Photoelectrodes For Photoelectrochemical 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.

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.

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.

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.

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.

Organic Semiconductor-Based Photoelectrochemical Cells for Efficient Solar-to-Chemical Conversion

Organic semiconductor-based photoelectrodes are gaining significant attention in photoelectrochemical (PEC) value-added chemical production systems, which are promising architectures for solar energy harvesting. Organic semiconductors consisting of conjugated carbon–carbon bonds provide several advantages for PEC cells, including improved charge transfer, tunable band positions and band gaps, low cost, and facile fabrication using organic solvents. This review gives an overview of the recent advances in emerging single organic semiconductor-based photoelectrodes for PEC water splitting and the various strategies for enhancing their performance and stability. It highlights the importance of photoelectrodes based on donor–acceptor bulk heterojunction (BHJ) systems for fabricating efficient organic semiconductor-based solar energy-harvesting devices. Furthermore, it evaluates the recent progress in BHJ organic base photoelectrodes for producing highly efficient PEC value-added chemicals, such as hydrogen and hydrogen peroxide. Finally, this review highlights the potential of organic-based photoelectrodes for bias-free solar-to-chemical production, which is the ultimate goal of PEC systems and a step toward achieving reliable commercial technology.

Crystal Reconstruction of Mo:BiVO4: Improved Charge Transport for Efficient Solar Water Splitting

AbstractA multifaceted Mo:BiVO4 (mf‐BVO) photoanode is grown on F‐doped‐SnO2 substrates via achemical bath deposition, and the crystal reconstruction process of mf‐BVO is found to boost the charge transport efficiency significantly for photoelectrochemical (PEC) water splitting. The mf‐BVO exhibits columnar grains with an uncommon (121) texture with high‐index facets such as (112), (020), (132), and (204). The texture and high‐index facets facilitate rapid surface melting and grain fusion during thermal annealing, thus leading to crystal reconstructed micron‐sized BVO grains (cr‐BVO). The cr‐BVO has a photocurrent density ≈50 times larger than that of mf‐BVO. The reason is identified as the significantly improved charge transport efficiency resulting from the dopant activation (increased carrier concentration) and bulky grains (fewer defects). Additionally, the cr‐BVO exhibits improved photocorrosion resistance compared to the nanoparticle‐based BVO. After coating the oxygen evolution catalyst, the photocurrent density of cr‐BVO is further increased to 4.4 mA cm−2 for water oxidation reaction at 1.23 V versus the reversible hydrogen electrode, maintaining a high and stable faradaic efficiency of over 88% for 24 h. These results demonstrate that crystal reconstruction is a facile and effective pathway to improve the charge transport efficiency, opening a new avenue for developing efficient photoelectrodes for PEC water splitting.

Construction of Sb2S3/CdS/CdIn2S4 cascaded S-scheme heterojunction for improving photoelectrochemical performance

Antimony sulfide (Sb2S3) is a relatively abundant and environmentally friendly emerging photovoltaic material, which has been gradually applied in solar cells and photocatalysis. It has high light absorption capacity, but it suffers many deep-level defects and is prone to recombination of electron-hole pairs within itself. Here, by constructing the Sb2S3/CdIn2S4 S-scheme heterojunction, we avoided the problem that electrons and holes cannot be separated and transported effectively due to many Sb2S3 defects (more recombination centers), and improved its application in the field of photoelectrochemical water splitting. Meanwhile, in order to further improve the performance of Sb2S3/CdIn2S4 photoelectrode, we introduced CdS energy platform between Sb2S3 and CdIn2S4 to form a Sb2S3/CdS/CdIn2S4 cascaded S-scheme heterojunction. Compared with Sb2S3 monomer, Sb2S3/CdS/CdIn2S4 had higher absorbance intensity, IPCE value, ABPE value, and lower charge transfer resistance. In addition, the photocurrent density of the Sb2S3/CdS/CdIn2S4 photoelectrode was about 4.20 mA/cm2 (1.23 V vs. RHE), which was 1.3 times higher than that of the Sb2S3/CdIn2S4 photoelectrode (3.29 mA/cm2) and 3.2 times higher than that of monomer Sb2S3 photoelectrode (1.32 mA/cm2). This method offers new prospects for optimizing the performance of antimony chalcogenides photoelectrodes for photoelectrochemical water splitting.

