Photoanode Research Articles

Engineering and Design of Halide Perovskite Photoelectrochemical Cells for Solar‐Driven Water Splitting

AbstractPhotoelectrochemical cells (PEC) use solar energy to generate green hydrogen by water splitting and have an integrated device structure. Achieving high solar‐to‐hydrogen conversion (STH) efficiency along with a long operational lifetime in these cells is crucial for the production of low‐cost green hydrogen as a viable energy source. Several functional components, such as photo absorber, charge transport, and catalyst layers are interfaced in these cells to form a compact monolithic device. In this review, therefore, the engineering and design of the individual components of these cells, the interplay between them, and their interfaces are discussed in detail, as these factors determine the overall performance of the cells. The main emphasis is on halide perovskite (HP) photo absorbers, which have emerged as promising materials for use in these cells due to their superior optoelectronic properties. Recent advances in the development of efficient and stable perovskite‐based cells are highlighted and reviewed. The design of catalysts for water splitting and the effect of factors such as pH and supporting cations are also examined. Finally, the scientific challenges and future directions for designing perovskite‐based photoelectrochemical cells are discussed. This review can help researchers further advance this technology toward commercial production of green hydrogen.

Molecular Copper(I)-Sensitized Photoanodes for Alcohol Oxidation under Ambient Conditions.

Dye-sensitized photoelectrochemical cells can enable the production of molecules currently accessible through energetically demanding syntheses. Copper(I)-based dyes represent electronically tunable charge transfer and separation systems. Herein, we report a Cu(I)-bisdiimine donor-chromophore-acceptor dye with an absorbance in the visible part of the solar spectrum composed of a phenothiazine electron donor, and dipyrido[3,2-a:2',3'-c]phenazine electron acceptor. This complex is incorporated onto a zinc oxide nanowire semiconductor surface effectively forming a photoanode that is characterized spectroscopically and electrochemically. We investigate the photo-oxidation of hydroquinone, and the photosensitization of 2,2,6,6-tetramethylpiperidine-1-oxyl and N-hydroxyphthalimide for the oxidation of furfuryl alcohol to furfuraldehyde, resulting in near quantitative conversions, with poor selectivity to the alcohol.

In-situ spectroelectrochemical analysis: Irreversible deformation of cesium lead bromide Perovskite Quantum Dots in SiOx matrices

To practically utilized the organometallic lead halide perovskites to optoelectronic devices and photoelectrochemical cells, numerous efforts have been utilized to obtain the perovskites with low-energy process with coverage of various inorganic mediums to improve stability against humidity. By utilizing ligand-assisted reprecipitation process, under ambient condition at room temperature, the dimensionally confined perovskite quantum dots in silica matrices (PQD@SiOx) were obtained, and they were stable under several months under the ambient condition. To apply the PQD@SiOx to the photoelectrochemical cells by introducing direct contact between PQD@SiOx and electrolyte, the material/photophysical properties under electrochemical conditions are necessary to be studied. However, the role of silica coverage to the electrochemical behaviors of the PQD cores in the silica medium were not yet studied. In this work, under the electrochemical conditions, the oxidative and reductive behaviors of the PQD@SiOx were studied. Also, through in-situ spectroelectrochemical study, the electrochemically induced irreversible deformation process were tracked. The findings of this study could be used to understand role of silica coverage and develop the strategy to improve the protecting behavior of the silica for the PQD cores to utilize into the photoelectrochemical cells.

The removal and transformation of fipronil using a photoelectrochemical device combined with a carbonized TiO2 nanocomposite electrode

