Pluronic-assisted modifications of FeOOH precursor facilitate morphology adjustment and performance enhancement of Fe2O3 photoanodes

Morphology regulation and surface modification are crucial strategies to improving the photoelectrochemical water oxidation performance of Fe₂O₃ photoanodes. In this study, Pluronic F127-assisted synthesis and post-treatment were adopted to achieve surface modification of FeOOH nanorods prepared by hydrothermal technique, thereby adjusting the morphology and surface properties of Fe₂O₃ photoanodes after calcination. Although the morphology of FeOOH barely changed, the creation of porous nanorods through F127-assisted synthesis and morphological change from worm-like nanorods into nanoplates by F127-assisted post-treatment were realized, and the electrochemically active surface area, crystallinity, number of surface disorders, and photoabsorption property were affected. Furthermore, relatively high intensity of lattice defects and low-valent ferrous ions (Fe²⁺) were generated after F127-assisted synthesis, and charge transfer from the surface states was increased. Consequently, Fe₂O₃ photoanode subjected to F127-assisted synthesis exhibited a reduction in the onset potential by 60 mV. The photocurrent density of Fe₂O₃ increased by 77% at 1.23 V versus reversible hydrogen electrode following a synergistic effect of F127-assisted synthesis and post-treatment.     

Outstanding stability and photoelectrochemical catalytic performance of (Fe,Ni) co-doped Co3O4 photoelectrodes for solar hydrogen production

In this work, pure and (Fe, Ni) co-doped Co₃O₄ nanostructured photoelectrodes of different doping levels and thicknesses were manufactured at constant substrate temperature (450 °C) using the spray pyrolysis technique. In addition to the chemical compositions; the structural, optical, electrical, and photoelectrochemical (PEC) properties were investigated through the use of various analysis techniques. By increasing the codpoing ratio to 6%, the low energy band gap is decreased from 1.43 to 1.3 eV and the high energy bandgap is increased from 2.63 to 2.87 eV, in addition to the reduction in particle size from 30.2 to 12.0 nm. The high energy gap vanishes by increasing the codoped film's spread volume to 60 ml. X-ray photoelectron spectroscopy of 6%(Fe, Ni)-60ml Co₃O₄ confirms the existence of Ni^2+,3+ and Fe^2+,3+. Among the studied photoelectrodes, the 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode displays a photocatalytic hydrogen output rate of 150 mmol/h.cm² @-1V in 0.3M Na₂SO₄ electrolyte. The photocurrent density of 6%(Fe, Ni)-60ml photoelectrode reached up to 13.6 mA/cm²@-1V with an IPCE (incident photon to current conversion efficiency) of ～42%@405 nm and STH (solar to hydrogen conversion efficiency) of ～11.37%, which are the highest values yet for Co₃O₄-based photocatalysts. The value of ABPE(applied bias photon-to-current efficiency) is 0.34%@(-0.28V and 636 nm). Interestingly, this photoelectrode shows a photogenerated current density of ?0.14 mAcm^?2 at 0 V and a PEC current onset over 0.266V. The thermodynamic parameters, corrosion parameters, PEC surface areas, Tafel slopes, and impedance spectroscopies are also being studied to confirm and classify the PEC H₂ production mechanism. The 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode stability/reusability shows only a 6.6% reduction in PEC performance after ten successive runs at -1V with a corrosion rate of 1.2 nm/year. This work offered a new codoping strategy for the design of a highly active Co₃O₄ based photocatalyst for the generation of solar light-driven hydrogen.     

Syngas production through CH4-assisted co-electrolysis of H2O and CO2 in La0.8Sr0.2Cr0.5Fe0.5O3-δ-Zr0.84Y0.16O2-δ electrode-supported solid oxide electrolysis cells

High temperature co-electrolysis of H₂O/CO₂ allows for clean production of syngas using renewable energy, and the novel fuel-assisted electrolysis can effectively reduce consumption of electricity. Here, we report on symmetric cells YSZ-LSCrF | YSZ | YSZ-LSCrF, impregnated with Ni-SDC catalysts, for CH₄-assisted co-electrolysis of H₂O/CO₂. The required voltages to achieve an electrolysis current density of ?400 mA·cm^?2 at 850 °C are 1.0 V for the conventional co-electrolysis and 0.3 V for the CH₄-assisted co-electrolysis, indicative of a 70% reduction in the electricity consumption. For an inlet of H₂O/CO₂ (50/50 vol), syngas with a H₂:CO ratio of ≈2 can be always produced from the cathode under different current densities. In contrast, the anode effluent strongly depends upon the electrolysis current density and the operating temperature, with syngas favorably produced under moderate current densities at higher temperatures. It is demonstrated that syngas with a H₂:CO ratio of ≈2 can be produced from the anode at a formation rate of 6.5·mL min^?1·cm^?2 when operated at 850 °C with an electrolysis current density of ?450 mA·cm^?2.     

