Spray drying assisted synthesis of porous carbons from whey powders for capacitive energy storage

Supercapacitor is a promising energy storage device, which requires porous high surface carbon materials to achieve efficient capacitive energy storage. Whey powder is a cheap by-product of cheese and casein production process. In this work, spray drying was used to produce uniform composite particles containing whey powers and KOH, in which KOH serves as an activation agent to create uniform pores during carbonization at 800 °C, and the proteins in the whey powders act as N dopants. At the optimal KOH concentration of 13 wt %, the resulting carbon materials contain 3 ± 1 at.% N, have a large specific surface area of 1320 ± 50 m2/g with abundant micropores centered at 0.7, 0.8, 1.2 and 1.5 nm, and deliver a specific capacitance of 139 ± 3 F g−1 at 2 mV s−1. Electrochemical impedance spectroscopy analysis indicates that the carbon material has a good ionic conductivity at the electrode-electrolyte interface and efficient diffusion of electrolyte ions into its bulk. A two-electrode symmetric supercapacitor was assembled, delivering a specific capacitance of 110 F g−1 and an energy density of 19.8 Wh kg−1 at a power density of 149 W kg−1, which is comparable to other carbon-material based supercapacitors. This study offers a sustainable process to synthesize electrochemical carbon materials using food and agricultural by-products.