Photoelectrochemical Water Splitting Process Research Articles

Enhancing solar-driven hydrogen production through photoelectrochemical methods via dual transition metal doping of titanium oxide to form an impurity energy band

Developing a photoanode that is stable, efficient, and cost-effective for photoelectrochemical water splitting poses a significant challenge. To address this, we have successfully synthesized cobalt and chromium-doped Titanium dioxide (CoCrTiO2) using the hydrothermal method. This innovative approach results in an efficient, stable, and economical material. The introduction of Co and Cr through doping creates an intermediate band energy within TiO2, thereby enhancing charge separation and movement. The performance of CoCrTiO2 in the photoelectrochemical water splitting process is noteworthy. At 0 V vs Ag/AgCl, CoCrTiO2 exhibits a photocurrent density of 3.45 mAcm−2, representing an impressive 8.5 times increase compared to bare TiO2. Furthermore, when employed as a photoanode, CoCrTiO2 demonstrates a significant increase in hydrogen production. The amount of hydrogen generated is measured at 67.8 μmolecm−2, surpassing bare TiO2 by a factor of 5.6. Analysis data strongly supports CoCrTiO2 as an excellent candidate for advancing the field of photoelectrochemical water splitting due to its exceptional performance characteristics.

Enhanced PEC generation of hydrogen from seawater driven by efficient and stable Ti-Fe2O3 photoanode

Incorporation of Ti4+ ions into the hematite (α-Fe2O3) photoanodes has garnered significant consideration for the photoelectrochemical water splitting process since it improves the charge transport and optical properties of pristine hematite material. Herein, we have approached a facile route to fabricate the thin films of Ti-Fe2O3 by spray pyrolysis treatment. The Ti-Fe2O3 photocurrent density delivers 1.34 mA/cm2 at 1.23 V RHE in an alkaline seawater environment, showing its excellent performance for photoelectrochemical water- splitting applications. Moreover, it offers outstanding stability in seawater (0.5 M NaCl + 1 M KOH) at applied 1.23 V for 20 h and produces 21.79 µmol/cm2.h of hydrogen. Hence, it will hold a tremendously promising electrode within this area for efficient solar hydrogen generation.

Boosting photoelectrochemical performance through appling magnetic field in manganese-doped cobalt ferrite photoanodes

An efficient photoelectrochemical water-splitting process is of paramount importance as it provides a sustainable and clean method for generating hydrogen fuel, which is crucial for addressing the world’s growing energy needs while mitigating environmental concerns. Herein, the effects of applying a magnetic field on the photoelectrochemical performance of photoanodes composed of Cobalt ferrite (CoFe2O4) and Manganese (Mn)-doped CoFe2O4 are investigated. The CoMnxFe2-xO4 nanoparticles were synthesized using a sol–gel method, with varying values of x (0.0, 0.1, 0.3, and 0.5). X-ray diffraction analysis consistently reveals a singular cubic spinel structure for all four samples. Magnetic analyses demonstrate an enhancement in magnetic characteristics, including saturation magnetization, coercivity, and anisotropy field in the CoMn0.3Fe1.7O4 sample compared to the other three samples. Photoelectrochemical (PEC) measurements indicate that the photocurrent increases in all four samples when a static magnetic field is applied. However, the CoMn0.3Fe1.7O4 sample shows a more pronounced enhancement. Specifically, the dark current density increases by more than 115 % when a magnetic field of 190 ± 20 mT is applied. Additionally, it rises by 387 % under light illumination with the magnetic field. This enhancement in PEC performance is attributed to electron spin polarization adjusted through the external magnetic field.