Elaboration and characterization of the brownmillerite Ca2Fe2O5 synthesized by citrate sol-gel method. Application for photocatalytic H2-Production under visible light over Ca2Fe2O5/ZnO hetero-system

The present work is devoted to the synthesis of the ferrite Ca₂Fe₂O₅ as photocatalyst crystallizing in the brownmillerite structure. The ternary oxide is prepared by sol-gel auto combustion and characterized by physical and electrochemical methods. The thermal analysis (TG/DSC) shows that, the formation of the brownmillerite is observed above 660 °C. The X-ray diffraction and BET analysis show respectively a single phase with an active surface area of ～6 m² g^?1. The SEM micrographs exhibit an inhomogeneous structure formed by agglomeration of irregular shaped grains, confirmed by the laser granulometry analysis. The forbidden band (～2.3 eV) determined from the diffuse reflectance, permits to explore ～ 30% of the sun spectrum into chemical energy. The p-type comportment of Ca₂Fe₂O₅ is demonstrated by the capacitance-potential (C^?2 - E) graph with a flat band potential (E_fb = 0.93 V_SCE), due to oxygen over-stoichiometry. The negative potential of the conduction band (?1.06 V_SCE) predicts the feasibility of the H₂ generation. Indeed, Ca₂Fe₂O₅ is chemical stable in a wide pH domain and is positively experimented as photocatalyst for the H₂-production under visible light. The best performance is obtained in alkaline medium (NaOH, 0.1 M) with a mean evolution rate of 18 μmol g^?1 min^?1. However, Ca₂Fe₂O₅ coupled to ZnO sol-gel (ZnO-SG) improves the catalytic performance. The H₂ evolution rate over (Ca₂Fe₂O₅/ZnO-SG) reached 24 μmol g^?1 min^?1 after 60 min. It has also been shown that ZnO–P, prepared by precipitation, is more efficient than that synthetized by sol-gel method (ZnO-SG) and TiO₂–P25.     

First demonstration of photoelectrochemical water splitting by commercial W–Cu powder metallurgy parts converted to highly porous 3D WO3/W skeletons

Hydrogen evolution through photoelectrochemical (PEC) water splitting by tungsten oxide-based photoanodes, as a stable and environmental-friendly material with moderate band gap, has attracted significant interest in recent years. The performance of WO₃ photoanode could be hindered by its poor oxygen evolution reaction kinetics and high charge carrier recombination rate. Additionally, scalable and cost-effective commercial procedure to prepare nanostructured electrodes is still challenging. We present, for the first time, a novel and scalable method to fabricate highly efficient self-supported WO₃/W nanostructured photoanodes from commercial W–Cu powder metallurgy (P/M) parts for water splitting. The electrodes were prepared by electrochemical etching of Cu networks followed by hydrothermal growth of WO₃ nanoflakes. Interconnected channels of W skeleton provided high active surface area for the growth of WO₃ nanoflakes with a thickness of ~40 nm and lateral dimension of ~250 nm. The optimized photoelectrode having 35% interconnected porosity exhibited an impressive current density of 4.36 mA cm⁻² comprising a remarkable photocurrent of 1.71 mA cm⁻² at 1.23 V vs. RHE under 100 mW cm⁻² simulated sunlight. This achievement is amongst the highest reported photocurrents for WO₃ photoelectrodes with tungsten substrate reported so far. Impedance and Mott-Schottky analyses evidenced fast charge transfer, low recombination rate, and accelerated O₂ detachment provided by optimum 3D porous WO₃/W electrode. Due to the nature of the commercial P/M parts and low-temperature hydrothermal processing, the procedure is cost-effective and scalable which can pave a new route for the fabrication of highly porous and efficient water splitting electrodes.     

Surface engineering of Ba-doped TiO2 nanorods by Bi2O3 passivation and (NiFe)OOH Co-catalyst layers for efficient and stable solar water oxidation

The rational design of heterostructures as an ideal photoelectrode system for H₂ and O₂ conversion in photoelectrochemical (PEC) system has been regarded as an essential key to boost PEC performance. In this work, to demonstrate the energetic photoanode cell, deposition of a thin layer of Bi₂O₃ is utilized to hybridize with the 5 wt% Ba-doped TiO₂ nanorod heterostructure under the cascading band diagram, where Ba-doping can enhance the charge transport/separation rate in bulk phase, in terms of increasing the donor density, enhancing the bulk electronic conductivity, and increasing the band bending. Furthermore, with optimizing the thickness (～15 nm) of Bi₂O₃, the (NiFe)OOH as a cocatalyst was adapted to improve the interfacial charge transfer rate in the PEC cell, reaching the high photocurrent density (J) of ～4.1 mA/cm² at 1.23 V (vs. Reversible Hydrogen Electrode) and stability retention of 100%, even after 15 h at 1 M NaOH under 1 Sun illumination condition. The improvement mainly comes from the extended absorption of visible light from the thin Bi₂O₃ layer, effective transfer/separation of photogenerated charge carriers, and acceleration of water oxidizing reaction, caused by the narrowed band gap and the favorable charge transfer under the cascading band alignment built by the heterojunction, as well as electrocatalyst, offering the timely consumption of photogenerated holes accumulated at the electrode surface.     

