Photoelectrochemical Water Splitting Research Articles

Engineering the SiOx interfacial layer of Si-based metal-insulator-semiconductor junction for photoelectrochemical hydrogen production

Photoelectrochemical (PEC) water splitting provides a potential method to produce renewable hydrogen energy, but there is still plenty of room for improving the efficiency and stability of photoelectrodes. In this paper, we present a metal–insulator-semiconductor (MIS) structure based on p-Si that enables stable and efficient water splitting by engineering the interfacial insulating layer. The silicon oxide (SiOx) film with appropriate thickness and low defects is regrown by a chemical oxidation process, which provides a high-quality insulating layer to passivate the p-Si. The carrier flux, barrier height and interfacial resistance of p-Si based MIS junction can be systematically tuned by controlling the thickness and quality of SiOx layer. Under AM 1.5G illumination, the optimized p-Si/SiOx/Ti/Pt photoelectrode shows an onset potential of 0.5 V vs. RHE, a maximum photocurrent of 28 mA/cm2 and a high applied bias photon-to-current efficiency (ABPE) of 6 %. These results have significant implications for constructing MIS photoelectrodes towards effective water splitting.

Dual-layer cocatalysts of Co-Pi and Ni(OH)2 on BiVO4 photoanodes for efficient water oxidation

Abstract Slow oxygen evolution kinetics and severe corrosion limit the further application of BiVO4 photoelectrodes in photoelectrochemical water splitting. Here, BiVO4/Co-Pi/Ni(OH)2 photoanodes were synthetized aiming at improving its photoelectric conversion efficiency and stability. Compared with pure BiVO4 photoanode, the BiVO4/Co-Pi/Ni(OH)2 photoanode enhanced the photocurrent from 1.1 mA/cm2 to 4.5 mA/cm2 at 1.23 V versus reversible hydrogen electrode. In addition, Ni(OH)2 acted as a corrosion protection layer on the surface of the photoanode, allowing the BiVO4/Co-Pi/Ni(OH)2 photoanode to exhibit excellent stability.

Enhancing photoelectrochemical properties of α-Fe2O3 using Zr-doped HfO2 ferroelectric nanoparticles

Hematite (α-Fe2O3) as a semiconductor photoanode for photoelectrochemical (PEC) water splitting is a promising candidate material. However, its PEC performance is limited by the slow charge transfer kinetics at the α-Fe2O3/electrolyte interface. Ferroelectric materials can be used as a tool for carrier separation in photoelectrochemical water splitting due to their spontaneous polarization electric field characteristics. Here, we deposited Hf0.5Zr0.5O2 (HZO) ferroelectric nanoparticles on the surface of α-Fe2O3 and use the spontaneous polarization field of ferroelectric HZO to promote the separation of photogenerated carriers, promote the charge transfer from α-Fe2O3 to the electrolyte, and enhance the PEC of hematite. After depositing the HZO nanoparticles, the photogenerated holes are efficiently extracted from α-Fe2O3 and then directed into the electrolyte to participate in water oxidation reaction at α-Fe2O3/HZO interfaces, which enhanced the charge separation efficiency by 58 % compared to that of pure α-Fe2O3. Consequently, the α-Fe2O3/HZO photoanode exhibits a 65 % boost in photocurrent density, reaching up to 0.28 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) compared to that of pure α-Fe2O3. This study introduces a method to engineer the photoanode/ferroelectric interface, enhancing carrier separation and thereby optimizing PEC water splitting performance.