Fipronil has been a critical environmental concern due to its potential risks to aquatic environments. However, research on the effective removal of fipronil using photoelectrochemical (PEC) devices is still limited. This study represents the pioneering application of a PEC device for the efficient removal of pesticides. A carbonized titanium dioxide nanocomposite electrode was employed as the electrode in the PEC device. The extent of fipronil degradation in the PEC device was also monitored. The PEC device demonstrated higher efficiencies than the reported oxidation treatments. The applied voltage and illumination from the light source initiated the formation of various reactive species, which exhibited the ability to degrade fipronil in the PEC device. Importantly, the presence of singlet oxygen and ozone in the PEC device was demonstrated for the first time, providing new insights into the degradation mechanism in the PEC system. Furthermore, this study unveiled four byproducts that were previously unreported. The presence of fipronil chlorinated byproducts in the device resulted in the generation of reactive chlorine species, which contributed to fipronil decomposition. When the detoxification of fipronil was compared between the PEC and electrochemical devices, the PEC device demonstrated higher degradation efficiencies and more effective detoxification, providing valuable insight into removing pesticides. Novelty statementThe degradation of fipronil and the identification of its degradation byproducts, along with toxicity testing, have been extensively investigated. Previous studies have indicated that many oxidation processes for fipronil degradation lead to the formation of byproducts with higher toxicity or require extended periods to reduce toxicity. In this study, a photoelectrochemical advanced oxidation process was applied for the first time to degrade pesticides. The developed PEC degradation process demonstrated the ability to rapidly remove fipronil and effectively reduce its toxicity, showing significant potential for various applications. Furthermore, our research revealed the formation of singlet oxygen and ozone in a PEC degradation system, providing novel insights into the degradation mechanism within the PEC system. Utilizing the carbonized titanium dioxide nanocomposite electrode developed in this study, successful fipronil decomposition was achieved for the first time through a PEC device.

Thymus schimperi Ronniger plant flower extract dye-sensitized solar cells

The demand for energy is greatly increasing due to the world’s population growth and technological advancement. Natural dye-sensitized solar cells are attracting research as an alternative and renewable energy source due to their simple preparation technique, availability, cost effectiveness and environmental friendliness. In the present work, we have successfully fabricated dye-sensitized solar cells (DSSCs) from Thymus schimperi Ronniger plant flowers for the first time. The solvents used for extraction of the flower dye were deionized water and its mixture with ethanol. The T. schimperi Ronniger flower extract dye solutions and sensitized photoanodes were characterized by Fourier transform infrared and ultraviolet–visible techniques. The crystallinity of TiO2 films was analyzed by x-ray diffraction, and the films showed pure anatase phase behavior. The photoelectrochemical solar cell performance parameters, such as short circuit current density, open circuit voltage, fill factor and efficiency, were evaluated from current density–voltage measurements using a Keithley 2450 source meter. DSSCs sensitized with dye solution extracted by a mixture of water and ethanol showed better performance (1.37%) than those sensitized with dye solution extracted by deionized water alone (1.02%).

Strontium ferrite oxide (Sr3Fe2O7) decorated TiO2 photoanode improves the photo-absorption and photoelectrochemical cell efficiency

In this study, a coating of strontium ferrite oxide (SFO), Sr3Fe2O7, on TiO2 demonstrated an enhancement in photoelectrochemical cell (PEC) performance. Pure TiO2 and SFO decorated TiO2 (SFO/TiO2) were synthesized using the hydrothermal method. The concentration of SFO precursor in this study varied between 0.5, 1.0, and 1.5 mmol. Most of the optimized SFO concentration showed the better Applied Bias Photon-to-current Efficiency than the pure TiO2. The structure, chemistry, and surface morphology of TiO2 and SFO/TiO2 materials were investigated using several techniques, including X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The UV–visible spectra revealed that SFO was able to reduce the energy band gap of pristine TiO2 from 3.09 to 2.55 eV. The photoluminescence spectroscopy displayed that almost SFO/TiO2 materials exhibited the lower recombination time than the pristine TiO2. Moreover, 1.0 mmol of SFO/TiO2 exhibited the highest photocurrent density, at approximately 12.5 μA/cm2, which was 12 times greater than pure TiO2. The Mott-Schottky analysis revealed the energy band edge of SFO and the TiO2 was well alignment. Therefore, SFO plays a crucial role in improving the photo-absorption efficiency of PEC cell. The enhanced PEC performance was achievable due to the materials’ tailored light response.

Nesting BiVO4 nanoislands in ZnO nanodendrites by two-step electrodeposition for efficient solar water splitting

