Electrochemically Exfoliated Graphite Nanosheet Films for Electromagnetic Interference Shields

Electrochemical exfoliation of graphite is one of the most efficient and easiest processes to produce high-quality graphene materials. In this study, the efficiency of exfoliation methods for graphite to develop graphene-based electromagnetic interference (EMI) shields with high electrical conductivity was investigated. Exfoliation of graphite was performed in four aqueous solutions of inorganic salts of Na2SO4, (NH4)2SO4, NH4NO3, and (NH4)2HPO4, and the electrochemically exfoliated graphene (EEG) was thoroughly screened to separate out the more defective and small sheets. A 30 μm thick film composed of stacked and overlapped co-doped EEG sheets prepared in (NH4)2SO4 had a room-temperature electrical conductivity of 28 400 S/m and an EMI shielding effectiveness (EMI SE) of ∼62 dB in the X-band frequency (8.2–12.4 GHz), without any reduction of EEG sheets. These are both high values compared to values reported in the literature for “graphene” films with comparable thickness. This is an excellent EMI SE for a shield thickness of just 30 μm, compared to the very thick initial graphite sheet’s EMI SE of ≈70 dB with a thickness of 1.5 mm (50 times thicker). An original finding in this paper is that using the (NH4)2HPO4 electrolyte, we were able to prepare thermally stable EEG films with excellent EMI performance (shielding effectiveness of ∼50 dB after 3-day exposure to 500 °C in air). These high values for overall EMI shielding and electrical conductivity confirm the feasibility of electrochemical exfoliationfor high-performance EMI shields; i.e. it is possible to use a method that does not involve treatment with harsh chemicals or oxidizers and does not require high energies or high temperatures.