Photoelectrodes For Water Splitting Research Articles

Carbon coated iron pyrite (C–FeS2) photo-electrode for photo-electrochemical water splitting

In this paper, we present fabrication of ‘FeS2’ and carbon coated FeS2 (C–FeS2) photo-electrodes and demonstrated that coating of carbon on FeS2 significantly enhanced photo-electrochemical properties. The hydrothermal method has been adopted for the synthesis of FeS2 and carbon coating on FeS2 was achieved by CVD technique. The materials are subsequently characterized using X-ray diffraction, Raman spectroscopy and Field enhanced scanning electron microscope (FESEM) techniques for phase identification and morphological studies, respectively. The photo-electrochemical measurements revealed significant enhancement in the current density from ∼2 to 3.7 mA/cm2 (∼1.8 times higher) for C–FeS2 in comparison to the FeS2 photo-electrode under visible light. The enhancement in FeS2 after carbon coating has been attributed to reduction in recombination of photo generated charge carriers, enhancement in the band bending and lowering the charge transfer resistance at the semiconductor/electrolyte interface. To date, very few studies have been reported on FeS2 based composites for water splitting applications and use of carbon coating can be a novel approach for developing efficient solar to hydrogen conversion devices. The mechanism for the photocurrent enhancement was supported by Mott-Schottky and electrochemical impedance spectroscopy measurements.

Modulating band alignment at the 3D metal/semiconductor interface of liquid metal-embraced semiconductor photoelectrodes for water splitting

Modulating band alignment at the 3D metal/semiconductor interface of liquid metal-embraced semiconductor photoelectrodes for 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).

Particle-based Photoelectrodes for PEC Water Splitting: Concepts and Perspectives.

This comprehensive review delves into the intricacies of the photoelectrochemical (PEC) water splitting process, specifically focusing on the design, fabrication, and optimization of particle-based photoelectrodes for efficient green hydrogen production. These photoelectrodes, composed of semiconductor materials, potentially harness light energy and generate charge carriers, driving water oxidation and reduction reactions. The versatility of particle-based photoelectrodes as a platform for investigating and enhancing various semiconductor candidates is explored, particularly the emerging complex oxides with compelling charge transfer properties. However, the challenges presented by many factors influencing the performance and stability of these photoelectrodes, including particle size, shape, composition, morphology, surface modification, and electrode configuration, are highlighted. The review introduces the fundamental principles of semiconductor photoelectrodes for PEC water splitting, presents an exhaustive overview of different synthesis methods for semiconductor powders and their assembly into photoelectrodes, and discusses recent advances and challenges in photoelectrode material development. It concludes by offering promising strategies for improving photoelectrode performance and stability, such as the adoption of novel architectures and heterojunctions. This article is protected by copyright. All rights reserved.

Investigation of O/N Ordering in Perovskite-Type Oxynitrides La1−xYxTa(O,N)3 on Long Range and Short Scale

Oxynitrides such as LaTa(O,N)3 are attractive materials as photoelectrodes for photoelectrocatalytic solar water splitting. The potential anionic ordering in their perovskite-type structure has been shown to impact the materials’ properties. Given the importance attributed to it, the present study reports a detailed experimental analysis supported by simulations of the anionic ordering of La1−xYxTa(O,N)3. The influence of O/N and yttrium content on the anionic order was assessed. Neutron diffraction analysis was performed on four different nominal compositions—LaTaON2, LaTaO2N, La0.9Y0.1TaON2, and La0.9Y0.1TaO2N—at 10 K and 300 K to study potential long-range ordering. Neutron pair distribution function (PDF) analysis was performed on all samples at 10 K and on non-Y-substituted samples at 300 K to evaluate short-range ordering. There was no evidence of long-range O/N order in any of the compounds. In contrast, at a short range (1.5 Å ≤ r < 6 Å), a Pnma (a−b+a−) tilting pattern and local cis-ordering of the anions were seen. The latter faded rapidly, leaving the Pnma tilting pattern in a 6 Å ≤ r ≤ 11 Å range. At higher distances, the PDF analysis agreed with the Imma (a−b0a−) O/N disordered long-range structure. As the O/N content changed, not much difference in behavior was observed. Yttrium substitution introduced some disorder in the structure; nonetheless, it showed marginal influence on octahedral tilting and anionic ordering.

