Simultaneously improving solar water oxidation kinetics and passivating surface states of hematite by loading an amorphous Ni doped cobalt phosphate layer

High surface states density of hematite photoanodes results in their low water oxidation kinetics and high surface electrons-holes recombination. To overcome these inherent drawbacks, various methods have been adopted, especially loading oxygen evolution catalysts and depositing oxide passivation layers. We report here an efficient way to promote the photocurrent of Fe₂O₃ photoanodes via depositing a thin layer of Co_0.84Ni_0.16-Pi. With the Co_0.84Ni_0.16-Pi deposit on its surface, the photocurrent density of Fe₂O₃ increases by ca. 42% at 0.23 V vs. Ag/AgCl, and the onset potential shifts 200 mV cathodically. In contrast, Co-Pi@Fe₂O₃ photoanode shows only 20% enhancement in photocurrent density under otherwise identical condition. The dark current densities of the photoanodes give an evidence that both Co_0.84Ni_0.16-Pi and Co-Pi are good oxygen evolution catalysts. Moreover, different from sparsely distributed Co-Pi nanoparticles, a 2–3 nm amorphous Ni doped cobalt phosphate layer can be also an effective passivation layer for surface states of hematite, which has been demonstrated by the analyses of Mott-Schottky plots and electrochemical impedance spectroscopy. This work demonstrates the dual roles of an amorphous oxygen evolution co-catalyst on hematite photoanodes and provides a simple method for designing highly efficient photoanodes.     

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 Fe_xNi_1-xOOH cocatalyst (Fe_xNi_1-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 Fe_xNi_1-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 Fe_xNi_1-xOOH cocatalyst provides a novel strategy for the construction of efficient photoanodes by surface engineering.     

Convex-nanorods of α-Fe2O3/CQDs heterojunction photoanode synthesized by a facile hydrothermal method for highly efficient water oxidation

Morphology controlling and surface modification of semiconductors is the key for efficient photoelectrochemical (PEC) water splitting systems. This work provides a new strategy for achieving morphology control and heterojunction construction simultaneously by one-step hydrothermal method. The α-Fe₂O₃/CQDs heterojunction photoanode with convex-nanorods morphology is successfully prepared by hydrothermal method in CQDs (Carbon Quantum Dots) aqueous contained iron precursor followed by low temperature annealing treatment. Compared with bare hematite photoanode, the α-Fe₂O₃/CQDs photoanode has 8.5 time higher photocurrent density (at 1.23 V vs. RHE) of 0.35 mA cm^?2 and a negative shift of onset potential about 300 mV. The enhanced photoelectrochemical response is attributed to the convex-nanorods which benefit higher absorbance of light and the formed α-Fe₂O₃/CQDs heterojunction, which can efficiently enhance the electron-hole separation and reduce the surface charge recombination. The morphology and properties of the sample were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fouriertrans form infrared spectroscopy (FTIR), UV–vis spectra, X-ray diffractometry (XRD), X-ray photoelectron spectra (XPS), and photoelectrical measurements.     

Fast and low-cost fabrication of 1D hematite photoanode in pure water vapor and air atmosphere: Investigation the effect of the oxidation atmosphere on the PEC performance of the hematite photoanodes

In this study, hematite photoanodes were successfully fabricated by thermal oxidation of the commercial cold-rolled steel at 500 °C in pure water vapor and air atmosphere. The crystal phase structure, surface morphology, and optical properties of the hematite photoanodes were characterized using an X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) and UV–VIS spectrophotometer, respectively. The results showed that hematite photoanodes had high crystalline phase and the annealing atmosphere influenced the morphology of the hematite photoanodes. Moreover, nanowhisker and nanorod shaped nanostructures were observed on the substrate. The optical band gap values of the hematite photoanodes varied between 2.38 and 2.70 eV. Photoelectrochemical (PEC) studies of the hematite photoanodes were assessed in the 0.1 M NaOH electrolyte solution using the Mott–Schottky analysis and electrochemical impedance spectroscopy techniques. The PEC findings exhibited that the hematite photoanode annealed 15-min in water vapor had best PEC performance achieving photocurrent density 0.244 mA/cm² at 1.6 V vs. V_RHE and highest carrier density value (N_D = 1.15 × 10²¹ cm^?3). Furthermore, the photoanodes annealed in water vapor atmosphere revealed at least three times higher PEC performance than that of photoanodes annealed in air. Thermal oxidation method in water vapor is an efficient methods for fabrication of hematite photoanodes.     

