Fe2O3 Photoanode Research Articles

A Review: Research Progress on Photoelectric Catalytic Water Splitting of α-Fe2O3

Abstract: Photoelectric catalytic water splitting for hydrogen production is considered a promising method for hydrogen production, which can convert clean and renewable solar energy into sustainable and pollution-free hydrogen energy. An in-depth understanding of the relationship between the properties and functions of photocatalytic materials can help design and prepare efficient photodegradable water systems. Among them, α-Fe2O3 has a suitable band gap, can absorb visible light below 600 nm, and has the advantages of abundant raw materials high stability, and has become one of the most promising photoelectrode materials. However, as a photoelectrode material, α-Fe2O3 has the shortcomings of short photogenerated hole diffusion distance, low oxidation kinetics, poor conductivity, ease to be corroding, and so on, resulting in a very low photoelectric conversion efficiency, which limits its application in the field of photoelectric catalysis. This paper reviews the research progress of α-Fe2O3 as a photoanode. Firstly, the principle of photoelectric catalytic water splitting for hydrogen production and the main preparation methods of α-Fe2O3 photoanode is described; Secondly, the research work on modification of α- Fe2O3 photoanode by morphology control, element doping, construction of the heterojunction, surface modification and thermal excitation assisted effect in recent years is introduced. The photochemical performance of α-Fe2O3 photoanode is enhanced by improving the photocurrent density and the transfer of photo-generated carriers.

Extremely low onset potential of modified Fe2O3 photoanode for water oxidation

The photoelectrochemical (PEC) performance of hematite (α-Fe2O3)-based photoanodes is still far from its theoretical value because they are constrained by serious charge recombination and sluggish water oxidation kinetics. Herein, we developed a heterostructural photoanode by coating boron doped graphite carbon nitride nanolayers onto an Fe2O3 nanoarray (BCN/Fe2O3), followed by modification with NiCo(OH)x cocatalyst. The constructed NiCo(OH)x/BCN/Fe2O3 demonstrates a significantly improved photocurrent density of 2.7 mA cm−2 at 1.23 VRHE (V versus reversible hydrogen electrode), which is 3.2 times higher than that of pristine Fe2O3. Additionally, it exhibits an extremely negative onset potential of 0.60 VRHE. Detailed studies reveal that the BCN/Fe2O3 heterojunction endows a driving force for charge separation and establishes a direct pathway for their transport, while NiCo(OH)x acts as a cocatalyst to accelerate the surface water oxidation reaction.

Fabrication of WO3[formula omitted] heterostructure photoanode by PVD for photoelectrochemical applications

The bottleneck of cost-effective green hydrogen production through the photoelectrochemical (PEC) water splitting process is lack of suitable materials. To address the material challenge, we have fabricated a heterostructure nanorod of WO3/ Fe2O3 utilizing a high-throughput radio frequency (RF) sputtering Physical vapor deposition (PVD) technique. With optimized parameters, such as as-deposited Fe of 70 nm, a deposition angle of 70°, and an annealing temperature of 500 °C, WO3/ Fe2O3 photoanodes with a morphology of vertically aligned nanorods were fabricated. A rod-like morphology with WO3 nanoparticles was synthesized by the addition of 15 nm of tungsten oxide (WO3) to the Fe2O3 nanorods. To study the optical behavior and morphology, the pristine and WO3 /Fe2O3 heterostructure thin films were characterized by ultraviolet photoelectron spectroscopy (UPS), ultraviolet UV, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). This has led to a 5-fold improvement in PEC performance (0.588 mA/cm2 at 1.23 V vs. RHE for the mixture compared to 0.122 mA/cm2 at 1.23 V vs. RHE for the pristine). As a co-catalyst, WO3 successfully suppressed recombination and assisted in the hole transfer, which immediately increased the photocurrent density of fabricated photoanodes. This was illustrated via the electrochemical impedance spectra including both Nyquist and Mott-Schottky plots with or without illumination. When sustained in steady illumination for 900 s, this photoanode displayed highly stable behavior under PEC conditions.

