will alter the concentration ratio. However, the Nernst equation is limited, as it is modeled without a time component and voltammetric experiments vary applied potential as a function of time. Other mathematical models, primarily the Butler-Volmer equation, the Tafel equation, and Fick's law address the time dependence. The Butler–Volmer equation relates concentration, potential, and current as a function of time. It describes the non-linear relationship between the electrode and electrolyte voltage difference and the electrical current. It helps make predictions about how the forward and backward redox reactions affect potential and influence the reactivity of the cell. This function includes a rate constant which accounts for the kinetics of the reaction. A compact version of the Butler-Volmer equation is as follows: Where: : electrode current density, A/m2 (defined as j = I/S) : exchange current density, A/m2 : electrode potential, V : equilibrium potential, V : absolute temperature, K : number of electrons involved in the electrode reaction : Faraday constant : universal gas constant : so-called cathodic charge transfer coefficient, dimensionless : so-called anodic charge transfer coefficient, dimensionless : activation overpotential (defined as ). At high overpotentials, the Butler–Volmer equation simplifies to the Tafel equation. The Tafel equation relates the electrochemical currents to the overpotential exponentially, and is used to calculate the reaction rate. The overpotential is calculated at each electrode separately, and related to the voltammogram data to determine reaction rates. The Tafel equation for a single electrode is: Where: the plus sign under the exponent refers to an anodic reaction, and a minus sign to a cathodic reaction : overpotential, V A: "Tafel slope", V : current density, A/m2 : "exchange current density", A/m2. As the redox species are oxidized and reduced at the electrodes, material accumulates at the electrode/electrolyte interface. Material accumulation creates a concentration gradient between the interface and the bulk solution. Fick's laws of diffusion is used to relate the diffusion of oxidized and reduced species to the faradaic current used to describe redox processes. Fick's law is most commonly written in terms of moles, and is as follows: Where: J: diffusion flux (in amount of substance per unit area per unit time) D: diffusion coefficient or diffusivity. (in area per unit time) φ: concentration (in amount of substance per unit volume) x: position (in length) Types of voltammetry History The beginning of voltammetry was facilitated by the discovery of polarography in 1922 by