Photoelectrochemical water oxidation performance promoted by a cupric oxide-hematite heterojunction photoanode

Hematite is a promising material for photoelectrochemical (PEC) water oxidation due to its narrow bandgap and chemical stability in alkaline electrolytes. However, the PEC performance of hematite is known to be inhibited by a short carrier diffusion length and slow kinetics for the oxygen evolution process. The rational control of morphology, crystallinity, and interfacial charge transfer plays an important role in tuning the PEC performance of α-Fe₂O₃ photoelectrodes. In this study, different iron oxide nano/microstructures are synthesized by the sintering of iron sheets in air at different temperatures. The synergetic effect of the surface morphology and crystallinity on the photocurrent and onset potential of the photoanode is investigated. The coral-like structure with high index (104) facets prepared at a high temperature shows a decreased onset potential, suggesting a strong correlation between the onset potential and crystalline orientation. To further improve the photocurrent density of this hematite photoanode, cupric oxide-hematite heterostructures are explored. An obvious improvement in the photocurrent density is observed from 1.1 to 1.6 V. The resulting α-Fe₂O₃/CuO photoanode exhibits a photocurrent density of 1.5 mA cm⁻² at 1.6 V, 25% higher than that of the pristine hematite. The Mott-Schottky plot and EIS measurement indicate that the α-Fe₂O₃/CuO heterojunction facilitates the extraction of the accumulated holes in the hematite through a type-II band alignment and the CuO can serve as a catalyst for promoting the oxygen evolution reaction.     

The coupling effect of carbon spheres and cobalt-involved carbon nitrides stacked on TiO2 nanorod arrays for promoted solar water oxidation

Photoanode materials typically exhibit good stability and environmentally and economically properties in solar water splitting cells, while they always suffer from the narrow light absorption range, heavy surface charge combination and sluggish surface reaction kinetics. Herein, we design an efficient and reproducible photoanode by stacking amorphous carbon spheres (CSs) and cobalt-involved carbon nitrides (Co-CNs) on surface of TiO₂ nanorod arrays. CSs work as light sensitizer for broadening the light absorption range of photoanode and promoting the utilization of solar energy, which further improved by Co-CNs partially. In addition, CSs increase the conductivity of photoanode, as a transport channel for improving the charge migration. Co-CNs introduce many active sites on surface of photoanode for facilitated solar water oxidation. The best constructed TiO₂/CSs/Co-CNs photoanode exhibits an impressive photocurrent density of ∼1.73 mA/cm² (at 1.23 V vs RHE). The staking method of various functional materials provides one promising strategy for the modification of catalysts.     

Mutual effect of extrinsic defects and electronic carbon traps of M-TiO2 (M = V,Co, Ni) nanorod arrays on photoexcited charge extraction of CdS for superior photoelectrochemical activity of hydrogen production

