Short Hole Diffusion Length Research Articles

Fe2O3 Nanoflakes - WS2 Nanosheets Heterojunctions for Multi-Fold Enhancement in Photoelectrochemical Solar Energy Conversion.

Fe2O3-based photoanodes show great potential in photoelectrochemical water splitting due to their excellent stability, moderate band gap, and abundance. However, a short hole diffusion length limits its photocurrent density. Here, a multi-fold enhancement in photocurrent density from Fe2O3 nanoflakes - WS2 nanosheets heterojunction is reported. The heterojunction exhibits a synergistic photocurrent density of 0.52mA cm-2 at 1.3V (versus RHE) under AM 1.5G simulated sunlight, which is 2.23 times higher than pristine Fe2O3 nanoflakes. The Mott-Schottky and Nyquist plots indicate a higher charge density with lower charge transfer resistance at the semiconductor-electrolyte junction. The density functional theory (DFT) -based first-principles calculations are performed by designing a heterostructure between Fe2O3(110) and WS2(001) similar to the experimentally found arrangement of crystal planes. Free energy analysis and relative band extrema positions, obtained from DFT calculations and valence band spectroscopy, indicate the formation of type II heterojunction with partial oxygen terminated surface of Fe2O3. The type-II band alignment with a charge transfer of 4.8 × 10-4 e per interfacial WS2 to Fe2O3, helps in easy separation of photogenerated charges. The work establishes both an experimental design and a theoretical framework of highly crystalline nanoflakes-nanosheet heterojunctions for efficient photoelectrochemical solar energy conversion.

Synthesis, characterization and photoelectrochemical performance of Bi2Fe4O9 thin films

Mullite-type Bi2Fe4O9 has been little explored in thin film form as a photoanode for photoelectrochemical water splitting. In this study, Bi2Fe4O9 thin films have been prepared using the sol-gel technique from a simple precursor solution based on the corresponding metal salts, acetic acid, and polyvinyl alcohol. The films were deposited by dip-coating onto fluorine-doped tin oxide substrates and dried at 350 °C, repeating the dipping-drying cycle six times, and finally sintered at 600 °C. The films were characterized by GIXRD, revealing the formation of the material in its orthorhombic phase. Raman spectroscopy showed the Ag and B1g vibrational modes, validating the formation of the bismuth iron oxide. UV–Vis transmittance measurements revealed that the material exhibits two optical transitions: a direct band gap of 2.86 eV and an indirect band gap of 1.98 eV. FESEM micrographs and AFM images showed a uniform nanostructured surface morphology. The photoelectrochemical properties of the Bi2Fe4O9 films were studied using cyclic voltammetry and chronoamperometry with front side illumination, demonstrating the stability of the material in aqueous media and the generation of photocurrent in the presence of H2O2. Furthermore, results from intensity-modulated photocurrent spectroscopy (IMPS) revealed that the photocurrent is limited by both bulk and surface recombination and a short hole diffusion length.

BiVO4 Photoanode with NiV2O6 Back Contact Interfacial Layer for Improved Hole-Diffusion Length and Photoelectrochemical Water Oxidation Activity.

The short hole diffusion length (HDL) and high interfacial recombination are among the main drawbacks of semiconductor-based solar energy systems. Surface passivation and introducing an interfacial layer are recognized for enhancing HDL and charge carrier separation. Herein, we introduced a facile recipe to design a pinholes-free BiVO4 photoanode with a NiV2O6 back contact interfacial (BCI) layer, marking a significant advancement in the HDL and photoelectrochemical activity. The fabricated BiVO4 photoanode with NiV2O6 BCI layer exhibits a 2-fold increase in the HDL compared to pristine BiVO4. Despite this improvement, we found that the front surface recombination still hinders the water oxidation process, as revealed by photoelectrochemical (PEC) studies employing Na2SO3 electron donors and by intensity-modulated photocurrent spectroscopy measurements. To address this limitation, the surface of the NiV2O6/BiVO4 photoanode was passivated with a cobalt phosphate electrocatalyst, resulting in a dramatic enhancement in the PEC performance. The optimized photoanode achieved a stable photocurrent density of 4.8 mA cm-2 at 1.23 VRHE, which is 12-fold higher than that of the pristine BiVO4 photoanode. Density Functional Theory (DFT) simulations revealed an abrupt electrostatic potential transition at the NiV2O6/BiVO4 interface with BiVO4 being more negative than NiV2O6. A strong built-in electric field is thus generated at the interface and drifts photogenerated electrons toward the NiV2O6 BCI layer and photogenerated holes toward the BiVO4 top layer. As a result, the back-surface recombination is minimized, and ultimately, the HDL is extended in agreement with the experimental findings.

