Investigating the excellent electrochemical energy storage performance in heterogeneous interfaces of Co9S8@NiMn oxide by photoirradiation

Abstract

Excellent heterointerface combination can adjust energy band structure to reduce interface resistance, improve electron transfer rate and then play an important role in promoting the kinetics of redox reaction. In this work, a hierarchical core-shell structure with novel heterointerface of Co9S8 nanotubes coupling with NiMn oxide nanosheets is designed on flexible carbon cloth substrate (Co9S8@NiMn oxide/CC). Because of the NiMn oxide has higher conduction band and valence band than Co9S8, which facilitates the carrier migration. The electrons are easy to flow from NiMn oxide to Co9S8, and the holes can flow from Co9S8 to NiMn oxide. Along with the holes’ accumulation on NiMn oxide and electrons’ accumulation on the Co9S8, it is easy to form a built-in electric field. Meanwhile, the accumulation of the holes on NiMn oxide side makes NiMn oxide positively charged, which is in favor of OH− adsorption and accelerating the reaction processes, and then promoting the electrochemical performance. At a current density of 1mA cm−2, a high area capacitance of 5.34 F cm−2 (741.7 μAh cm−2) was achieved. By photoirradiation, the area capacitance increases from 3.485 to 4.07 F cm−2 at the current density of 5 mA cm−2, which further proved that the excellent heterointerface combination due to the photoirradiation can induce effective photo-generated charge separation at the heterogeneous interface with suitable energy band matching, thus promoting the electrochemical redox reaction and effectively improving the electrochemical energy storage performance. The all-solid asymmetric supercapacitors (AAS) with Co9S8@NiMn oxide/CC as cathode and active carbon (AC) as anode can reach a high energy density of 44.6 W h kg−1 (0.1472 mW h cm−2) at power density of 242.53 W kg−1 (0.8 mW cm−2) and show an outstanding cycling stability. And the AAS device can serve as a power source for lighting up some electronic products, which indicates that as prepared nanotube arrays have practical application value.