Photoelectrochemical activation of peroxymonosulfate using Sn-doped α-Fe2O3 thin film for degradation of anti-inflammatory pharmaceutical drug

Introduction of oxygen vacancies (OVs) has been investigated as a promising way to improve the electrical and catalytic characteristics of a hematite (α-Fe2O3) based photoelectrode. In this work, we develop a novel method for preparing porous Sn-doped α-Fe2O3 (Sn:Fe2O3) thin films with intrinsic OVs. The procedure included spin-coating an iron precursor onto a fluorine-doped tin oxide (FTO) substrate, followed by thermal treatment at elevated temperatures. The influence of Sn dopant on the optoelectronic properties of α-Fe2O3 was demonstrated by X-ray photoelectron spectroscopy and photoelectrochemical (PEC) measurements. The combined effect of OVs and Sn doping was found to play a synergistic role in reducing the charge recombination’s. The Sn:Fe2O3 photoanodes were used as a dual catalyst to oxidise water and break down an anti-inflammatory drug called 2-(4-isobutylphenyl)propanoic acid (IBPA). The Sn:Fe2O3 thin film with a 30-minute heat treatment time displayed the highest incident photon-to-current efficiency. For the first time, Sn:Fe2O3 thin films were utilised in the effective PEC degradation of IBPA employing peroxymonosulfate (PMS) under visible light illumination. The hydroxyl radicals (OH), singlet oxygen (1O2), photogenerated holes (h+), and sulfate radicals (SO4−) were discovered to be the main reactive species during PEC degradation. IBPA degradation and the formation of new compounds were verified using liquid chromatography-mass spectrometry. The Lepidium sativum L phytotoxicity test reveals that PEC-treated wastewater with IBPA exhibits decreased toxicity.

MnOx Co-Catalysts Improved the Photoelectrochemical Properties of Fe2O3

The associated use of limited fossil fuels has also aroused an urgent need to seek for alternative, renewable energy sources. In this regard, hydrogen is the potential and green alternative to replace fossil fuels. Photo-electrochemical (PEC) water splitting towards the production of hydrogen is one of research hotspots, which has received significant attention due to its easy setup and great flexibility for further integrating with energy conversion and storage systems. Hematite (Fe2O3) has been widely utilized in photoelectrochemical (PEC) cells due to its suitable band gap and high electrochemical stability. However, its efficiency is limited by poor charge dynamics and slow reaction kinetics. Surface modification with an amorphous MnOx co-catalyst has been adopted to improve the PEC efficiency of Fe2O3. In this work, the mechanistic origin of introducing amorphous nano-fibrous MnOx as co-catalysts on the PEC performance of Fe2O3 photoanodes has been explored. Introduction of MnOx over Fe2O3 with an optimized thickness results in enhanced efficiency towards PEC water splitting, showing four-fold enhanced photocurrent over bare Fe2O3. The improved PEC performance of Fe2O3/MnOx can be assigned to the synergistic effect between Fe2O3 and MnOx, which led to improved charge dynamics at interface, anodic shift of valence band and increased electrochemical active sites.

The synergism of Co3O4 co-catalysis and Pt-doping boosting hematite photoanode for efficient solar H2O2 synthesis

Photoelectrochemical (PEC) syntheses is a green approach for the production of H2O2, which depends on the semiconductor photoanode to initiate the two-electron oxidation of H2O into H2O2. At present, the development of cheap and efficient photoanodes for H2O2 production holds great promise, but remains challenging. Herein, a Co3O4@Pt-Fe2O3 photoanode was designed and investigated for H2O2 production, based on the assistance of Co3O4 co-catalysis and Pt-doping. The Co3O4@Pt-Fe2O3 photoanode demonstrated superior PEC performance towards H2O2 production, a H2O2 production Faraday efficiency of 77.38% and a H2O2 yield of 0.073 μmol cm−2 be achieved at 1.00 V vs. RHE under AM 1.5 G irradiation. The experimental investigations and theoretical calculations jointly revealed the synergistic effect of Co3O4 co-catalysis and Pt-doping on the Co3O4@Pt-Fe2O3 photoanode for H2O2 production. Specifically, Pt-doping introduces defect sites into Fe2O3 photoanode, which could improve the bulk carrier mobility and density. Meanwhile, Co3O4 co-catalysis is conducive to achieve two-electron water oxidation on Pt-Fe2O3 photoanode selectively, and weaken the decomposition of H2O2 product in cell. Furthermore, the internal electric field of Co3O4/Pt-Fe2O3 can promote the separation of surface carrier for H2O2 production. The present work presents an efficient Co3O4@Pt-Fe2O3 photoanode for H2O2 production, which could inspire the development of similar materials for H2O2 synthesis.

