The BV equation can be written in many different notations, depending on the underlying assumptions made. For example, the form of the BV equation given by assumes the interfacial reaction to be an elementary one-step, single-electron reaction with electron-transfer as the rate-determining step, so the transfer coefficient is assumed to be αa + αc = 1 . However, in real electrochemical systems, complex multi-step interfacial reactions can occur, where the apparent (i.e., experimentally measured) value of α can differ from the intrinsic α value(s) for the individual reaction step(s) . The measured α value can also be strongly influenced by porous electrode phenomena . As strictly defined by IUPAC, the transfer coefficient is a directly determined experimental quantity, the value of which can only be obtained by measuring the relationship between current and overpotential at high overpotentials (i.e., from the Tafel slope), according to :