Photo-assisted Electrodeposition Research Articles

Design of type II quaternary double-decker heterostructure Cu-WO3-BiVO4-Bi2S3[sbnd]NiOOH photoanode for stable and efficient photoelectrochemical water splitting

BackgroundBismuth vanadate (BiVO4) and nickel oxyhydroxide (NiOOH) are the prominent photo(electro)catalysts for water-splitting photoelectrodes. The strong visible light absorbers of the Bi2S3 decorated type II photoanode of WO3/BiVO4/NiOOH efficiently improve the photo-excitons in the photoanodes. MethodsIn this work, type II semiconductors heterostructure photoanodes are fabricated as Cu:WO3/BiVO4/Bi2S3/NiOOH. The bottom layer of heavily Cu- doped n-type WO3 nanoplatelets is grown on FTO to make nano-heterostructure Cu:WO3/BiVO4 photoanodes. The Bi2S3 semiconductor has been grown on the BiVO4 by chemical bath deposition and NiOOH deposited using the photo-assisted electrodeposition method. The resulting periodically ordered BiVO4/WO3 platelets distinctly outperform by the Bi2S3 and NiOOH-decorated quaternary photoanodes. Significant findingsAs a result, the as-prepared photoanode shows a high photocurrent density of 6.85 mA cm−2 at 0 V vs. Ag/AgCl under the irradiation of 100 mW/cm2 AM 1.5 G simulated sunlight. With the higher photoactivity of Bi2S3 and NiOOH cocatalysts, the photoanode substantially gains stability at higher saturation photocurrents. Overall, the photoanode resulted in a low charge transfer resistance (387.4 Ohm.cm2) and a higher built-in potential of 180 mV, with 2.67 % of ABPE and 2.1 % of STH efficiencies at 0.3 V vs. Ag/AgCl.

Boosting synergistic hole separation and transfer in the TiO2-MXene photoanode by depositing amorphous NiOOH/CoOOH cocatalysts

The efficient separation and transport of photogenerated charge carriers within the photoanode are pivotal for achieving high-performance photoelectrochemical (PEC) water splitting. In this study, TiO2-MXene nanowire arrays (NWAs) adorned with amorphous CoOOH/NiOOH (CN) were fabricated using hydrothermal and photo-assisted electrodeposition techniques. TiO2-MXene-CN NWAs demonstrated a photocurrent density of 1.51 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (vs. RHE), which is 1.46 times and 2.79 times that of TiO2-CN and TiO2, respectively. Electrochemical impedance spectroscopy, photoluminescence, time-resolved photoluminescence, and Mott-Schottky analysis unveiled that the incorporation of MXene and CN substantially augmented the separation of photogenerated electron-hole pairs and efficient charge carrier utilization. Furthermore, the loading of MXene-CN layers ameliorated the light absorption performance of bare TiO2 NWAs. This work provides valuable insights for the design of photoelectrodes employing wide-bandgap materials.

Amorphous NiB layer deposition and piezoelectric field assisted for efficient photocatalytic degradation of Sb2S3

The poor surface charge reaction efficiency and electrical conductivity limit the further application of Sb2S3 in photocatalytic degradation of pollutants. An amorphous NiB layer was deposited on the surface of Sb2S3 by photo-assisted electrodeposition, and the presence of the NiB layer accelerated the charge transport and catalytic reactivity, which greatly enhanced the degradation ability. The photocurrent density of NiB-Sb2S3 was about 0.12 mA/cm2, which was 6 times of that of pure Sb2S3. After increasing the applied mechanical site by ultrasonication, the photocurrent of NiB-Sb2S3 was further increased to 0.19 mA/cm2, which was almost 9.5 times that of pure Sb2S3 under photocatalytic conditions alone. The catalytic kinetic curves show that the degradation rate of RhB by NiB-Sb2S3 under piezoelectric-photocatalytic conditions is significantly increased, being 11.48 times of the degradation rate of Sb2S3 under photocatalytic conditions. The detailed experimental data indicate that the amorphous NiB layer not only changes the electronic structure of the catalyst surface, but also increases the number and activity of the catalyst active sites, and reduces the chance of electron and hole recombination after photoexcitation. The introduction of an applied piezoelectric field provided a driving force for carrier migration to the catalyst surface, which further improved the separation ability. This study provides a new strategy to further improve the photocatalytic degradation.

