Cobalt nickel double hydroxides (CoxNi1-x LDHs) nanoparticles were synthesized by a polyvinyl pyrrolidone-assisted chemical co-precipitation method. It was found that the ratio between Co and Ni had a significant effect on their electrochemical activities. The specific capacitance of 2614 Fg(-1) was achieved when the atomic ratio of Co to Ni was equal to Co0.57Ni0.43. This Co0.57Ni0.43 LDH sample had a BET specific surface area of 109.8 m(2) g(-1) and total pore volume of 0.6036 cm(3) g(-1), and its pore size distribution was mainly in the range of 1.5-5 nm, which led to the high liquid-solid interfacial area and further increased the utilization of the active materials. Additionally, the Co0.57Ni0.43 LDH electrode exhibited a good electrochemical stability with 86.4% of the initial capacitance over 1000 consecutive cycles at 5 A g(-1). (C) 2012 Elsevier Ltd. All rights reserved.