Trapezoidal Cyclic Voltammetry as a Baseline for Determining Reverse Peak Current from Cyclic Voltammograms

Abstract

Several techniques for determining the reverse peak current from a cyclic voltammogram (CV) for a reversible system are described in the literature: CV itself as a baseline with long switching potential (<italic>E</italic><italic>λ</italic>) that serves as a baseline for other CVs, Nicholson equation that uses CV parameters to calculation reverse peak current and linear extrapolation of the current obtained at the switching potential. All methods either present experimental difficulties or large errors in the peak current determination. The paper demonstrates, both theoretically and experimentally, that trapezoidal cyclic voltammetry (TCV) can be used as a baseline to determine anodic peak current (<italic>i</italic><italic>ap</italic>) with high accuracy and with a switching potential shorter than that used by CV, as long as <italic>E</italic><italic>λ</italic> is at least 130 mV away from the cathodic peak. Beyond this value of switching potential the electroactive specie is completely depleted from the electrode surface. Using TCV with <italic>E</italic><italic>λ</italic> = 0.34 V and a switching time (<italic>t</italic><italic>λ</italic>) of 240 s as a baseline, the determination of the reverse peak current presents a deviation from the expected value of less than 1% for most of the CVs studied (except cases when <italic>E</italic><italic>λ</italic> is close to the direct potential peak). This result presents better accuracy than the Nicholson equation and the linear extrapolation of the current measured at the switching potential, in addition to presenting a smaller error than that obtained in the acquisition of the experimental current. Furthermore, determining the reverse peak current by extrapolating the linear fit of <italic>i</italic><italic>ap</italic> vs. <inline-formula><mml:math id="m1" display="inline"><mml:semantics id="sm1"><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:msqrt><mml:mrow><mml:msub><mml:mrow><mml:mi>t</mml:mi></mml:mrow><mml:mi>λ</mml:mi></mml:msub></mml:mrow></mml:msqrt></mml:mrow></mml:semantics></mml:math></inline-formula> to infinite time gave a reasonable approximation to the expected value. Experiments with aqueous potassium hexacyanoferrate (II) and ferrocene in acetonitrile confirmed the theoretical predictions.