Effect of the energy band bending on surface by Cu-poor layer of Cu(In, Ga)Se2-related photoelectrode for water splitting

To achieve the field of photoelectrochemical water splitting, the modulating of the valence band maximum (VBM) grading on the surface of Cu(In, Ga)Se2 (CIGS) photoelectrodes via the deposition of additional In and Se (forming Cu-poor-CIGS layer) following CIGS growth was investigated. The resulting downshift of the Fermi level was likely to occur around the surface of the CIGS films for modulating the VBM grading, increasing the onset potential of the CIGS-related photoelectrodes. Moreover, a hole-blocking layer was obtained via modulated VBM grading of the CIGS-related photoelectrode, which increased the photocurrent density of the CIGS-related photoelectrode. Subsequently, a Cu-poor-CIGS/CIGS interface was formed for modulating the VBM grading using Cu-poor-CIGS, which contributed to increasing the photocurrent density owing to the enhancement of charge separation by the depletion layer in the Cu-poor-CIGS/CIGS interface. This study shows that water splitting can be effectively improved by modulating the VBM grading on the surface of CIGS-related photoelectrodes.

Recent advances on three-dimensional ordered macroporous metal oxide-based photoelectrodes for photoelectrochemical water splitting

Recent advances in 3DOM metal oxide-based photoelectrodes for PEC water splitting are summarized. The advantages of an ordered structure from the perspective of photo-electrocatalysis mechanism and morphological design are also introduced.

Heterometallic {Re4Mo2Qi8} cluster-based building blocks: towards the rational nanoarchitectonics of optimized photoelectrodes for solar cells and water splitting

The mixing of rhenium and molybdenum within the same heterometallic cluster enables to modulate optoelectronic properties of the photo-active layers. Such {Re4Mo2Q8}-based photoelectrodes appear promising for the photoelectrochemical water splitting.

A review on the advancements of graphitic carbon nitride-based photoelectrodes for photoelectrochemical water splitting

This review offers a comprehensive depiction of g-C3N4-based materials for PEC water splitting. The fundamentals of PEC water splitting, along with the applications of g-C3N4-based materials as photoanodic and photocathodic materials are discussed.

(Invited) In Situ Photoelectron Spectroscopy Reveals the Chemical Nature of Semiconductor Surface States

The accessible photovoltage of semiconducting photoabsorbers is typically 0.5-1 V below the theoretically achievable values predicted by the Shockley-Queisser limit [1]. Although the reason for this is still not well understood, surface and interface states within the photoabsorbers energy band gap may play a crucial role as they generally induce Fermi level pinning [2]. Within the PEC community, two key elements have been identified for the maximization of the photovoltage in photoelectrodes for water splitting: (i) the passivation of surface defects which is needed to avoid Fermi level pinning, and (ii) the increase of the minority carrier concentration at the interface to improve contact selectivity and optimize carrier extraction [3,4].To understand the role of surface defects on Fermi level pinning, detailed information on the chemical nature and electronic properties of surface states is needed. Such information is usually obtained with UHV surface science techniques such as XPS, but the photoelectrode surface under UHV conditions has little, if any, relevance to the electrified surface when immersed in the electrolyte. Moreover, recent studies have shown that semiconductor surfaces are not static, but undergo extensive structural and chemical transformations during PEC device operation [5,6]. In this talk, we will show our recent development of state-of-the-art techniques to study the structure and dynamics of semiconductor/water interfaces under practically relevant conditions [7]. The chemical nature of the electronic states for selected semiconductors prepared at the Institute for Solar Fuels has been explored using synchrotron-based resonant, ambient pressure soft and hard X-ray photoelectron spectroscopy (AP-XPS and AP-HAXPES) [6,8-11], and with in situ/operando Raman and photoluminescence spectroscopy. In particular, we will show that it is possible to study photon-induced chemical changes at solid/liquid interfaces using AP-XPS and AP-HAXPES [6,8].We will conclude this contribution by discussing about future perspectives and technical implementations for multimodal in situ/operando investigations of photoelectrocatalytic processes.[1] M.T. Mayer. Curr. Opin. Electrochem. 2017, 2, 104.[2] A. J. Bard et al. J. Am. Chem. Soc. 1980, 102, 3671.[3] A.G. Scheuermann et al., Nat. Mater. 2016, 15, 99.[4] M. Schleuning et al., Sustainable Energy Fuels, 2022, 6, 3701.[5] F.M. Toma et al., Nat. Commun. 2016, 7, 12012.[6] M. Favaro et al., J. Phys. Chem. B 2018, 122, 801.[7] M. Favaro et al., Surf. Sci. 2021, 713, 121903.[8] M. Favaro et al., J. Phys. D: Appl. Phys. 2021, 54, 164001.[9] M. Favaro et al., J. Phys. Chem. C 2019, 123, 8347.[10] W. Wang et al., J. Am. Chem. Soc. 2022, 144, 17173.[11] P. Schnell et al., Sol. RRL 2023, 2201104.

