Yogurt: a novel precursor for heavily nitrogen doped supercapacitor carbon†
Yogurt is used as a novel precursor to synthesize high quality heavily nitrogen doped porous carbon for supercapacitor applications. It is an easily scalable and manufactureable food item containing casein as the major protein, in addition to some whey proteins. The yogurt forming process is mediated by bacteria, and thus this precursor has a high nitrogen content that can get doped into carbon upon controlled precursor pyrolysis. Indeed our material retains a high (12 wt%) nitrogen percentage even after high temperature pyrolysis in the presence of an activating agent. A surface area of 1300 m2 g−1 is attained with a good density of mesopores, apart from abundant micropores. The material offers a high capacitance of 225 F g−1 at 2 A g−1, which decreases only to 200 F g−1 even at a high current density of 20 A g−1 in an aqueous electrolyte. An energy density of 7 W h kg−1 is delivered at a power density of 5000 W kg−1. We have also examined the cathode performance of our material vs. nickel cobalt sulfide (NCS) in an asymmetric configuration. The energy density in an asymmetric assembly goes as high as 27 W h kg−1 at a power density of 364 W kg−1 and 17.8 W h kg−1 at a power density of 6400 W kg−1.