FaradayEffizienz

Faraday efficiency, also known as Faradaic efficiency, is a measure of how efficiently electric charge is used to drive a specific electrochemical transformation. It expresses the fraction of the total current that contributes to the formation of a desired product, rather than to side reactions such as solvent reduction or evolution of gas. The concept is central to evaluating the selectivity of electrochemical processes.

The Faraday efficiency for a given product j is defined as FE_j = (moles of electrons that actually form product j × Faraday constant) divided by the total charge passed, Q = ∫ I dt. Equivalently, FE_j = (n_j × z_j × F) / Q, where n_j is the amount of product j formed, z_j is the number of electrons transferred per molecule of j, and F is the Faraday constant. In practice FE_j is often reported as a percentage: FE_j = 100 × [charge used for product j] / [total charge passed]. When multiple products are formed, the sum of their Faradaic efficiencies approximates 100%, within experimental error.

Measurement methods combine product quantification with charge data. Gas products are quantified by collection and volumetric or chromatographic analysis; dissolved or deposited products are quantified by concentration measurements and stoichiometry. The total charge is obtained by integrating the current over time.

Applications and implications: FE provides a direct indicator of reaction selectivity and is used to optimize catalysts, electrode materials, and operating conditions. High Faradaic efficiency is desirable for energy efficiency and process economy, but achieving it often involves trade-offs with reaction rate or overpotential.