Improving the photovoltage of Cu2O photocathodes with dual buffer layers

Cuprous oxide (Cu2O) is a promising oxide material for photoelectrochemical water splitting (PEC), and increasing its photovoltage is the key to creating efficient overall PEC water-splitting devices. Previous reports are mostly focused on optimizing the energy band alignment between Cu2O and the n-type buffer layer to improve the photovoltage of Cu2O photocathodes. However, the band alignment between the n-type buffer layer and the protective layer is often ignored. In this work, Cu2O photocathodes with a single buffer layer (Ga2O3) and dual buffer layers (Ga2O3/ZnGeOx) are fabricated, and their PEC performances are compared. Results show that after inserting the second buffer layer (ZnGeOx), the onset potential of the Cu2O photocathode increases by 0.16 V. Operando electrochemical impedance spectroscopy measurements and analysis of the energy-level diagrams of each layer show that an energy level gradient between Ga2O3 and TiO2 is created when ZnGeOx is introduced, which eliminates the potential barrier at the interface of Ga2O3/TiO2 and improves the photovoltage of the Cu2O photocathode. Our work provides an effective approach to improve the photovoltage of photoelectrodes for solar water splitting by introducing dual buffer layers.

Unraveling the impact of tetravalent and pentavalent ions on the charge dynamics of hematite photoelectrodes for solar water splitting

This study focuses on understanding the impact of tetravalent (Hf4+) and pentavalent (Nb5+) ions in hematite photoelectrodes using a two-step synthesis approach. Structural, morphological, and compositional analyses confirms that Nb5+ is segregated over the hematite crystal surface while Hf4+ is allocated over the crystal surface and between the fluorine-doped tin oxide substrate (FTO)-hematite interface. Our results indicate that the modifier insertion led to substantial improvements in overall efficiency and photoelectrochemical (PEC) performance. However, it creates additional surface states, as evidenced by shifts in the anodic onset potential (Vonset) observed in the linear sweep voltammetry curves. For Nb-modified photoelectrodes, Vonset shift of ∼20 mV with respect to hematite was observed and confirmed by intensity modulated photocurrent spectroscopy (IMPS). For Hf-modified hematite, this Vonset shift is more pronounced (∼30 mV). When combined with NiFeOx, Nb5+ acted synergistically showing a 4-fold efficiency increase compared to hematite and ∼70 mV cathodic shift in the Vonset. Otherwise, NiFeOx showed no significant impact in the Hf4+ modified hematite photoelectrodes, suggesting that Hf4+ role lies in enhancing electron collection at the FTO-hematite interface. This study not only sheds light on the charge dynamics of modified hematite photoelectrodes but also provides strategies for boosting the PEC devices efficiency.

Architecture design of TiO2 with Co-doped CdS quantum dots photoelectrode for water splitting.