Unbiased overall photoelectrocatalytic water-splitting over micropyramid Si/In2O3/CuO/ZnO photocathode and Ni/BiVO4 photoanode under simulated solar-light illumination

Micropyramid Si/In2O3/CuO/ZnO photocathode and Ni/BiVO4 photoanode have been synthesized using a magnetron sputtering method with different conditions and characterized for a photoelectrochemical water-splitting process. The as-designed heterojunction of Si/In2O3/CuO/ZnO photocathode successfully induces a facile electron transfer to generate hydrogen in 0.5 M H2SO4. Similarly, Ni/BiVO4 photoanode evolves oxygen in 0.1 M Na2B4O7. Both photoreactions are done under concentrated solar-light irradiation (AM 1.5G, 500 mA/cm2). The analysis shows that IPCE values of photocathode and photoanode reached 40 and 60 % at 300 and 400 nm wavelengths, respectively. Furthermore, the ABPE of photocathode and photoanode achieved 14.9% and 0.8% at 0.21 and 1.15 VRHE, respectively. Photoelectrochemical analysis indicates that half cells of the photocathode and photoanode can reach photocurrents of ∼120 and ∼20 mA/cm2 at 0 and 1.23 VRHE, respectively. The outstanding performances indicate a facile charge transfer during redox reactions at the photocathode and photoanode. In addition, combining the photoelectrodes to form a cell configuration of Si/In2O3/CuO/ZnO//Ni/BiVO4 with a proton exchange membrane generates an unbiased photocurrent of 0.26 mA/cm2 at 0.55 VRHE. The combined cell has been tested for its stability in splitting water molecules into hydrogen and oxygen, indicating a promising result to overcome energy and environmental issues.

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.

Hematite Hollow-Sphere-Array Photoanodes for Efficient Photoelectrochemical Water Splitting.

Constructing 3D nanophotonic structures is regarded as an effective method to realize efficient solar-to-hydrogen conversion. These photonic structures can enhance the absorbance of photoelectrodes by the light trapping effect, promote the charge separation by designable charge transport pathway and provide a high specific surface area for catalytic reaction. However, most 3D structures reported so far mainly focused on the influence of light absorption and lacked a systematic investigation of the overall water splitting process. Herein, hematite hollow-sphere-array photoanodes are fabricated through a facile hydrothermal method with polystyrene templates. Validating by simulations and experiments, the hollow sphere array is proved to enhance the efficiency of light harvesting, charge separation and surface reaction at the same time. With an additional annealing treatment in oxygen, a photocurrent density of 2.26mA cm-2 at 1.23V versus reversible hydrogen electrode can be obtained, which is 3.70 times larger than that with a planar structure in otherwise the same system. This work gains an insight into the photoelectrochemical water splitting process, which is valuable for the further design of advancing solar driven water splitting devices.

Fe- and S-Modified BiOI as Catalysts to Oxygen Evolution and Hydrogen Evolution Reactions in Overall Photoelectrochemical Water Splitting.

Developing catalysts with superior activity to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is equally important to the overall photoelectrochemical water splitting to produce hydrogen. In this work, bismuth oxyiodide (BiOI), iron-modified bismuth iodide Fe/BiOI, and the sulfurized S-Fe/BiOI were prepared using the solvothermal method. The three materials all have good absorption ability for visible light. The photoelectrochemical catalytic activity of BiOI to oxygen evolution reaction (OER) is significantly enhanced after iron modification, while the sulfurized product S-Fe/BiOI exhibits better catalytic activity to hydrogen evolution reaction (HER). Hence, OER and HER can be simultaneously catalyzed by using Fe/BiOI and S-Fe/BiOI as anodic and cathodic catalysts to facilitate the overall photoelectrochemical water splitting process.

A review on the photosensitizers used for enhancing the photoelectrochemical performance of hydrogen production with emphasis on a novel toxicity assessment framework

The significance of hydrogen fuel and its green production is one of the challenges of recent research. This study focuses on photosensitizers, which is the main component of the photoelectrode in the photoelectrochemical water splitting process as a method to produce hydrogen from a solar source. This review article collects, classifies and reviews all the sensitizers used in recent years. Accordingly, photosensitizers include dyes, quantum dots, metal-organic frameworks, conducting polymers, and chalcogenides, which increase optical current density and visible light absorption. Finally, based on the presented framework for evaluating the toxicity of hydrogen production based on the periodic table and RDI, the toxicity of the sensitizers was evaluated.

