Electrochemically-deposited nanostructured Co(OH)₂ flakes on three-dimensional ordered nickel/silicon microchannel plates for miniature supercapacitors

Silicon microchannel plates (Si-MCPs) coated with a nickel layer are an excellent substrate in miniature supercapacitors. Nanometer-sized Co(OH) ₂ flakes serving as the active materials are electrodeposited on ordered three-dimensional (3D) Ni/Si-MCPs and the Co(OH)₂ flakes have different structures depending on the solvent used. The cobalt hydroxide synthesized from a de-ionized water solvent is composed of compact nano-flakes, whereas that synthesized from an alcohol containing solvent is composed of loosely packed nano-flakes, and that from acetone are nano-flakes with nano-particles. The three types of electrode materials are investigated from the perspective of electrochemical capacitors by means of cyclic voltammogram, galvanostatic charge-discharge measurements and electrochemical impedance spectroscopy. The highest specific capacitance of 6.90 F cm^-2 is achieved from the samples prepared in acetone at a discharge current density of 10 mA cm^-2 and it is much better than the 1.46 F cm^-2 observed in previous studies, thus demonstrating excellent capacity retention.