MnO₂ nanosheets grown on N and P co-doped hollow carbon microspheres for high performance asymmetric supercapacitor

The rapid development of supercapacitors has led to an increasing demand for the exploitation of stable and excellent electroactive electrode materials. Herein, a novel hybrid material of N, P co-doped hollow carbon microspheres (N/P-HCS) and ultrathin MnO₂ nanosheets was facilely constructed for the electrode material of supercapacitors through a two-step synthetic strategy including the preparation of N/P-HCS and subsequent growth of MnO₂ nanosheets on N/P-HCS. The N/P-HCS@MnO₂ hybrid possesses a N/P-HCS core and a porous shell composed of ultrathin MnO₂ nanosheets. Moreover, the morphology and content of MnO₂ in the hybrid can be controlled by designing the stoichiometric chemical reaction between N/P-HCS and KMnO₄. The hybrid electrode exhibits excellent electron transport, fast electrolyte ions diffusion, rapid and reversible Faradaic reaction, and good rate performance. Additionally, a green asymmetric supercapacitor was manufactured using typical hybrid N/P-HCS@MnO₂-30 as positive electrode and N/P-HCS as negative electrode, which displayed a high energy density of 32.21 Wh kg⁻¹ at a power density of 449.8 W kg⁻¹ and excellent cycling stability (capacitance retention of 94.5% after 3000 cycles). These results show that the N/P-HCS@MnO₂ might be an attractive electrode material for practical application in advanced supercapacitor.