Development and evaluation of a solar based integrated hydrogen energy system for mobile applications

Sustainable and nature-friendly energy systems are critical in playing a key role in meeting the needs for better energy security and reduced environmental impacts which appear among the primary concerns of today’s modern society in the 21st century. The present study, in this regard, undertakes the development and thermodynamic investigation of a unique solar energy-based multigenerational energy system for modular and transportable applications. Electricity, heat, hot water, hydrogen and clean water are the useful commodities generated by this uniquely integrated energy system. This system employs a photoelectrochemical reactor stack for wastewater treatment and hydrogen production. The hydrogen generated from the photoelectrochemical water splitting process is employed within a proton exchange membrane fuel cell providing electricity and heat for hot water. The system’s energetic and exergetic efficiencies under different operational conditions are investigated and comparatively evaluated. The key effects of varying prime operational conditions and state properties on the system performance and hence the efficiency, as considered in the system analysis, are parametrically investigated, and the obtained results are comprehensively discussed along with explanations about the main drivers. The integrated system provides 1.026 kW electrical power along with, 2.1 kW space heating, 0.6 kW heat for hot water, and hydrogen and clean water production rates of 22.97 mg/s and 9.79 g/s, respectively. An overall energy efficiency of 16.79 % and an overall exergy efficiency of 17.31 % are obtained and discussed. The presently developed system is capable of operating as a self-standing system in an off-grid manner. Furthermore, the number of PEC reactors required to sustain the system needs to be maintained, which can be achieved by potential improvement in PEC water splitting process.

Ligand‐Engineered Quantum Dots Decorated Heterojunction Photoelectrodes for Self‐Biased Solar Water Splitting

A cost-effective and high-efficiency photoelectrochemical (PEC) water splitting system based on colloidal quantum dots (QDs) represents a potential solar-to-hydrogen (STH) conversion technology to achieve future carbon neutrality. Herein, a self-biased PEC cell consisting of BiVO4 photoanode and Cu2 O photocathode both decorated with Zn-doped CuInS2 (ZCIS) QDs is successfully fabricated. The intrinsic charge dynamics of the photoelectrodes are efficiently optimized via rational engineering of the surface ligands capped on QDs with controllable chain lengths and binding affinities to the metal oxide electrodes. It is demonstrated that the short-chain monodentate 1-dodecanethiol ligands are beneficial to ZCIS QDs for suppressing charge recombination, which enables the construction of tight heterojunction with coupled metal oxide electrodes, leading to effective photo-induced charge transfer/injection for enhanced PEC performance. The QD decorated BiVO4 and Cu2 O photoelectrodes in pairs demonstrate a self-biased PEC water splitting process, delivering an STH efficiency of 0.65% with excellent stability under AM 1.5 G one-sun illumination. The results highlight the significance of synergistic ligand and heterojunction engineering to build highly efficient and robust QDs-based PEC devices for self-biased solar water splitting.

TiO2 nanoparticles modified with ZnIn2S4 nanosheets and Co-Pi groups: Type II heterojunction and cocatalysts coexisted photoanode for efficient photoelectrochemical water splitting