Efficient BiVO4 Photoanode with an Excellent Hole Transport Layer of CuSCN for Solar Water Oxidation

AbstractBismuth vanadate (BiVO4) is reported as a key material in photoelectrocatalysis owing to high theoretical efficiency, relatively narrow band gap of 2.4 eV, and favorable conduction band edge position for hydrogen evolution. However, the sluggish hole transport dynamics lead to slow photogenerated charge separation and transport efficiencies, which result in charge recombination due to aggregation. Herein, a novel hole transport layer of copper(I) thiocyanate (CuSCN) with the aim of significantly enhancing the efficiency of charge transport and stability of BiVO4 photoanodes is reported. The introduction of the hole transport layer could provide an appropriate intermediate energy level for photogenerated hole transfer and avoid charge recombination and trapping. After a photoassisted electrodeposition process of NiCoFe‐Bi catalysis, the obtained photoanode achieves a photocurrent density of 5.6 mA cm−2 at 1.23 V versus reversible hydrogen electrode under AM 1.5 G simulated solar radiation, and an applied bias photon to current efficiency of 2.31%. With the CuSCN layer, BiVO4 photoanode presented impressive stable photocurrent during 50 h continuous illumination. Meanwhile, the unbiased tandem device of the NiCoFe‐Bi/CuSCN/BiVO4 photoanode and the Si solar cell exhibit a solar‐to‐hydrogen efficiency of 5.75% and excellent stability for 14 h.

Au-decorated Sb2Se3 photocathodes for solar-driven CO2 reduction.

Photoelectrodes with FTO/Au/Sb2Se3/TiO2/Au architecture were studied in photoelectrochemical CO2 reduction reaction (PEC CO2RR). The preparation is based on a simple spin coating technique, where nanorod-like structures were obtained for Sb2Se3, as confirmed by SEM images. A thin conformal layer of TiO2 was coated on the Sb2Se3 nanorods via ALD, which acted as both an electron transfer layer and a protective coating. Au nanoparticles were deposited as co-catalysts via photo-assisted electrodeposition at different applied potentials to control their growth and morphology. The use of such architectures has not been explored in CO2RR yet. The photoelectrochemical performance for CO2RR was investigated with different Au catalyst loadings. A photocurrent density of ∼7.5 mA cm-2 at -0.57 V vs. RHE for syngas generation was achieved, with an average Faradaic efficiency of 25 ± 6% for CO and 63 ± 12% for H2. The presented results point toward the use of Sb2Se3-based photoelectrodes in solar CO2 conversion applications.

A Synergic Effect of Bi-metallic Layered Hydro-Oxide Cocatalyst on 1-D TiO2 Driven Photoelectrochemical Water Splitting

ABSTRACT Photoelectrochemical (PEC) water splitting is one of the most sustainable approaches for converting solar energy into hydrogen fuel. Affordable and robust photoelectrodes are crucial for the commercialization of PEC technologies. Recently, transition metal-based co-catalysts, especially Ni- and Fe-based catalysts, have attracted much interest owing to their exceptional OER characteristics. Given this, we here proposed the decoration of a Fe-Ni-based cocatalyst on the surface of the TiO2 photoanode for PEC water splitting. The TiO2 photoanode was hydrothermally synthesized and then decorated by Fe-Ni hydroxide catalyst using photo-assisted electrodeposition. The optimized TiO2/FeNiOOH photoanode exhibited the maximum photocurrent density value of 1.36 mA cm−2, which is almost twice the value obtained for bare TiO2, at 1.23 V vs RHE under the AM 1.5 G illumination. Due to the enhanced light absorption in the UV region, the optimized photoanode exhibited remarkable IPCE and photoconversion efficiency of 87.8% and 0.93%, respectively. Furthermore, excellent faradaic efficiencies of ∼90% for H2 and ∼70% for O2 generations were obtained. Predominantly, the enhancement in the photocurrent potentials was explained in detail. Our study shows the roles and benefits of using bimetallic catalysts with TiO2 photoanodes for sustainable water-splitting applications.