Photoanodes with a large electrochemically active surface area, rapid charge transfer, and broadband light harvesting capacity are required to maximize the photoelectrochemical (PEC) water splitting performance. To address these features, we demonstrate that 3D hierarchal ZnO nanodendrites (NDs) can be sensitized with BiVO4 nanoislands by chemical and thermal treatments of electrodeposited Bi metal films. The flat band measurements and optical characterization suggested that the resulting heterojunction had type-II band alignment with a viable charge transfer from BiVO4 to ZnO NDs. In parallel, PL analysis revealed inhibition of the charge recombination rate by the electron transfer between BiVO4 and ZnO NDs. Upon AM 1.5 G illumination, BiVO4/ZnO NDs heterojunction yielded the highest photocurrent efficiency (0.15 mA·cm−2 at 1.2 V vs. NHE), which was attributed to its enhanced surface area (due to the presence of small dendrite branches), extended broadband light absorption extending from UV to visible light regions, and the most efficient interfacial charge transfer as proven by electrochemical impedance spectroscopy (EIS) studies. Besides, the incident photon-to-current conversion efficiency and applied bias photon-to-current efficiency tests confirmed an improved spectral photoresponse of the heterojunction based photoanode, particularly towards the visible light spectrum. The results outline a promising synthesis route for building heterojunctions between visible light active and wide band gap semiconductors for the use as a highly efficient photoanodes in a PEC cell.

Sensitization of TiO2 Nanotube Arrays by Mixed Oxovanadium(IV) Complex for Enhanced Photoelectrochemical Cells Performance

Sensitization of TiO2 Nanotube Arrays by Mixed Oxovanadium(IV) Complex for Enhanced Photoelectrochemical Cells Performance

Sludge reduction and hydrogen production in a microbial photoelectrochemical cell with a g-C3N4/CQDs/BiOBr composite photocathode

ABSTRACT Hydrogen (H2) remains a pivotal clean energy source, and the emergence of Solar-powered Microbial Photoelectrochemical Cells (MPECs) presents promising avenues for H2 production while concurrently aiding organic matter degradation. This study introduces an MPEC system employing a g-C3N4/CQDs/BiOBr photocathode and a bioanode, successfully achieving simultaneous H2 production and sludge reduction. The research highlights the effective formation of a Z-type heterojunction in the g-C3N4/CQDs/BiOBr photocathode, substantially enhancing the photocurrent response under light conditions. Operating at – 0.4 V versus RHE, it demonstrated a current density of – 3.25 mA·cm−2, surpassing that of g-C3N4/BiOBr (−2.25 mA·cm−2) by 1.4 times and g-C3N4 (−2.04 mA·cm−2) by 1.6 times. When subjected to visible light irradiation and a 0.8 V applied bias voltage, the MPEC system achieved a current density of 1.0 mA·cm−2. The cumulative H2 production of the MPEC system reached 8.9 mL, averaging a production rate of 0.13 mL·h−1. In the anode chamber, the degradation rates of total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS), proteins, polysaccharides, and volatile fatty acids (VFA) in the sludge were recorded at 57.18%, 82.64%, 64.98%, 86.39%, 42.81%, 67.34%, and 29.01%, respectively.

Advancing BiVO4 Photoanode Activity for Ethylene Glycol Oxidation via Strategic pH Control.

The photoelectrochemical (PEC) conversion of organic small molecules offers a dual benefit of synthesizing value-added chemicals and concurrently producing hydrogen (H2). Ethylene glycol, with its dual hydroxyl groups, stands out as a versatile organic substrate capable of yielding various C1 and C2 chemicals. In this study, we demonstrate that pH modulation markedly enhances the photocurrent of BiVO4 photoanodes, thus facilitating the efficient oxidation of ethylene glycol while simultaneously generating H2. Our findings reveal that in a pH = 1 ethylene glycol solution, the photocurrent density at 1.23 V vs. RHE can attain an impressive 7.1 mA cm-2, significantly surpassing the outputs in neutral and highly alkaline environments. The increase in photocurrent is attributed to the augmented adsorption of ethylene glycol on BiVO4 under acidic conditions, which in turn elevates the activity of the oxidation reaction, culminating in the maximal production of formic acid. This investigation sheds light on the pivotal role of electrolyte pH in the PEC oxidation process and underscores the potential of the PEC strategy for biomass valorization into value-added products alongside H2 fuel generation.

Selective Oxidation of Alcohol to Valuable Aldehydes Using Water as a Promoter in a Photoelectrochemical Cell.