Green biomediated synthesis of anodized WO3 nanocatalysts using Melia azedarach leaves extract for the energetic transition: Solar hydrogen and Li-ion batteries

This study reports the bio-mediated synthesis of tungsten trioxide nanostructures from aqueous extracts of Melia azedarach (L.) dry leaves. The synthesis was carried out by electrochemical anodization of tungsten foils in the presence of different volume percentages of leaves extracts. These nanostructures were afterwards completely characterized by Field-Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), impedance measurements, linear sweep voltammetry in the presence of simulated solar light and UV-Vis spectroscopy. Finally, these nanoelectrodes were used as (photo)electrocatalysts in the photoelectrochemical water splitting process to obtain green hydrogen and as anodes in Li-ion rechargeable batteries. Nanostructures fabricated with 5% M. azedarach leaves extract provided the best (photo)electrocatalytic behavior for both applications, since in that biogenic electrolyte, thin nanorods arranged in very porous and spongy layers were formed. Therefore, the significant increase in specific surface area found for nanostructures fabricated following this green route, in comparison with the blank sample (i.e., nanostructure formed following a non-green route), was essential to enhance their performance as promising efficient (photo)electrocatalysts.

Laser-Printed Photoanode: Femtosecond Laser-Induced Crystalline Phase Transformation of WO3 Nanorods for Space-Efficient and Flexible Thin-Film Solar Water-Splitting Cells.

Despite its potential for clean hydrogen harvesting, photoelectrochemical (PEC) water-splitting cells face challenges in commercialization, particularly related its harvesting performance and productivity at an industrial scale. Herein, a facile fabrication method of flexible thin-film photoanode for PEC water-splitting to overcome these limitations, based on laser processing technologies, is proposed. Laser-induced graphene, a carbon structure produced through direct laser writing carbonization (DLWC), plays a dual role: a flexible and stable current collector and a substrate for the hydrothermal synthesis of tungsten trioxide (WO3) nanorods (NRs). To facilitate water-splitting, a femtosecond-pulsed laser (fs laser) is focused on the WO3 NRs, converting their crystalline phase from pristine orthorhombic to monoclinic structure without thermal damage. With NiFe layered double hydroxide (LDH) catalyst, the flexible thin-film photoanode exhibits good PEC performance (1.46mAcm-2 at 1.23 VRHE) and retains ≈90% of its performance after 3000 bending cycles. With its excellent mechanical properties, the flexible photoanode can be operated in various shapes with different curvatures, enabling space-efficient PEC water-splitting by loading larger photoanode within a given space. This study is expected to contribute to the advancement of large-scale solar water-splitting cells, introducing a new approach to enhance H2/O2 production and expand its application range.

Engineering tantalum nitride for efficient photoelectrochemical water splitting

Engineering tantalum nitride for efficient photoelectrochemical water splitting

In2S3 nanoparticles modify the porous Fe2V4O13 nanostructure photoanode to enhance charge separation efficiency and photoelectrochemical water splitting performance

In this study, we demonstrate for the first time a promising photoanode of Fe2V4O13/In2S3 (FVO/IS) nanoparticles (NPs) for photoelectrochemical (PEC) water splitting. Most importantly, this work presents the first application of X-ray photoelectron spectroscopy in tracking electron flow direction within FVO/IS to reveal the formation of heterojunction having the electron flow from IS to FVO. Mott-Schottky measurement confirms that the modification of IS NPs establishes the type II heterojunction between FVO and IS, favorable for the transport and separation of carriers. Spectral measurements of electrochemical impedance spectroscopy, photoluminescence and Bode diagram confirm the effective separation of carriers and the prolongation of the charge lifetime in the FVO/IS heterojunction photoanode. Moreover, the electrochemical measurements evidently demonstrate the substantial enhancement in the charge separation efficiency (ηseparation) and charge transfer efficiency (ηtransfer) of the photoanode, leading to significantly enhanced PEC water splitting capability. As a result, in contrast with the pure FVO NPs photoanode, the photocurrent density of the constructed FVO/IS NPs photoanode is increased by 27 times without bias. This study paves a new approach for boosting the PEC water splitting activity of FVO photoanodes by constructing heterostructures through modification with other semiconductors.