Enhancement of charge separation and hole utilization in a Ni2P2O7-Nd-BiVO4 photoanode for efficient photoelectrochemical water oxidation

It is necessary for photoelectrochemical (PEC) water splitting to reduce the electron-hole recombination rate and enhance the water oxidation reaction kinetics. Here, we prepared Ni2P2O7-Nd-BiVO4 composite photoanodes by coupling Ni2P2O7 co-catalysts to neodymium (Nd)-doped BiVO4 surfaces through photo-assisted electrodeposition. The Ni2P2O7-Nd-BiVO4 photoanode exhibits a high photocurrent density of 3.6 mA cm−2 at 1.23 V vs reversible hydrogen electrode (RHE), which is three times higher than that of the bare BiVO4 (1.2 mA cm−2). Detailed characterizations demonstrate that Nd doping reduces the band gap, significantly increases the carrier density and effectively reduces the charge transfer resistance. More importantly, the Ni2P2O7 co-catalyst has multiple roles. Specifically, it can act as a hole extraction layer to accelerate hole migration and inhibit hole-electron recombination. At the same time, it significantly improves the water oxidation reaction kinetics. In addition, it also provides more water oxidation active sites. This work provides ideas for the design and study of efficient BiVO4-based photoanodes.

A BiVO4 Photoanode with a VOx Layer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting.

Sluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO4 ) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VOx ) with enriched oxygen vacancies conformally grown on BiVO4 photoanodes by a simple photo-assisted electrodeposition process. The optimized BiVO4 /VOx photoanode exhibits a photocurrent density of 6.29 mA cm-2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge-transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VOx that forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium-based catalysts for PEC water oxidation.

The PEC performance of BiVO4 was enhanced by preparing the CoFeBi/BiVO4 photoanode using an ultrafast photoassisted electrodeposition method

The BiVO4 photoanode modified with bimetallic CoFeBi exhibits a significant enhancement in photoelectrochemical (PEC) water splitting performance.

Characterization of high absorbance and high-emissivity black Ni[sbnd]Ce oxide composite coatings produced via photo-assisted electrodeposition

Q235 steel, whose nominal composition (wt%) is 0.14–0.22 C, 0.30–0.65 Mn, ≤0.30 Si, ≤0.045 P, ≤0.055 S and Fe balance, has played an important role in the development of human history and the establishment of modern industry due to its excellent mechanical and engineering performance. In this study, black NiCe oxide composite coatings were electrodeposited on Q235 steel under photo-illumination and the effect of potential was studied. A 300 W ultra-high power xenon lamp with 300–2500 nm wavelength was the light source and provided 220,000 Lux irradiation intensity. After deposition of 40 min, black, uniform, and compact coatings were obtained; their colour gradually deepened when the potential changed from −0.7 to −0.9 V vs. saturated calomel electrode. The composite coatings improved the corrosion resistance of the substrate. Ni and Ce(III) content in the composite coating increased, whereas the hardness decreased at a more negative deposition potential. A black composite coating with both high absorptivity and high emissivity was obtained at a deposition potential of −0.8 V with photo-illumination, which exhibited an emissivity of 0.846 and absorptivity of approximately 95 % in the ultraviolet band, 90 % in the visible region, and 92 % in the near-infrared band. Exposure experiments showed that the absorptivity and emissivity decreased very little on exposing to a natural environment for one month. The electrodeposition mechanism and possible reasons for the above behavior are discussed in detail. The study provides an idea to prepare black coatings with high absorptivity and emissivity that are expected to be used in the naval, aerospace industry, photothermal conversion and optical instruments.

