Anodic TiO2 nanotubes decorated by Pt nanoparticles using ALD: An efficient electrocatalyst for methanol oxidation

Abstract

Anodic TiO2 nanotube layers (TNTs) of different thicknesses (≈ 1, 5 and 20 µm) were homogeneously decorated with Pt nanoparticles using atomic layer deposition (ALD) and explored for the electrocatalytic activity in methanol oxidation reaction (MOR). Six different numbers of ALD cycles (NALD) - 24, 40, 56, 72, 88 and 104 - were used. Pt nanoparticles with diameter in the range of 1.3 to 4.6 nm were obtained for the first five NALD and a complete coating was achieved for the highest NALD (104). The SEM/TEM analyses revealed that Pt nanoparticles uniformly decorated exteriors and interiors of TNTs. A linear increase of the particle diameter of Pt was revealed with increasing NALD. Highest electrocatalytic activities of Pt/TNTs electrodes represented by current density of 74 mA/cm2 were obtained for NALD = 88 and for thickest TNTs (20 µm). The electrooxidation performance of Pt-decorated TiO2 nanotube layers was thoroughly compared to reference substrates: Pt-decorated graphite sheets and TiO2 flat layers (on annealed Ti foils) as well as for a commercial Pt/C catalyst attached on graphite sheets. From chronoamperometric measurements it turned out that the catalytic activity of Pt-loaded nanotube layers is superior and long lasting compared to other substrates, where significant degree of catalyst poisoning takes place. The presented ALD decoration approach is an effective strategy for the homogeneous distribution of precious Pt nanoparticles on a high surface area catalyst support for high-performance electrocatalysis.