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Graphical abstract Highlights • Porous carbon flakes (PCFs) are prepared from PS waste using MgO as template. • PCFs are used as carbon support for deposition of MnO 2 forming PCF-MnO 2 hybrid. • PCF-MnO 2 exhibits good electrochemical properties as electrode in supercapacitor. • This work provides a practical way to recycle polymeric waste in large-scale. Abstract Due to white pollution related environmental concern and sustainable development requirement, it is desirable to recycle the widely used plastic wastes into products with commercial value, such as high-valued carbon materials which can be applied in electrochemical fields. In this work, porous carbon flakes (PCFs) are produced by direct pyrolysis of polystyrene waste through template method. Furthermore, manganese dioxide (MnO 2) nanosheets are selectively deposited on the surface of resultant PCFs to form hybrid (PCF-MnO 2). Because of the large specific surface area (1087 m2/g) and high conductivity of PCFs, native high specific capacity of MnO 2 , and positive synergistic interaction between PCF and MnO 2 , the resulting hybrid materials show an ultrahigh capacitance of 308 F/g at 1 mV/s and 247 F/g at 1 A/g in LiCl electrolyte, and excellent cycle stability of 93.4% capacitance retention over 10,000 cycles at 10 A/g in symmetric supercapacitor device. This work demonstrates a convenient method for the preparation of cost-effective and high-performance electrode material for electric capacitor. More importantly, it provides a potential way to recycle polystyrene waste into high-valued product in large-scale with disposing of polymeric waste to alleviate environmental concerns. [ABSTRACT FROM AUTHOR]

With the purpose to turn wastes into wealth and develop renewable energy, much effort has been focused on converting biowastes into porous carbons and exploring their application for supercapacitors. In this study, inspired by natural porous structure of biomass and small size of Sn nanoparticles, a one-step strategy was developed to convert waste wolfberry fruits into porous carbons by SnCl 2. The as-fabricated carbon exhibited large specific surface area of 1423 m2 g−1 and hierarchical porosity with total pore volume of 1.36 cm3 g−1. Meanwhile, the newly produced SnCl 2 with more than 95% recovery rate was reused as catalyst. Moreover, the porous carbon was applied for supercapacitive electrode. In three-electrode 6 M KOH system, it displayed outstanding capacitance of 365 F/g at 0.2 A g−1, good rate capability of 75% capacitance retention at 20 A g−1 and excellent cycling stability of 96.4% capacitance retention after 10000 cycles. In two-electrode 1 M Li 2 SO 4 system, its energy density reached 23.2 Wh kg−1 at a power density of 225 W kg−1. The current work provided a facile and low-cost method to recycle renewable biowastes into high-valued carbon material, and further expanded its application for high-performance energy storage devices. [Display omitted] [ABSTRACT FROM AUTHOR]