Hydrothermal Synthesis of Binary Ni-Co Hydroxides and Carbonate Hydroxides as Pseudosupercapacitors

A series of binary Ni-Co hydroxides and Ni-Co carbonate hydroxides with various shapes and compositions was successfully synthesized by a one-step and reliable method assisted by an amphiphilic block copolymer. After thermal treatment at 200 degrees C, the as-prepared samples could be activated and their surface areas could be increased. With increasing Co content, the shapes of the final products changed from flower-to fiber-and plate-like structures. The synthesized binary Ni-Co sample with an optimized composition of Ni2+/Co2+ = 25:75 exhibited high surface area and a capacitance of 632 Fg(-1) at 5 mVs(-1) with negligible capacitance loss after 1000 cycles. The capacitance value of the binary Ni-Co sample is higher than that of Ni hydroxide itself, and this improved electrochemical performance is attributed to the binary Co2+/Co3+ and Ni2+/Ni3+ couples that afford rich faradic capacitance and enhanced conductivity.