A comparison between structural and electrochemical properties of iridium oxide-based electrocatalysts prepared by Sol-Gel and reactive sputtering deposition

The great interest of the electrochemical industry toward materials that exhibit high electrocatalytic activity and long service-life in electrolytic processes has constantly prompted fundamental research, enhancing the understanding of electrode behavior and the improvement of their performance. One of the most important class of industrial devices is represented by the so-called DSAs, which consist of an electrocatalytic oxide film (usually based on RuO2 and/or IrO2) deposited on a suitable metal support (titanium). To increase the stability of the material, other oxides (TiO2, SnO2, etc.) are added to the electrocatalytic one, with the double purpose of increasing the corrosion resistance of the coating and of diluting the main oxide (to minimize the production costs). In this work, mixtures of 35 mol% IrO2 – 65 mol%TiO2 deposited on titanium supports have been studied by ex-situ (RBS, XRD, ERDA, AFM) and on-site (CV) techniques. Electrodes prepared by an updated sol-gel method and reactive sputtering, at two different temperatures (350 and 450◦C), were investigated with the aim of correlating structural information with electrochemical performances, in terms of number of active electrocatalytic iridium sites. Based on roughness indexes, morphological properties, and of data obtained by nuclear methods for surface analysis and cyclic voltammetry, the behavior of iridium sites has been discussed, attempting a qualitative distinction of roles of roughness and intrinsic catalytic activity in a model-electrochemical reaction, like oxygen evolution reaction. Sputtered samples appear, in general, more compact than sol-gel ones, and a low temperature of pyrolysis favours a more extended electroactive surface. The study of OER demonstrates that the kinetics of gas evolution proceeds via the electrochemical oxide formation pathway (Volmer-Heyrovsky mechanism) on all samples.