RuOx nanoparticles deposited on TiO2 nanotube arrays by ion-exchange method as electrocatalysts for the hydrogen evolution reaction in acid solution

Abstract

Nanocomposite cathodes for the hydrogen evolution reaction (HER) were prepared by deposition of RuOx catalyst particles on self-organized titania nanotube (TiNT) arrays of highly developed surface area, following a procedure that involved the initial cathodic intercalation of H+ into the TiNT walls and the subsequent two-step ion-exchange process. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analyses of obtained Ru-TiNT samples revealed that the concentration of RuOx particles in the size range of a few nanometers was the highest at the surface of the TiNT layer and steadily decreased to a minimum value at about 4.5 mu m inside the tubes. The capacitive behavior and electrocatalytic activity for the HER of Ru-TiNT nanocomposites, hydrogenated TiNT samples (H-TiNT) and compact TiO2 were investigated in 1.0 M HClO4 solution at room temperature by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and steady-state polarization measurements. It was shown that cathodic hydrogenation treatment induced a four orders of magnitude higher concentration of electron donors in TiNT structures providing their quasimetallic behavior in the range of potentials corresponding to the HER. Ru-TiNT cathodes exhibited a more than 250 mV lower overpotential for the HER with respect to bare H-TiNT substrates at the current density of -50 mA cm (2). A decrease of the Tafel slope from about -120 mV/dec for H-TiNT samples to as low as -70 mV/dec for the Ru-TiNT sample with longer tubes was explained by the formal kinetics approach.