Transition‐Metal‐Doped TiO2 Nanorods with High‐Visible‐Light Response via a Simple Hydrothermal Method

Transition‐metal‐ion doping is an effective method to shorten bandgap and enhance visible‐light absorption of TiO2, but there are still some serious challenges for most doping technologies, such as nonuniform doping, severe lattice damages, metal atoms agglomeration, and inactivated impurities. Herein, a simple and universal hydrothermal method is developed to realize the effective transition‐metal ions doping of TiO2 (including Fe, Co, Mn, Cu, V, and Cr). The photoelectrochemical water splitting performances of Cr‐doped TiO2 nanorods with multifarious Cr ion valence states (Cr3+ or Cr6+ ions), various Cr‐ion concentrations, with or without oxygen vacancy activation are emphatically and systematically studied. Experiments and theoretical calculations demonstrate that the remarkably enhanced carrier separation and injection efficiencies are the key factors to improve the visible‐light photoactivity, benefiting from the homogeneous distribution of impurity atoms and the incorporation of oxygen vacancies. The Cr3+‐ion‐doped TiO2 nanorod arrays with oxygen vacancy activation (Cr3+/Ov–TiO2) displays an impressive incident photon‐to‐electron conversion efficiency of 5.4% at 450 nm visible light, far superior to the pure TiO2 of 0.03%. Furthermore, no obvious photocurrent decay is observed in the Cr3+/Ov–TiO2 photoanode after 12 h continuous light illumination.

Systematic Constructing FeOCl/BiVO4 Hetero-Interfacial Hybrid Photoanodes for Efficient Photoelectrochemical Water Splitting.

Bismuth vanadate (BiVO4), as a promising photoanode for photoelectrochemical (PEC) water splitting, suffers from poor charge separation efficiency and light absorption efficiency. Herein, iron oxychloride (FeOCl) is introduced as a novel cocatalyst simply grafted on BiVO4 to construct an integrated photoanode, enhancing PEC performance. The optimized FeOCl/BiVO4 photoanode exhibits a superior photocurrent density value of 5.23mAcm-2 at 1.23V versus reversible hydrogen electrode (RHE) under AM 1.5G illuminations. From experimental analysis, such high PEC performance is ascribed to the unique properties of FeOCl, facilitating charge transport, increasing light absorption efficiency, and promoting water oxidation kinetics. Density functional theory calculations further confirm that FeOCl optimizes the Gibbs free energy of H and O-containing intermediates (OOH*) during PEC processes, boosting the catalytic kinetics of PEC water splitting. This work presents FeOCl as a promising catalyst for constructing high efficient PEC water-splitting photoanodes.

Coating effect of metal organic complex (Co-DTPMP) layer on enhancing PEC water oxidation performance of BiVO4 photoanode

Photoelectrochemical (PEC) water splitting is a promising method for transforming solar energy into clean and sustainable energy. However, PEC is severely limited, and they cannot achieve the predicted photocurrent density owing to the severe photochemical deterioration of the electrode and the recombination of photogenerated carriers. In this study, BiVO4/Co-diethylenetriamine Penta (methylene phosphonic acid) (BVO/Co-DTPMP) co-catalyst was successfully prepared as a nanoporous photoanode. Diethylenetriamine Penta (methylene phosphonic acid) was crosslinked with Co ions and coated on the BiVO4 surface by successive ionic layer adsorption and reaction (SILAR) to reduce fast recombination, which correlated with the BiVO4 photoanode. Various characterization and PEC measurements were conducted, revealing that the co-catalyst thin layer enhanced the charge separation and electrons transfer which significantly affected on the PEC performance of BiVO4, and the current density by BVO/Co-DTPMP was 4 mA cm−2 at 1.23 V vs. RHE. Furthermore, the co-catalyst exhibited improved charge transport and long-term stability.