Understanding the photoexcited charge carrier dynamics such as separation, transportation and extraction in smart hybrid nanocomposites is the key to high performance solar cells. Nanocomposites possess advantage of broader solar absorption with their fast photoexcited charge separation and transportation but their use as photocorrosion-stable material is yet to be explored. Also, bulk and surface defects in individual components of the nanocomposites boost the efficiency of the solar cells, despite of the fact the recombination of the photoexcited charges at the interfaces lead to a substantial loss of charges and realizing a big challenge. Herein, the extrinsic defects like bulk and surface defects are induced by transition metal (M = V, Co, Ni) doping of M ? TiO₂ nanorod arrays. Consequently, the hydrothermal synthesis method offers the tuning of the carbon trapping states depending upon the type of the metal doped in M ? TiO₂ that decelerates the charge carrier dynamics in the M-TiO₂/CdS (M = V, Co, Ni) nanocomposites with the increase in the amount of carbon. Excellent charge extraction is observed in VTiO₂ (4% carbon) from its CdS sensitizer with photocurrent density of 2.06 mA/cm² than NiTiO₂ (14.6% carbon), TiO₂ (18.94% carbon) and CoTiO₂ (39.2% carbon) with photocurrent densities of 1.83, 1.46 and 1.34 mA/cm² at 0 V versus Ag/AgCl under 100 mW/cm² light intensity, respectively. This shows primary dependence of photoexcited charge dynamics upon the density of the carbon trapping states to be least while secondary dependence upon the density of the extrinsic defects in M ? TiO₂ to be maximum. This work creates a paradigm for future studies to have a broader insight of the photocatalyst's overall functioning to boost the efficiencies in solar cells by controlling the amount of electronic carbon traps during the synthesis of a large class of inorganic semiconductor photocatalysts.     

Earth abundant ZnO/CdS/CuSbS2 core-shell nanowire arrays as highly efficient photoanode for hydrogen evolution

CuSbS₂ is regarded as a promising photo-absorber for solar energy conversion due to its proper bandgap, high absorptivity and earth abundance. Herein, novel low-cost ZnO/CdS/CuSbS₂ core-shell nanowire arrays were constructed as photoanode for hydrogen evolution through non-aqueous electrodeposition and cation exchange. The nanowire demonstrates even and compact multilayer structure. The optimal ZnO/CdS/CuSbS₂ photoanode achieves a photocurrent of 6.48 mA/cm² at 0 V versus Ag/AgCl and the remarkable IPCE value with approximately 52% at 480 nm in an electrolyte solution containing 0.35 mol/L Na₂SO₃ and 0.25 mol/L Na₂S. It also exhibited a good stability, maintained 87.9% of the initial current after 1 h measurement. The high performance benefits from well-crystalline and compact multilayer structure, high absorptivity of CuSbS₂ and CdS, p-n junction formed between CdS and CuSbS₂ which promotes the electron-hole separation and ZnO nanowire array as three dimensional scaffolds for electron percolation pathway. This work suggests the potential applications of low-cost p-n junction core-shell nanowire arrays as a highly efficient photoanode for hydrogen evolution in oil-field waste water with reductive sulfide.     

Efficient suppression of surface charge recombination by CoP-Modified nanoporous BiVO4 for photoelectrochemical water splitting

BiVO₄ is a promising photoanode material for water splitting due to its substantial absorption of solar light as well as favorable band edge positions. However, the poor water oxidation kinetics of BiVO₄ results in its insufficient photocurrent density. Herein, we demonstrate the use of CoP nanoparticles for facile surface modification of nanoporous BiVO₄ photoanode in potassium borate buffer solution (pH 9.0), which can generate a tremendous cathodic shift of ~430 mV in the onset potential for photoelectrochemical water oxidation. In addition, a remarkable photocurrent density of 4.1 mA cm^?2 is achieved at 1.23 V vs. RHE under AM 1.5G illumination. The photoelectrochemical measurement using sodium sulfite as a hole scavenger clearly shows that the greatly improved performances are attributed to the efficient suppression of interfacial charge recombination through loading of CoP catalyst. Moreover, the maximum surface charge injection yield can reach >81% at 1.23 V vs. RHE and the maximum IPCE of CoP/BiVO₄ can reach 75.8% at 420 nm, suggesting the potential application of CoP-modified BiVO₄ photoanode for overall solar water splitting in cost-effective tandem photoelectrochemical cells.     

