TiO2-coated rutile oxide catalysts for acidic oxygen evolution: a design principle

Abstract

Green hydrogen production through water electrolysis under acidic conditions is limited by the efficiency of the anodic oxygen evolution reaction (OER). In this study, we outline a design principle for developing active and potentially stable rutile oxide electrocatalysts for acidic OER. Using density functional theory, we find that the adsorption energies for Ti, Sn, and Zr active sites correlate with the position of the Fermi level relative to the oxygen 2s states as the surrounding oxide composition is varied. This trend is not observed for platinum-group elements. We attribute this difference to the inability of Ti, Sn, and Zr active sites to access oxidation states above the 4+ of the rutile structure, according to changes in geometry and charge. Ti emerges as an adsorption site of special interest, since varying the composition of the surrounding rutile oxide allows titanium sites to reach theoretical overpotentials as low as 0.14 V. We then demonstrate tunable activity for TiO₂-coated conductive rutile substrates. Based on literature evidence that TiO₂ coatings improve stability under acidic OER conditions without substantially compromising activity, we suggest that a TiO₂ overlayer can serve as both an active site and corrosion protection. We propose a composition-based model that successfully finds Ir and Ru free compositions (W_xPt_1−xO₂, W_0.46Pd_0.54O₂) that can activate the applied TiO₂ overlayer.