Bulk embedding of Ti-defected TiO2 nano-heterointerfaces in hematite photoanode for boosted photoelectrochemical water splitting

The practical application of the most promising α-Fe2O3 photoanode in solar hydrogen generation is facing an awkward challenge arising from its poor bulk carrier transport. Present work demonstrates the acceleration of the carrier transport via embedding the p-type Ti-defected TiO2 (TiO2-VTi) nanocrystals in the n-type Fe2O3 photoanode matrix, which results in significantly improved photoelectrochemical performance. By embedding sub-5 nm TiO2-VTi nanocrystals in the bulk of α-Fe2O3 photoanode, numerous p-n nano-heterointerfaces were constructed for the first time in Fe2O3 photoanode matrix. The formed p-n nano-heterointerfaces lead to 10 times enhancement of charge transfer rate constant (ktran), and 1.5 times reduction of the charge recombination rate constant (krec), which is due to the formation of the built-in electric fields and effective carrier transport and separation at the p-n nano-heterointerfaces of TiO2-VTi/Fe2O3. Such strategy leads to the Fe2O3 photoanode with a reduction of photogenerated carrier transport time by 3 times, resulting in an excellent photocurrent density as high as 1.45 mA cm−2 at 1.23 VRHE, 5 times higher than that of pristine hematite (0.27 mA cm−2). We thus believe that our study opens up a route to regulate hematite or even metal-oxide semiconductor chemical/physical features via p-n nano-heterostructure embedding.

Fabrication of Hematite Photoanode Consisting of (110)-Oriented Single Crystals.

In this work, α-Fe2 O3 photoanode consisted of (110)-oriented α-Fe2 O3 single crystals were synthesized by a facile hydrothermal method. By using particular additive (C4 MimBF4 ) and regulation of hydrothermal reaction time, the Fe-25 consisted of a single-layer of highly crystalline (110)-oriented crystals with fewer grain boundaries, which was vertically grown on the substrate. As a result, the charge separation efficiency and photoelectrochemical (PEC) performance of Fe-25A (Fe-25 after dehydration treatment) have been greatly improved. Fe-25A yields a photocurrent of 1.34 mA cm-2 (1.23 V vs RHE) and an incident photon-to-current conversion efficiency (IPCE) of 31.95 % (380 nm). With the assistance of cobalt-phosphate water oxidation catalyst (Co-Pi), the PEC performance could be further improved by enhancing the holes transfer at electrode/electrolyte interface and inhibiting surface recombination. Fe-25A/Co-Pi yields a photocurrent of 2.67 mA cm-2 (1.23 V vs RHE) and IPCE value of 50.8 % (380 nm), which is 3.67 times and 2.39 times as that of Fe-2A/Co-Pi. Our work provides a simple method to fabricate highly efficient Fe2 O3 photoanodes consist of characteristic (110)-oriented single crystals with high crystallinity and high quality interface contact to enhance charge separation efficiencies.

Multiphysics model for assessing photoelectrochemical phenomena under concentrated irradiation

A multiphysics model was developed for a photoelectrochemical (PEC) cell at the device level to simulate water splitting operating under concentrated irradiation (between 50 to 600 kW m−2). The 2D model couples charge, heat, mass, photon, and momentum transfer to predict local current densities, potential distributions, temperature profiles, volumetric gas fractions, pressure, and velocities profiles in the electrolyte. Electrode kinetics and electrolyte resistance were considered for the electrochemical processes, and two-phase bubbly-flow under laminar conditions for momentum transfer. The effects of bubbles on the incident photon flux and the thermal and electrical conductivities of the electrolyte were also considered. Photocurrent densities were estimated using a semiempirical correlations dependent on potential, charge transfer efficiencies, and temperature. The model was applied to a custom-made cell utilising a spray pyrolysed Sn-doped Fe2O3 photoanode, a material with well-known photoelectrochemical behaviour and stability. Transparent conductive glass and titanium foil were investigated as two possible photoanode substrates. Predictions indicate that commercial conductive glasses are not suitable substrates due to a significant ohmic drop caused by high current densities. The model illustrates that thermal and bubble management are critical to improving the overall performance of a PEC cell subjected to high photon flux. Furthermore, the model can be used to decouple the phenomena that occur under such conditions and could assist in the study of photoelectrode materials under high irradiance.

Roles of Cobalt-Coordinated Polymeric Perylene Diimide in Hematite Photoanodes for Improved Water Oxidation.