Ultrathin Ti-doped hematite photoanode by pyrolysis of ferrocene

Ultrathin Ti-doped α-Fe₂O₃ photoanode was prepared by a facile atmospheric pressure chemical vapor deposition method through pyrolysis of ferrocene at 450 °C on Ti foil. The as prepared ultrathin hematite thin film has a surface feature size of 70 × 30 nm and a thickness of 50 nm. The photocurrent of this ultrathin hematite photoanode prepared at 450 °C in 1 M NaOH reaches 900 μA/cm² at 0.6 V_SCE under AM 1.5G illumination. The superior performance to the thin films prepared on FTO glass was ascribed to the diffusion and doping of Ti⁴⁺ from the metal substrate during pyrolysis deposition of hematite on Ti substrate.     

Experimental investigation and analysis of a new photoelectrochemical reactor for hydrogen production

In this research paper, an experimental investigation of photoactive material titanium dioxide (TiO₂) coated on 180 cm² 316 stainless steel anode is undertaken to study the photoresponse on photoelectrochemical (PEC) hydrogen production. The TiO₂ nanoparticles are first prepared via sol-gel method. A large surface 316 stainless steel anode is coated with TiO₂ nanoparticles by a dip coating apparatus at a withdraw rate of 2.5 mm/s. The nanoparticles are carried on the stainless steel substrate by two-step annealing procedure. The potentiostatic studies confirm the photoactivity of TiO₂ nanoparticles in a photoelectrochemical reactor when exposed to solar ultraviolet (UV) light. The photon to current efficiency measurements carried out on the PEC reactor with TiO₂ coated large surface stainless steel as photoanode demonstrate a significant increase of photoresponse in UV light compared to the uncoated stainless steel prepared under similar conditions. Upon illumination at a power density of 600 W/m², the hydrogen production is observed in TiO₂ coated stainless steel substrate at a measured rate of 51 ml/h while no illumination conditions show a production rate of 42 ml/h. In comparative assessments, the TiO₂ coated substrate shows an increase in photocurrent of 10 mA with an energy efficiency of 1.32% and exergy efficiency of 3.42% at an applied potential of 1.6 V. The present results show a great potential for titanium nanoparticles semiconductor metal oxide in photoelectrochemical hydrogen production application.     

Boosting the performance of hematite photoanodes for solar water oxidation by synergistic W-incorporation and Zr-passivation

Incorporating impurities into hematite is an effective approach to enhance the photoelectrochemical (PEC) water splitting performance of hematite photoanode. Here, we report an efficient W-incorporation in hematite (W-Fe₂O₃) to enhance the PEC performance by depositing a WO₃ underlayer onto the FTO substrate. The W-incorporation dramatically enhances the photocurrent density of hematite by a factor of ∼2. Moreover, it can be well coupled with Zr to achieve a high photocurrent of 2.0 mA cm⁻² at 1.23 V vs. RHE by simultaneously depositing a ZrO₂ underlayer on the FTO substrate. A large cathodic shift of the onset potential up to 120 mV can also be obtained. The boosted PEC performance can be attributed to the synergistic effect of W and Zr in hematite, which can both improve the carrier density (by W-incorporation) and suppress the charge recombination (by Zr-passivation).     

Iron oxide ores as carriers for the production of high purity hydrogen from biogas by steam–iron process

Production of high purity hydrogen (<50 ppm CO) by steam–iron process (SIP) from a synthetic sweetened biogas has been investigated making use of a natural iron ore containing up to 81 wt% of hematite (Fe₂O₃) as oxygen carrier. The presence of a lab-made catalyst (NiAl₂O₄ with NiO excess above its stoichiometric composition) was required to carry out the significant transformation of mixtures of methane and carbon dioxide in hydrogen and carbon monoxide by methane dry reforming reaction. Three consecutive sub-stages have been identified along the reduction stage that comprise A) the combustion of CH₄ by lattice oxygen of NiO and Fe₂O₃, B) catalyzed methane dry reforming and C) G–G equilibrium described by the Water-Gas-Shift reaction. Oxidation stages were carried out with steam completing the cycle. Oxidation temperature was always kept constant at 500 °C regardless of the temperature used in the previous reduction to minimize the gasification of eventual carbon deposits formed along the previous reduction stage. The presence of other oxides different from hematite in minor proportions (SiO₂, Al₂O₃, CaO and MgO to name the most significant) confers it an increased thermal resistance against sintering respecting pure hematite at the expense of slowing down the reduction and oxidation rates. A “tailor made” hematite with additives (Al₂O₃ and CeO₂) in minor proportions (2 wt%) has been used to stablish comparisons in performance between natural and synthetic iron oxides. It has been investigated the effect of the reduction temperature, the proportion of methane to carbon dioxide in the feed (CH₄:CO₂ ratio) and the number of repetitive redox cycles.     