Combined effects of annealing treatment and compounding with FeOOH cocatalyst on efficiency and stability of BiVO4/Ag3PO4 photoanode

Bismuth vanadate (BiVO4) is a promising metal oxide photoabsorber for photoanode applications but is limited by its relatively short hole diffusion length resulting in severe charge complexation and limited performance. Herein, Ag3PO4 was compounded on BiVO4 through photodeposition of Ag followed by solution oxidation. The annealing of the composite BiVO4/Ag3PO4 heterojunction at 400 °C precipitated some Ag from Ag3PO4 on BiVO4/Ag3PO4 to form a new ternary photoanode BiVO4/Ag3PO4/Ag. Compared to the unannealed sample, the light trapping and crystal quality enhanced, resulting in increased photocurrent density of the annealed BiVO4/Ag3PO4 photoanode (4.46 mA cm−2) by 59.9 % when compared to the unannealed photoanode (2.79 mA cm−2). To further optimize the photoanode, co-catalyst iron hydroxyl oxide (FeOOH) was deposited to yield BiVO4/Ag3PO4/Ag/FeOOH photoanode with maximum photocurrent density of 4.71 mA cm−2 at 1.23 V (vs. reversible hydrogen electrode, VRHE), equivalent to about 3.7-fold the value of BiVO4 photoanode. The photoanode maintained 90.8 % of its initial current density after 3 h stability tests. Besides, the photoelectrocatalytic degradation of Rhodamine B pollutant by BiVO4/Ag3PO4/Ag and BiVO4/Ag3PO4/Ag/FeOOH photoanode showed performance enhancement when compared to BiVO4/Ag3PO4. Overall, the proposed strategy looks very promising for the rational fabrication of high-efficiency heterojunction photoanodes.

Decoupled Crystallization and Particle Growth of BiVO4 via Rapid Thermal Process for Enhanced Charge Separation

AbstractBiVO4 is one of the most promising candidates for photoelectrochemical water oxidation. However, the poor crystallinity and short hole diffusion length limit its charge separation. One bottleneck stems from the contradiction between high crystallinity and small particles via conventional furnace heating processes. This paper describes the design and fabrication of BiVO4 photoanodes via rapid thermal process (RTP), rather than furnace heating, to decouple the constraints between nucleation, crystallization, and growth processes of BiVO4. The higher heating ramp rate of RTP compared with furnace heating promotes the fast diffusion of reactant molecules, which elevates the nucleation rate above the particle growth rate of BiVO4, leading to small particles with high crystallinity. Moreover, the ultra‐high heating temperature makes it possible to crystallize the small BiVO4 particle within a short time. Thus, a high crystallinity can be obtained for the RTP‐treated BiVO4 while maintaining small particle size, achieving a charge separation efficiency of up to 82%, 30% higher than that of furnace‐treated BiVO4 photoanode.

Hematite (α-Fe2O3) with Oxygen Defects: The Effect of Heating Rate for Photocatalytic Performance.

Hematite (α-Fe2O3) emerges as an enticing material for visible-light-driven photocatalysis owing to its remarkable stability, low toxicity, and abundance. However, its inherent shortcomings, such as a short hole diffusion length and high recombination rate, hinder its practical application. Recently, oxygen vacancies (Vo) within hematite have been demonstrated to modulate its photocatalytic attributes. The effects of Vo can be broadly categorized into two opposing aspects: (1) acting as electron donors, enhancing carrier conductivity, and improving photocatalytic performance and (2) acting as surface carrier traps, accelerating excited carrier recombination, and deteriorating performance. Critically, the generation rate, distribution, role, and behavior of Vo significantly differ for synthesis methods due to differences in formation mechanisms and oxygen diffusion. This complexity hampers simplified discussions of Vo, necessitating careful investigation and nuanced discussion tailored to the specific method and conditions employed. Among various approaches, hydrothermal synthesis offers a simple and cost-effective route. Here, we demonstrate a hydrothermal synthesis method for Vo introduction to hematite using a carbon source, where variations in the heating rate have not been previously explored in terms of their influence on Vo generation. The analyses revealed that the concentration of Vo was maximized at a heating rate of 16 °C/min, indicative of a high density of surface defects. With regard to photocatalytic performance, elevated heating rates (16 °C/min) fostered the formation of Vo primarily on the hematite surface. The photocatalytic activity was 7.1 times greater than that of the sample prepared at a low heating rate (2 °C/min). These findings highlight the crucial role of surface defects, as opposed to bulk defects, in promoting hematite photocatalysis. Furthermore, the facile control over Vo concentration achievable via manipulating the heating rate underscores the promising potential of this approach for optimizing hematite photocatalysts.