Highly efficient visible-light-driven photocatalytic H2 production over a p−n Mn0.2Cd0.8S/NiCo2O4 heterojunction modified with Ni2P

In this work, the Mn_0.2Cd_0.8S/NiCo₂O₄ composite modified with Ni₂P as a co-catalyst was fabricated via a simple two-step hydrothermal method. The as-prepared ternary Mn_0.2Cd_0.8S/NiCo₂O₄/Ni₂P composite displayed excellent H₂ production performance. The ternary composite loaded with 5 wt% NiCo₂O₄ and 2 wt% Ni₂P obtained the optimal H₂ production performance of 24.47 mmol g^?1 h^?1 and a maximum AQE of 23.75%. The enhanced H₂ production activity was assigned firstly to efficient spatial charge separation through the p?n Mn_0.2Cd_0.8S/NiCo₂O₄ heterojunction and secondly to sufficient surface active sites provided by Ni₂P co-catalysts. This research provides a new approach to design effective ternary heterojunction.     

Drawing the distinguished graphite carbon nitride (g-C3N4) on SnO2 nanoflake film for solar water oxidation

Tin dioxide (SnO₂) nanoflakes electrodes were developed by a simple hydrothermal synthesis with a length of ~1.5 μm. Based on this electrode, g-C₃N₄ layer with an energetic band gap of about 2.7 eV was deposited by electrophoretic deposition under constant potential (30 V) for 3, 5 and 10 min, respectively. To enhance the chemical adsorption of g-C₃N₄ sheets on SnO₂ nanoflake film, the SnO₂ film was put in 0.5 M NaOH solution, and OH⁻ ions were coated via the entire surface area of SnO₂ film. As increasing the deposited time of the g-C₃N₄ layer to 5 min, the g-C₃N₄ nanosheets steadily covered the surface area. In particular, g-C₃N₄ (5min)/SnO₂ nanoflake film exhibited the maximum photocurrent density (J_SC), 0.15 mA/cm² at 1.23 V vs. Reversible Hydrogen Electrode under the full sun, and a slight photoresponse in the visible light of 400–450 nm contributes to the enhancement of J_SC, compared to that of SnO₂ nanoflake film. Furthermore, the interfacial resistance after the coating of g-C₃N₄ layer is sharply reduced, which is resulted from the electrocatalytic effect of g-C₃N₄ layer. Thus, the heterojunction developed between the core SnO₂ layer showing a high conductivity and the shell g-C₃N₄ layer as the visible light absorbing medium can improve the photoelectrochemical performance.     

Fabrication of the SnS2/ZnIn2S4 heterojunction for highly efficient visible light photocatalytic H2 evolution

A series of SnS₂/ZnIn₂S₄ (x-SS/ZIS) photocatalysts with different mass ratios of SnS₂ were prepared by a hydrothermal method. The resulted composites were used for photocatalytic hydrogen evolution under visible light excitation. All the SS/ZIS composites exhibited significantly enhanced photocatalytic activity for H₂ evolution. Obviously, the highest H₂ evolution rate of 769 μmol g^?1 h^?1 was observed over 2.5-SS/ZIS, which was approximately 10.5 times that of the ZnIn₂S₄ (73 μmol g^?1 h^?1). The enhanced photocatalytic performance was attributed to the successful construction of SnS₂/ZnIn₂S₄ heterojunctions, leading to rapid charge separation and fast transfer of the photo-generated electrons and holes under light irradiation. On the basis of PL, electrochemical impedance spectroscopy (EIS), photocurrent measurements and the H₂ evolution tests, a plausible photocatalytic mechanism was proposed.     

ZnBi38O60/Bi2O3 photocathode for hydrogen production from water splitting

Hydrogen production from water splitting into photoelectrochemical cells is a promising alternative for reducing the use of fossil fuels. Here, we synthesize by spray pyrolysis a porous ZnBi₃₈O₆₀/γ-Bi₂O₃ film with a surface area of 744 m² g⁻¹ for use as a photocathode in water-splitting cells. The film of ZnBi₃₈O₆₀ with 3 wt% Bi₂O₃ has 2.3 eV bandgap energy and a conduction band energy of −2.14 V vs. RHE at pH 6.99, which is thermodynamically suitable for reducing H⁺ to H₂. Under illumination, the film produces a current density of −1.55 mA cm⁻² at 0 V vs. RHE with an onset potential of 0.84 V vs. RHE. HC-STH efficiency is 0.09% at 0.17 V vs. RHE and IPCE at 0 V vs. RHE is 3.8% at 480 nm. Under continuous operation, the ZnBi₃₈O₆₀/γ-Bi₂O₃ film shows a stable photocurrent of −0.4 mA cm⁻² at 0 V vs. RHE for 1800 s with 100% Faradaic efficiency.     