The optimization of photoelectrode is the key issue for the efficient photoelectrochemical water splitting process. In this work, the TiO2 photoanode is synthesized and modified with ZnIn2S4 nanosheets and Co-Pi cocatalyst (TiO2/ZnIn2S4/Co-Pi) for a favorable photoelectrochemical performance. The synthesis and modification process of the TiO2 photoanode are optimized. The physical and chemical characterizations indicate that the TiO2 has a nano-cauliflower-like structure and rutile crystal form modified with a network hexagonal ZnIn2S4 nanosheets and amorphous Co-Pi groups. After optimization of the hydrothermal and annealing process, the optimized TiO2 photoanode manifests a photocurrent density of 1.82 mA cm−2, 1.73-fold of the pristine TiO2 photoanode (1.05 mA cm−2). With the surficial ZnIn2S4 and Co-Pi modification, the photocurrent density of the TiO2/ZnIn2S4/Co-Pi photoanode is raised to 5.05 mA cm−2, 5.32-fold of the optimized TiO2 photoanode (1.82 mA cm−2). The applied bias photon-to-current efficiency, the charge separation and injection efficiencies of the TiO2/ZnIn2S4/Co-Pi photoanodes are 8.79, 3.40, and 1.64-folds of the optimized TiO2 photoanode. Combined the Tauc plot, valence band XPS spectra, EIS and Mott-Schottky analysis, the PEC water splitting mechanism could be that: (i) the type II heterojunction formed by the TiO2 and ZnIn2S4 semiconductors improves the charge separation/injection efficiencies; (ii) the Co-Pi groups facilitate the oxygen evolution kinetics; (iii) the Co-Pi groups and 2D ZnIn2S4 nanosheets synergistically enhance the charge separation efficiency. This investigation could offer a prospect of practical implementation for photoelectrochemical water splitting.

Direct Observation of Surface Hole Accumulation Under Water Oxidation Conditions By Efish and Impedance Measurements

Water oxidation reaction is considered the bottleneck and rate-determining step in photoelectrochemical water-splitting process. To achieve efficient water oxidation on photoanode, sufficient built-in potential on semiconductors should be maintained. Herein, we introduced in-situ Electric Field Induced Second Harmonic Generation (EFISH) technique to probe the change of built-in potential under water oxidation reaction process of a single-crystal rutile TiO2 photoanode. The band flattening effect caused by the reduction of built-in potential on photoanode was investigated by EFISH. Up to 600 mV built-in potential screening on TiO2 was observed at 1 V vs Ag/AgCl applied bias under 15mW/cm2 on TiO2 photoanode, in accordance with the anodic shift of flat-band potential. This phenomenon can be explained by the contribution of hole accumulation at surface states and local pH variation in an insufficiently buffered electrolytes, indicating that surface OH· is the rate determining step in water oxidation process. Built-in potential under excitation can be well maintained in a sufficiently buffered electrolytes, suggesting a different rate determining step in water oxidation process.

Rational modulation for electron migration in CdS/Au/TiO2 photoanode for efficient photoelectrochemical water oxidation

Hydrogen production from photoelectrochemical water splitting process to convert solar energy to chemical energy has aroused plenty of attention owing to its carbon-free procedure and economic sustainability. The oxide semiconductors such as nanorods (TNRs) have widely been used as photoanodes materials because of its high stability against photocorrosion, and long minority diffusion length. We design and fabricate a ternary CdS/Au/TNRs photoanode, which exhibits high photocurrent density of 2.78 mA/cm2 at 1.23 V vs RHE and of a further negatively shifted onset potential at −145 mV. The influence of CdS and Au on PEC performance of CdS/Au/TNRs heterojuntion has been systematically studied. We demonstrate that the CdS and Au can effectively enhance the charge separation and improve the conductivity for carrier transport. This work would pave the way towards design heterojunction functional material.

CoP imbedded g-C3N4 heterojunctions for highly efficient photo, electro and photoelectrochemical water splitting