A non-enzymatic photoelectrochemical sensor based on Co-Pi modified one-dimensional titanium oxide embedded microscale reactor

Photoelectrochemical (PEC) sensing systems are promising candidates for detecting low concentrations of biological molecules; they are particularly encouraging when offered in a non-enzymatic format. A pitfall of non-enzymatic PEC sensors is their specificity. This, however, is often resolved by utilizing inorganic nanocatalyst. Here, we describe a novel non-enzymatic sunlight-driven PEC sensor based on cobalt phosphate (Co-Pi) deposition on a one-dimensional titanium dioxide (1D-TiO2) nanorod array for the ultra-low detection of glucose. The 1D-TiO2 nanorod array was prepared through a simple hydrothermal method and modified with Co-Pi using photo-assisted electrodeposition. The result was a microscale fluidic reactor. The modified electrodes with various Co-Pi thicknesses photocatalyst were characterized through a variety of techniques, including HRTEM, XRD, UV–vis spectroscopy, electrochemical impedance spectroscopy, and chronoamperometry. The characterization methods served to study and confirm the optimal electrode structure. The novel 1D-TiO2/Co-Pi electrode exhibited enhanced absorbance in the visual range of the nanorods with increased photoactivity and no drastic modification of the array’s surface. The PEC sensor microscale reactor exhibited a low limit of detection of 0.031 nM and a high sensitivity of 900 μA mM−1 cm−2 over a linear range of 0.1–10000 nM, demonstrating ultrasensitive detection of glucose. Overall, the surface modification of TiO2 by Co-Pi improved the sensor properties resulting in high selectivity, high stability, and high reproducibility.

Surface modification of p/n heterojunction based TiO2-Cu2O photoanode with a cobalt-phosphate (CoPi) co-catalyst for effective oxygen evolution reaction

The cobalt-phosphate decorated TiO2-Cu2O efficient heterojunction photoanode was successfully prepared using hydrothermal and electrodeposition methods. First, TiO2 was deposited onto fluorine-doped tin oxide-coated glass slides by the hydrothermal method, after which a layer of Cu2O was deposited by electrodeposition. Lastly, the surface of the TiO2-Cu2O electrode was further modified with cobalt-phosphate using photo-assisted electrodeposition. Prepared samples were characterized by X-ray diffractometry, field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy, and UV–Visible spectrophotometry. Substantial increase in photocurrent density, i.e., from 1.13 mA/cm2 to 1.66 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) was observed when the optimized Cu2O layer was applied to the bare TiO2 photoanode. Moreover, the highest photocurrent density, i.e., 1.94 mA/cm2 at 1.23 V vs RHE was obtained when the surface of the TiO2-Cu2O heterojunction photoanode was further modified using a cobalt-phosphate co-catalyst. The remarkable performance of the p-n heterojunction structure photoanode was mainly attributed to improved light harvesting in the visible region and improved charge dynamics due to the band alignment between TiO2 and Cu2O.

A hierarchical SiPN/CN/MoSx photocathode with low internal resistance and strong light-absorption for solar hydrogen production

The Si/MoSx photocathode is usually fabricated by electrochemical deposition, which high interfacial resistance is usually solved by building a buried junction or inserting a metal layer between Si and MoSx. Both methods, however, involve toxic gas sources or harsh conditions of high pressure. Here, a green and mild route has been designed to insert the N-doped carbon (CN) layer between Si and MoSx by in situ polymerization and post-annealing, which improves the transfer of interfacial carriers and avoids unnecessary absorption of incident light by itself. Meanwhile, combining two-step wet etching and photo-assisted electro-deposition, the SiPN/CN/MoSx photocathode with antireflective structure was obtained.The SiPN/CN/MoSx hybrid photocathode shows excellent performance (0.23 V onset potential and 10 mA·cm−2 photocurrent at 0 V vs RHE in 0.5 MH2SO4 under the condition of simulated sunlight). The design of SiPN/CN/MoSx photocathode will provide a new idea for PEC water splitting.

Photo-assisted electrodeposition of NiMoZn on hematite nanostructures and their photoelectrochemical application as photoanode for corrosion protection of stainless steel

In this study, hematite nanostructures (HN) were prepared on iron plates through anodization method, followed by the deposition of NiMoZn on the nanostructures by photo assisted electrodeposition method to produce NiMoZn/HN electrodes. The deposition time greatly effects on the photoeletrochemical performance of prepared photoelectrodes. In comparison with the bare hematite, the photocurrent density of NiMoZn/HN electrode was enhanced up to 5 times. In addition, the photocathodic protection characteristics of the NiMoZn/HN were evaluated by measuring the photo induced open circuit potential (OCP) and Tafel curves under light. The results showed that the photocurrent density of NiMoZn/HN samples increased from 0.11 to 0.51 mA cm−2 compared with the bare hematite sample. In addition, the photo induced OCP of the best NiMoZn/HN photoanode was decreased by about − 620 mV vs. Ag/AgCl with regards to photocathodic protection application. The results indicate that the NiMoZn photo-electrodeposition on the hematite photoelectrodes is a facile and efficient method for the protection of stainless steel from corrosion.

