Investigation of IrO2–SnO2 thin film evolution from aqueous media

The thermal evolution process of IrO2–SnO2/Ti mixed oxide thin films of varying noble metal content has been investigated under in situ conditions by thermogravimetry–mass spectrometry, Fourier transform infrared emission spectroscopy and cyclic voltammetry. The gel-like films prepared from aqueous solutions of the precursor salts Sn(OH)2(CH3COO)2 xClx and H2IrCl6 on titanium metal support were heated in an atmosphere containing 20% O2 and 80% Ar up to 600 8C. The thermal decomposition reactions practically take place in two separate temperature ranges from ambient to about 250 8C and between 300 and 600 8C. In the low temperature range the liberation of solution components and – to a limited extent – an oxidative cracking reaction of the acetate ligand takes place catalyzed by the noble metal. In the high temperature range the evolution of chlorine as well as the decomposition of surface species formed (carbonyls, carboxylates, carbonates) can be observed. The acetate ligand shows extreme high stability and is decomposed in the 400–550 8C range, only. Since the formation and decomposition of the organic surface species can significantly influence the morphology (and thus the electrochemical properties) of the films, the complete understanding of the film evolution process is indispensable to optimize the experimental conditions of electrode preparation.