Nitrogen phosphorous derived carbons from Peltophorum pterocarpum leaves as anodes for lead–carbon hybrid ultracapacitors

Abstract Lead–carbon hybrid ultra-capacitors are emerging as an alternative to a lead-acid battery, owing to the absence of sulfation, thereby enhancing cycle life and C rate performances. In this work, Nitrogen and Phosphorous derived carbons are synthesized from the Peltophorum pterocarpum leaves by treating with phosphoric acid followed by carbonization at 550 °C for 3 hrs. These carbons contain about 3.76% of Nitrogen and 1.26% of Phosphorous and have a BET surface area of 443 m2 g−1. Specific capacitances of 1032 F g−1 and 640 F g−1 at current densities of 1 A g−1 and 10 A g−1, respectively in 4.5 M. sulfuric acid are achieved for these carbon-based electrodes. The hybrid ultra-capacitor fabricated by using PbO2 positive electrode and Nitrogen and Phosphorous derived carbons coated on to graphite sheet as a negative electrode shows cycling stability with capacitance retention of >95% for about 15,000 cycles at an applied current density of 5 A g−1. The pseudocapacitive nature of as-synthesized carbon exhibits significant improvement in electrochemical performance in lead–carbon ultra-capacitors.