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

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 degrees 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 m(2) 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 carbonbased 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.