Artificial photoelectrochemistry (PEC) has emerged as a promising and efficient technology for the sustainable conversion of solar energy into chemicals. In this study, we present a refined PEC process that enables the highly selective and stable production of piperonal and other valuable aldehydes through the oxidation of the corresponding alcohols. By employing Fe2O3 or TiO2 as the photoanode material and 2,2,6,6-tetramethylpiperidinooxy (TEMPO) as a redox mediator in an H2O/acetonitrile solution, we achieve 100% selectivity and a >95% Faradaic efficiency for piperonal production from piperonyl alcohol (PA) oxidation. Remarkably, we reveal the enhancing effect on the PA oxidation reactivity of appropriate-amount water in the solvent as it plays a crucial role in inhibiting the photoelectron-hole recombination efficiency and facilitating charge transfer. Mechanistic analysis suggests that TEMPO-mediated PA oxidation involves the formation of •O2- radicals by the reduction of oxygen on the cathode, resulting in water as the sole byproduct. Furthermore, our PEC oxidation system exhibits applications on the 100%-selective production of various conjugated aldehydes, including 4-anisaldehyde, cuminaldehyde, and the vitamin B6 derivative. By implementing a TiO2//Fe2O3 dual-photoanode system, we achieve an enhanced piperonal production rate of 31.2 μmol h-1 cm-2 at 1.0 V vs Ag/Ag+ and demonstrate its stability over a 102 h cyclic test, ensuring near-quantitative yield. This research illuminates the potential of the PEC strategy as a generally applicable method for the efficient production of high-value aldehydes.

SYNTHESIS OF STRUCTURED ZINC SELENIDE FOR OPTOELECTRONIC APPLICATIONS

In this paper, synthesis of Zinc Selenide (ZnSe) based photovoltaic materials deposited by electrode position method. The material lms have been characterized for their optical properties using UV-VIS spectrophotometer with wavelength range of 300 nm – 900 nm and electrical conductivity using photoelectrochemical (PEC) cell measurement. The conductivity type of the electrodeposited materials was investigated together with the tuning of the optical phenomena. The materials deposited were obtained by varying deposition time from 5 minutes to 15 minutes for ZnSe. It was observed that the optical properties of the materials increased with an increase in the time of deposition. The optical band gap of ZnSe was found to be in the range between 2.03 and 2.46 eV. The PEC signal results revealed ZnSe as an n-type material.

Photoelectrochemical properties of self-powered corundum-structured Ga2O3 nanorod array/fluorine-doped SnO2 photodetectors modulated by precursor concentrations

Herein, corundum-structured Ga2O3 (α-Ga2O3) nanorod array/fluorine-doped SnO2 (FTO) structures have been fabricated by hydrothermal and thermal annealing processes with different precursor concentrations from 0.01 to 0.06 M. The diameter and length of the nanorod arrays are much larger with increasing precursor concentrations due to more nucleation sites and precursor ions participating in the reaction procedures. The optical bandgap decreases from 4.75 to 4.47 eV because of the tensile stress relieving with increasing the precursor concentrations. Based on self-powered photoelectrochemical (PEC) photodetectors, the peak responsivity is improved from ∼0.33 mA W−1 for 0.06 M to ∼1.51 mA W−1 for 0.02 M. Schottky junctions can be formed in PEC cells. More photogenerated carriers can be produced in wider depletion region. From Mott–Schottky plots, the depletion regions become much wider with decreasing the precursor concentrations. Therefore, the enhance responsivity is owing to the wider depletion regions. Due to the reduced possibility of photogenerated holes captured by traps ascribed from fewer green and yellow luminescence defects, smaller charge transfer resistance, and shorter transportation route, the decay time becomes much faster through decreasing the precursor concentrations. Compared with the other self-powered α-Ga2O3-nanorod-array-based PEC photodetectors, it shows the fastest response time (decay time of 0.005 s/0.026 s) simply modulated by precursor concentrations for the first time without employing complex precursors, seed layers or special device designs. Compared with other high-responsivity monoclinic Ga2O3 (β-Ga2O3) self-powered photodetectors, our devices also show comparable response speed with simple control and design. This work provides the realization of fast-speed self-powered Ga2O3 based solar-blind ultraviolet photodetectors by simple modulation processes and design, which is a significant guidance for their applications in warnings, imaging, computing, communication and logic circuit, in the future.

Remarkably enhanced acidic photoelectrochemical glycerol oxidation achieving the theoretical maximum photocurrent of BiVO4 through anion modulation

Converting biomass waste into valuable chemicals, while concurrently producing H2 via photoelectrochemical (PEC) water splitting, offers a compelling solution to energy and environmental issues, with a substantial challenge to boost the output of these high-value chemicals and H2. Herein, we report an anion modulation strategy to significantly increase the photocurrent of BiVO4 photoanodes, enabling the efficient oxidation of glycerol, alongside the hydrogen production. We find that NO3−, with its lesser affinity for BiVO4 compared to SO42−, allows for the exposure of more active bismuth sites for the oxidation of glycerol, while accelerating the reaction kinetics. The BiVO4 photoanode, in the HNO3 electrolyte, attains an unprecedented photocurrent density of 7.52 mA cm−2 at 1.23 VRHE, surpassing existing records for PEC glycerol oxidation and maintaining stability for over 10 h. The versatility of the anion modulation approach can be extended to a wide array of alcohols, promoting the upcycling of bio-waste into valuable chemical products and fuels like H2.