Photoelectrochemical hydrogen production is a critical key to solving the carbon-zero goal of countries due to renewable sources of solar light and combustion products of hydrogen-only water. Here, an architecture design for an n-type nano rosettes-rod TiO2 (RT) surface using CdS and Co-doped CdS quantum dots (QDs) is carried out utilizing the SILAR (simple ionic layer adsorption and reaction) method. Furthermore, the photocatalytic behaviour of Co-doped CdS QDs SILAR cycles deposition is investigated in various cycles, including 5, 8, 10, and 12. The FESEM, Raman XRD, Uv-Vis spectrometer, and vibration modes are used to evaluate the photoelectrode surface structure, crystal structure, and solar light absorption, respectively. FESEM images and XRD pattern revealed successive CdS QDS and Co-doped CdS QDs deposition on the RT boundary and rising SILAR cycles of Co-doped CdS QDs lead to further coverage of RT surface. UV-vis spectrometer indicated shifting solar light absorption to the visible region by applying more SILAR cycles of Co-doped CdS QDs deposition. The electrochemical parameters obtained from EIS showed total polarization resistance (Rp) of the RT electrode dramatically decreased with 10 SILAR cycle Co-doped CdS QDs deposition (5093 Ω cm2 and 617 Ω cm2). Linear sweep voltammetry (LSV) and chronoamperometric photocatalytic performance measurements indicated Co-doped CdS QDs on RT extremely enhanced photoresponse under solar irradiation and 10 SILAR cycle Co-doped CdS QDs improved photocurrent density about fourfold according to blank RT electrode.

Single Atom Catalysts for Photoelectrochemical Water Splitting

AbstractSingle atom catalysts (SACs) have attracted increasing attention in electrocatalysis due to their unprecedented catalytic activity with excellent atomic utilization efficiency derived from unique electronic states and coordination environments. In photoelectrochemical (PEC) water splitting, atomically dispersed metal catalysts anchored to photoelectrodes offer the breakthrough to outperform the conventional thin‐film PEC catalysts by enlarging the catalytic sites and facilitating photogenerated charge carrier kinetics. Herein, we present a comprehensive review of SAC‐incorporated photoelectrodes for efficient PEC water splitting. Firstly, the representative characterization techniques for the identification of SACs and investigations in respect of photogenerated charge carrier kinetics and photon‐to‐current efficiency will be discussed. Then, we will introduce the state‐of‐the‐art PEC‐SACs classified into noble metal, non‐noble metal, and dual metal SACs. Finally, critical outlooks to realize the full potential of SACs in photoelectrocatalysis will be highlighted.

Photoelectrochemical Schlenk cell functionalization of multi-junction water-splitting photoelectrodes

Photoelectrochemical Schlenk cell functionalization of multi-junction water-splitting photoelectrodes

Controllable synthesis of CdS nanospheres photoelectrode for photoelectrochemical water splitting

CdS nanospheres were grown on indium tin oxide (ITO) substrate using a hydrothermal method. The crystal structure, morphology and electronic structure of the samples synthesized were characterized in detail. The results confirm that the crystallinity, size, crystal defects of the CdS nanospheres and the film thickness of CdS photoelectrodes can be tuned by varying the precursor Cd2+ concentration. Combined with charge transfer dynamics analysis, it can be found that proper particle size and film thickness, as well as fewer defects, will result in better charge separation efficiency of the prepared CdS/ITO photoelectrodes, thereby exhibiting better photoelectrochemical performance for water splitting. The optimized CdS/ITO photoelectrode synthesized with a Cd2+ concentration of 0.14 mol·L−1 gave a photocurrent density of 5.10 mA·cm−2 at potential of 1.23 V versus the reversible hydrogen electrode (RHE), under a simulated solar illumination of 100 mW·cm−2.

Electrochemical Properties of BaTaO2N Photocatalyst with Visible‐Light‐Driven Water Splitting Capability

AbstractA BaTaO2N (BTON) particulate photocatalyst enables solar water splitting in response to visible light irradiation at wavelengths of up to 640 nm. The specific nitridation conditions produced distinct types of BTON particles with the capability of one‐step overall water splitting (Active‐BTON) and without the overall water splitting activity (Inactive‐BTON). Unveiling the intrinsic differences between the active‐ and inactive‐BTON particles is crucial for obtaining more in‐depth information about the water splitting activity. Herein, we investigated the electrochemical (EC) and photoelectrochemical (PEC) properties of these BTON photocatalysts using the particulate‐based photoelectrodes for water splitting. EC measurements, including Mott–Schottky analysis, revealed that the flat band potential of Active‐BTON is located at a potential that is more positive than that of Inactive‐BTON, whereas the carrier concentration of Active‐BTON is one‐tenth lower than that of Inactive‐BTON. Irrespective of the pH value of the 1.0 M potassium phosphate aqueous solution, the Active‐BTON‐based photoelectrodes showed a higher photocurrent than that of Inactive‐BTON under simulated AM 1.5G solar illumination. The PEC performance of the BTON was found to be limited by the electrocatalytic activity of the CoOx co‐catalyst, specifically the electrolyte pH.

