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How Ohmic Resistance Shapes Your Voltammogram

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The iR drop , also known as the ohmic drop , refers to the reduction in effective potential at the working electrode interface due to the resistance of the electrolyte solution. This drop affects both the potential applied by the potentiostat and the potential it measures, thereby distorting the observed electrochemical response. In the absence of mass transport limitations, the redox reaction can be modelled using an equivalent electrical circuit that describes the interfacial behaviour between the reference and working electrodes: Here: R s – the solution resistance (also known as the electrolyte or uncompensated resistance). R ct – the charge transfer resistance, associated with the kinetics of the electron transfer reaction. C dl – the double-layer capacitance, representing the electrochemical double layer at the electrode interface. The potentiostat continuously regulates the potential difference between the reference ...
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Understanding cyclic voltammetry: Electron Transfer Mechanism

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Cyclic voltammetry (CV) is a widely used electrochemical technique for analyzing the charge transfer of a redox-active species during a linearly cycled potential sweep. It provides valuable information about interfacial processes, redox thermodynamics, diffusion coefficients, electrode surface properties, and charge-transfer kinetics. However, despite its popularity, CV is often misunderstood due to the simultaneous occurrence of multiple processes, complicating the interpretation of voltammograms. Let's consider the following redox reaction: \[ Fe^{2+}\underset{k_b}{\overset{k_f}{\rightleftharpoons}}Fe^{3+}\] The rate of this reaction can be described phenomenologically as: \[ r=k_f[Fe^{2+}]-k_b[Fe^{3+}] \] In the classical chemical kinetics, the kinetic constant depends exponentially with temperature according to the Arrhenius equation: \[ k=A\exp\left(-\frac{Ea}{RT}\right) \] This equation tells us that the rate constant increases exponentially with tempera...
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Understanding Surface Adsorption in Electrochemical Reactions

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In many electrochemical systems, electroactive species can adsorb onto the electrode surface — especially under non-equilibrium conditions . This adsorption introduces complexity into redox processes, as charge transfer may occur from both the dissolved species in the bulk solution and those adsorbed on the electrode surface . As a result, the system exhibits dual charge-transfer pathways , requiring more sophisticated kinetic models. Examples of Surface-Confined Redox Systems Several well-known systems exhibit this dual charge transfer behaviour, including: Quinone/Hydroquinone redox couple on glassy carbon electrodes [4]. Ferrocene derivatives on gold electrodes [5]. Ruthenium bipyridine complexes on platinum electrodes [6]. Hemoglobin and myoglobin on carbon electrodes [7]. These systems are particularly challenging because they involve two simultaneous charge transfer pathways : Bulk charge transfer \( \boldsymbol{k_{red/ox,bulk}} \) — occurs b...
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