Synergistic effect of heat treatment and concentration of polydopamine enhance the electrochemical performances of hollow nitrogen-doped carbon microspheres

Herein, hollow nitrogen-doped carbon microspheres (HNCMs) have been synthesized with controlled shell thickness and high surface area by pyrolysis of polydopamine-coated polystyrene (PS@PDA) core-shell microspheres. A polystyrene (PS) core was removed from the core-shell structures by pyrolysis at 500 °C under N2 atmosphere. Charge transfers, redox transformations (caused by N–H/catechol groups of the polydopamine (PDA)), and pyrolysis (introduce the nitrogen atoms along with a high degree of graphitization) may be attributed to the increase in the electrochemical and electrocatalytic performances. Our resulting material exhibited the improved electrochemical behavior towards supercapacitors with the maximum specific capacitance of 261.6 F g−1 at a scan rate of 2 mV s−1. It also showed moderate electrocatalytic properties via a 4-electron pathway mechanism (with high onset potential of 0.919 V vs. RHE at 1600 rpm) during oxygen reduction reaction. Importantly, the synergistic effect of heat treatment and a suitable concentration of PDA enhance the electrochemical performances of HNCMs.