Effect of H2SO4/H2O2 pre-treatment on electrochemical properties of exfoliated graphite prepared by an electro-exfoliation method

Abstract

The effect of pre-treating graphite sheets in a H₂SO₄/H₂O₂ solution before electro-exfoliation is reported. It was revealed that the volume fraction of H₂SO₄ to H₂O₂ during pre-treatment could control the degree of exfoliation of the resulting exfoliated graphite (EG). X-ray diffraction (XRD), Raman, and Fourier transform infrared (FTIR) spectroscopy analyses have suggested that EG produced by first pre-treating the graphite sheet in H₂SO₄/H₂O₂ solution with the H₂SO₄ : H₂O₂ volume fraction of 95 : 5 demonstrates the highest exfoliation degree. This sample also demonstrated excellent electrochemical properties with good electrical conductivity (36.22 S cm⁻¹) and relatively low charge transfer resistance (R_ct) of 21.35 Ω. This sample also showed the highest specific capacitance of all samples, i.e., 71.95 F g⁻¹ at 1 mV s⁻¹ when measured at a voltage range of −0.9 to 0 V. Further measurement at an extended potential window down to −1.4 V revealed the superior specific capacitance value of 150.69 F g⁻¹. The superior morphology characteristics and the excellent electrical properties of the obtained EG are several reasons behind its exceptional properties. The pre-treatment of graphite sheets in H₂SO₄/H₂O₂ solution allegedly leads to easier and faster exfoliation. The faster exfoliation is allegedly able to prevent massive oxidation, which frequently induces the formation of graphite/graphene oxide (GO) in a prolonged process. However, too large H₂O₂ volume fraction involved during pre-treatment seems to cause excessive expansion and frail structure of the graphite sheets, which leads to an early breakdown of the structure during electrochemical exfoliation and prohibits layer by layer exfoliation.