Epitaxial Grown Sb2Se3@Sb2S3 Core-Shell Nanorod Radial-Axial Hierarchical Heterostructure with Enhanced Photoelectrochemical Water Splitting Performance.

Antimony selenide (Sb2Se3) as a light-harvesting material has gradually attracted the attention of researchers in the field of photoelectrocatalysis. Uniquely, the crystal structure consists of one-dimensional (Sb4Se6)n ribbons, with an efficient carrier transport along the ribbon [001] direction. Herein, a novel Sb2Se3@Sb2S3 core-shell nanorod radial-axial hierarchical heterostructure was successfully fabricated by epitaxial growth strategy. Taking advantage of the isomorphous and anisotropic binding modes of (Sb4S(e)6)n ribbons for Sb2Se3 and Sb2S3, the epitaxially grown core-shell heterostructure forms a van der Waals heterojunction across the radial direction and covalently bonded heterojunction along the axial direction. A photocurrent of 1.37 mA cm-2 was achieved at 0 V vs RHE for the hierarchical Sb2Se3@Sb2S3 nanorod photoelectrode with [101] preferred orientation, up to 40 times higher than for pure Sb2Se3. Moreover, the FeOOH was introduced as a cocatalyst. The photoelectrode decorated with FeOOH shows better stability with a H2 generation rate of 18.9 μmol cm-2 h-1 under neutral conditions. This study provides a new insight into the design of antimony chalcogenide heterostructure photoelectrodes for photoelectrochemical water splitting.

Engineering Interfacial Band Bending over ZnIn2S4/SnS2 by Interface Chemical Bond for Efficient Solar‐Driven Photoelectrochemical Water Splitting

AbstractDeveloping a simple and effective strategy to modulate the energy band bending of heterojunction photoelectrodes is pivotal in terms of photoelectrochemical (PEC) water splitting. Herein, it is demonstrated that the introduction of the interfacial InOSn chemical bonds at the ZnIn2S4/SnS2 interface regulates the band bending of ZnIn2S4/SnS2 heterojunction photoanodes, reverses the charge transport direction, and reduces the oxygen evolution reaction (OER) overpotential. Detailed analysis indicates that the interfacial InOSn bond makes band adaptation to promote carrier separation and transfer through ultraviolet photoelectron spectrometry, hydroxyl radical production tests, and surface photovoltage measurements. Due to the special nanosheet morphology with exposed edges of the heterojunction interface, the InOSn bonds are partially exposed, which can reduce the OER overpotential and boost the surface injection efficiency according to the PEC impedance spectroscopy and density functional theory calculations. The synergistic modulation of InOSn bond yields a photocurrent of 4.57 mA cm−2 at 1.23 V (vs reversible hydrogen electrode, AM 1.5 G) and a low onset potential of −0.14 VRHE. This work provides a new solution for energy band regulation to improve the performance of heterojunction photoelectrodes for PEC water splitting.

Structural and Compositional Investigations on the Stability of Cuprous Oxide Nanowire Photocathodes for Photoelectrochemical Water Splitting.

Cuprous oxide (Cu2O) is a promising photocathode material for photoelectrochemical (PEC) water splitting. Recently, the PEC performances of Cu2O-based devices have been considerably improved by introducing nanostructures, semiconductor overlayers, and hydrogen evolution reaction (HER) catalysts. However, Cu2O devices still suffer from poor stability in aqueous solution, especially in strong acidic or alkaline conditions, despite the use of an intrinsically stable oxide overlayer as a protection layer. Thus, it is essential to fully understand the stability of the entire Cu2O photocathodes in these conditions for establishing suitable protection strategies to achieve durable PEC water splitting. In this work, the stability of bare and protected Cu2O nanowire (NW) photocathodes was evaluated in detail using microscopy techniques and compositional analyses. The insights gained in this work will guide the design and synthesis of durable photoelectrodes for PEC water splitting.

