Ir-based catalysts supported on Sn-doped titania nanotubes for the oxygen evolution reaction in acidic media

Abstract

The oxygen evolution reaction (OER) is sluggish in acidic media, such as in proton exchange water electrolysers, and demand highly active and stable catalysts. Ir-based materials offer excellent performance but are scarce and expensive, motivating efforts to reduce Ir loading while maintaining catalytic efficiency. In this work, Ir nanoparticles (NPs) were deposited via a microwave-assisted polyol method on previously synthesised anatase titania nanotubes (TNTs), doped with 3 at.% Nb or Sn, with a 40 wt.% Ir loading. TNTs were prepared hydrothermally, and structural characterization by Raman spectroscopy and XRD confirmed successful doping, although partial SnO₂ segregation was observed. XPS and Mott–Schottky analyses of the supports revealed the electron-donor character of the dopants, thus enhancing their electrical conductivity, especially in TNT–Sn. The well-dispersed Ir NPs 2 nm in size presented mixed oxidation states, including Ir⁰, IrOx, and IrO2, the first being dominant in Ir/TNT-Sn. The cyclic voltammograms after activation showed reversible redox Ir(III)/Ir(IV) transitions with flat peaks, shifted to more positive potentials than those of the reference Ir Black, indicating strong Ir–support interaction. The linear sweep voltammograms demonstrated the superior activity of the synthesised catalysts over Ir Black, with Ir/TNT–Sn showing the lowest overpotential, and the highest specific current density and turnover frequency. The better activity of the latter was attributed to the structural properties of the TNTs doped with Sn, which allowed increasing the support conductivity and facilitated an even stronger metal-support interaction.