highoverpotential

In electrochemistry, overpotential (η) is the extra potential beyond the thermodynamic equilibrium potential required to drive an electrochemical reaction at a given rate. When the applied potential deviates from the equilibrium potential by a substantial amount, the resulting current reflects a high overpotential. High overpotential thus indicates poorer energetic efficiency for the reaction of interest.

Overpotential comprises several components. Activation overpotential accounts for the energy barriers at the electrode surface that must be overcome for electron transfer. Concentration overpotential arises from changes in ion concentration near the electrode due to mass transport limits. Ohmic overpotential results from the resistance of the electrolyte, electrodes, and contacts in the circuit. The total overpotential is the sum of these contributions, and it generally increases with current density.

High overpotential has direct implications for energy efficiency and heat generation in electrochemical systems. It can result from poor catalytic activity, unsuitable electrode materials, surface passivation, insufficient mass transport, or high electrolyte resistance. System design choices, such as electrolyte concentration, cell geometry, and electrode architecture, also influence overpotential.

Experimentally, high overpotential is observed in polarization curves as the voltage required to achieve increasing current. The relationship between overpotential and current density is often described by the Tafel equation at higher overpotentials and by the more general Butler-Volmer equation.

Mitigation strategies include using catalysts that lower activation barriers, increasing active surface area, employing nanostructured or novel electrode materials, improving electrolyte conductivity and cell design to reduce resistance, enhancing mass transport (for example, through flow cells or porous electrodes), and optimizing operating conditions to minimize polarization losses.