Nanorod-like CoP nanoparticles were fabricated from different precursors of Co(OH)2 and Co3O4 by gas-solid reaction, then further embedded into g-C3N4 nanosheets to form intimate heterojunctions via the (011) crystal planes of CoP nanoparticles. The heterojunction hybrid obtained from Co(OH)2 exhibits superior activity in photo, electro and photoelectrochemical water splitting processes. In photocatalytic water half-splitting for hydrogen evolution reaction, the as-obtained 0.5% CoP-CN achieved a rate at 959.4 μmol·h−1·g−1 and 59.1 μmol·h−1·g−1 when irradiated by simulated sunlight and visible light respectively, almost 3.1 times and 15.8 times that of pristine g-C3N4, For photocatalytic water full-splitting, a stoichiometric evolution of H2 (14.7 μmol·h−1·g−1) and O2 (7.6 μmol·h−1·g−1) was observed on 3%Pt-0.5% CoP-CN composite. The onset potential for electrochemical HER process was drastically reduced after deposition with 0.5% CoP. Meanwhile, a higher photocurrent response and larger anodic photocurrent was detected over 0.5% CoP-CN photoanode during the photoelectrochemical water splitting process, relative to pristine g-C3N4 and its analogues. The comprehensive enhancements for catalytic activity of 0.5% CoP-CN could be attributed to its reduced over-potentials, more negative photo-reductive potentials, boosted interfacial charge transfer efficiency, as well as a much higher solar to hydrogen efficiency. The contrastive redox roles of CoP in both photocatalytic water half-splitting and full-splitting processes have been fully explored and revealed. This design on covalent organic framework of highly efficient CoP-based heterojunctions holds great promise for direct water splitting applications in utilizing solar energy.

Near Infrared Light-Driven Photoelectrocatalytic Water Splitting over P-Doped g-C3N4

Because infrared (IR) light accounts for almost 50% of solar light, exploring IR-response materials for the photoelectrochemical water-splitting process is of great interest. In this work, phosphor...

Theoretical analysis of an intermediate band in Sn-doped hematite with wide-spectrum solar response

Hematite α-Fe2O3 is exposed to be an efficient photocatalytic material for the photoelectrochemical water splitting process under visible light. In the present work, we have improved the photocatalytic activity of hematite by varying tin concentration substituted for Fe in pristine hematite. To investigate the influence of the contents of Sn on the photocatalytic activity, various key properties like electronic structure and optoelectronic properties were studied based on density functional theory using generalized gradient approximation plus on-site Hubbard interaction within the WIEN2k computer program. The results of the electronic band structure show the insulating character of the pristine hematite exhibits a bandgap of 2.17 eV equals to Exp. one. The electronic structure calculations of the Sn-doped hematite explore the engineering of the orbitals around the Fermi level and result in a reduction in the bandgap, which is attributed to the corresponding Sn contents. The doping of Sn in Fe2O3 would introduce sub-bands (intermediate band) in between the valence band maximum (VBM) and Fermi level EF, and more interestingly, half-filled intermediate bands appear around the Fermi level with the increase of Sn contents. To see the effect of intermediate bands on the optoelectronic features of the Sn-doped hematite, we also calculated the optical properties of pristine and doped hematite, which predict extra peaks assigned to transitions of electrons from intermediate bands in the infrared region. Our findings explore that the presence of intermediate bands facilitates the PEC activity of water splitting of Fe2O3, shifting from visible light to infrared region. Here, we demonstrate the idea of intermediate bands in hematite for distinctive device applications.

Engineering of a high-efficiency water splitting photoanode by synergistic effects of doping, compositing, and coupling on TiO2 nanoparticles

Highly efficient photoelectrochemical (PEC) water splitting is achieved by Ag doped hierarchical porous TiO2 nanoparticles in compositing with GQDs (TiO2:Ag-GQDs). The unique optical properties of VO2 (m), monoclinic phase of VO2, is a motivation to use it in PEC processes. To further improve the efficiency of TiO2:Ag-GQDs photoanode, it is coupled with undoped and doped VO2 (m) with earth alkali metals. This coupling strategy is used to engineer the interfacial and optical properties and charge separation/transport on the photoanodes for PEC water splitting. Hence, the efficiency of the photoanodes with structures of TiO2:Ag-GQDs/VO2 or (Mg, Ca, Sr, or Ba)-doped VO2 in PEC water splitting process is investigated. A remarkable photocurrent density of 1.5 mA/cm2 at 1.23 V vs. RHE is achieved for FLGs/TiO2:Ag-GQDs/VO2:Ba photoanode. This value is 20 times higher than that of reported previously for pristine TiO2 photoanode (0.07 mA/cm2 at 1.23 V vs RHE).

