Roles of cocatalysts in semiconductor-based photocatalytic hydrogen production

Abstract

A photocatalyst is defined as a functional composite material with three components: photo-harvester (e.g. semiconductor), reduction cocatalyst (e.g. for hydrogen evolution) and oxidation cocatalyst (e.g. for oxidation evolution from water). Loading cocatalysts on semiconductors is proved to be an effective approach to promote the charge separation and transfer, suppress the charge recombination and enhance the photocatalytic activity. Furthermore, the photocatalytic performance can be significantly improved by loading dual cocatalysts for reduction and oxidation, which could lower the activation energy barriers, respectively, for the two half reactions. A quantum efficiency (QE) as high as 93 per cent at 420 nm for H 2 production has been achieved for Pt–PdS/CdS, where Pt and PdS, respectively, act as reduction and oxidation cocatalysts and CdS as a photo-harvester. The dual cocatalysts work synergistically and enhance the photocatalytic reaction rate, which is determined by the slower one (either reduction or oxidation). This work demonstrates that the cocatalysts, especially the dual cocatalysts for reduction and oxidation, are crucial and even absolutely necessary for achieving high QEs in photocatalytic hydrogen production, as well as in photocatalytic water splitting.

Synthesis of Ultra‐Small Palladium Nanoparticles Deposited on CdS Nanorods by Pulsed Laser Ablation in Liquid: Role of Metal Nanocrystal Size in the Photocatalytic Hydrogen Production

“…On the other hand, the CdS‐PdPt nanocomposites exhibit a strong emission band at 523 nm and small emission bands centered at 594, 646, and 688 nm. A strong emission band is observed at 534 nm for CdS, which corresponds to the band‐edge emission, and weak‐intensity emission bands centered at 594, 646, and 688 nm correspond to shallow trap‐state‐related luminescence . In accordance with the experimental results, the CdS‐PdPt nanocomposites exhibit the lowest‐intensity emission, whereas bare CdS exhibits the highest‐intensity emission.…”

“…Movement such as the migration, recombination, and transfer of the photogenerated electron/hole pairs of the pure CdS and other nanocomposites was examined by photoluminescence (PL) emission spectroscopy . In other words, PL can be used to investigate the role of co‐catalysts as the materials preventing charge recombination and enhancing the activities as photocatalysts.…”

Impact of the annealing temperature on Pt/g-C 3 N 4 structure, activity and selectivity between photodegradation and water splitting

“…XPS data and TEM micrographs supporting the presence of platinum in its reduced form after photocatalytic testing are presented in Figure S 2 and Figure 2 g). The positive impact of introducing platinum as co-catalyst has been reported numerous times on a various set of photocatalytic systems; it acts as an electron sink and therefore increases holes and electron separation [20,21], it is also thought to provide sites for H-H bond formation [22]. This same figure shows that the activity of the Pt/g-C3N4 catalyst decreases from 3900 µmol.h -1 g -1 for CN450 to 1710 µmol.h CN650.…”

Photo-catalytic hydrogen production over Au/g-C3N4: effect of gold particle dispersion and morphology

“…The effect of metal deposition on the semiconductor activity for hydrogen production has been reported numerous times with various photocatalysts/metal systems, and is generally assigned to transfer of electrons from the semiconductor to the metal and in some cases to providing centers for hydrogen-hydrogen bond formation. [55][56][57] In the case of gold, LSPR properties may also play a role in promoting photocatalytic hydrogen evolution. 9,12 As observed in Fig.…”