Metal–Organic Framework‐Based Materials for Solar Water Splitting

Solar‐driven water splitting is a promising way to produce renewable hydrogen. The design of efficient semiconductor photocatalysts plays a vital role in this process. The recent dynamic development of metal–organic framework (MOF) materials provides a good opportunity to design efficient composite photocatalysts toward solar water splitting. Herein, a critical review of the design and development of MOF/semiconductor composite photocatalysts for solar‐driven water splitting is presented. The designing strategies of MOF‐based composite photocatalysts, including the use of organic ligands, quantum dots and carbon‐based materials to form heterostructures, and the combination of MOF layers with semiconductors to fabricate thin‐film photoelectrodes for photoelectrochemical water splitting, are introduced. The remaining challenges and future perspectives of the MOF‐based composites with the hope of achieving improved solar water splitting are also discussed.

Design and fabrication of Bi2O3/BiFeO3 heterojunction film with improved photoelectrochemical performance

In this work, high-quality BiFeO3 (BFO), Bi2O3, Bi2O3/BFO films on indium tin oxide (ITO) substrates were prepared by pulse laser deposition (PLD). Photoelectrochemical measurements were carried out to determine their potential as photoelectrodes for photoelectrochemical water splitting. The photocurrent of Bi2O3 /BFO heterojunction film was found to be twice higher than that of pure BFO film, and the onset potential was positively shifted by 240 mV. To understand the mechanism of such improved performance, detailed characterization and analysis of the band alignment and charge-carrier dynamics for all of the samples were carried out. A type II junction was formed at the interface between Bi2O3 and BFO for the heterojunction film, which resulted in the promoted electron-hole separation process under AM 1.5G light simulation. The present study suggests that Bi2O3/BFO type II junction film with superior photoelectrochemical response could be applied for designing and fabricating high-performance photoelectrochemical cells.

Bismuth based photoelectrodes for solar water splitting

Photoelectrochemical water splitting is a sustainable path to generate valuable hydrogen using sunlight and water as the only inputs. Despite significant efforts to date, it is still a challenge to achieve photoelectrode with superior performance and long-term stability.Many bismuth-based semiconductor materials have demonstrated excellent visible light harvesting capability and suitable band edge for water splitting. Herein, we summarized the latest studies conducted on bismuth-based photoelectrodes for photoelectrochemical water splitting. Specifically, photoelectrochemical properties of copper bismuth oxide (CuBi2O4), bismuth ferrites (BiFeO3, Bi2Fe4O9), bismuth vanadate (BiVO4), bismuth tungstate (Bi2WO6), bismuth molybdate(Bi2MoO6) and bismuth oxyhalids (BiOX, X = I, Cl, Br) are presented. Strategies to achieve high stability and photolectrochemical performance were discussed in the aspects of nanostructure formation, heterostructure assembly, practical defect engineering, preferential facet growth and oxygen evolution catalyst incorporation.

Recent progress on post-synthetic treatments of photoelectrodes for photoelectrochemical water splitting

The review summarizes various post-synthetic treatments reported in the past five years, including chemical treatments, electrochemical and irradiation-based treatments, and post-annealing treatments, for PEC water splitting application.

Research Progress and Challenges ofα-Fe2O3 Photoanode for Photoelectrochemical Water Splitting

In recent years,photoelectrochemical(PEC)water splitting to produce hydrogen provides a clean and renewable pathway for future energy demands.hematite(α-Fe2O3)is a promising photoanode material owing to its narrow band gap(~2.1 eV),non-toxicity,natural abundance,and photo-stability.However,some drawbacks greatly limited the photoconversion efficiencies of Fe2O3-based photoanodes,such as poor electrical conductivity,short hole diffusion length(2~4 nm),sluggish surface oxygen evolution kinetics,and short excited-state lifetime(<10×10^-12 sec).Here,we review the recent progressof hematite photoanodes for PEC water oxidation,focused on enhancing surface water oxidation reaction,accelerating charge separation and transport in bulk,improving light absorption.Finally,perspectives on the key challenges and future development of hematite photoelectrodes for PEC water splitting are given.

