Mixed Cd-Zn sulfides / Pt-TiO2 composites : bottlenecks limiting efficiency of photocatalytic water reduction

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Abstract

Visible-light driven photocatalytic water reduction on composite materials consisting of platinized titania (Pt-TiO2) and transition metal sulfides (CdS or Cd0.5Zn0.5S) was investigated in detail. Sulfides were prepared by hydrothermal synthesis and room-temperature precipitation. The parameters limiting performance of these composite systems were elucidated. All composites with Pt-TiO2 demonstrated similar hydrogen evolution rates independent from their textural properties, bandgaps, electron transfer between components and intrinsic activities of the sulfides. Moreover, all platinized sulfides, except for the precipitated CdS, were more active than the corresponding composites with Pt-TiO2. This behavior – counterintuitive to the improved charge carrier separation found in the materials with heterojunctions – was rationalized by the low mobility of the conduction band electrons in TiO2. The slow electron transport severely limits efficiency of the investigated composite materials in the photocatalytic water reduction. This effect is especially apparent for highly active sulfides but less so for materials with inherently low activity. The low driving force of bare CdS toward water reduction results in an apparent synergy with Pt-TiO2 and makes the corresponding composites sensitive to Pt poisoning as the hydrogen evolution reaction predominantly takes place on Pt-TiO2. On the other hand, mixed sulfides, being more active water reduction photocatalysts, compete with Pt particles in this process making corresponding composites less sensitive to the state of Pt. The findings are discussed in terms of the intrinsic photocatalytic activity of sulfides, electron transfer from sulfides to titania, electrochemical potentials of conduction band electrons, poisoning of Pt nanoparticles, and charge carrier mobility.
Original languageEnglish
Pages (from-to)16-24
JournalApplied Catalysis. B, Environmental
Volume198
DOIs
Publication statusPublished - 19 May 2016

Fingerprint

Sulfides
sulfide
Water
Composite materials
electron
water
Electrons
poisoning
Conduction bands
Charge carriers
titanium
Hydrogen
Titanium
hydrogen
Carrier mobility
Hydrothermal synthesis
transition element
Photocatalysts
Transition metals
Heterojunctions

Keywords

  • Sulfide
  • Titania
  • Hydrogen evolution
  • Composites
  • Photocatalysis
  • Mechanism

Cite this

@article{61451956a3694574a2e355a37f4e24de,
title = "Mixed Cd-Zn sulfides / Pt-TiO2 composites : bottlenecks limiting efficiency of photocatalytic water reduction",
abstract = "Visible-light driven photocatalytic water reduction on composite materials consisting of platinized titania (Pt-TiO2) and transition metal sulfides (CdS or Cd0.5Zn0.5S) was investigated in detail. Sulfides were prepared by hydrothermal synthesis and room-temperature precipitation. The parameters limiting performance of these composite systems were elucidated. All composites with Pt-TiO2 demonstrated similar hydrogen evolution rates independent from their textural properties, bandgaps, electron transfer between components and intrinsic activities of the sulfides. Moreover, all platinized sulfides, except for the precipitated CdS, were more active than the corresponding composites with Pt-TiO2. This behavior – counterintuitive to the improved charge carrier separation found in the materials with heterojunctions – was rationalized by the low mobility of the conduction band electrons in TiO2. The slow electron transport severely limits efficiency of the investigated composite materials in the photocatalytic water reduction. This effect is especially apparent for highly active sulfides but less so for materials with inherently low activity. The low driving force of bare CdS toward water reduction results in an apparent synergy with Pt-TiO2 and makes the corresponding composites sensitive to Pt poisoning as the hydrogen evolution reaction predominantly takes place on Pt-TiO2. On the other hand, mixed sulfides, being more active water reduction photocatalysts, compete with Pt particles in this process making corresponding composites less sensitive to the state of Pt. The findings are discussed in terms of the intrinsic photocatalytic activity of sulfides, electron transfer from sulfides to titania, electrochemical potentials of conduction band electrons, poisoning of Pt nanoparticles, and charge carrier mobility.",
keywords = "Sulfide, Titania, Hydrogen evolution, Composites, Photocatalysis, Mechanism",
author = "A. Litke and Th. Weber and J.P. Hofmann and E.J.M. Hensen",
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day = "19",
doi = "10.1016/j.apcatb.2016.05.035",
language = "English",
volume = "198",
pages = "16--24",
journal = "Applied Catalysis. B, Environmental",
issn = "0926-3373",
publisher = "Elsevier",

}

Mixed Cd-Zn sulfides / Pt-TiO2 composites : bottlenecks limiting efficiency of photocatalytic water reduction. / Litke, A.; Weber, Th.; Hofmann, J.P.; Hensen, E.J.M.