Sputtered nanocrystalline samarium doped CuO photoelectrode for efficient photoelectrochemical water splitting

Copper oxide (CuO) is a promising photoelectrode for photoelectrochemical (PEC) energy generation because of its fascinating properties, including high earth availability and inexpensive. In this context, samarium (Sm)-doped CuO thin films are deposited on a glass substrate through the sputtering technique to serve as photocatalysts in PEC water splitting. The structural characterizations of sputtered films were performed with X-ray diffraction (XRD) spectroscopy, while the morphology and elemental composition of all films were studied with the help of field-emission scanning electron microscopy (FE-SEM) connected with a dispersive energy X-ray analyzer. XRD pattern has shown that all films are polycrystalline with a preferred orientation of (−111) crystallographic plane. FE-SEM images and ImageJ analysis showed that all deposited particles are uniformly distributed as disassembled particles over the substrate area. The optical energy band gap (Eg) was increased by adding the Sm contents in the CuO films. The photocurrent density for the photoelectrode was improved by Sm dopants as compared to the pure sample and recorded its maximum value of − 4.66 mA/cm2 at ∼ − 0.385 V vs. RHE which was about 4 times higher than that of the pure sample with feasible photostability retention. Additionally, the value of the charge transfer resistor for the CuO photocathode with the smallest amount of Sm ions was the lowest as compared to other photocathodes. These results offer a practical method for creating a brand-new fabrication technique for PEC devices with remarkable water-splitting efficiency.

Self-Enhancement of Water Electrolysis by Electrolyte-Poled Ferroelectric Catalyst.

Efficient and durable electrocatalysts with superior activity are needed for the production of green hydrogen with a high yield and low energy consumption. Electrocatalysts based on transition metal oxides hold dominance due to their abundant natural resources, regulable physical properties, and good adaptation to a solution. In numerous oxide catalyst materials, ferroelectrics, possessing semiconducting characteristics and switchable spontaneous polarization, have been considered promising photoelectrodes for solar water splitting. However, few investigations noted their potential as electrocatalysts. In this study, we report an efficient electrocatalytic electrode made of a BiFeO3/nickel foam heterostructure, which displays a smaller overpotential and higher current density than the blank nickel foam electrode. Moreover, when in contact with an alkaline solution, the bond between hydroxyls and the BiFeO3 surface induces a large area of upward self-polarization, lowering the adsorption energy of subsequent adsorbates and facilitating oxygen and hydrogen evolution reaction. Our work demonstrates an infrequent pathway of using functional semiconducting materials for exploiting highly efficient electrocatalytic electrodes.

Ru-P pair sites boost charge transport in hematite photoanodes for exceeding 1% efficient solar water splitting

Fast transport of charge carriers in semiconductor photoelectrodes are a major determinant of the solar-to-hydrogen efficiency for photoelectrochemical (PEC) water slitting. While doping metal ions as single atoms/clusters in photoelectrodes has been popularly used to regulate their charge transport, PEC performances are often low due to the limited charge mobility and severe charge recombination. Here, we disperse Ru and P diatomic sites onto hematite (DASs Ru-P:Fe2O3) to construct an efficient photoelectrode inspired by the concept of correlated single-atom engineering. The resultant photoanode shows superior photocurrent densities of 4.55 and 6.5 mA cm-2 at 1.23 and 1.50 VRHE, a low-onset potential of 0.58 VRHE, and a high applied bias photon-to-current conversion efficiency of 1.00% under one sun illumination, which are much better than the pristine Fe2O3. A detailed dynamic analysis reveals that a remarkable synergetic ineraction of the reduced recombination by a low Ru doping concentration with substitution of Fe site as well as the construction of Ru-P bonds in the material increases the carrier separation and fast charge transportation dynamics. A systematic simulation study further proves the superiority of the Ru-P bonds compared to the Ru-O bonds, which allows more long-lived carriers to participate in the water oxidation reaction. This work offers an effective strategy for enhancing charge carrier transportation dynamics by constructing pair sites into semiconductors, which may be extended to other photoelectrodes for solar water splitting.