Au@CdS Core-Shell Nanoparticles-Modified ZnO Nanowires Photoanode for Efficient Photoelectrochemical Water Splitting.
ABSTRACT: Hydrogen production from water splitting using solar energy based on photoelectrochemical (PEC) cells has attracted increasing attention because it leaves less of a carbon footprint and has economic superiority of solar and hydrogen energy. Oxide semiconductors such as ZnO possessing high stability against photocorrosion in hole scavenger systems have been widely used to build photoanodes of PEC cells but under visible light their conversion efficiencies with respect to incident-photon-to-current conversion efficiency (IPCE) measured without external bias are still not satisfied. An innovative way is presented here to significantly improve the conversion efficiency of PEC cells by constructing a core-shell structure-based photoanode comprising Au@CdS core-shell nanoparticles on ZnO nanowires (Au@CdS-ZnO). The Au core offers strong electronic interactions with both CdS and ZnO resulting in a unique nanojunction to facilitate charge transfer. The Au@CdS-ZnO PEC cell under 400 nm light irradiation without any applied bias provides an IPCE of 14.8%. Under AM1.5 light illumination with a bias of 0.4 V, the Au@CdS-ZnO PEC cell produces H2 at a constant rate of 11.5 ?mol h-1 as long as 10 h. This work provides a fundamental insight to improve the conversion efficiency for visible light in water splitting.
Project description:Solar water splitting represents one of the most promising strategies in the quest for clean and renewable energy. However, low conversion efficiency, use of sacrificial agents, and external bias for current water splitting system limit its practical application. Here, a gold-sensitized Si/ZnOcore/shell nanowire photoelectrochemical (PEC) cell is reported for efficient solar water oxidation. We demonstrated gold-sensitized n-Si/n-ZnO nanowire arrays exhibited higher energy conversion efficiency than gold-sensitized p-Si/n-ZnO nanowire arrays due to the favorable energy-band alignment characteristics. Without any assistance from an external electrical source and sacrificial reagents, gold-sensitized n-Si/n-ZnO core/shell nanowire array photoanode achieved unbiased water splitting under simulated solar light illumination. This method opens a promising venue to cost-efficient production of solar fuels.
Project description:A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0?mA cm(-2) at 0.0?V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000?s. These results suggest that the CdS/Zn1-xCdxS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system.
Project description:Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal-organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This synergetic combination of doping and nanoscale surface functionalization boosts the current density and functional lifetime of the photoanodes while achieving an unprecedented incident photon to current efficiency (IPCE) of 75% at 350 nm, which is over 2 times that of pristine ZnO. A theoretical model and band structure for the core-shell nanostructure is provided, highlighting how this nanomaterial combination provides an attractive pathway for the design of robust and highly efficient semiconductor-based photoanodes that can be translated to other semiconducting oxide systems.
Project description:In this report, the growth of zinc oxide (ZnO) nanocrystals with various morphologies, nanoflower, nanosheet, and nanorod, on flexible stainless steel (SS) foils to be utilized as photoanodes in photoelectrochemical (PEC) solar cells has been presented. It has been aimed to provide flexibility and adaptability for the next generation systems with the incorporation of SS foils as electrode into PEC cells. Therefore, physical deformation tests have been applied to the prepared ZnO thin film photoanodes. These thin films have been thoroughly characterized before and after straining for better understanding the relationship between the morphology, straining effect and photoelectrochemical efficiency. We observed a notable increase in the maximum incident photon-to-current efficiency (IPCE) and durability of all ZnO photoelectrodes after straining process. The increase in IPCE values by 1.5 and 2.5 folds at 370 nm has been observed for nanoflower and nanorod morphologies, respectively after being strained. The maximum IPCE of 69% has been calculated for the ZnO nanorod structures after straining. Bending of the SS electrodes resulted in the more oriented nanorod arrays compared to its flat counterpart, which improved both the light absorption and also the photo-conversion efficiency drastically. The finite-difference time-domain simulations have also been carried out to examine the optical properties of flat and bent ZnO electrodes. Finally, it has been concluded that SS photoanodes bearing ZnO semiconducting material with nanoflower and nanorod morphologies are very promising candidates for the solar hydrogen generator systems in terms of efficiency, durability, flexibility, and lightness in weight.
Project description:One-dimensional zinc oxide nanorods array exhibit excellent electron mobility and thus hold great potential as photoanode for photoelelctrochemical water splitting. However, the poor absorption of visible light and the prominent surface recombination hider the performance improvement. In this work, Au nanoparticles and aluminium oxide were deposited onto the surface of ZnO nanorods to improve the PEC performance. The localized surface plasmon resonance of Au NPs could expand the absorption spectrum to visible region. Simultaneously, the surface of passivation with Au NPs and Al2O3 largely suppressed the photogenerated electron-hole recombination. As a result, the optimal solar-to-hydrogen efficiency of ZnO/Au/Al2O3 with 5 cycles was 6.7 times that of pristine ZnO, ascribed to the synergistic effect of SPR and surface passivation. This research reveals that the synergistic effect could be used as an important method to design efficient photoanodes for photoelectrochemical devices.
