In the solid electrolyte cell, copper-RbCu4Cl3I2-I-2, glassy carbon, the EMF values at open circuit were measured as a function of time. Iodine was generated through anodic electrochemical decomposition of the electrolyte RbCu4Cl3I2 and this iodine then further reacted with the fresh electrolyte. An equation was deduced which relates the EMF values to the iodine concentration at the glassy carbon surface. It was shown that slow diffusion of the iodine in the reaction product layer is a limiting step in the chemical interaction of iodine with RbCu4Cl3I2. For the compressed RbCu4Cl3I2 sample investigated, the iodine diffusion coefficient was calculated to be 6.2 x 10(-7) cm(2)/s. Iodine loss from the glassy carbon surface was about 1.1 x 10(-4) g/cm(2) s. The thickness of the RbCu4Cl3I2 sample was equal to 2 mm. (C) 2001 Elsevier Science B.V. All rights reserved.