Nitrogen and Phosphorus Co-doped Nanoporous Carbons from Phosphoprotein/Silica Self-Assemblies for Energy Storage in Supercapacitors

In this work, nanoporous, heteroatom-doped carbon materials with tailorable structures and excellent charge/energy storage properties are synthesized using casein (a phosphoprotein) as a precursor and silica gel as a template via a facile synthetic route. The synthesis involves carbonization and etching. In the synthesis, an appreciable amount of the N and P atoms in casein make it as dopants into the nanoporous carbons, enabling the materials to efficiently store charge. The structures and compositions as well as the overall charge storage properties of the materials are easily tuned by varying the relative amount of silica gel template used with casein in the precursors. By using an optimal amount of silica in the casein/silica self-assemblies, a nanoporous carbon with low resistance to Faradaic processes and good capacitance and pseudocapacitance is obtained. This material gives a capacitance of ca. 261 F g⁻¹ at 1 A g⁻¹, which is higher than those of many recently reported carbon materials in the literature. Moreover, the material retains 95 % of the initial capacitance with ca. 100 % of coulombic efficiency after 10,000 charge-discharge cycles.