Influência do tratamento por plasma reativo em eletrodos de grafeno e aplicações em eletroquímica

Abstract

Carbon electrodes, such as graphene, are usually used in electrochemistry. The electron transfer capacity of graphene electrodes can be improved with physical and chemical changes on their surface and can be carried out by means of reactive plasma. The objective of this work was to treat graphene electrodes in reactive plasmas under different conditions (time, position of the samples in the reactor and oxygen pressure) and to investigate the effects of these parameters on the chemical and physical properties of these materials. The graphene electrodes were prepared with a mass of 80 mg, pressed at 20 kgf and individually treated in the plasma, changing the time, the oxygen pressure and the position of the sample in relation to the plasma discharge in three levels. Cyclic voltammetry and galvanostatic charge-discharge tests were carried out in a solution of 1 mol L-1 of H2SO4 to estimate the capacitances of the electrodes in both tests. Afterwards in a solution of 1mmol L-1 K3 [Fe(CN)6] and 0.1 mol L-1 KCl with pH 3, cyclic voltammetry was performed again in order to analyze the electrode transfer. The electrodes were also characterized by Raman spectroscopy and atomic force microscopy. The electrodes that showed good results were used to manufacture flexible supercapacitors in solid state and potential sensors. The supercapacitors were characterized by cyclic voltammetry and galvanostatic charge-discharge and the electrodes, with potential application as sensors, by cyclic voltammetry in K3 [Fe(CN)6] and KCl solution in the same concentrations of the previous tests. Plasma-treated electrodes showed larger electroactive areas, greater capacitances and better electronic transfers compared to untreated electrodes. Through Raman spectroscopy and atomic force microscopy, it was observed that the samples treated in plasma showed a higher degree of defects. The solid-state supercapacitors showed no significant improvement in capacitances compared to the capacitor with untreated electrode. The electrodes used as sensors showed improvement with the treatment in plasma with better electron transfer in electrochemical studies. The electrodes chosen for the tests as supercapacitors as well as most of the electrodes tested as potential sensors have in common the position of the sample in the most intense plasma region. Higher oxygen pressure was also important in sensor testing.