Reduced core-shell structured MnCo2O4@MnO2 nanosheet arrays with oxygen vacancies grown on Ni foam for enhanced-performance supercapacitors

Abstract

In this work, reduced core-shell structured MnCo2O4@MnO2 (rMnCo2O4@rMnO2) nanosheet arrays with appropriate oxygen vacancies grown on Ni foam have been prepared via a two-step hydrothermal process with facile annealing and NaBH4 solution treatment. The good designs of 2D-2D MnCo2O4@MnO2 core-shell nanosheet arrays and in situ introduce of oxygen vacancies provide abundant reactive sites and effective electronic transmission, endowing the rMnCo2O4@rMnO2 an excellent electrochemical performance. And the rMnCo2O4@rMnO2-2h electrode exhibits an aerial capacitance of 3.39 F cm−2 (or 0.4 mA h cm−2) at the current density of 3 mA cm−2, much higher than those of MnCo2O4 (1.27 F cm−2, or 0.15 mA h cm−2) and MnCo2O4@MnO2 (1.89 F cm−2, or 0.22 mA h cm−2). Also, the electrode possesses pretty rate performance of 1.66 F cm−2 (or 0.19 mA h cm−2) at 60 mA cm−2 and cycling property with 92.5% capacity retention after 3000 cycles. Furthermore, the assembled rMnCo2O4@rMnO2-2h//AC asymmetric supercapacitor yields an energy density of 32.4 W h kg−1 at a power density of 904.9 W kg−1, 27.3 W h kg−1 even at 4524.2 W kg−1 and maintains 81.8% of initial capacitance at 50 mA cm−2 after 5000 cycles, which indicate the rMnCo2O4@MnO2-2h should be applicable electrode materials for supercapacitors.