Interfacial charge recombination is a permanent issue that impedes the photon energy utilization in photoelectrochemical (PEC) water splitting. Herein, a conjugated polymer, urea linked perylene diimide polymer (PDI), is introduced to the designation of hematite-based composite photoanodes. On account of its unique molecule structure with abundant electronegative atoms, the O and N atoms with lone electron pairs can bond with Fe atoms at the surface of Zr4+ doped α-Fe2 O3 (Zr:Fe2 O3 ) and thus establish charge transfer channels for expediting hole separation and migration. Meanwhile, PDI molecules can passivate the surface states in Zr:Fe2 O3 , which is in favor of suppressing carrier recombination. Particularly, Co2+ is used to coordinate with PDI (Co-PDI) to accelerate hole extraction as well as utilization, and the as-obtained Co-PDI form type-II heterojunction with Zr:Fe2 O3 . Such a photoanode configuration takes advantage of the unique molecule structure of PDI, and the target Co-PDI/Zr:Fe2 O3 photoanodes eventually attain a photocurrent density of 2.17mAcm-2 , which is inspirational for unearthing the potential use of conjugative molecules in PEC fields.

Ti-doped Fe2O3 photoanodes on three-dimensional titanium microfiber felt substrate for photoelectrochemical oxygen evolution reaction

The macroporous structure of conductive substrates with large surface areas is crucial for fabricating semiconductor electrodes that offer better photoelectrochemical (PEC) performance in the water-splitting reaction. In this study, three-dimensional (3D) titanium microfiber felt (Ti felt) was used as a conductive substrate to prepare a Ti-doped Fe2O3 photoanode via a hydrothermal method with a two-step annealing treatment in air and argon atmospheres. Compared to conventional two-dimensional (2D) substrates, such as fluorine-doped tin oxide (FTO)-coated glass and Ti sheets, the loading amount of Fe2O3 on Ti felt was 2–5 times higher for a similar substrate geometric area. The thickness of Fe2O3 on the Ti felt (∼0.6 µm) was less than that on the 2D substrates. Ti-doped Fe2O3 on Ti felt (Ti-felt/Ti-Fe2O3) exhibits a higher photocurrent density than FTO/Ti-Fe2O3 and Ti-sheet/Ti-Fe2O3. Mott–Schottky analysis shows that the donor density of Ti-felt/Ti-Fe2O3 (8.58 × 1021 cm−3) was more than 10 times higher than that of FTO/Ti-Fe2O3 and Ti-sheet/Ti-Fe2O3. Analyses of the incident photon-to-current conversion efficiency (IPCE) and Faradaic efficiency indicated that Ti-felt/Ti-Fe2O3 showed higher PEC activity for the oxygen evolution reaction (OER) than FTO/Ti-Fe2O3. The enhanced PEC activity is ascribed to the higher donor density and moderate thickness of the Ti-doped Fe2O3 layer, which contribute to a short electron transport distance. Furthermore, the high loading of Fe2O3 on the Ti-felt substrate increased the photoabsorption in the UV and visible light regions and the photocurrent response at wavelengths near the band edge, even at low light intensities. This study provides new insights for preparing hematite photoanodes with higher PEC activity for the OER using a 3D porous substrate, rather than conventional 2D substrates.

In Situ Synthesis of Ti:Fe2O3/Cu2O p-n Junction for Highly Efficient Photogenerated Carriers Separation

High photoelectrochemical water oxidation efficiency can be achieved through an efficient photogenerated holes transfer pathway. Constructing a photoanode semiconductor heterojunction with close interface contact is an effective tactic to improve the efficiency of photogenerated carrier separation. Here, we reported a novel photoanode p-n junction of Ti:Fe2O3/Cu2O (n-Ti:Fe2O3 and p-Cu2O), Cu2O being obtained by in situ reduction in CuAl-LDH (layered double hydroxides). The Ti:Fe2O3/Cu2O photoanode exhibits a high photocurrent density reaching 1.35 mA/cm2 at 1.23 V vs. RHE is about 1.67 and 50 times higher than the Ti:Fe2O3 and α-Fe2O3 photoanode, respectively. The enhanced PEC activity for the n-Ti:Fe2O3/p-Cu2O photoelectrode is due to the remarkable surface charge separation efficiency (ηsurface 85%) and bulk charge separation efficiency (ηbulk 72%) formed by the p-n junction and the tight interface contact formed by in situ reduction. Moreover, as a cocatalyst, CuAl-LDH can protect the Ti:Fe2O3/Cu2O photoanode and improve its stability to a certain extent. This study provides insight into the manufacturing potential of in situ reduction layered double hydroxides semiconductor for designing highly active photoanodes in the field of photoelectrochemical water oxidation.