Surface plasmonic hot hole driven Ag2S/Au/Al2O3 photocathode for enhanced photoelectrochemical water splitting performance

Herein, Ag2S/Au/Al2O3 photoelectrode was fabricated for superior photoelectrochemical (PEC) water splitting response. The working electrodes were deposited using the glancing angle deposition (GLAD) method followed by RF sputtering and atomic layer deposition (ALD). The as-prepared Ag2S/Au/Al2O3 samples revealed a higher photocurrent density of 2.50 mA/cm2 (at 0.95 V Ag/AgCl) as compared to bare Ag2S (1.70 mA/cm2) with a corresponding less charge transfer resistance at the semiconducting interface. The superior PEC response may be ascribed to the synergic effect of plasmonic Au nanoparticles and the tilted Ag2S nanorods. The plasmonic effect of Au nanoparticles increases the visible-light response of Ag2S as well as provides the hot holes to enhance the photocurrent density. In addition, the increased trapping of light due to the tilted architecture of Ag2S nanorods resulted in an effective absorption of light. The theoretical simulations based on finite difference time domain (FDTD) were also performed to explore the distribution of the electric-field intensity and optical trapping of light between the nanorods of Ag2S and Ag2S/Au. The experimental and theoretical results show a deeper insight into the role of plasmonic nanostructures decorated Ag2S nanorods and shed light on designing hybrid hot hole harvesting semiconductor nanostructures for the next generation photoelectrodes.

A core/shell Bi2S3/BiVO4 nanoarchitecture for efficient photoelectrochemical water oxidation.

The construction of nanostructured heterostructure is a potent strategy for achieving high-performance photoelectrochemical (PEC) water splitting. Among these, constructing BiVO4-based heterostructure stands out as a promising method for optimizing light-harvesting efficiency and reducing severe charge recombination. Herein, we present a novel approach to fabricate a type II heterostructure of core/shell Bi2S3/BiVO4 using electrolytic deposition and successive ionic layer adsorption and reaction (SILAR) methods. We identify the type II heterostructure and the difference in fermi energy using UV-Vis spectroscopy, X-ray photoelectron spectroscopy, and PEC measurements. This redistribution of charges due to the fermi energy difference induces an interfacial built-in electric field from BiVO4 to Bi2S3, reinforcing the photogenerated hole transfer kinetics from BiVO4 to Bi2S3. The Bi2S3/BiVO4 heterostructure exhibits a superior photocurrent (6.0 mA cm-2), enhanced charge separation efficiency (85%), and higher open-circuit photovoltage (350 mV). Additionally, the heterostructure displays a prolonged average lifetime of charge (1.63 ns), verifying this heterojunction could boost interfacial carriers' migration via an additional nonradiative quenching pathway. Furthermore, the lower photoluminescence (PL) intensity demonstrates the interfacial built-in electric field is beneficial for boosting charge migration.

Double oxygen evolution co-catalysts modified BiVO4 to boost photoelectrochemical water oxidation performance

Improving the kinetics of oxygen evolution is crucial for enhancing the performance of photoelectrochemical (PEC) water splitting. Herein, this study utilizes a chemical self-growth method to grow NiFe tannic acid complex (NFTA) and Co(OH)2 on the surface of BiVO4 photoanode (BiVO4/NFTA/Co). As a result, the synergistic effects of NFTA and Co(OH)2 layers promote the efficiency and stability of BiVO4 photoanode towards PEC water oxidation. The photocurrent density of the obtained BiVO4/NFTA/Co photoanode reaches 4.97 mA cm−2, which is significantly greater than those of BiVO4/NFTA (4.36 mA cm−2), BiVO4/Co (2.51 mA cm−2), BiVO4 (1.34 mA cm−2), respectively. Detailed analysis confirms that NFTA could provide an efficient way to hasten the transfer of photo-generated holes on the photoanode surface and diminish the surface charge transfer resistance. In other hand, Co(OH)2 could be served as a cocatalyst to accelerate charge transfer for efficient oxygen evolution reaction as well as a protective layer to maintain the long-term stability of NFTA on the surface of BiVO4 during water oxidation. Such double oxygen evolution co-catalysts decoration strategy paves an effective pathway to enhance the PEC water oxidation performance of BiVO4 photoanode.

