Remarkable enhancement of the electrochemical properties of Co3O4 nanowire arrays by in situ surface derivatization of an amorphous phosphate shell

Abstract

It is a highly desirable but still a challenging task to find a simple, fast and straightforward method to greatly improve the electrochemical properties of a Co₃O₄ electrode for pseudocapacitors. In this study, we demonstrate that developing an amorphous Co–phosphate (Co–Pi) shell via in situ surface derivatization on a Co₃O₄ nanowire (NW) surface facilitates the diffusion and reaction of electrolyte ions and leads to distinctive conductivity. Because of these advantages, 1D nanostructures and the synergistic effect between Co₃O₄ and amorphous Co–Pi, the resulting core–shell Co₃O₄@Co–Pi nanowire (NW) array exhibits high capacitance (1692 F g⁻¹ at current density of 1 A g⁻¹). In addition, high rate capabilities and retention capacity of 86% after 6000 cycles at 20 A g⁻¹ are achieved. By using the Co₃O₄@Co–Pi core–shell hybrid NW array and activated carbon as the anode and cathode, respectively, asymmetric pseudocapacitors are assembled that exhibit high capacitance (energy density of 35.69 W h kg⁻¹ at power density of 558 W kg⁻¹) and super-long cycle life (82% capacitance retention after 40 000 cycles). Our synthesis method provides a new technology for the design of composites of transition metal oxides/hydroxides and phosphates for electrochemical energy storage applications.