Vapor Phase Fabrication of Nanoheterostructures Based on ZnO for Photoelectrochemical Water Splitting

Abstract

especially in nanostructured forms in order to attain improved system performances. [11,20,26,32] In this regard, ZnO, a transparent semiconducting oxide with a large exciton binding energy (60 meV) and high carrier mobility, has attracted an extensive interest. [5,15,18,[32][33][34] Nevertheless, its performances are detrimentally affected by its wide band gap (E G = 3.3 eV), [3,14,[35][36][37][38][39] limiting radiation absorption to the UV interval (≈5% of the overall solar spectrum), [1,2,38,[40][41][42][43] and by the rapid charge carriers recombination. [33,[35][36][37]44] To tackle these obstacles and extend the system photo response into the vis range, [1,15,39] various investigators have focused on doping with substitutional elements to the Zn and O sites. [3,21,32,40,41,43] Appreciable efforts have also been devoted to the coupling of ZnO with other suitable semiconductors, with the aim of tailoring their interfacial energetics to the targeted photoactivated processes. [2,22,27,36,45,46] In this regard, various heterojunctioncontaining composites based on ZnO-TiO 2 , [8] ZnO-NiO, [31] ZnOCdS, [11] ZnO-CdSe, [34] ZnO-CdTe, [43] ZnO-M(OH) x with M = Co, Ni, [16] ZnO-BiVO 4 , [42] ZnO-WO x coupled with CdSe-CdS, [45] ZnO-ZnS-FeS 2 , [39] and ZnO-CdS-NiO [17] have been developed and tested for solar-driven H 2 O splitting. In this broad scenario, an attractive option involves the use of Fe 2 O 3 and WO 3 as functional activators of ZnO systems for the fabrication of vis-light absorbing photoanodes. In particular, Fe 2 O 3 , an abundant and cheap oxide with a narrow band gap (E G = 2.2 eV), [9,26,28,35] has gained a considerable attention, but its sluggish oxygen evolution kinetics, low carrier lifetime, and short exciton diffusion

Boosting the Performance of WO3/n‐Si Heterostructures for Photoelectrochemical Water Splitting: from the Role of Si to Interface Engineering

“…A key element of any PEC system is the semiconductor material, which transforms absorbed solar photons into excited electronic states [5] . Among all the semiconductor materials, metal oxides, such as TiO2, WO3, Fe2O3, and BiVO4, have been studied elaborately as the functional layer for catalyzing PEC water splitting reactions because of their chemical stability and low cost [6][7][8][9][10][11][12][13][14] . To supply sufficient energy (including overpotential) for splitting water, the band gaps of metal oxides tend to be substantial (≥ 1.9) [3] , which limits their absorption of solar light, however.…”

Physical and Chemical Defects in WO3 Thin Films and Their Impact on Photoelectrochemical Water Splitting

“…This is attributed to its low light harvesting efficiency and high electron-hole recombination rate. Several studies have focused on overcoming these issues, such as selective doping of metal and nonmetal semiconductors 19,20 , adding of co-catalysts, like CoOx or Co-Pi, to improve the water oxidation kinetics 21,22 , forming a heterojunction via introduction of another semiconductor layer, like BiVO4, Bi2S3, Cu2O, to enhance the electron transport properties [23][24][25] , or using nano/micro-structured substrates 26,27 . Various thin film deposition techniques have been used to achieve improved film structures, including hydrothermal method 28 , sputtering 29 , pulsed laser deposition (PLD) 30 , and atomic layer deposition (ALD) 14 .…”

Design of Core–Shell‐Structured ZnO/ZnS Hybridized with Graphite‐Like C3N4 for Highly Efficient Photoelectrochemical Water Splitting

“…However, it is not sufficient to improve the visible‐light photocatalytic activity for the wide bandgap ZnO. Numerous methods such as morphology control, coupling of graphene derivatives, elemental doping, or formation of heterojunction have been reported to be effective pathways to enhance the charge transport and improve the separation of photogenerated electron–hole pairs for better PEC performance. In all methods, the construction of heterojunction of ZnO with the narrow bandgap semiconductors is a promising way to extend the light absorption and improve the light usage.…”