Vanadium- and molybdenum-doped as well as undoped oxotungstate films electrodeposited on fluoride doped tin oxide (FTO) from peroxide-free solutions are considered as mediator electrocatalysts for inorganic anions reduction (by the example of IO3-). The most risky aspect related to oxide degradation is addressed in electrochromic and voltammetric experiments. Potential-dependent optical absorption (300-1100 nm spectral range), coloration-decoloration kinetics, and capacity of the films are studied. Two-step coloration mechanism is ascertained, and the optimal wavelength (1100 nm) is chosen for further monitoring of the film redox state in the course of stability tests. The comparison of cycling stability in 0.5 and 2.0 M H2SO4 in terms of capacity and coloration efficiency indicates the change of film degradation mechanism from dissolution to mechanical peeling with increase of acidity. The latter mechanism is shown to be less important for the film stability. (C) 2013 Elsevier Ltd. All rights reserved.