The Effects of Different Types of Graphite and Ionic Liquids on the Properties of Carbon Paste Electrodes
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The carbon paste electrodes (CPEs), which are a type of electrode packed with a mixture of carbon (graphite) powder and a pasting liquid binder, have been widely used in electrochemical analysis for 60 years due to their high conductivity, high replaceability, low cost and low background current. Starting from 1964, different forms of modifiers were applied to CPEs to improve the sensitivity and selectivity. Ionic liquids (ILs), which are organic salts with melting point below 100˚C with negligible volatility, low melting point, high thermal and chemical stability, non-flammability, tunable viscosity, high conductivity and wide electrochemical window, were first used as CPE modifier in 2005. Compared to classic CPEs, the ionic liquid-based carbon paste electrodes (ILCPEs) exhibit better voltammetric signals, including lower overpotential and higher peak current. Although there are diverse carbonaceous materials used as the main conductive component of CPEs, spectroscopic graphite (SG) is most frequently employed in research by far. Expanded graphite (EG) is a special form of graphite with loose, porous wormlike shape structure. The large surface area, high bulk volume and electrical conductivity make it an ideal material for battery systems. In this study, we compare the performance of CPEs with these two types of graphite under different weight percentages, and modified with two different ionic liquids, 1-heptyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([C7C1im][NTf2]) and 1-benzyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([BnzC1im][NTf2]). Cyclic voltammetry (CV) was used to determine the cathodic peak current ipc, the cathodic to anodic peak current ratio ipc/ipa and the potential difference between the cathodic and anodic peaks ΔE. Statistical t-tests were employed for results comparison and correlation. The EG was found to work better on CPEs compared to SG due to the higher sensitivity, better reversibility and lower resistance. The sensitivity and conductivity of CPE were greatly improved by adding ILs, and [C7C1im][NTf2] worked better than [BnzC1im][NTf2] because of its higher mobility in carbon pastes.