Amino Acid Protic Ionic Liquids: Multifunctional Carbon Precursor for N/S Codoped Hierarchically Porous Carbon Materials toward Supercapacitive Energy Storage

Amino acids (AAs) are abundant in nature as the basic constituent unit of waste proteins. Amino acid protic ionic liquids (AA-PILs) rich in C, N, O, and S elements can be easily synthesized, making them a promising potential precursor of N/S codoped carbon materials for high-performance supercapacitors. A series of 21 AA-PILs were prepared and directly carbonized with various carbon yields due to the different alkyl group of AA-PILs, indicating that the carbon yield of aromatic AA-PILs was much higher than that of aliphatic and heterocyclic AA-PILs. To further develop the electrochemical properties, hierarchically porous carbon materials were prepared via activation, possessing high surface area, a micromesopores structure, and excellent electrical conductivity. The prepared Lys-K2CO3 exhibited an ultrahigh specific capacitance of 350 F g–1 at 1 A g–1 with almost 100% specific capacitance retention after 5000 cycles at 5 A g–1 in 6 M KOH electrolyte for a three-electrode system. The symmetric supercapacitors can light up a red bulb, demonstrating the application potential in energy storage devices. These results will help to develop techniques for the synthesis and fabrication of N/S codoped carbon electrode materials for supercapacitors, providing a new strategy for the realization of natural waste proteins energy utilization.