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 V_RHE, which is about 3.0 times of activated Ti–Fe₂O₃ (a-Ti-Fe₂O₃) and 1.5 times of activated CoO_x/Ti–Fe₂O₃. Tungstate promotes the surface reconstruction of cobalt-based cocatalyst, resulting in a significant increase in bulk charge separation efficiency (η_sep) and surface charge injection efficiency (η_inj). 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.     

New method for improving the bulk charge separation of hematite with enhanced water splitting

Due to its poor bulk charge separation efficiency, the photoelectrochemical (PEC) performance of pristine hematite prepared directly from an electrodeposited Fe film is limited. Au-modification of hematite via a simple immersion method improves the PEC performance two-fold to 0.31 mA cm⁻². The Au nanoparticles deposited from HAuCl₄ act as plasmonic photosensitizers and electron collectors to improve the light absorption and bulk charge separation efficiency of the photoanode. In addition, the increase in the (110) plane and specific surface area induced by HAuCl₄ enhances the bulk charge separation efficiency. After further modification with Ti, the photocurrent response of the resulting Ti/Au/α-Fe₂O₃ photoanode improves to 0.51 mA cm⁻²; this increase is attributed to its increased light absorption, bulk charge separation efficiency (η_bulk), and surface charge injection efficiency (η_surface). In this work, the effect of Au and Ti on the crystalline structure, morphology and PEC performance of the novel electrodeposited hematite photoanode are investigated by systematical characterization.     

Investigation of V-doped TiO2 as an anodic catalyst support for SPE water electrolysis

A modified evaporation-induced self-assembly (EISA) method was employed to prepare titania samples doped with different amounts of vanadium (0, 10, 20, 30 at.%), which were further evaluated as catalyst supports for the oxygen evolution reaction (OER) catalyst IrO₂ in the solid polymer electrolyte water electrolyzer (SPEWE). The effects of V dopant on titania supports are proved to be twofold: i) enhancing the simplification of phase composition and consequently improving the homogeneity of porous morphology; ii) introducing redox couple V (IV)/V (V) to the surface of titania. As a result, the catalyst's OER activity is improved with the increase of V dopant in the titania support after loading IrO₂ via Adams fusion method. In single cells, the OER performance gradually increases with V dopant from 0 to 20 at.%, followed by a performance deterioration with V amount reaching 30 at.% due to the corrodible V₂O₅ precipitate.     

Metallic iron doped vitamin B12/C as efficient nonprecious metal catalysts for oxygen reduction reaction

The development of efficient nonprecious metal catalysts for oxygen reduction reaction (ORR) is crucial but challenging. Herein, one simple and effective strategy is developed to synthesize bimetallic nitrogen-doped carbon catalysts by pyrolyzing Fe-doped Vitamin B12 (VB12) supported carbon black (Fe-VB12/C). A typical Fe₂₀-VB12/C catalyst with a nominal iron content of 20 wt% pyrolyzed at 700 °C exhibits remarkably ORR activity in alkaline medium (half-wave potential of 0.88 V, 10 mV positive than that of commercial Pt/C), high selectivity (electron transfer number > 3.93), excellent stability (only 6 mV negative shift of half-wave potential after 5000 potential cycles) and good methanol-tolerance. The superior ORR activity of the composite is mainly attributed to the improved mesoporous structure and co-existence of abundant Fe-N_x and Co-N_x active sites. Meanwhile, the metallic Fe are necessary for the improved ORR activity by means of the interaction of metallic Fe with neighboring active sites.     

