TiO2 nanotube arrays decorated with Ir nanoparticles for enhanced hydrogen evolution electrocatalysis

Abstract

Designing cost-effective hydrogen evolution reaction (HER) electrocatalysts containing highly active, but expensive platinum group metals (PGMs) is key to the commercialization of polymer electrolyte membrane water electrolysis systems for green hydrogen production. Our recent investigations have shown that efficient and durable HER composite cathodes can be prepared by spontaneous deposition of PGM nanoparticles on self-aligned titania nanotube (TNT) arrays formed by anodization [1]. In this synthesis route, anatase TNTs are first cathodically protonated (H-TNT), and then used as the reducing agent for PGM ions at room temperature. Herein, we employ the galvanic displacement strategy to decorate H-TNT arrays with ultrafine Ir nanoparticles [2]. We demonstrate that transforming the top surface morphology of supporting TNT arrays from ordered open-top tubes to bundled nanowires (“nanograss”) is beneficial for exposing more Ir active centers during the HER operation. Consequently, applying very low concentrations of Ir(III) ions in the galvanic displacement step is sufficient to produce exceptionally active nanograss-modified Ir@TNT composites. An optimum Ir@TNT, possessing a low Ir loading of 5.7 μgIr cm–2, requires an overpotential of only –63 mV to reach a current density of –100 mA cm–2 and shows a stable long-term performance in a 1 M HClO4 solution. Computational simulations suggest that the hydrogen-rich TiO2 support not only strongly interacts with anchored Ir particles and weakens their H binding strength to a moderate level, but also actively provides hydrogen for rejuvenation of the Ir active sites at the Ir|H-TiO2 interface, thereby significantly enhancing HER catalysis.

[1] U.Č. Lačnjevac, R. Vasilić, T. Tokarski, G. Cios, P. Żabiński, N. Elezović and N. V. Krstajić, Nano Energy 47 (2018) 527. [2] U. Lačnjevac, R. Vasilić, A. Dobrota, S. Đurđić, O. Tomanec, R. Zbořil, S. Mohajernia, N.T. Nguyen, N. Skorodumova, D. Manojlović, N. Elezović, I. Pašti, P. Schmuki, Journal of Materials Chemistry A 8 (2020) 22773.