Introducing Platinum Nanoparticles on Inorganic/Organic Nanoheterostructures for Enhancing their Efficiency toward the Photoelectrochemical Urea Oxidation Reaction

Introducing Platinum Nanoparticles on Inorganic/Organic Nanoheterostructures for Enhancing their Efficiency toward the Photoelectrochemical Urea Oxidation Reaction

Experimental investigation of a new photoelectrochemical cell design featuring a unique photocathode configuration for solar hydrogen production

The electrodeposition process and the subsequent assessment of a novel cuprous oxide photocathode are conducted for solar light-based hydrogen production. The mesh dome photocathode helps facilitate the optimal light harvesting, enabling the efficient collection of the maximum accessible light from the solar simulator. This particular design also ensures that light reaches the remote surfaces of the photocathode through penetrating the mesh structure. The electrodeposition method is then employed to coat cuprous oxide onto the stainless-steel electrode. The subsequent examination of this photocathode occurs within an alkaline solution of potassium dioxide to assess its performance in hydrogen production. The study investigates the impact of the new design of the mesh photocathode on hydrogen generation rates, as well as related efficiencies of energy and exergy, under varying light angles during daylight hours. The present experimental findings reveal that the maximum rates of hydrogen production, achieved at a 45° tilt light and 0.25 M KOH, are 15.38 μg/s and it is 15.83 μg/s for vertical light positions. Furthermore, the highest recorded system exergy and energy efficiencies under vertical light conditions are 2.19% and 3.20%, respectively, compared to 2.14% and 3.12% at applying tilted light. The new photocathode design contributes to a notable 80.3% improvement in hydrogen generation rate at tilted light angles in comparison to vertical light conditions.

Development of Bio-Photoelectrochemical Hybrids for Solar Energy Conversion

Recent advancements in solar energy conversion have identified bio-photoelectrochemical hybrids as one of the most promising sustainable techniques. This study integrates BiVO4 and TiO2 semiconductors with photoautotrophic microorganisms (e.g., Algae) to enhance solar energy conversion. Thin films of these materials were prepared and characterized, revealing a relatively smooth surface for BiVO4 while structures for TiO2 thin films deposited as nanorods. Optical properties showed band gaps of ≤ 3.1 and 2.4 eV for TiO2 and BiVO4, respectively. The point of zero charge of materials was investigated, indicating that naturally occurring biofilm formation might not be favorable for as-prepared materials. To overcome this challenge, we aimed to use polyelectrolytes to enhance attachment of cells on the surface of semiconductor and in this regards we determined the biocompatibility of using this approach. Photoelectrochemical (PEC) measurements were conducted to evaluate solar energy conversion efficiency. This study offers insights into optimizing biosystem attachment, biofilm stability, and PEC performance of coupled semiconductors with photoautotrophic microorganisms as one photoelectrode in PEC cell, advancing sustainable solar energy conversion technologies.

Optical Control of Directional Exciton Migration in Porphyrin‐Based Metal−Organic Frameworks

AbstractPorphyrin‐based metal‐organic frameworks (MOFs) have received great attention for solar photochemistry applications. Manipulating the direction of energy (exciton) migration plays an essential role in boosting the light‐harvesting efficiency of porphyrin‐based MOFs. Here, based on the time‐dependent exciton‐exciton annihilation rate, an optical control of directional exciton migration is demonstrated in cobalt‐porphyrin surface‐supported MOF nanofilms (Co‐TCPP SURMOFs). Utilizing photocarrier densities or lattice temperature as the control knob, the dynamic form of exciton migration in Co‐TCPP SURMOFs can be switched between the nearest‐neighbor 1D interaction and the quasi‐isotropic 2D interaction, which is well explained using a diffusion model of exciton‐exciton scattering. This results provide an optical approach to regulating exciton migration in MOFs, which enhances understanding of the excitonic behavior in artificial light harvesters.

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.

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.