Integration of surficial oxygen vacancies and interfacial two-dimensional NiFe-layered double hydroxide nanosheets onto bismuth vanadate photoanode for boosted photoelectrochemical water splitting

Considering its outstanding cost-to-efficiency ratio, N-type bismuth vanadate (BiVO4) is an ideal photoanode for photoelectrochemical (PEC) water splitting. Nevertheless, the widespread application of BiVO4 is being hindered commercially by innate challenges such as its poor carrier mobility, short hole diffusion length, and sluggish oxidation chemistry. Herein, we report the unique integration of surficial oxygen vacancies (Ovac) in conjunction with two-dimensional (2D) nickel-iron (NiFe) layered double hydroxide (LDH) nanosheets onto pristine BiVO4 photoanode to tweak the charge transfer kinetics during water splitting. The introduction of oxygen vacancies efficiently modulates band energetics, amplifies light absorption, and augments the carrier density. Concurrently, the 2D NiFe-LDH nanosheets play a dual role by facilitating interfacial hole transfer, thereby reducing excessive defect states, and serving as a protective layer against photocorrosion, ultimately resulting in a notable improvement in solar-driven water oxidation efficiency. The results of PEC water-splitting experiments demonstrate that the BiVO4 photoanode enriched with surficial oxygen vacancies and NiFe-LDH (BiVO4:Ovac/NiFe-LDH) achieved a photocurrent density of 2.92 mA cm−2 with ∼3-fold enhancement compared with a pristine BiVO4 photoanode. The engineered BiVO4 system yielded an impressive photoconversion efficiency of 1.29 %, charge separation efficiency (ηsep) > 40 %, and charge transport efficiency (ηtrans) > 35 %, clearly evidencing a boost in the charge dynamics of pristine BiVO4. Furthermore, during long-term stability testing, BiVO4:Ovac/NiFe-LDH retained 91 % of its initial photocurrent density for ∼20 h without any significant deterioration. This work sheds light on the role of integrating surface and interface engineering tactics for enhancing photo-induced charge transport in BiVO4, thereby providing efficient and stable PEC water splitting.

α-Fe2O3 mediated periodate activation for selective degradation of phenolic compounds via electron transfer pathway under visible irradiation

Periodate (PI)-photoactivated advanced oxidation process (AOP) has recently received increasing attention for the removal of micropollutants from water. However, periodate is mainly driven by high-energy ultraviolet light (UV) in most cases, and few studies have extended it to the visible range. Herein, we proposed a new PI visible light activation system employing α-Fe2O3 as catalyst. It is completely different from traditional PI-AOP based on hydroxyl radicals (•OH) and iodine radical (•IO3). The vis-α-Fe2O3/PI system can selectively degrade the phenolic compounds via non-radical pathway under the visible range. Notably, the designed system not only shows a well pH tolerance and environmental stability, but also exhibits a strong substrate-dependent reactivity. Both quenching experiments and electron paramagnetic resonance (EPR) experiments demonstrate that photogenerated holes are the main active species in this system. Moreover, a series of photoelectrochemical experiments reveal that PI can effectively inhibit the carrier recombination on the α-Fe2O3 surface, thereby improving the utilization of photogenerated charges and increasing the number of photogenerated holes, which effectively reacts with 4-CP through electron transfer way. In a word, this work proposes a cost-effective, green and mild mean to activate PI, and provides a facile way to solve the fatal shortcomings (i.e., inappropriate band edge position, rapid charge recombination and short hole diffusion length) of traditional iron oxide semiconductor photocatalysts.

Facile preparation of nickel phosphide for enhancing the photoelectrochemical water splitting performance of BiVO4 photoanodes.

