Catal Lett DOI 10.1007/s10562-017-2197-z
Comparing the Reaction Rates of Plasmonic (Gold) and NonPlasmonic (Palladium) Metal Particles in Photocatalytic Hydrogen Production M. A. Khan1 · M. Al‑Oufi1 · A. Toseef2 · M. A. Nadeem1 · H. Idriss1
Received: 24 June 2017 / Accepted: 15 September 2017 © The Author(s) 2017. This article is an open access publication
* H. Idriss
[email protected] 1
SABIC Corporate Research and Development (CRD), KAUST, Thuwal, Saudi Arabia
SABIC Technology and Innovation Center, Riyadh, Saudi Arabia
2
Graphical Abstract 5.0E-02
H2 producon over Au/TiO2 (anatase)
4.0E-02 H2 mol/gCagtal.
Abstract Both Pd and Au metal particles are used in photocatalytic hydrogen generation. Yet while both act as electron sink only gold is poised to respond to visible light due to its plasmonic response. In order to quantitatively gauge their relative contribution into the reaction, the photocatalytic H2 production, from Au/TiO2 and Pd/TiO2 catalysts was studied under UV and UV–Vis light. While under UV light excitation, a weak dependence on the work function of the metal is observed, under UV–Vis light, Au is found to be twice more active than Pd. Under identical UV–Vis light irradiation, the turn over frequency calculated from XPS at.% is found to be 2.8 and 1.8 s−1 for Au and Pd, respectively. The effect is far more pronounced when the rates are normalized to the number of particles of each metal. Both the semiconductor TiO2 (UV light) and the plasmonic metal (visible light) need to be excited for the enhancement to occur; visible light alone causes a negligible reaction rate. Photocurrent measurements further confirmed the difference in the photocatalytic activity under UV and UV–Vis light excitation. Moreover, because of the presence of Au particles responding to visible light the reaction rate is enhanced due to “light penetration depth” effect.
y = 9.9 x 10-5x UV excitation
3.0E-02
2.0E-02
y = 2.84 x 10-4x UV+Vis excitation
1.0E-02 0.0E+00
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Keywords Photocatalysis · Hydrogen production · Plasmon · Au/TiO2 · Metal particle size · Reaction rate
1 Introduction Photocatalytic hydrogen production from renewables is a promising route for future economies to replace fossil fuels for transportation and chemical manufacturing. The development of an active, scalable and stable photocatalyst remains one of the biggest challenges in modern day catalysis. Many families of semiconductors have been made and tested including oxide semiconductors such as T iO2, ZnO, WO3, BiVO4, [1–4] sulfide semiconductors such as CdS, ZnS, MoxSy, [5–7] and nitride semiconductors such as GaN, InGaN, C3N4 [8–10]. These semiconductors alone or in mixed forms including solid solutions and abrupt interfaced materials such as layer by layer growth or layer
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plus island growth, have not, yet, provided the needed activity nor stability [11–14]. TiO2 is widely regarded as one of the leading candidates for solar hydrogen production because of its excellent stability. Nonetheless, TiO2 suffers from low solar to hydrogen conversion efficiency because of high charge carrier recombination rates and limited light absorption (