Dual-suppression of bulk and surface charges recombination for hematite photoanode

Surface treatments are considered as one of the most effective strategies to overcome charges recombination of photoanodes. Herein, the E–Ti–Fe2O3 photoanode was prepared by hydrothermal, electrodepositon and subsequent KOH treatment methods on the surface of Ti–Fe2O3 photoanode. The photocurrent density of E–Ti–Fe2O3 reached 3.1 mA/cm2 at 1.23 V versus reversible hydrogen electrode (vs. RHE), which was about 6.5 times than that of Ti–Fe2O3 (0.48 mA/cm2 at 1.23 V vs. RHE). The photocurrent density of E–Ti–Fe2O3 was further improved by the modification of CoPi (4.1 mA/cm2 at 1.23 V vs. RHE). The excellent PEC activity can be attributed to the dual-suppression of bulk and surface charges recombination, which was proved by work function (WF) measurements, transient photovoltage (TPV) measurements and photoelectrochemistry (PEC) tests. This research provided a deep insight into the bulk and surface charge recombination of the photogenerated charges for photoanode.

Electrolyte Engineering Stabilizes Photoanodes Decorated with Molecular Catalysts.

Molecular catalysts are promising oxygen evolution promoters in conjunction with photoanodes for solar water splitting. Maintaining the stability of both photoabsorber and cocatalyst is still a prime challenge, with many efforts tackling this issue through sophisticated material designs. Such approaches often mask the importance of the electrode-electrolyte interface and overlook easily tunable system parameters, such as the electrolyte environment, to improve efficiency. We provide a systematic study on the activity-stability relationship of a prominent Fe2 O3 photoanode modified with Ir molecular catalysts using in situ mass spectroscopy. After gaining detailed insights into the dissolution behavior of the Ir cocatalyst, a comprehensive pH study is conducted to probe the impact of the electrolyte on the performance. An inverse trend in Fe and Ir stability is found, with the best activity-stability synergy obtained at pH 9.7. The results bring awareness to the overall photostability and electrolyte engineering when advancing catalysts for solar water splitting.

Hierarchical Zr-doped Fe2O3 photoanodes decorated with in situ Au nanoparticles via a surfactant-assisted one-step hydrothermal approach for efficient photoelectrochemical water splitting

The influence of CTAB and metallic Au NPs on the PEC activity of a Zr-doped Fe2O3 photoanode is described. CTAB surfactant assists the in situ adsorption of Au NPs on Zr-FeOOH during hydrothermal synthesis.

Deep surface reconstruction of Co-based cocatalyst on Ti-doped α-Fe2O3 photoanode for highly efficient water oxidation

Transition metal-based cocatalysts play important roles in promoting the surface kinetics of hematite (α-Fe2O3) photoanode. However, their performances are restricted by the shallow reconstruction process for generating highly efficient metal oxyhydroxides, where the oxygen evolution reaction (OER) occurs. Therefore, a Brnsted base-regulated strategy is developed to promote the in situ surface reconstruction of cocatalysts on Ti-doped α-Fe2O3 (Ti–Fe2O3) under photoelectrochemical conditions. After deep surface reconstruction by electrochemical activation, the CoWO4 cocatalyst decorated Ti–Fe2O3 photoanode (a-CoWO4/Ti–Fe2O3) delivers a photocurrent density of 0.88 mA cm−2 at 1.23 VRHE, which is about 3.0 times of activated Ti–Fe2O3 (a-Ti-Fe2O3) and 1.5 times of activated CoOx/Ti–Fe2O3. Tungstate promotes the surface reconstruction of cobalt-based cocatalyst, resulting in a significant increase in bulk charge separation efficiency (ηsep) and surface charge injection efficiency (ηinj). Moreover, the type-II heterojunction between CoWO4-derived CoOOH and a-Ti-Fe2O3 drives the rapid separation and transfer of photogenerated electron-hole pairs, and enhances the performance of Ti–Fe2O3 photoanode.

Bias-Free Solar-Driven Syngas Production: A Fe2 O3 Photoanode Featuring Single-Atom Cobalt Integrated with a Silver-Palladium Cathode.

