Photoelectrochemical Methanol Oxidation on TiN@Au Core-Shell Nanoparticles Supported on TiO2

Abstract

Refractory transition metal nitrides such as TiN and ZrN are a new class of plasmonic materials that exhibit plasmonic resonance in the visible and near-infrared regions [1, 2]. The similarity of optical appearance of TiN to gold makes one wonder whether inexpensive and chemically and mechanically robust TiN can replace Au in plasmon-mediated photocatalytic reactions. Prior research [3] has shown that cubic 50 nm TiN nanoparticles supported on TiO2 nanowires provide greater photocurrent enhancement for the photoelectrochemical water splitting compared to spherical Au nanoparticles. This has been attributed to more efficient hot carrier generation by TiN nanoparticles, followed by more efficient collection of hot electrons by TiO2. 50 nm TiN nanoparticles (NPs), however, proved to be inefficient in promoting photocatalytic activity of TiO2 towards methanol oxidation in the visible region [4]. This was likely due to a lack of catalytic activity of the TiN NPs’ surface for CH3OH oxidation. Here, we explore the plasmon-mediated photocatalytic methanol oxidation on hybrid core-shell nanoparticles consisting of a thin gold shell and TiN core and compare the effect of TiO2-supported TiN@Au nanoparticles to that of Au on the photon-to-electron conversion efficiency. The TiO2-supported TiN@Au photocatalysts were made by the deposition of a thin Au shell on 20 and 50 nm TiN NPs (PlasmaChem) followed by the dispersion of the TiN@Au NPs onto TiO2 nanoparticle support (Degussa). Electrochemical experiments were conducted in a three-electrode photoelectrochemical cell. The thin films of TiN@Au/TiO2 on FTO-coated glass served as working electrodes (WEs), while platinum foil and Ag/AgCl in 3 M NaCl (BioLogic, Inc) were used as counter and reference electrodes, respectively. LED lights were used as light sources. X-Ray Photoelectron Spectroscopy, Powder X-Ray Diffraction, and high resolution transmission electron microscopy were used for characterization of catalysts surface composition and morphology.