One-step growth of Ni2Co(PO4)2 microspheres for high energy density supercapacitors

Nickel and cobalt phosphates as a kind of low-cost inorganic materials are promising electroactive materials. The structure stability and good dispersibility of micro-spherical materials make them popular in the energy storage field. Therefore, the fabrications of Ni–Co phosphate microspheres with some facile and cost-effective methods have attracted lots of attentions. In this work, we present one-step growth of Ni2Co(PO4)2 microspheres using urea as pH regulator. Urea decomposes into NH3 and CO2 during the hydrothermal reaction process, resulting in the precipitation of Ni–Co phosphates. The as-prepared Ni2Co(PO4)2 microspheres exhibit uniform and well-dispersed spherical morphology. Compared with traditional Ni2Co(PO4)2 particles, Ni2Co(PO4)2 microspheres exhibit larger electrochemical specific surface area and smaller resistance of electrons/ions transfer. The specific capacity of Ni2Co(PO4)2 microspheres reaches as high as 153 mAh g-1 at a current density of 1 A g-1, which is 1.59 times higher than that of traditional Ni2Co(PO4)2 particles. In addition, this facile one-step synthetic method can be applied to fabricate series of Ni–Co phosphates with different Ni/Co atomic ratios. This work provides a facile synthetic method of fabricating Ni–Co phosphate materials, which has potential applications in large-scale manufacture.