Photoelectrochemical syngas production from aqueous CO2 is a promising technique for carbon capture and utilization. Herein, we demonstrate the efficient and tunable syngas production by integrating a single-atom cobalt-catalyst-decorated α-Fe2 O3 photoanode with a bimetallic Ag/Pd alloy cathode. A record syngas production activity of 81.9 μmol cm-2 h-1 (CO/H2 ratio: ≈1 : 1) was achieved under artificial sunlight (AM 1.5 G) with an excellent durability. Systematic studies reveal that the Co single atoms effectively extract the holes from Fe2 O3 photoanodes and serve as active sites for promoting oxygen evolution. Simultaneously, the Pd and Ag atoms in bimetallic cathodes selectively adsorb CO2 and protons for facilitating CO production. Further incorporation with a photovoltaic, to allow solar light (>600 nm) to be utilized, yields a bias-free CO2 reduction device with solar-to-CO and solar-to-H2 conversion efficiencies up to 1.33 and 1.36 %, respectively.

Enabling high low-bias performance of Fe2O3 photoanode for photoelectrochemical water splitting

Fe2O3 is a promising photoanode material used for photoelectrochemical water splitting due to its narrow bandgap and excellent stability in solution. However, because the nanorods shrink and coalesce when annealed under high temperatures, the charge separation and injection efficiencies are suppressed in the conventional nanocoral Fe2O3, resulting in its high bias potential and low photocurrent density. Herein, by improving the radial growth of FeOOH precursor, highly dispersed Fe2O3 nanorods could be prepared. It enabled them to have sufficient light-harvesting and short charge transport distance, high light absorption and charge separation/injection efficiencies, increased photocurrent density and reduced onset potential Von. The optimized Fe2O3 photoanodes obtained a remarkable low-bias photocurrent density of 0.84 mA cm−2 at 1.0 V versus reversible hydrogen electrode (vs. RHE). It was further improved to 1.36 mA cm−2 at 1.0 V vs. RHE with the Von reduced to 0.50 V vs. RHE when post-treated with a solvothermal method and loaded with NiOOH/FeOOH cocatalysts. The applied bias photo-to-current conversion efficiency was maximized to 0.45% at 0.84 V vs. RHE.

Magnetron Sputtered Al Co-Doped with Zr-Fe2O3 Photoanode with Fortuitous Al2O3 Passivation Layer to Lower the Onset Potential for Photoelectrochemical Solar Water Splitting

In this paper, we investigate the magnetron sputtering deposition of an Al-layer on Zr-doped FeOOH (Zr-FeOOH) samples to fabricate a Zr/Al co-doped Fe2O3 (Al-Zr/HT) photoanode. An Al-layer is deposited onto Zr-FeOOH through magnetron sputtering and the thickness of the Al deposition is regulated by differing the sputtering time. Electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, Mott-Schottky and time-resolved photoluminescence spectra analyses were used to study, in depth, the correlations between sputtered Al-layer thicknesses and PEC characteristics. High-temperature quenching (800 °C) assists in diffusing the Al3+ in the bulk of the Zr-doped Fe2O3 photoanode, whilst an unintended Al2O3 passivation layer forms on the surface. The optimized Al-Zr/HT photoelectrode achieved 0.945 mA/cm2 at 1.0 VRHE, which is 3-fold higher than that of the bare Zr/HT photoanode. The Al2O3 passivation layer causes a 100 mV cathodic shift in the onset potential. Al co-doping improved the donor density, thus reducing the electron transit time. In addition, the passivation effect of the Al2O3 layer ameliorated the surface charge transfer kinetics. The Al2O3 passivation layer suppressed the surface charge transfer resistance, consequently expediting the hole migration from photoanode to electrolyte. We believe that the thickness-controlled Al-layer sputtering approach could be applicable for various metal oxide photoanodes to lower the onset potential.

Surface selective passivation and FexNi1-xOOH co-modified Fe2O3 photoanode toward high-performance water oxidation

Improving the water-splitting performance of hematite (α-Fe2O3) is still hindered due to its severe charge recombination and poor water oxidation kinetics. Herein, borate-treated Ti–Fe2O3 combined with a FexNi1-xOOH cocatalyst (FexNi1-xOOH/B/Ti–Fe2O3) greatly improved the performance of Ti–Fe2O3, and reached a notable photocurrent density of 3.39 mA/cm2 at 1.23 V vs. RHE. Transient surface photovoltage spectroscopy (TPV) directly reveals that [B(OH)4]− as a Lewis base can selectively passivate acceptor surface states on Ti–Fe2O3 photoanode surface, efficiently enhancing the charge separation efficiency. Moreover, the FexNi1-xOOH thin layer is devoted to further facilitate holes injection into the electrolyte, accelerating the water oxidation kinetics of Ti–Fe2O3 photoanode. The synergetic integration of acceptor surface states passivation and FexNi1-xOOH cocatalyst provides a novel strategy for the construction of efficient photoanodes by surface engineering.