Photocatalytic Hydrogen Generation Efficiencies in One-Dimensional CdSe Heterostructures

Abstract

To better understand the role nanoscale heterojunctions play in the photocatalytic generation of hydrogen, we have designed several model one-dimensional (1D) heterostructures based on CdSe nanowires (NWs). Specifically, CdSe/CdS core/shell NWs and Au nanoparticle (NP)-decorated core and core/shell NWs have been produced using facile solution chemistries. These systems enable us to explore sources for efficient charge separation and enhanced carrier lifetimes important to photocatalytic processes. We find that visible light H2 generation efficiencies in the produced hybrid 1D structures increase in the order CdSe < CdSe/Au NP < CdSe/CdS/Au NP < CdSe/CdS with a maximum H2 generation rate of 58.06 ± 3.59 μmol h(-1) g(-1) for CdSe/CdS core/shell NWs. This is 30 times larger than the activity of bare CdSe NWs. Using femtosecond transient differential absorption spectroscopy, we subsequently provide mechanistic insight into the role nanoscale heterojunctions play by directly monitoring charge flow and accumulation in these hybrid systems. In turn, we explain the observed trend in H2 generation rates with an important outcome being direct evidence for heterojunction-influenced charge transfer enhancements of relevant chemical reduction processes.

Recent Progress in Energy‐Driven Water Splitting

“…It was demonstrated that the quantum dots have the ability to store and donate multiple electrons to the adsorbed cobaloxime catalysts, playing a key role in improving the photocatalytic efficiency. Tongying et al reported that the core‐shell CdSe/CdS nanowires exhibited very high photocatalytic efficiency for hydrogen generation, which is thirty times higher than that of the bare CdSe nanowires 112. CdSe is the active species responsible for chemical reduction processes despite of the presence of a CdS shell on it.…”

Synthesis and Application of Solution-Based II–VI and IV–VI Semiconductor Nanowires

“…For example, CdSe NWs coated with 6 and 10 monolayers CdS exhibit PL quantum which increase from 0.14 % (uncoated) to 0.25 and 0.46 %, respectively [48]. As will be discussed later in this chapter, photocatalytic hydrogen generation efficiencies also increase due to enhanced carrier lifetimes [10].…”

“…CdSe/CdS NWs have likewise been made by decomposing CdMe 2 /(TMS) 2 S [49] or CdMe 2 /S powder [10] precursor pairs in a noncoordinating solvent such as squalane. Resulting shells appear rough and exhibit islanding (Fig.…”

“…This results in Au NP nucleation and growth along the NW length [62]. Finally, Tongying et al have successfully decorated CdSe and CdSe/CdS core/shell NWs with nanometer-sized Au NPs [10] using a procedure adapted from Menagen et al [63]. In this study, a solution of AuCl 3 was added to a suspension of CdSe and CdSe/CdS core/shell NWs under vigorous stirring and under simultaneous UV illumination.…”

“…These features make them desirable for use in various applications. As illustrations, II-VI NWs have been used in photodetectors [1][2][3][4], solar cells [5][6][7][8][9] and in photocatalytic applications [10,11]. Likewise, IV-VI NWs, especially the lead chalcogenides, have been used in infrared photodetectors [12], thermoelectric devices [13,14] and in field effect transistors (FETs) [15][16][17].…”