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

Abstract

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.