Electrochemical surface area

In electrochemistry, the electrochemical surface area (ECSA) is the portion of a catalyst's surface that actively partakes in redox reactions.The surface area of a catalyst exposed to the electrolyte, known as the geometric surface area, does not fully correspond to the area involved in electrochemical reactions while the ECSA accounts for the truly active catalyst surface and offers a metric for comparing electrocatalytic materials. In particular, it allows the computation of the efficacy of the electrocatalyst and it is used for the optimization process of the performance and lifetime of catalyst layers in applications such as fuel cells, water electrolysis, and metal-air batteries.

Source: Wikipedia — Electrochemical surface area (CC BY-SA 4.0)