Spray-processed nanoporous BiVO4 photoanodes with high charge separation efficiency for oxygen evolution

Spray pyrolysis is a convenient method for fabricating BiVO4 photoanondes from a precursor solution. As the precursor solution of spray pyrolysis can significantly influence the nanostructure and the amount of oxygen vacancies of the final films, modifying the precursor solution is an efficient strategy for improving the photoelectrochemical (PEC) performance of BiVO4 photoanodes. Herein, an ultraviolet and ultrasonic treatment for modifying a vanadium precursor solution of spray pyrolysis was developed to produce efficient nanoporous BiVO4 photoanodes. By the simple treatment, the AM 1.5 photocurrent density of the photoanode reached 1.76 mA/cm2 at 1.23 V vs the reversible hydrogen electrode (RHE) for water oxidation, which is 12.3 times higher than the untreated BiVO4 photoanode. The good PEC performance was mainly attributed to the excellent charge separation that reached approximately 94.2% at 1.23 V vs RHE. Systematic studies revealed that the treatment for the precursor solution could tune the nanoporous structure and increase the amount of oxygen vacancies in the final films. This finding offers a facile and effective approach for fabricating efficient photoelectrodes for PEC water splitting.

Tuning Light-Driven Water Oxidation Efficiency of Molybdenum-Doped BiVO4 by Means of Multicomposite Catalysts Containing Nickel, Iron, and Chromium Oxides.

Mo-doped BiVO4 has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light-driven water oxidation. We present the influence of an oxygen-evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:BiVO4 photoanodes. The photoanodes are prepared by spray-coating, enabling compositional and thickness gradients of the incorporated catalyst. Two different configurations are evaluated, namely with the catalyst embedded into the Mo:BiVO4 film or deposited on top of it. Both configurations provide a significantly different impact on the photoelectrocatalytic efficiency. Structural characterisation of the materials by means of SEM, TEM and XRD as well as the photoelectrocatalytic activity investigated by means of an optical scanning droplet cell and in situ detection of oxygen using scanning photoelectrochemical microscopy are presented.

3D-printed Cu2O photoelectrodes for photoelectrochemical water splitting.

Photoelectrochemical (PEC) water splitting is an alternative to fossil fuel combustion involving the generation of renewable hydrogen without environmental pollution or greenhouse gas emissions. Cuprous oxide (Cu2O) is a promising semiconducting material for the simple reduction of hydrogen from water, in which the conduction band edge is slightly negative compared to the water reduction potential. However, the solar-to-hydrogen conversion efficiency of Cu2O is lower than the theoretical value due to a short carrier-diffusion length under the effective light absorption depth. Thus, increasing light absorption in the electrode–electrolyte interfacial layer of a Cu2O photoelectrode can enhance PEC performance. In this study, a Cu2O 3D photoelectrode comprised of pyramid arrays was fabricated using a two-step method involving direct-ink-writing of graphene structures. This was followed by the electrodeposition of a Cu current-collecting layer and a p–n homojunction Cu2O photocatalyst layer onto the printed structures. The performance for PEC water splitting was enhanced by increasing the total light absorption area (Aa) of the photoelectrode via controlling the electrode topography. The 3D photoelectrode (Aa = 3.2 cm2) printed on the substrate area of 1.0 cm2 exhibited a photocurrent (Iph) of −3.01 mA at 0.02 V (vs. RHE), which is approximately three times higher than that of a planar photoelectrode with an Aa = 1.0 cm2 (Iph = −0.91 mA). Our 3D printing strategy provides a flexible approach for the design and the fabrication of highly efficient PEC photoelectrodes.