Elucidation the role of Co-MOF on hematite for boosting the photoelectrochemical performance toward water oxidation

Developing an efficient photoanode to convert solar energy into hydrogen fuel confronts big challenges owing to the sluggish water oxidation kinetics. Herein, we proposed a feasible method to coat Co-based metal-organic framework (Co-MOF) on Ti doped α-Fe₂O₃ and revealed its functions on the oxygen evolution reaction (OER) and photoelectrochemical (PEC) water oxidation. The Co-MOF/Ti–Fe₂O₃ showed a photocurrent density of 1.01 mA/cm² (1.23V_RHE) with a low turn-on voltage (V_on) of 0.80 V_RHE. The significant improvement of photocurrent density which was ca. 3 times higher than the pristine Fe₂O₃, was contributed by the improved charge separation efficiency on the surface rather than in the bulk. And this was validated by the increased trapping capacitance (C_trap) and reduced charge transport resistance (R_ct). Additionally, the low V_on was attributable to the compromise of introduced surface states and the catalytic effect of the Co-MOF. In this work, we discovered the Co-MOF not only offered catalysis sites for OER, but shed light on its influence on the overall PEC water oxidation, and led to an in-depth understanding of cocatalysts on the PEC water splitting.     

Effect of acid passivation and H2 sputtering pretreatments on the adhesive strength of sol–gel derived Hydroxyapatite coating on titanium surface

In this study, in order to increase the adhesive strength of a Hydroxyapatite (HA) coating, deposited on the surface of commercially pure titanium, acid passivation and hydrogen sputtering pretreatments were used. The pure titanium surfaces were passivized by acid solution and treated by hydrogen sputtering, at a temperature of 300 °C for 1 h. Ca(NO₃)₂·4H₂O and NH₄H₂PO₄ were chosen as starting precursors for Ca and P sources. HA coatings on the titanium surface were deposited using the sol–gel method and sintered in air at the temperatures of 750^oC-900 °C for 1 h. XRD, SEM, EDS and AFM analysis techniques were used for structural and morphological characterization. Scratch test was performed for determining the adhesion of HA coatings. The experimental results indicated that compact and crack free HA coating, which has a Ca/P ratio of 1:6, was formed on pure Titanium (Ti) surface. The adhesive strength values of the HA coating, pretreated with H₂ sputtering and acid passivation were found to be 72.84 MPa and 55.83 MPa at temperature of 900 °C, respectively. It was observed that H₂ plasma sputtering pretreatment, improved the adhesive strength of the HA coatings compared to pretreatment with acid passivation.     

Preparation and photocatalytic H2-production on α-Fe2O3 prepared by sol-gel

In this work, the hematite α-Fe₂O₃ was synthesized by sol-gel method and characterized by X-ray diffraction and optical properties. The XRD patterns realized at different temperatures, show that pure hematite is obtained above 500 °C. The diffuse reflectance gives respectively direct and indirect optical transitions at 2.17 and 2.04 eV, in agreement with the red color. The capacitance measurement of α-Fe₂O₃ indicates p type behavior with a conduction band (?1.14 V vs. SCE), more cathodic than the H₂ evolution (～?0.8 V vs. SCE). The oxide was successfully tested for the hydrogen production under visible irradiation (29 mW cm^?2). α-Fe₂O₃ is photo-electrochemically stable in alkaline medium by hole consumption reactions involving X^2? (= SO₃^2? and S₂O₃^2?) as hole scavengers. The best photocatalytic activity for H₂ production was obtained on α-Fe₂O₃, calcined at 500 °C, in (Na₂S₂O₃ 0.025 M, pH ～ 13), with an average evolution rate of 0.015 cm³ h^?1 (mg catalyst)^?1 and a quantum efficiency of 0.26%. The system shows a tendency toward saturation, due to the competitive reduction of end products with the water reduction and the cathodic shift of the H₂ potential.