One-pot solvothermal synthesis of ternary Ni-Co-P micro/nano-structured materials for high performance aqueous asymmetric supercapacitors

The ternary Ni-Co-P micro/nano-structured materials were synthesized via a facile one-pot solvothermal strategy and further served as positive electrode materials for supercapacitors. X-ray diffraction (XRD) showed that the optimal Nis-Col-P materials exhibited the two major phases of M12P5 and M2P (M = Ni, Co). X-ray photoelectron spectroscopy (XPS) revealed the binding energy shifts of P2p, Ni2p and Co2p of Ni-8-Co-1-P materials compared with the bare Ni-P and Co-P, indicating the formation of ternary materials. Transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) mapping exhibited the micro/nano-structured morphology with rich surface nanowires (5-10 nm in diameter) and the consistent distribution of Ni, Co and P elements of the Nis-Col-P materials respectively. Nitrogen sorption measurements illustrated the mesoporous structure of the Nis-Col-P materials with the specific surface area of 257 m(2) g(-1). Due to the richer Ni, Co surface electroactive sites and the stronger synergistic effect of Ni and Co redox species, the Nis-Col-P materials showed superior specific capacitance, rate capability and charge transfer kinetics (1448 F g(-1) at 1 A g(-1), 1173 F g(-1) at 16 A g(-1), 333 SI) than the Ni-Co-P with other Ni/Co ratios (1:0, 16:1, 4:1, 2:1, 0:1). The mass ratio optimized activated carbon (AC)//Ni-8-Co-1-P asymmetric capacitor (m+/m- = 1:2) exhibited high energy and power densities (22.8 Wh kg(-1), 4.32 kW kg(-1)) together with excellent cycle life (no decay after 5000 cycles at 4 A g(-1)). The high performance makes the ternary Ni-Co-P micro/nano-structured materials promising electrode materials for supercapacitors. (C) 2017 Elsevier B.V. All rights reserved.