The photoelectrochemical (PEC) water splitting performance of BiVO4 (BVO), a promising photoanode material, is constrained by its extremely short hole diffusion length and slow water oxidation kinetics. Modification of oxygen evolution cocatalysts (OECs) by appropriate methods is a practical solution to enhance the PEC water splitting performance of BVO. In this work, two different nickel phosphides Ni2P and Ni12P5 were prepared by a facile and mild one-step solvothermal method, and used as OECs to modify a BVO photoanode for enhancing the PEC water splitting performance. The BVO/Ni2P and BVO/Ni12P5 photoanodes showed impressive photocurrent densities of 3.3 mA cm-2 and 3.1 mA cm-2, respectively. In addition, the PEC water splitting stability of the BVO/Ni2P photoanode was greatly enhanced compared to that of the bare BVO photoanode. Further characterization and photoelectrochemical analysis revealed that the significant improvement of the BVO photoanode performance was attributed to the effective inhibition of surface charge recombination, facilitation of interfacial charge transfer, and acceleration of water oxidation kinetics after Ni2P and Ni12P5 modification.

Type-II Heterojunction CdIn2S4/BiVO4 Coupling with CQDs to Improve PEC Water Splitting Performance Synergistically.

Bismuth vanadate (BiVO4) has been considered as a promising photoelectrocatalytic (PEC) semiconductor, but suffers from severe hole recombination, attributed to the short hole-diffusion length and the low carrier mobility. Herein, a type-II heterojunction CdIn2S4/BiVO4 is designed to improve the photocurrent density from 1.22 (pristine BiVO4) to 2.68 mA cm-2 at 1.23 V vs the reversible hydrogen electrode (RHE), accelerating the bulk separation of photogenerated carriers by the built-in field from the matched energy band. With the introduction of CQDs, CQDs/CdIn2S4/BiVO4 increases the photocurrent density to 4.84 mA cm-2, enhancing the light absorption and cathodically shifting its onset potential, due to the synergetic effect of the heterojunction and CQDs. Compared with BiVO4, CQDs/CdIn2S4/BiVO4 promotes the bulk separation efficiency to 94.6% and the surface injection efficiency to 72.2%. Additionally, spin-coating of FeOOH on CQDs/CdIn2S4/BiVO4 could further improve the PEC performance and keep a long stability for water splitting. The density function theory (DFT) calculations illustrated that the type-II heterojunction CdIn2S4/BiVO4 could decrease the oxygen evolution reaction (OER) overpotential and accelerate bulk charge separation for the built-in field of the aligned band structure.

Reduction of charge carrier recombination by Ce gradient doping and surface polarization for solar water splitting

Photoelectrochemical (PEC) water splitting is one of the most strategies for solar energy storage and utilization. Hematite as one of the promising candidates for PEC research, has a short hole diffusion length and short carrier lifetime, resulting in PEC conversion efficiency far below the theoretical value. In this work, a facile but efficient strategy was introduced for the growth of gradient Ce doped hematite nanorods, following with the sequent photoactivation process. The gradient Ce doping not only increased the conductivity of bulk material, but also importantly, constructed a built-in electric field by the addition of Ce element, which remarkably enhanced the charge separation and transfer from the bulk to the surface. Moreover, the surface polarization under illumination was applied for the reduction of overpotential and the enhancement of photocurrent density, taking a role of cocatalyst decoration. It reduced the oxygen vacancies concentration at the surface, which further reduced the surface recombination owing to the passivation from photoactivation. According to these, the resulting photoanode exhibited a photocurrent of 1.92 and 2.50 mA cm−2 at 1.23 and 1.50 VRHE, respectively, with onset potential of 0.64 VRHE under AM 1.5G illumination. This work opens a useful strategy of modifying the electronic structure and constructing the interface structure for improving PEC performance on hematite-based photoelectrodes for solar energy storage and utilization.

Enhanced Photoelectrochemical Performance of Hematite Photoanode by Decorating NiCoP Nanoparticles Through a Facile Spin Coating Method

Hematite (α-Fe2O3) is a potential photoanode material for photoelectrochemical (PEC) water splitting, but its short hole diffusion length and low water oxidation kinetics prevent its practical application. In general, the hole transport rate and the water oxidation kinetics could be improved by modifying the oxygen evolution cocatalysts (OECs) in the proper way. In this work, we designed and synthesized a bimetallic phosphides NiCoP nanoparticles (NPs) modified (Ti, Zr)-codoped hematite photoanode (TZ-H) by a facile spin coating method to achieve the uniform and close interface contact of semiconductor/OECs. Under the optimal conditions, the as-prepared photoanode exhibits high and stable PEC performance with a current density of 2.38 mA/cm2 at 1.23 V vs. RHE, which is one of the best performances of noble-metal-free hematite-based photoanodes for water oxidation. Moreover, the surface efficiency of charge separation is improved by NiCoP modification, which is increased from 59% to 91% at 1.23 V vs. RHE and reached nearly 99% at higher potential. This work not only proves that NiCoP NPs are outstanding OECs but also provides a new strategy for the design of noble-metal-free semiconductor/OECs photoanodes with high-quality interface contact.