Boosting Hole Transfer in the Fluorine-Doped Hematite Photoanode by Depositing Ultrathin Amorphous FeOOH/CoOOH Cocatalysts.

The charge transfer is a key issue in the development of efficient photoelectrodes. Here, we report a method using F-doping and dual-layer ultrathin amorphous FeOOH/CoOOH cocatalysts coupling to enable the inactive α-Fe2O3 photoanode to become highly vibrant for the oxygen evolution reaction (OER). Fluorine doping is revealed to increase the charge density and improve the conductivity of α-Fe2O3 for rapid charge transfer. Furthermore, ultrathin FeOOH was deposited on F-Fe2O3 to extract photogenerated holes and passivate the surface states for accelerated charge carrier transfer. Moreover, CoOOH as an excellent cocatalyst was coated onto FeOOH/F-Fe2O3 with the photoassisted electrodeposition method remarkably expediting OER kinetics through an optional pathway of holes utilized by Co species. Ultimately, the CoOOH/FeOOH/F-Fe2O3 photoanode exhibits a satisfactory photocurrent density (3.3-fold higher than pristine α-Fe2O3) and a negatively shifted onset potential of 80 mV. This work showcases an appealing maneuver to activate the water oxidation performance of the α-Fe2O3 photoanode by an integration strategy of heteroatom doping and cocatalyst coupling.

Photoelectrochemical performance of α-Fe2O3@NiOOH fabricated with facile photo-assisted electrodeposition method

This study adopted a photo-assisted electrodeposition method to fabricate NiOOH on α-Fe2O3 photoanode. The detailed microstructure and chemical composition characterizations suggested that the NiOOH particles were selectively deposited on the α-Fe2O3 surface to form hybrid nanocomposites. Photoelectrochemical measurements revealed the important role of NiOOH as a cocatalyst for water splitting under visible light illumination. The prepared photoanode exhibited essentially enhanced photoelectrochemical activity, which was about fourfold higher than that of α-Fe2O3 photoanode. Further study suggested that loading NiOOH by photo-assisted electrodeposition method on α-Fe2O3 surface can facilitate the water splitting process by providing substantial active reaction sites and promoting the transfer and consumption of photogenerated holes. Contribution of this work is to supply a facile method to develop efficient photoelectrochemical anode.

Enhancement of the photoelectrochemical water splitting by perovskite BiFeO3via interfacial engineering

Ferroelectric semiconductors like BiFeO3 are increasingly being investigated for applications in solar energy conversion and storage due to their intrinsic ability to induce ferroelectric polarization-driven separation of the photogenerated charge carriers resulting in above-bandgap photovoltages. Nevertheless, the BiFeO3 has been commonly prepared using complex and expensive fabrication techniques, e.g., epitaxial growth, radio frequency sputtering and pulsed laser deposition, which are not economically viable for large-scale production. Herein, we report a facile and scalable method for the fabrication of porous perovskite BiFeO3 photoanodes, as well as sequential interfacial engineering methods to enhance their photoelectrochemical performance for water splitting. Upon atomic layer deposition of a TiO2 overlayer and photo-assisted electrodeposition of a cobalt oxide/oxyhydroxide co-catalyst, the photocurrent density of the engineered photoanode for oxygen evolution reaction (1 M NaOH) significantly increased from negligible photocurrent of the pristine BiFeO3 to 0.16 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under simulated 1 sun irradiation (100 mW cm−2, AM1.5G spectrum). Furthermore, such functionalization of the BiFeO3 photoanodes shifts the photoelectrochemical oxidation onset potential by 0.7 V down to 0.6 V vs. RHE. The significantly enhanced photoelectro-oxidation activity is facilitated by the improved charge transfer and electrochemical kinetics.

