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Controlled Surface Modification of ZnO Nanostructures with Amorphous TiO2 for Photoelectrochemical Water Splitting
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gasparotto, Alberto Maccato, Chiara Sada, Cinzia Carraro, Giorgio Kondarides, Dimitris I. Bebelis, Symeon Petala, Athanasia Porta, Andrea La Altantzis, Thomas Barreca, Davide |
| Copyright Year | 2019 |
| Abstract | Photoelectrochemical (PEC) water splitting, harvesting sunlight to produce hydrogen from water, holds a significant promise for sustainable energy generation.[1–4] Since the first demonstration of PEC water splitting over TiO2 photoelectrodes in 1972, great efforts have been made to develop cost-effective semiconductor-based photoelectrode materials with improved catalytic activity and enhanced operational stability.[5–7] Nevertheless, the limited process efficiency[8–10] has continuously stimulated the search for novel strategies aimed at the sizeand morphology-controlled design of oxide-based photoelectrode materials with improved performances. Various efforts have also been dedicated to their modification with dopants, quantum dots, plasmonic nanoparticles, electrocatalysts, or to the controlled fabrication of heterostructures with engineered interfacial properties.[2,3,6,11–16] In this context, ZnO, a largely abundant, low-cost, and nontoxic n-type semiconductor with a direct band gap of 3.3 eV, has emerged as an appealing photoanode material, since it combines suitable band energetics for water oxidation with high electron mobility (10–100 times larger than TiO2). In addition, ZnO easily develops high surface area nanostructures that are desirable to maximize the contact area with the reaction medium, and typically feature high crystallinity and reduced grain boundary content, thus favoring charge transport phenomena.[9,15,18,19] Nevertheless, these ZnO advantages are at least partially eclipsed by a poor catalytic activity, a limited stability in aqueous solutions, and a high recombination rate of photogenerated charge carriers.[1,6,13,14] A valuable approach to circumvent these limitations involves the coupling of ZnO with TiO2, thus developing composite materials featuring a synergistic combination of the single oxide properties. In fact, ZnO– TiO2 systems offer a higher chemical reactivity and enhanced stability, along with the passivation of traps centers on ZnO surface responsible for charge recombination.[4,17,18,20,21] In addition, due to a type-II band offset in which both the valence and conduction band edges of titania lie above those of ZnO, the formation of ZnO–TiO2 heterojunctions yields a more efficient separation of photogenerated electrons and holes, disclosing attractive perspectives for PEC end-uses.[5,10,16,21–26] Although The utilization of solar radiation to trigger photoelectrochemical (PEC) water splitting has gained interest for sustainable energy production. In this study, attention is focused on the development of ZnO–TiO2 nanocomposite photoanodes. The target systems are obtained by growing porous arrays of highly crystalline, elongated ZnO nanostructures on indium tin oxide (ITO) by chemical vapor deposition. Subsequently, the obtained nanodeposits are functionalized with TiO2 via radio frequency-sputtering for different process durations, and subjected to final annealing in air. Characterization results demonstrate the successful formation of high purity composite systems in which the surface of ZnO nanostructures is decorated by ultra-small amounts of amorphous titania, whose content can be conveniently tailored as a function of deposition time. Photocurrent density measurements in sunlighttriggered water splitting highlight a remarkable performance enhancement with respect to single-phase zinc and titanium oxides, with up to a threefold photocurrent increase compared to bare ZnO. These results, mainly traced back to the formation of ZnO/TiO2 heterojunctions yielding an improved photocarrier separation, show that the target nanocomposites are attractive photoanodes for efficient PEC water splitting. |
| Starting Page | 1900046 |
| Ending Page | 1900046 |
| Page Count | 1 |
| File Format | PDF HTM / HTML |
| DOI | 10.1002/adsu.201900046 |
| Volume Number | 3 |
| Alternate Webpage(s) | http://nano.uantwerpen.be/nanorefs/pdfs/OA_10.1002adsu.201900046.pdf |
| Alternate Webpage(s) | https://doi.org/10.1002/adsu.201900046 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