Project description:Photoanodes based on In2S3/ZnO heterojunction nanosheet arrays (NSAs) have been fabricated by atomic layer deposition of ZnO over In2S3 NSAs, which were in situ grown on fluorine-doped tin oxide glasses via a facile solvothermal process. The as-prepared photoanodes show dramatically enhanced performance for photoelectrochemical (PEC) water splitting, compared to single semiconductor counterparts. The optical and PEC properties of In2S3/ZnO NSAs have been optimized by modulating the thickness of the ZnO overlayer. After pairing with ZnO, the NSAs exhibit a broadened absorption range and an increased light absorptance over a wide wavelength region of 250-850 nm. The optimized sample of In2S3/ZnO-50 NSAs shows a photocurrent density of 1.642 mA cm-2 (1.5 V vs. RHE) and an incident photon-to-current efficiency of 27.64% at 380 nm (1.23 V vs. RHE), which are 70 and 116 times higher than those of the pristine In2S3 NSAs, respectively. A detailed energy band edge analysis reveals the type-II band alignment of the In2S3/ZnO heterojunction, which enables efficient separation and collection of photogenerated carriers, especially with the assistance of positive bias potential, and then results in the significantly increased PEC activity.
Project description:Solution-based ZnO nanorod arrays (NRAs) were modified with controlled N doping by an advanced ion implantation method, and were subsequently utilized as photoanodes for photoelectrochemical (PEC) water splitting under visible light irradiation. A gradient distribution of N dopants along the vertical direction of ZnO nanorods was realized. N doped ZnO NRAs displayed a markedly enhanced visible-light-driven PEC photocurrent density of ~160??A/cm(2) at 1.1?V vs. saturated calomel electrode (SCE), which was about 2 orders of magnitude higher than pristine ZnO NRAs. The gradiently distributed N dopants not only extended the optical absorption edges to visible light region, but also introduced terraced band structure. As a consequence, N gradient-doped ZnO NRAs can not only utilize the visible light irradiation but also efficiently drive photo-induced electron and hole transfer via the terraced band structure. The superior potential of ion implantation technique for creating gradient dopants distribution in host semiconductors will provide novel insights into doped photoelectrode materials for solar water splitting.
Project description:The particulate semiconductor La5Ti2CuS5O7 (LTC) with a band gap energy of 1.9 eV functioned as either a photocathode or a photoanode when embedded onto Au or Ti metal layers, respectively. By applying an LTC/Au photocathode and LTC/Ti photoanode to, respectively, photoelectrochemical (PEC) water reduction and oxidation concurrently, zero-bias overall water splitting was accomplished under visible light irradiation. The band structures of LTC/Au and LTC/Ti calculated using a semiconductor device simulator (AFORS-HET) confirmed the critical role of the solid/solid junction of the metal back contact in the charge separation and PEC properties of LTC photoelectrodes. The prominently long lifetime of photoexcited charge carriers in LTC, confirmed by transient absorption spectroscopy, allowed the utilization of both photoexcited electrons and holes depending on the band structure at the solid/solid junction.
Project description:While bismuth vanadate (BiVO4) has emerged as a promising photoanode in solar water splitting, it still suffers from poor electron-hole separation and electron transport properties. Therefore, the development of BiVO4 nanomaterials that enable performing high charge transfer rate at the interface and lowering charge recombination is urgent needed. Herein, cobalt borate (Co-B) nanoparticle arrays anchored on electrospun W-doped BiVO4 porous nanotubes (BiV0.97W0.03O4) was prepared for photoelectrochemical (PEC) water oxidation. One-dimensional, free-standing and porousBiV0.97W0.03O4/Co-B nanotubes was synthesized through electrospun and electrodeposition process. BiV0.97W0.03O4/Co-B arrays exhibit a unique self-supporting core-shell structure with rough porous surface, providing abundant conductive cofactor (W) and electrochemically active sites (Co) exposed to the electrolyte. When applied to PEC water oxidation. BiV0.97W0.03O4/Co-B modified FTO electrode displays high incident photon-to-current conversion efficiency (IPCE) of 33% at 405 nm (at 1.23 V vs. RHE) and its photocurrent density is about 4 times to the pristine nanotube. The higher PEC water oxidation properties of BiV0.97W0.03O4/Co-B porous nanotubes may be attributed to the effectively suppress the electron-hole recombination at electrolyte interface due to its self-supporting core-shell structure, the high electrocatalytic activity of Co and the good electrical conductivity of BiV0.97W0.03O4 arrays. This work offers a simple preparation strategy for the integrated Co-B nanoparticle with BiV0.97W0.03O4 nanotube, demonstrating the synergistic effect of co-catalysts for PEC water oxidation.
Project description:Photoelectrochemical (PEC) water splitting has great application potential in converting solar energy into hydrogen energy. However, what stands in the way of the practical application of this technology is the low conversion efficiency, which can be promoted by optimizing the material structure and device design for surface functionalization. In this work, we deposited gold nanoparticles (Au NPs) with different loading densities on the surface of InGaN nanorod (NR) arrays through a chemical solvent route to obtain a composite PEC water splitting system. Enhanced photocatalytic activity, which can be demonstrated by the surface plasmon resonance (SPR) effect induced by Au NPs, occurred and was further confirmed to be associated with the different loading densities of Au NPs. These discoveries use solar water splitting as a platform and provide ideas for exploring the mechanism of SPR enhancement.