(Keynote) Iridium Deposition By Galvanic Displacement of Cu on a One-Pot Configuration
Authors: Thorbjørnsen Kristian Fredrik Klepp , Reksten Anita Hamar , Sunde Tor Olav , Hanslin Sander Øglænd , Akola Jaakko , Sunde Svein 
Published: February 2024

Water electrolysis with proton exchange membranes (PEMWE) is expected to play a vital role in the future hydrogen infrastructure. The hydrogen evolution is effectively catalyzed by platinum, and iridium oxide is a highly active and reasonably stable catalyst for the oxygen-evolution reation (OER) [1]. However, iridium is costly and scarce, and efficient utilization of it is necessary for large-scale deployment of PEMWE technology. This can be achieved in various ways, such as dilution with other and cheaper compounds such as Ta2O5 [2] and alloying with more abundant metals followed by post-synthesis-treatment such as de-alloying or surface enrichment [3]. A possible solution is the application of ultra-thin layers of iridium oxide on a less costly substrate. A suitable method for achieving such layers is that of surface-limited galvanic displacement [4], i.e. the underpotential deposition of a metal M followed by its oxidation by another and more noble metal N.
In this work we have investigated Ir plating onto a polycrystalline gold electrode by successive galvanic displacement of Cu monolayers in a one-pot method, i.e by performing the Cu underpotential-deposition step in a solution also containing iridium precursors. The process is indicated in the figure. By using low concentrations of the precursors H2IrCl6 and IrCl3 in H2SO4, Cu submonolayers could be formed on a Au(poly) rotating disc electrode by underpotential deposition without any significant direct electrochemical formation of Ir or IrO2. The Cu submonolayer formed was then available for reaction with the Ir precursor before a new Cu submonolayer was formed. By evaluating the amount of Cu deposited in each submonolayer and the resulting Ir deposit, our results indicate that H2IrCl6 is reduced onto the Au electrode as metallic Ir via the formation of Ir(III). Due to transport of Ir(III) away from the reaction surface, this resulted in a low yield. No Ir deposited was achieved from IrCl3 solutions, possibly due to adsorption of irreducible species onto the Au surface.
The results will be discussed in terms of possible reaction paths and the relative stability of iridium complexes in chloride-containing solutions.

Acknowledgements

This work was performed within the project "Metal(-oxide) catalyst-monolayer as cost-effective electrocatalysts for PEM water electrolysis" funded by the Research Council of Norway, contract no. 254976/E20.

References

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Brankovic, J. X. Wang, and R. R. Adžic, “Metal monolayer deposition by replacement of metal adlayers on electrode surfaces,” Surface Science, vol. 474, L173–L179, 2001.

Figure 1