A p-n-p Configuration Based on the Cuprous Oxide/Silicon Tandem Photocathode for Accelerating Solar-Driven Hydrogen Evolution.

Photoelectrochemical splitting of water into hydrogen is a potential route to motivate the application of solar-driven conversion to clean energy but is regularly limited by its low efficiency. The key to addressing this issue is to design a suitable photocathode configuration for high-efficiency photogenerated carrier separation and transmission to photocathode-surface reaction sites. In this work, we report a Si-Cu2O tandem photocathode featuring a p-n-p configuration for solar-driven hydrogen evolution in an alkaline solution. Driven by this built-in field, the electrons induced from Si were transferred through FeOOH, which acted as electron tunnels, to combine with the holes from Cu2O, triggering more electrons generated from Cu2O to particiate in the surface reaction. Under simulated sunlight, the optimized photocathode achieved and maintained a photocurrent density of -11 mA/cm2 at 0 VRHE in alkaline conditions for 120 min, outperforming the reported tandem cell consisting of Si and Cu2O photocathodes. Our results provide valuable insight into a feasible way to construct an optimized photocathode for efficient solar-driven H2 evolution.

Super-hydrophilic electrode encapsulated lead halide-perovskite photoanode toward stable and efficient photoelectrochemical water splitting

Lead halide perovskites with excellent optoelectronic properties have been recognized as one of the most promising photoelectrode materials for photoelectrochemical water splitting during the past decade. However, fabricating stable and efficient halide-perovskite photoanodes remains a considerable challenge due to the degradation of halide perovskites in electrolyte environment and the lack of effective encapsulating techniques. Herein, we report a unique halide-perovskite photoelectrochemical cell by using an inverted fluorine-doped tin oxide coated glass (FTO/glass) as the waterproof hole-transport layer for encapsulation, and inserting a two-dimensional (2D) perovskite layer for passivation. The halide-perovskite photoanode achieves high-efficiency oxygen evolution reaction, fast bubble releasing and an outstanding long-term stability of 30.9 h at 90 % of the initial photocurrent density (up to 16.55 mA cm−2 at 1.23 V versus the reversible hydrogen electrode) under solar illumination. Our unique and cost-effective encapsulation method could be a potential solution for realizing stable and efficient halide-perovskite photoelectrodes for solar-fuel energy conversion.

Insights into interface engineering of g-C3N4/NaNbO3 heterojunction for photoelectrochemical water splitting

Green hydrogen is a very attractive energy source, a widely studied strategy among scientists to produce it is using metal oxide semiconductors as photoanodes for photoelectrochemical water splitting. The main challenge is to produce a photocatalyst that is stable and efficient enough to be commercially viable. In this sense, several different combinations of materials have been studied. Here, we report the preparation of g-C3N4/NaNbO3 coupled to Pt-based species (Pt-g-C3N4/NaNbO3) and its potential application as a photoanode for water photosplitting. NaNbO3 was chosen for its suitable properties, g-C3N4 was used to enhance the visible light activity, and Pt species were added to perform as a co-catalyst avoiding recombination of photogenerated charges. The main innovations are the reduced time and energy-consuming procedure to prepare NaNbO3 and the direct polymerization of the g-C3N4 on the NaNbO3. Results demonstrate the successful synthesis of the Pt-g-C3N4/NaNbO3 heterojunction; however, the resultant system showed low efficiency, probably for forming a layer of g-C3N4 on the top of NaNbO3 and electrically active surface states at the semiconductor/solution interfaces. Besides that, this study contributes valuable insights into the design of photoelectrodes for sustainable hydrogen production, especially due to the detailed research on the formation of the heterojunction.