Vacancy defect engineering of BiVO4 photoanodes for photoelectrochemical water splitting.

Photoelectrochemical (PEC) water splitting has been regarded as a promising technology for sustainable hydrogen production. The development of efficient photoelectrode materials is the key to improve the solar-to-hydrogen (STH) conversion efficiency towards practical application. Bismuth vanadate (BiVO4) is one of the most promising photoanode materials with the advantages of visible light absorption, good chemical stability, nontoxic feature, and low cost. However, the PEC performance of BiVO4 photoanodes is limited by the relatively short hole diffusion length and poor electron transport properties. The recent rapid development of vacancy defect engineering has significantly improved the PEC performance of BiVO4. In this review article, the fundamental properties of BiVO4 are presented, followed by an overview of the methods for creating different kinds of vacancy defects in BiVO4 photoanodes. Then, the roles of vacancy defects in tuning the electronic structure, promoting charge separation, and increasing surface photoreaction kinetics of BiVO4 photoanodes are critically discussed. Finally, the major challenges and some encouraging perspectives for future research on vacancy defect engineering of BiVO4 photoanodes are presented, providing guidelines for the design of efficient BiVO4 photoanodes for solar fuel production.

Fabrication of Bilayer Fe<sub>2</sub>O<sub>3</sub>/ZnO Photoanode and its Photoelectrochemical Performance

Hematite (Fe2O3) is one of the abundant magnetic materials in nature. Hematite has good absorption ability in the region visible light and good electrochemical stability, which make this material is potential as photoanode for photoelectrochemical (PEC) cells. However, Fe2O3 has some disadvantages such as short hole diffusion length and low hole mobility. Therfore, it is necessarily to combine Fe2O3 with photocatalyst material to improve photoelectrochemical performances. ZnO is ones of photocatalist material with good electron mobility, wide band gaps, cheap and are easily fabricated. The aim of this study is to investigate the performance of bilayer Fe2O3/ZnO as photoanode for photoelectrochemical cell. The bilayer Fe2O3/ZnO was prepared by spin-coating techniques and doctor blade methods. The samples were characterized by X-ray diffarction, and Scanning Electron Microscopy. The performance of photoelectrochemical cell was investigated by Cyclic Voltammetry (CV) under light illumination. The result indicate that bilayer Fe2O3/ZnO has good photoelectrochemical properties.

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.

Optimization of Hematite to Improve PEC Performance in Water Splitting

Thus far, semiconductor materials explored to achieve theoretical solar to hydrogen efficiency (STH), included cadmium selenide (CdSe), zinc oxide (ZnO), copper(I)oxide (Cu2O), tungsten trioxide (WO3) and hematite (α-Fe2O3). Of these materials, hematite has received much attention for photoelectrochemical water splitting attributed to its stability in aqueous solution, a small band gap of 1.90 eV-2.20 eV, non-toxicity and abundance. However, it has associated limitations such as high electron-hole recombination rate, short hole diffusion length (2-4 nm) accompanied by short excited lifetime of 10 ps, and poor minority charge carrier mobility of 0.1 cm2 V-1s-1, leading to low photocurrent during water splitting. Furthermore, hematite promises a maximum theoretical STH efficiency of ~16.8 %, with photocurrent densities above 12 mAcm-2, but the reported findings are far below 10 mAcm-2. Using interfacial layers , annealing and doping, we have prolonged lifetimes and increased the photocurrent. In this work, hematite thin films and nanostructures were synthesized using dip coating and spray pyrolysis.