In: Applied Catalysis. B, Environmental, Vol. 198, 19.05.2016, p. 16-24.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Mixed Cd-Zn sulfides / Pt-TiO2 composites : bottlenecks limiting efficiency of photocatalytic water reduction

AU - Litke, A.

AU - Weber, Th.

AU - Hofmann, J.P.

AU - Hensen, E.J.M.

PY - 2016/5/19

Y1 - 2016/5/19

N2 - Visible-light driven photocatalytic water reduction on composite materials consisting of platinized titania (Pt-TiO2) and transition metal sulfides (CdS or Cd0.5Zn0.5S) was investigated in detail. Sulfides were prepared by hydrothermal synthesis and room-temperature precipitation. The parameters limiting performance of these composite systems were elucidated. All composites with Pt-TiO2 demonstrated similar hydrogen evolution rates independent from their textural properties, bandgaps, electron transfer between components and intrinsic activities of the sulfides. Moreover, all platinized sulfides, except for the precipitated CdS, were more active than the corresponding composites with Pt-TiO2. This behavior – counterintuitive to the improved charge carrier separation found in the materials with heterojunctions – was rationalized by the low mobility of the conduction band electrons in TiO2. The slow electron transport severely limits efficiency of the investigated composite materials in the photocatalytic water reduction. This effect is especially apparent for highly active sulfides but less so for materials with inherently low activity. The low driving force of bare CdS toward water reduction results in an apparent synergy with Pt-TiO2 and makes the corresponding composites sensitive to Pt poisoning as the hydrogen evolution reaction predominantly takes place on Pt-TiO2. On the other hand, mixed sulfides, being more active water reduction photocatalysts, compete with Pt particles in this process making corresponding composites less sensitive to the state of Pt. The findings are discussed in terms of the intrinsic photocatalytic activity of sulfides, electron transfer from sulfides to titania, electrochemical potentials of conduction band electrons, poisoning of Pt nanoparticles, and charge carrier mobility.

AB - Visible-light driven photocatalytic water reduction on composite materials consisting of platinized titania (Pt-TiO2) and transition metal sulfides (CdS or Cd0.5Zn0.5S) was investigated in detail. Sulfides were prepared by hydrothermal synthesis and room-temperature precipitation. The parameters limiting performance of these composite systems were elucidated. All composites with Pt-TiO2 demonstrated similar hydrogen evolution rates independent from their textural properties, bandgaps, electron transfer between components and intrinsic activities of the sulfides. Moreover, all platinized sulfides, except for the precipitated CdS, were more active than the corresponding composites with Pt-TiO2. This behavior – counterintuitive to the improved charge carrier separation found in the materials with heterojunctions – was rationalized by the low mobility of the conduction band electrons in TiO2. The slow electron transport severely limits efficiency of the investigated composite materials in the photocatalytic water reduction. This effect is especially apparent for highly active sulfides but less so for materials with inherently low activity. The low driving force of bare CdS toward water reduction results in an apparent synergy with Pt-TiO2 and makes the corresponding composites sensitive to Pt poisoning as the hydrogen evolution reaction predominantly takes place on Pt-TiO2. On the other hand, mixed sulfides, being more active water reduction photocatalysts, compete with Pt particles in this process making corresponding composites less sensitive to the state of Pt. The findings are discussed in terms of the intrinsic photocatalytic activity of sulfides, electron transfer from sulfides to titania, electrochemical potentials of conduction band electrons, poisoning of Pt nanoparticles, and charge carrier mobility.

KW - Sulfide

KW - Titania

KW - Hydrogen evolution

KW - Composites

KW - Photocatalysis

KW - Mechanism

U2 - 10.1016/j.apcatb.2016.05.035

DO - 10.1016/j.apcatb.2016.05.035

M3 - Article

VL - 198

SP - 16

EP - 24

JO - Applied Catalysis. B, Environmental

JF - Applied Catalysis. B, Environmental

SN - 0926-3373

ER -