Unveiling the promotion of dual-metal-atom Ir-Fe pair sites on charge transfer for photoelectrochemical water splitting

Unveiling the promotion of dual-metal-atom Ir-Fe pair sites on charge transfer for photoelectrochemical water splitting

Precursor-concentration-controlled Morphology of TiO2 Nanorod/Nanoflower Films for Enhanced Photoelectrochemical Water Splitting and Investigating Their Growth Mechanism

Titanium dioxide (TiO2) has been considered as one of the most promising photocatalysts for photoelectrochemical (PEC) water splitting. Therefore, numerous efforts have been devoted to improving its PEC water splitting performance. In this study, TiO2 nanorod/nanoflower (NRF) films with controlled morphology were synthesized on fluorine-doped tin oxide (FTO) glass substrates by following a facile one-step hydrothermal method. The TiO2 NRF films were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectrometer (EDS), and ultraviolet-visible (UV-Vis) spectrophotometer. FE-SEM showed that the TiO2 films are composed of a simultaneous growth of a primary layer of TiO2 nanorod arrays (NRAs) and a second layer of TiO2 nanoflowers (NFs). The proposed growth mechanism highlighted the influence of precursor concentration on nucleation sites, affecting the preferred crystallographic plane growth of rutile TiO2 and nanorod alignment on the FTO substrate. Intriguingly, TiO2 NRF films prepared with 1.0 mL of titanium butoxide exhibited a maximum photocurrent density of 3.58 mA.cm−2 at 1.23 V versus (vs.) the reversible hydrogen electrode (RHE), along with a maximum photoconversion efficiency of 0.69%. The enhanced photocurrent density and photoconversion efficiency were attributed to the optimum thickness in the range of 4.52-7.31 µm, which caused the film to be formed with a unique morphology of the primary layer with well-vertically aligned nanorods and the second layer of flowers consisting of numerous rods stacked on top of one another. This study demonstrates the importance of designing semiconductors with 1D nanorod/3D nanoflower structures as high-performance photoelectrodes for PEC water splitting. Copyright © 2024 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Enhanced photoelectrochemical water splitting by a 3D hierarchical sea urchin-like structure: ZnO nanorod arrays on TiO2 hollow hemisphere

A hierarchical sea urchin-like hybrid metal oxide nanostructure of ZnO nanorods deposited on TiO2 porous hollow hemispheres with a thin zinc titanate interface layer is specifically designed and synthesized to form a combined type I straddling and type II staggered junctions. The HHSs, synthesized by electrospinning, facilitate light trapping and scattering. The ZnO nanorods offer a large surface area for improved surface oxidation kinetics. The interface layer of zinc titanate (ZnTiO3) between the TiO2 HHSs and ZnO nanorods regulates the charge separation in a closely coupled hierarchy structure of ZnO/ZnTiO3/TiO2. The synergistic effects of the improved light trapping, charge separation, and fast surface reaction kinetics result in a superior photoconversion efficiency of 1.07% for the photoelectrochemical water splitting with an outstanding photocurrent density of 2.8 mA cm−2 at 1.23 V versus RHE.

Nanocone-substrated BiVO4-Mo/MOFs photoanodes for highly efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) performance of photoanode is limited by the cascade-dynamic processes, mainly including light absorption, charge separation, and surface reaction. This work adopted a strategy of nanocones modification on FTO substrate (FTO-NC) to enhance light utilization and photoelectrons collection for improved PEC water splitting. Comparative studies showed that FTO-NC enhanced the light scattering, promoting the conversion process of photon to electron/hole and enlarging the effective surface area of BiVO4 for surface reaction. Meanwhile, cooperative Mo-doping and Co-MOF decoration improved the bulk electron transportation in BiVO4, hole migration towards the electrode surface, and accelerated the water oxidation reaction of photogenerated holes. The photocurrent density of FTO-NC/BiVO4-Mo/MOFs reached 3.56 mA cm−2, 6.14 times that of pristine BiVO4. The IPCE of FTO-NC/BiVO4-Mo/MOFs photoanode achieve 60% at 1.23 V vs. RHE, demonstrating a significantly enhanced light utilization performance. This work presents new insight into boosting cascade-dynamic processes through collaborative strategies for highly efficient PEC water-splitting.