Synthesis of nitrogen-doped flower-like carbon microspheres from urea-formaldehyde resins for high-performance supercapacitor

Nitrogen-doped carbon microspheres are synthesized from urea-formaldehyde (UF) resins by a direct carbonization method without any surfactants. UF resins provide not only carbon source, but also nitrogen source. The flower-like urea-formaldehyde resins carbon (UFC) has been successfully obtained through adjusting preparation parameters, including mole ratio of urea to formaldehyde, stirring time, reaction time, pH value, curing condition of HCI and heating rate. Flower-like UFC microspheres consist of nanosheets with the thickness of 50 nm. UFCN2 (UF resins carbonized in N-2 atmosphere) possesses a high N element percent of 11.73%, the large specific surface area of 611 m(2) g(-1) and a large specific capacitance of 276.79 F g(-1) at the scan rate of 2 mV s(-1). Even at 500 mV s(-1), the specific capacitance still maintains 127.50 F g(-1). More importantly, UFCN2 exhibits a high capacitance retention of 98.41% after 5000 charge/discharge cycles at 1 A g(-1), indicating its good cycle stability. (C) 2019 Elsevier B.V. All rights reserved.