Examining the surface evolution of LaTiOxNy an oxynitride solar water splitting photocatalyst

Abstract

LaTiO x N y oxynitride thin films are employed to study the surface modifications at the solidliquid interface that occur during photoelectrocatalytic water splitting. Neutron reflectometry and grazing incidence x-ray absorption spectroscopy were utilised to distinguish between the surface and bulk signals, with a surface sensitivity of 3 nm. Here we show, contrary to what is typically assumed, that the A cations are active sites that undergo oxidation at the surface as a consequence of the water splitting process. Whereas, the B cations undergo local disordering with the valence state remaining unchanged. This surface modification reduces the overall water splitting efficiency, but is suppressed when the oxynitride thin films are decorated with a co-catalyst. With this example we present the possibilities of surface sensitive studies using techniques capable of operando measurements in water, opening up new opportunities for applications to other materials and for surface sensitive, operando studies of the water splitting process.

Semi-transparent quaternary oxynitride photoanodes on GaN underlayers

“…The LaTiO 2 N thin film developed a net photocurrent of approximately 20 mA cm À2 at 1.23 V vs. RHE. The photocurrent is comparable with the LaTiO 2 N film deposited on MgO/TiN and Nb:SrTiO 3 substrates via PLD and RF sputtering reported by Lippert 29 and Domen, 26 respectively. The dark-current contribution stems from photocorrosion of the oxynitride surface, which is a common phenomenon for unprotected metal oxynitrides and can be suppressed with protective layers.…”

“…[22][23][24] This renders semi-transparent quaternary metal oxynitrides generally as very promising photoanode candidates for PEC tandem cells, which could outperform Ta 3 N 5 -based devices. So far, semi-transparent quaternary metal oxynitride films have been mainly fabricated by means of reactive radiofrequency (RF) magnetron sputtering [25][26][27][28] or pulsed laser deposition (PLD) 29,30 on MgO or Nb:SrTiO 3 substrate. In case of the RF approach, the oxynitride sputtering targets have to be made first with multi-step processes, and harsh conditions (usually up to 1073 K for film deposition) are required, too.…”

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives

“…[263][264][265][266][267] Advances in this field have shown that the apparently stable perovskites can indeed transform into other phases when exposed to the corrosive conditions of water splitting. [268][269][270][271][272] Suntivich et al showed that in the initial stages of the catalysis, the crystalline Ba 0.5 Sr 0.5 Co 0.8 -Fe 0.2 O 3Àd mixed oxide (BSCF) changes and forms an amorphous mixed oxide shell on the surface, which acts as the true catalyst in the OER ( Fig. 14a-d).…”

Rare earth oxynitrides: promising visible-light-driven photocatalysts for water splitting

“…Lawley et al used TiN as the substrate and coated with MgO for deposition, and finally obtained LaTiO x N y (x + y = 3) thin films to study the surface modification of the solid-liquid interface during the photocatalytic water splitting. 59 The structure and morphological characteristics of LaTiO x N y thin film are shown in Fig. 7.…”