Length-dependent photo-electrochemical performance of vertically aligned hematite nanorods

Photo-electrochemical (PEC) cells have been widely studied as an eco-friendly method of producing hydrogen fuel. Among the various materials, hematite (α-Fe2O3) is one of the most promising candidates for PEC applications due to its chemical stability and visible-range bandgap. However, despite the aforementioned advantages, hematite-based PEC cells have suffered from an extremely short hole diffusion length and charge carrier lifetime, resulting in a solar-to-hydrogen efficiency far lower than the theoretical maximum. To overcome these drawbacks, we controlled the length of vertically aligned hematite nanorod (NRs) arrays on a fluorine-doped tin oxide substrate by adjusting the chemical concentrations of the precursor solutions. We confirmed that the PEC performance of the hematite NRs was strongly dependent on their length and showed an approximately inverse proportionality between the length of the hematite NRs and their photoactivity. In addition, the hematite NRs array, with an optimized length, was further modified by cobalt phosphate (Co-Pi) cocatalysts to enhance the water oxidation kinetics and showed 1.54 mA cm−2 of photocurrent at 1.23 V vs. RHE.

Photoelectrochemical water oxidation in α-Fe2O3 thin films enhanced by a controllable wet-chemical Ti-doping strategy and Co–Pi co-catalyst modification

The poor electrical conductivity, short hole diffusion length, and slow water oxidation reaction kinetics have severely limited the photoelectrochemical performance of the hematite (α-Fe2O3) photoanodes. In this paper, we report a facile wet-chemical approach to prepare the Ti-doping controllable hematite photoanode with subsequent Co–Pi electrocatalysts modification for solar water splitting. By optimizing the Ti-doping in Fe2O3, the Ti–Fe2O3 photoanodes can retain the primary morphology with the pristine Fe2O3 nanostructures, while simultaneously reducing the photogenerated charge carrier recombination rate in the films. Besides, by further decorating with Co–Pi co-catalysts on Ti–Fe2O3 surface, the formed Ti–Fe2O3/Co–Pi photoanode demonstrated an accelerated electrode/electrolyte kinetics during photoelectrochemical water oxidation reaction. As expected, the Ti–Fe2O3/Co–Pi photoanode produced an improved photocurrent density of 0.76 mA/cm2 at 1.23 V vs RHE, which is much higher than the photocurrent density of individual Fe2O3 (0.25 mA/cm2) and Ti–Fe2O3 photoanode (0.51 mA/cm2). This work provides a good insight for designing the composite photoanode to simultaneously enhance the charge transport and surface water oxidation kinetics for efficient solar fuel production.

Enhanced interface charge transfer via n-n WO3/Ti–Fe2O3 heterojunction formation for water splitting

Inevitable drawbacks on α-Fe2O3 photoanodes, such as poor conductivity, short hole diffusion length, high electron-hole recombination rate, limit their photoelectrochemical (PEC) performance for water oxidation. The construction of heterojunction is an effective approach to improve the PEC performance of photoanodes. Herein, we report the design of the WO3/Ti–Fe2O3 heterojunction photoanodes, which are synthesized by two simple hydrothermal method. The optimized WO3/Ti–Fe2O3 photoanode shows remarkably improved photocurrent of 2.15 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) without additional cocatalyst, which is higher than that of previous literatures. The improvement benefits from reduced charge transfer resistance in the bulk of Ti–Fe2O3 photoanode and improved charge separation efficiency, which can been further confirmed by electrochemical impedance spectroscopy (EIS), the transient photovoltage (TPV) and the work function (WF) measurement. The present work also provide new opportunities in developing high performance photoanodes for PEC water splitting.

Electrochemistry of Sputtered Hematite Photoanodes: A Comparison of Metallic DC versus Reactive RF Sputtering.

The water splitting activity of hematite is sensitive to the film processing parameters due to limiting factors such as a short hole diffusion length, slow oxygen evolution kinetics, and poor light absorptivity. In this work, we use direct current (DC) magnetron sputtering as a fast and cost-effective route to deposit metallic iron thin films, which are annealed in air to obtain well-adhering hematite thin films on F:SnO2-coated glass substrates. These films are compared to annealed hematite films, which are deposited by reactive radio frequency (RF) magnetron sputtering, which is usually used for depositing metal oxide thin films, but displays an order of magnitude lower deposition rate. We find that DC sputtered films have much higher photoelectrochemical activity than reactive RF sputtered films. We show that this is related to differences in the morphology and surface composition of the films as a result of the different processing parameters. This in turn results in faster oxygen evolution kinetics and lower surface and bulk recombination effects. Thus, fabricating hematite thin films by fast and cost-efficient metallic iron deposition using DC magnetron sputtering is shown to be a valid and industrially relevant route for hematite photoanode fabrication.