Intrinsically Activated SrTiO₃: Photocatalytic H₂ Evolution from Neutral Aqueous Methanol Solution in the Absence of Any Noble Metal Cocatalyst

Abstract

Noble metal cocatalysts are conventionally a crucial factor in oxide-semiconductor-based photocatalytic hydrogen generation. In the present work, we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO) powder can be used to engineer an intrinsic cocatalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional cocatalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO[100] single crystal as well as Nb-doped SrTiO[100] single crystal. For all types of SrTiO samples (nanopowders and either of the single crystals), hydrogenation under optimum conditions leads to a surface-hydroxylated layer together with lattice defects visible by transmission electron microscopy, electron paramagnetic resonance (EPR), and photoluminescence (PL). Active samples provide specific defects identified by EPR, PL, and electron-energy loss spectroscopy as Ti states in a defective matrix-this is in contrast to the inactive defects formed in other reductive atmospheres. In aqueous media, active SrTiO samples show a significant negative shift of the flatband potential (in photoelectrochemical as well as in capacitance data) and a lower charge-transfer resistance for photoexcited electrons. We therefore ascribe the remarkable cocatalyst-free activation of the material to a synergy between thermodynamics (altered interface energetics induced by hydroxylation) and kinetics (charge transfer mediation by suitable Ti states).

Vacancy Engineering in Semiconductor Photocatalysts: Implications in Hydrogen Evolution and Nitrogen Fixation Applications

“…have annealed commercially available SrTiO 3 and Nb‐doped SrTiO 3 single crystals at different temperatures under the H 2 atmosphere to synthesize intrinsically activated noble metal‐free photocatalysts for H 2 evolution. [ 99 ] The H 2 annealing ensued in the creation of oxygen vacancies in these materials, which were confirmed by EPR, XPS, HETEM, STEM, and elemental mapping techniques. The HRTEM and O‐mapping of SrTiO 3 annealed at 1100 °C for 4 h are depicted in Figure a,b, which displays the disordered layer at the edges of the particle.…”

“…a,d) HRTEM, elemental mapping, EELS line scan, and distribution of Ti 3+ and Ti 4+ in the selected area of SrTiO 3 annealed at 1100 °C for 4 h. Reproduced with permission. [ 99 ] Copyright 2018, ACS. e) Mechanism of H 2 evolution over SrTiO 3 /Cd0 .5 Zn 0.5 S photocatalyst.…”

Ethanol Solvothermal Treatment on Graphitic Carbon Nitride Materials for Enhancing Photocatalytic Hydrogen Evolution Performance

“…Owing to the abundance and renewability of sunlight and water, a solar-driven watersplitting process using photocatalysts is considered a long-term sustainable technology for producing hydrogen-a clean and renewable energy source. Even though various photocatalysts, such as TiO 2 , SrTiO 3 , CdS, TaON, ZrO 2 , and their assemblies, have been extensively studied, the development of novel photocatalysts that significantly enhance hydrogen production performance is still a challenging research area [1][2][3][4][5].…”

SrTiO3 nanocubes doped with ir as photocatalytic system for enhancing H2 generation from water splitting

“…In recent research, a similar kind of trend was observed by Fadlallah et al for cation codoped SrTiO 3 photocatalysts for water splitting. Photocatalytic activity of SrTiO 3 codoped metal transition such as Rh, V, Sb significantly improved as compared to pristine SrTiO 3 due to the reduction of the bandgap energy of host structure 27 . Ma et al reported that the H 2 production from water splitting of transition metal-doped SrTiO 3 photocatalysts exhibited higher than that of pristine SrTiO 3 due to the presence of sub-bandgap states in the SrTiO 3 lattice under visible light 28 .…”