Effect of Nitrogen and Phosphorous Based Additives on Electrochemical Synthesis of Modified Graphene for Supercapacitor Application
Authors: Rathuwadu Nadeesha P. W. , Sharmila Shehani 
Published: December 2024

Graphene is a good electrode material for electrochemical energy devices due to its excellent properties such as high electrical conductivity, thermal conductivity, surface area, and chemical and mechanical stability. There are numerous ways to synthesize graphene. Most of these methods are sophisticated, time consuming, expensive, and require hazardous chemicals. Electrochemical exfoliation of graphite is a less complex, quick, affordable, and a greener way to synthesize graphene. Nevertheless, it suffers from restacking of graphene sheets compromising the inherent properties. One of the approaches to overcome restacking is to modify the graphene structure through etching and/or functionalization. In this study an electrochemical synthesis method is proposed in the presence of nitrogen and phosphorous based additives to synthesize porous/functionalized graphene. The synthesized materials’ electrochemical performance were evaluated for supercapacitor applications. Supercapacitors are advantageous over batteries for their superior power density. Improving energy density of supercapacitors remains a challenge. The modified graphene (MG) synthesized via this proposed method is anticipated to improve the electrochemical performance of supercapacitors due to improved porosity/functionalization and controlled restacking. MG was synthesized in the presence of iminoacetic acid (IAA – N1), ethylene disuccinic acid (EDDS – N2), phytic acid (PA – P1), and etidronic acid (EA – P2) via electrochemical exfoliation of graphite. Graphene was synthesized under same conditions in the absence of any additives for comparison. Synthesized material was characterized structurally and electrochemically. UV-visible data confirmed the synthesis of graphene due to the presence of absorbance peak around 270 nm for all samples. Raman spectroscopy was carried out to analyse the ID/IG and I2D/IG ratios. The ID/IG ratios are 1.14 and 0.67 for MG-N1 and MG-P1 respectively compared to 0.21 of graphene. The data confirms few layer graphene is formed with high porosity in the presence of N additive and with low porosity in the presence of P additive. The low I2D/IG ratios 0.1 and 0.18 for N1 and P1 also confirm the synthesis of few layer porous graphene. The cyclic voltammetry data illustrated the double-layer capacitive behavior of MG by having the rectangular shapes within the respective potential windows even at higher scan rates such as 100mV/s. The specific capacitances of MG-N1, MG-N2, MG-P1, and MG-P2 demonstrated an enhancement of 59.1%, 35.6%, 41.6%, and 28.9% respectively at scan rate 5 mV/s compared to the graphene sample. Also, MG showed higher operating potential window compared to graphene. In addition, electrochemical impedance spectroscopy and galvanostatic charge discharge demonstrated the enhanced electrochemical performance for MG. In general, MG synthesized in the presence of N-based less sterically hindered molecule (MG-N1), demonstrates the highest performance among all additive materials. The higher electronegativity of nitrogen facilitates etching over functionalization and MG-N1 showed high porosity according to Raman data. N1 is also less sterically hindered and easily intercalated in graphite structure and contributed for porous graphene formation. The P-based additives, with less electronegativity of phosphorous, could participated in both functionalization and etching. According to Raman data also MG-P1 shows less porosity. These characterization results validate the successful synthesis of MG via etching and functionalization with enhanced electrochemical performances in the presence of additives while electrochemical exfoliation of graphite.