The Thermodynamics of Aqueous Water Electrolysis

Precise definitions are given of three thermodynamic parameters which characterize the water‐electrolysis reaction: the enthalpic voltage, the higher‐heating‐value voltage, and the thermoneutral voltage. Expressions are derived for these parameters and for the reversible potential, as functions of temperature between 25° and 250°C, and of pressure between 1 and 100 atm. Heat losses due to radiation, convection, and conduction are also considered, and a thermal‐balance voltage is defined; representative values are calculated. Electrical‐energy efficiency is related to the characteristic parameters, and thermodynamic limitations on its value are discussed.