Effect of citric acid on the synthesis of ZnWO4/ZnO nanorods for photoelectrochemical water splitting

ZnO nanorods (NRs) and ZnWO4/ZnO heterostructure, using TiO2 seed layers, were synthesized by two steps hydrothermal method and annealed at 450 °C for 2 hr. The results showed that the ZnWO4 was grown on the hexagonal ZnO NRs and change to hierarchically structure when the citric acid content was increased. All samples were applied as photoanode for photoelectrochemical (PEC) water splitting cell. As the result, the 50ZnW/ZnO sample showed the best performance of the PEC water splitting process than others. From the Electrochemical Impedance Spectroscopy (EIS) study, the Nyquist plot of 25ZnW/ZnO and 50ZnW/ZnO samples showed smaller arc compared to ZnO NRs. This is signified that the ZnWO4/ZnO heterostructure has greater charge transfer between the photoanode and electrolyte than the pristine ZnO. Hence, the modified ZnWO4 on the ZnO surface enhances the performance of ZnO NRs based PEC water splitting cell for the UV light hydrogen fuel generation.

Enhanced solar-driven water splitting of 1D core-shell Si/TiO2/ZnO nanopillars

In this work, 1D core-shell Si/metal oxide nanopillar (NP) photoanodes were synthesized for enhanced solar-driven water splitting processes. The core-shell structures were fabricated by atomic layer deposition of different metal oxides (TiO2 and ZnO) onto Si NP, which were synthesized by metal-assisted chemical etching and nanosphere lithography. In order to characterize produced photoanodes various experimental techniques (SEM/TEM, XRD, Transmittance, Reflectance, Raman spectroscopy) were applied. Photoelectrochemical (PEC) water oxidation of produced photoanodes was studied. It was shown that composition of n-Si/TiO2/ZnO NP exhibited enhanced photocurrents due to barrier effects. The enhanced PEC properties of core-shell Si/TiO2/ZnO NP are caused by efficient charge separation of photogenerated electron-hole pairs in the TiO2/ZnO shell and effective holes transfer to the shell-electrolyte interface. The superior photoelectrochemical performance of a photoanode based on core-shell Si/TiO2/ZnO NP has been confirmed through electrochemical impedance spectroscopy and voltamperometric measurements under electrode irradiation. 1D core-shell Si/TiO2/ZnO NP offer a new approach for preparing stable and highly efficient photoanodes for PEC water-splitting process.

Simultaneously efficient light absorption and charge transport of CdS/TiO2 nanotube array toward improved photoelectrochemical performance

CdS has been widely used to modify TiO2-based photoanodes for photoelectrochemical (PEC) water splitting. Due to the poor interface contact between chalcogenides and oxides, however, such CdS modified TiO2 materials usually exhibit inefficient separation and transport of charges, leading to an unsatisfactory efficiency during the PEC water splitting process. Addressing this issue, we herein report a CdS/TiO2 nanotube array (CdS/TNA) photoanode that was fabricated through a successive ion layer absorption and reaction (SILAR) method with an additional subsequent annealing. This post-annealing process is essential to enhance the interface contact between the CdS and the TNAs, resulting in an accelerated transfer of photogenerated electrons from the CdS to the TNAs. In addition, the post-annealing also improves the light absorption capability of the CdS/TNA photoanode. The simultaneous enhancement of charge transport and light absorption provided by the post-annealing is essential for improving the PEC performance of the CdS/TNA photoanode. The CdS/TNA photoanode obtained by this strategy exhibits a much enhanced PEC performance in water splitting, and its photocurrent density and solar-to-hydrogen conversion efficiency could reach 4.56 mA cm−2 at 1.23 V vs. reversible hydrogen electrode and 5.61%, respectively. This simple but effective route can provide a general strategy for obtaining high-performance oxide-based photoelectrodes.