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 °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 Ni 2+ /Co 2+ = 25:75 exhibited high surface area and a capacitance of 632 F g –1 at 5 mV s –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 Co 2+ /Co 3+ and Ni 2+ /Ni 3+ couples that afford rich faradic capacitance and enhanced conductivity.