Kai Zhuo

Dendritic nanoporous nickel oxides for a supercapacitor prepared by a galvanic displacement reaction with chlorine ions as an accelerator

Dendritic nanoporous nickel oxide and tube-like nickel–tin oxide electrodes were prepared by a galvanic displacement reaction in an aqueous electrolyte containing chlorine ions which dramatically accelerated the reaction. The nanoporous nickel oxide showed a capacitance of 1242 F g−1, 97.4% of which was retained even after 5000 charge–discharge cycles.

Surfactant Effects on the Morphology and Pseudocapacitive Behavior of V2O5⋅H2O

To overcome the drawback of low electrical conductivity within supercapacitor applications, several surfactants are used for nanoscale V2 O5 to enhance the specific surface area. Polyethylene glycol 6000 (PEG-6000), sodium dodecylbenzene sulfonate (SDBS), and Pluronic P-123 (P123) controllers, if used as soft templates, easily form large specific surface area crystals. However, the specific mechanism through which this occurs and the influence of these surfactants is not clear for V2 O5 ⋅H2 O. In the present study, we aimed to investigate the mechanism of crystal growth through hydrothermal processes and the pseudocapacitive behavior of these crystals formed by using diverse surfactants, including PEG-6000, SDBS, and P123. Our results show that different surfactants can dramatically influence the morphology and capacitive behavior of V2 O5 ⋅H2 O powders. Linear nanowires, flower-like flakes, and curly bundled nanowires can be obtained because of electrostatic interactions in the presence of PEG-6000, SDBS, and P123, respectively. Furthermore, the electrochemical performance of these powders shows that the nanowires, which are electrodes mediated by PEG-6000, exhibit the highest capacitance of 349 F g(-1) at a scan rate of 5 mV s(-1) of all the surfactants studied. However, a symmetric P123 electrode comprising curly bundled nanowires with numerous nanopores showed an excellent and stable specific capacitance of 127 F g(-1) after 200 cycles. This work is beneficial to understanding the fundamental role of the surfactant in the assisted growth of V2 O5 ⋅H2 O and the resulting electrochemical properties of the pseudocapacitors, which could be useful for the future design of appropriate materials.

Formation of nanoporous nickel oxides for supercapacitors prepared by electrodeposition with hydrogen evolution reaction and electrochemical dealloying

Highly nanoporous nickel oxide electrodes were obtained by electrodeposition accompanied by hydrogen evolution reaction and the selective electrochemical dealloying of copper from Ni-(Cu) porous foam. The nanoporous nickel oxide electrodes consequently have numerous dendritic morphologies composed of nanopores with 20–30 nm diameters. The specific capacitances were 428 F g−1 for as-deposited Ni-(Cu) foam electrode and 1,305 F g−1 for nanoporous nickel-oxide electrode after dealloying process, respectively. This indicates increased surface area by dealloying process leads to innovative increase of specific capacitance.

Effect of electrolyte composition on the morphological structures of dendritic copper powders prepared by a spontaneous galvanic displacement reaction

Dendritic copper powders are highly desirable in many applications, including electromagnetic interference shielding and conductive pastes, because of low cost and high conductivity. We prepared dendritic copper powders using the galvanic displacement reaction between the Al and Cu-ions in aqueous solution. This method is very simple and spontaneous at room temperature. During the process, the morphology of the copper powders is strongly affected by several variables, such as the displacement reaction rate and the amount of hydrogen evolution due to the reduction of proton. The effect of the different composition of electrolytes to morphological changes of copper powders was investigated in this study. In addition, the effects of concentration of chlorine ion, pH, termination time, and additives were monitored, which resulted in different morphology. Considering different applications, such as sensors, catalysts, and conductive pastes, the controllability of the morphology of dendritic copper powders plays an important role in achieving high performance in desired applications.