1 and a high power density of 8407.4 W kg−1 at an energy density of 21.7 Wh kg−1. Based on the above results, nickel copper carbonate hydroxides are of potential application for energy storage.

The crystallinity of electrode materials affects the electrochemical performances of supercapacitors, typically for some transition metal oxides. The influence of crystallinity on the capacitive behavior of metal sulfides has not been well investigated so far. In this work, amorphous and crystalline CuCo2S4 materials are prepared by anion−exchange and post−annealing. The annealing treatment under reasonable temperatures does not change the morphology and structure of CuCo2S4 significantly. But, the degree of crystallinity of CuCo2S4 can be easily changed by adjusting the annealing temperature. A high temperature results in a highly crystalline material. The electrochemical performance of CuCo2S4 is investigated and it is obviously influenced by the crystallinity. The material annealed at 200 °C exhibits a higher specific capacitance compared to the amorphous and those treated at higher temperatures. The optimal material has the highest specific capacitance of 424 F g−1 at 1 A g−1 and good stability. When it is assembled a hybrid capacitor with activated carbon as a negative electrode, the hybrid capacitor shows a high energy density of 22 Wh kg−1 at a power density of 405 W kg−1 in a potential window of 1.62 V.

Hierarchical and hexagonal cobalt oxide with porous structure was synthesized via a precipitation route followed by calcination. The shape and crystal size of cobalt oxide were greatly dependent on the chemicals and calcination temperature. The as-synthesized cobalt oxide reserved the shape of its hydroxide precursor. The calcination temperature was a key factor for controlling the pore volume and crystal sizes of as-prepared Co3O4 samples. The cobalt oxide prepared under different conditions was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen physisorption analysis. The gas-sensing properties were measured by a gas sensor measurement system using Co3O4 samples as a sensor material. The influence of gas concentrations, specific surface area and crystals size of Co3O4 on sensing properties were investigated. The porous hierarchical cobalt oxide with a small crystal size and high surface area showed a high response to ethanol vapor, while cobalt oxide platelets with a large crystal size and macropore exhibited a high response to acetone vapor.