Nitrogen Doped Carbon materials (NDCMs) from Organic Ionic Salts and Biopolymer Resources for Supercapcitor Application

Abstract

Nitrogen doped carbon materials (NDCMs) have been successfully synthesized, characterized and investigated as an electrode material for supercapacitor application. The synthesized NDCMs exhibited remarkable capacitor performance in terms of specific capacitances, rate capability, % capacitance retention and long cycle stability in a variety of aqueous electrolytes. Firstly, organic ionic dyes namely; eriochrome black-T (EBT) and murexide (MDE) were employed as N-rich precursors for the synthesis of NDCMs via a facile high temperature carbonization route. The effect of different experimental parameters such as heating profile, annealing temperature, post chemical activation and inert atmosphere was investigated in detail on NDCMs derived from EBT. Later, waste biopolymer; chicken feathers (CFs) were used as a low cost versatile N-rich precursor for the synthesis of NDCMs. Prior to carbonization, the thermogravimetric analysis (TGA) of all precursors was performed to evaluate the yield of carbon residue. The synthesized NDCMs were characterized by Raman analysis (RA), X-ray diffraction (XRD), surface area and porosity analysis (BET and BJH), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Afterwards, supercapacitor performance evaluation, electroanalytical techniques viz. cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were performed. After detailed physicochemical investigation of NDCMs, it was established that these NDCMs have achieved good graphitization, amorphous/crystalline phases coexistence, homogeneous distribution of nitrogen and oxygen, three different types of nitrogen configurations (pyridinic N- 6, pyrrolic N-5 and quaternary N-Q), porous sheet like morphology, and moderate surface area with hierarchical porosity (micro, meso and macroporosity). The electrochemical investigations in acidic (1.0 M H2SO4), alkaline (6.0 M KOH) and neutral (0.5 M Na2SO4) electrolytes revealed that acidic electrolyte 1.0 M H2SO4 was the most promising electrolyte for supercapacitor application because of its small ion-size and high mobility which provide pseudocapacitive contribution. Whereas, among different alkali metal sulfate solutions (Li2SO4, Na2SO4, K2SO4) studied as an electrolyte for supercapacitor study of synthesized NDCMs, Li2SO4 proved to be a good choice. In addition, among the four different concentrations of Li2SO4 (0.5 M, 1.0 M, 1.5 M and 2.5 M), the optimized concentration for supercapacitor study of NCM(CF)-700A electrode material was found to be 1.5 M Li2SO4 due to its neutral character and large hydrated Li ion size associated with low mobility. Moreover, the operational voltage window for NCM(CF)-700A material was successfully extended up to 2.0 V in 1.5 M Li2SO4 solution.