Relationship between the Photocatalytic Hydrogen Ion Reduction and Charge Carrier Dynamics of Pt/Cd_1–xNi_xS Catalysts

Abstract

The performance of a semiconductor photocatalyst is affected by bulk and surface doping because of changes in the charge carrier dynamics. Finding relationships between these changes upon doping and catalytic performance offers needed information for the fundamental understanding of the overall catalytic reaction. In this work, the electron transfer for the hydrogen ion reduction reaction over a prototype Pt/CdS catalyst doped with Ni2+ cations (Cd0.99Ni0.01S) was studied using fs-pump probe transient absorption spectroscopy (TAS) under photocatalytic reaction conditions. Cd0.99Ni0.01S is composed of both hexagonal and cubic phases (X-ray diffraction) with average particles of 7 nm in size (transmission electron microscopy). TAS of Cd0.99Ni0.01S in the presence and absence of a hole scavenger (benzyl alcohol) and in the presence and absence of Pt particles helped to further probe into the origin of the two most pronounced transient signals in the 400–800 nm range. These are the ground-state bleaching at ca. 480 nm and the photoinduced absorption signal at ca. 600 nm. The first is largely linked to electron de-excitation lifetime and the latter to hole lifetime. From the decay kinetics under catalytic reaction conditions, it was possible to compute for the charge transfer yields (ϕ) from the semiconductor to the Pt metal particles (electron transfer) and from the benzyl alcohol to the semiconductor (hole trapping). The rate of the photocatalytic hydrogen production shows a positive relationship with the decay kinetics obtained by fs-pump probe measurements. While the photocatalytic reaction rates were found to be constant for successive runs, X-ray photoelectron spectroscopy Pt 4f and Ni 2p lines of the used catalyst showed a decrease in their content. Thus, care needs to be taken when relying solely on reaction rate measurements to test for catalytic stability.

Boosting Hydrogen Evolution Performance of a CdS-Based Photocatalyst: In Situ Transition from Type I to Type II Heterojunction during Photocatalysis

“…In other words, the bleaching signals at 500 nm among the TAS spectra of CdS, CP-2, and CN-2 samples (Figure d–f) are assigned to the filling of the electron energy level of CdS . The order of bleaching lifetimes (τ 1 , τ 2 , and τ 3 ) is CN-2 < CdS < CP-2.…”

“…63 In other words, the bleaching signals at 500 nm among the TAS spectra of CdS, CP-2, and CN-2 samples (Figure 8d−f) are assigned to the filling of the electron energy level of CdS. 64 The order of bleaching lifetimes (τ 1 , τ 2 , and τ 3 ) is CN-2 < CdS < CP-2. According to the results of SPV, the electrons of NiS in CN-2 flow to CdS, so its lifetime for electron filling is the shortest.…”

Monitoring the Lifetime of Photoexcited Electrons in a Fresh and Bulk Reduced Rutile TiO2 Single Crystal. Possible Anisotropic Propagation

“…It was initially developed to study molecules and then extended to colloidal systems (nanoparticles) and polycrystalline materials. Information can be obtained related to interfacial charge transfer between semiconductors and between semiconductors and metals . In general, there are three regions of investigation (neglecting the bleach state near the excitation energy): the energetically shallow region at a fraction of an eV from the CB (in the mid-IR region), often attributed to excited polarons, the near IR region with an energy in the 1 to 2 eV range, mostly related to surface and bulk defects, and a visible region, mostly attributed to holes; , in wide band gap semiconductors it is above 2 eV.…”

Effect of Zn Vacancies in Zn3In2S6 Nanosheets on Boosting Photocatalytic N2 Fixation

“…Moreover, this view is further confirmed by transient fluorescence absorption spectra, which are recorded at 470 nm (Figures 7c and S8). 40,41 The carrier dynamics of Zn 3 In 2 S 6 prepared with different sulfur sources reflects that S-TAA performs slower carrier relaxation. The photogenerated charge carriers of S-TAA with abundant V Zn obviously decay much slower than those of S-Cys and S-TA.…”