Charge Accumulation in Nanoheterogeneous Iridium Oxide Films

Iridium oxide films with different values of crystallinity degree K are synthesized. Properties of the films and their morphological features are examined. The charging of the films in a 1 M H₂SO₄solution is studied voltammetrically. The most amorphous films (K = 0.08–0.26) acquire the largest overall charge q(in a fixed potential range) relative to films with higher crystallinity degrees; however, the qvs. K dependence is not additive, and the charge remains virtually invariant beginning with K 0.26. The contribution of slow charging processes, which is quite perceptible in the amorphous films, is absent in samples with higher crystallinity degrees, which have faster charge kinetics. The fast charging processes, which are not limited by diffusion, occur in boundary regions of IrO₂crystallites (and/or the oxide part of a crystalline hydrated iridium oxide) and the amorphous phase. The transport of charge-compensating ions in the boundary regions occurs without considerable complications, as in the loose network of amorphous phase IrO₂· xH₂O. The assumption about the formation of a metallic highly-conducting IrO₂cluster at K 0.26 is substantiated. The cluster rules out large resistances in the course of charge transport, which is a possible reason for the slow charging of amorphous films with K < 0.26.