Construction of internal and external defect electrode materials based on hollow manganese-cobalt-nickel sulfide nanotube arrays

Highlights: • Hollow trimetallic electrodes with internal and external defects are synthesized. • The electron density of metal ions and active sites increase greatly. • The specific capacitance significantly improves from 2944 to 3794F g⁻¹. • This provides a reference for later transition metal sulfide electrode materials. The deficient active sites and poor conductivity of transition metal sulfides result in low energy density of supercapacitors that limits their extensive application. In this work, hollow manganese-cobalt-nickel sulfide nanotube arrays with the pore diameter about 40 nm are synthesized by three steps, and then chemical reduction strategy is used to build hollow trimetallic electrode materials with internal and external defects. During the whole process, due to the strong reducibility and small radius of H⁻, metal ions, which locate inside and outside the tube, are partially reduced from high oxidation states to low oxidation states, then the corresponding metal-sulfur bonds are broken and sulfide ions escape from active materials to form sulfur vacancies. Enhanced electrochemical performance of the electrode with vacancy (from 2944F g⁻¹ to 3794F g⁻¹ at 1 A g⁻¹) demonstrates that the introduce of vacancy can facilitate electrochemical reaction kinetics due to the increased electron density of metal ions and active sites. In addition, the assembled asymmetric supercapacitor has a maximum voltage window of 1.8 V and displays a high energy density of 85.2 Wh kg⁻¹ under a power density of 1030 W kg⁻¹, showing the promising application in electrochemical energy storage fields.