Browsing by Subject "Photoelectrochemical water splitting"

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Open Access
Strong light-matter interaction in lithography-free perfect absorbers for photoconversion, photodetection, light emission, sensing, and filtering applications
(2022-01) Ghobadi, Amir
The efficient harvesting of electromagnetic (EM) waves by subwavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. These metamaterial based perfect light absorbers are of particular interest in many applications, including thermal photovoltaics, photovoltaics, emission, sensing, filtering, and photodetection applications. Although advances in nanofabrication have provided the opportunity to observe strong light-matter interaction in various optical nanostructures, the repeatability and upscaling of these nano units have remained a challenge for their use in large-scale applications. Thus, in recent years, the concept of lithography-free metamaterial absorbers (LFMAs) has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. In this thesis, the unprecedented potential of these LFMAs will be explored. This thesis explores the material and architecture requirements for the realization of a LFMA from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. For this aim, we theoretically investigate the required conditions to realize an ideal perfect absorber. Then, based on the operation wavelength and application, the proper material and design architecture is defined. Later, to experimentally realize these ideal LFMAs, lithography-free large-scale compatible routes are developed to generate nanostructures in centimeter scales. Finally, the application of these LFMAs has been demonstrated in various fields including filtering, sensing, emission, photodetection, and photoelectrochemical water splitting. This thesis study demonstrates that, by the use of proper material and design configuration, it is possible to realize these LFMAs in every portion of the EM spectrum with a vast variety of potential applications. This, in turn, opens up the opportunity of the practical application of these perfect absorbers in large-scale dimensions. In the last section of the thesis, we discuss the progress, challenges, and outlook of this field to outline its future direction.
Open Access
Strong light–matter interactions in Au plasmonic nanoantennas coupled with Prussian blue catalyst on BiVO4 for photoelectrochemical water splitting
(Wiley-VCH Verlag, 2020) Ulusoy-Ghobadi, Türkan Gamze; Ghobadi, Amir; Soydan, Mahmut Can; Vishlaghi, M. B.; Kaya, S.; Karadaş, Ferdi; Özbay, Ekmel
A facial and large‐scale compatible fabrication route is established, affording a high‐performance heterogeneous plasmonic‐based photoelectrode for water oxidation that incorporates a CoFe–Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO4) nanostructures, yielding Au‐capped BiVO4 (Au‐BiVO4). The formation of multiple size/dimension Au capping islands provides strong light–matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO4 (through the excitation of Fabry–Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub‐band‐gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au‐BiVO4/PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO4 photoanode was obtained as 190 μA cm−2, whereas it was boosted to 295 μA cm−2 and 1800 μA cm−2 for Au‐BiVO4 and Au‐BiVO4/PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic‐based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs.
Open Access
Subwavelength densely packed disordered semiconductor metasurface units for photoelectrochemical hydrogen generation
(American Chemical Society, 2022-03-10) Ulusoy Ghobadi, T. Gamze; Ghobadi, Amir; Odabaşı, Oğuz; Karadaş, Ferdi; Özbay, Ekmel
For most semiconductors, especially the visible-light-absorbing ones, the carrier diffusion length is significantly shorter than the light penetration depth, limiting their photoactivities. This limitation could be mitigated through the use of subwavelength semiconductor-based metasurfaces and metamaterials. In this paper, a large-scale compatible metasurface photocathode, made of densely packed disordered p-type chromium oxide (CrOX), is developed to be utilized in photoelectrochemical (PEC) hydrogen generation. For this purpose, first, tightly packed random Cr nanorods are fabricated using an oblique angle deposition technique. Afterward, an annealing step is applied to the sample to transform these metallic units into a semiconducting p-type CrOX-based metasurface. Based on the experimental characterization results and numerical simulations, the proposed design can provide strong light-matter interactions in an ultra-broadband-wavelength range, mainly due to its multidimensional random geometry and ultrasmall gap sizes. Finally, to substantiate the activity of the CrOXnanorods, a core-crown geometry is developed where the NiOXcapping layer catalyzes the hydrogen evolution reaction (HER). The proposed heterostructure metasurface absorber can impose photocurrent values as large as 50 μA cm-2with a photocurrent spectral response extended up to 500 nm. Moreover, the electrode shows outstanding operation under light irradiation for 9 hours. This work demonstrates a simple, scalable design strategy to fabricate low-cost and stable photocathodes for PEC hydrogen evolution. © 2022 American Chemical Society. All rights reserved.