Electrode potentials of were measured in solutions containing fixed amounts of ions or ions, as a function of pH. Oxygen overvoltage and ease of electrochemical reduction are correlated with anion adsorption and true surface area of the two oxide modifications. A method for synthesis of by chemical means is described. Differences in the solid‐ state properties between α‐ and are revealed by thermal degradation to the intermediate oxide , with . The unit cell of was determined to be orthorhombic with , , and .