Photoelectrochemical oxygen evolution with cobalt phosphate and BiVO4 modified 1-D WO3 prepared by flame vapor deposition

We demonstrate the cobalt phosphate (Co-Pi) modified 1-D WO3/BiVO4 nanowire heterojunction photoanode as oxygen evolution catalyst for photoelectrochemical (PEC) water splitting application. WO3 nanowires were prepared by flame vapor deposition (FVD) process and BiVO4 nanoparticles were spin-coated on top of WO3 nanowires. In order to improve oxygen evolution kinetics, WO3/BiVO4 heterojunction photoanode was modified by photo-assisted electrodeposition of Co-Pi. Co-Pi improve the PEC water oxidation efficiency of 1 D-WO3/BiVO4 by reducing the charge recombination, facilitating the hole transfer and reducing the overpotential of oxygen evolution reaction. The optimum amount of Co-Pi for high photocurrent density was proposed. The loaded Co-Pi has enhanced the overall PEC performance showing largely shifted onset potential (∼450mV) with significantly increased photocurrent (2.7 times at 1.23V vs. RHE). The prepared composite photoanode of 1-D WO3/BiVO4/Co-Pi shows the higher incident photon to current efficiency and applied bias photon-to-current efficiency than without Co-Pi loading. We obtain the highest level of PEC performance with WO3/BiVO4/Co-Pi heterojunction composite photoanode which is based on 1-D framework of WO3 prepared by facile, rapid and economical FVD in this study.

Cobalt Phosphate Cocatalyst Loaded-CdS Nanorod Photoanode with Well-Defined Junctions for Highly Efficient Photoelectrochemical Water Splitting

Cocatalysts play important roles in photocatalytic and photoelectrochemical water splitting reactions. However, the formation of well-defined junctions between low dimensional semiconductors and cocatalysts is still challenging. In this study, CdS nanorod photoanodes loaded with cobalt phosphate (CoPi) cocatalyst were synthesized by a facile two-step route, in which CdS nanorods were prepared using a hydrothermal method followed by photo-assisted electrodeposition of CoPi. It was found that the formation of intimate junctions between CoPi and CdS nanorods in the form of Co–S bonding effectively facilitated the charge separation and lowered the activation energy of the water oxidation reaction. This resulted in highly efficient and stable photoelectrochemical water splitting on the CdS photoanode. The optimal CdS/CoPi photoanode showed a maximum photocurrent of 4.7 mA/cm2 at 0 V versus reversible hydrogen electrode under an AM 1.5 G solar simulator, which was 5.5-fold higher than that of bare CdS photoanode. This work expands the potential application of the cocatalyst CoPi in CdS photoanode systems and improves our understanding of the nature of cocatalysts with well-defined interface junctions in semiconductors. Well-defined interfacial junction with Co–S bonding over cobalt phosphate cocatalyzed CdS nanorod photoanode facilitates the charge separation and lowers the activation energy, thus achieving a considerable photocurrent of 4.7 mA/cm2 at 0 V vs. RHE.

In situ depositing an ultrathin CoOxHy layer on hematite in alkaline media for photoelectrochemical water oxidation

Cocatalysts are usually deposited on semiconductors to accelerate charge transfer/separation and passivate their surface states. Although various methods have been developed to decorate cocatalysts on semiconductors, in situ depositing a transition metal oxide/oxyhydroxide catalyst in alkaline electrolyte remains a challenge. Herein, we present a facile in situ photo-assisted electrodeposition of ultrathin amorphous CoOxHy layer on hematite for efficient solar-driven water oxidation. Compared to Co(II) hydroxide, Co(III) hydroxide is much less soluble in alkaline electrolytes, thus being favorable for deposition above the anodic onset potential of Co(II)/(III). By using this metal valence dependent deposition-dissolution equilibrium, we prepared this highly efficient and adaptive CoOxHy layer on hematite for OER in 1.0 M NaOH containing 1.0 μM Co(II). This method is promising for loading cocatalysts on semiconductors for solar-driven water splitting and is general for developing in situ (photo)electrochemical deposition of nanoscale catalysts.