Solar hydrogen evolution over native visible-light-driven Sn3O4

Low-cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H₂ from water or alcohols will be critical to future hydrogen economies. Co-catalyst loading and/or doping of foreign element at host material have been crucial for semiconductor photocatalyst to produce significant H₂ evolution, so far. We synthesized native-visible-light driven Sn₃O₄ photocatalyst, which significantly catalyzed hydrogen evolution from various alcohol solutions under irradiation of visible light (λ > 400 nm), without co-catalyst. The H₂ production reaction proceeded through hydroxyalkyl radical reaction in the methanol solution. The apparent quantum yield was 0.4% for the Sn₃O₄ competitive to that of visible-light-sensitive co-catalyst loaded doped photocatalyst. The enhanced hydrogen evolution is attributed to the desirable band gap and band edge positions (CBM and VBM) of the Sn₃O₄ for H₂ production in visible light, which would originate from atomically layered structure of Sn₃O₄. The Sn₃O₄ material is good promising photocatalyst for solar hydrogen production from alcohols.     

Facile fabrication of visible light driven tin oxide photoanode and its photoelectrochemical water splitting properties

Photoelectrochemical water splitting is a promise way to transfer solar energy to hydrogen as chemical energy carrier. In this paper, visible light driven tin oxide based photoelectrodes were obtained through dipping SnCl₂·2H₂O EtOH solution on FTO or metal Ti substrate and with further heat treatment process. Photoelectrochemical measurements with three electrodes configuration revealed that this obtained photoelectrode showed n-type responsive properties and the photocurrent density reached mA/cm² level without any modification under visible light irradiation (λ > 420 nm). XRD, UV–Vis spectrum and control experimental results proposed that the visible light driven mechanism for the tin oxide based photoanode maybe ascribed to Sn⁴⁺/Sn²⁺ transformation and surface oxygen deficiency, and the tin oxide can be denoted as SnO_2−x.     

Influence of grain size on photoelectrocatalytic performance of CuBi2O4 photocathodes

CuBi₂O₄ is an ideal photocathode material owing to its suitable optical bandgap (～1.8 eV), positive onset potential (～1 V vs. RHE), and high theoretical photocurrent density (19.7–29 mA/cm²). However, its relatively poor efficiency in transporting carriers hinders it from achieving high photoelectrocatalytic performance. In this study, we propose the preparation of phase-pure large-grain CuBi₂O₄ thin film photocathodes through solvent pre-annealing and two-step annealing, with the aim of improving the carrier transport efficiency. The maximum grain size of CuBi₂O₄ reached an astonishing 1 μm at the optimal ethanol vapor concentration. Through time-resolved photoluminescence, we discovered that after treating CuBi₂O₄ with the proposed technique, the carrier lifetime improved by more than one order of magnitude. This improvement was achieved because the large grain size reduced the inhibition of carrier transport through grain boundaries. Therefore, the photocurrent density of large-grained CuBi₂O₄ reached 0.27 mA/cm², which is 27 times that of a direct annealing treatment. Finally, we used atomic layer deposition to load a ZnO protective layer and Pt catalyst onto the surface of CuBi₂O₄ photocathodes, and the photocurrent density of CuBi₂O₄/ZnO/Pt was further increased to 0.46 mA/cm² without using an electron scavenger (0.4 V vs. RHE).     

Highly efficient electrochemical generation of H2O2 on N/O co-modified defective carbon

The electrochemical oxygen reduction reaction (ORR) via two-electron pathway is a sustainable way of producing hydrogen peroxide. Nanostructured carbon materials are proved to be effective catalysts for 2e^? ORR. Herein, a series of mesoporous carbon with tunable nitrogen species and oxygen functional groups were synthesized by varying the added amount of dopamine hydrochloride as nitrogen and oxygen source. The modified catalysts exhibited higher content of pyrrolic-N and ether C–O groups which are confirmed by a series of characterization. Raman spectra and correlation analysis revealed that the increased proportion of defect sites in carbon materials are closely related to the introduced pyrrolic-N and ether C–O groups. And the rotating ring-disk electrode (RRDE) measurement carried out in 0.1 M KOH electrolyte showed the H₂O₂ selectivity increased with the content of defect sites. Among them, the optimized catalyst (NOC-6M) exhibited a selectivity of 95.2% and a potential of 0.71 V vs. RHE at ?1 mA cm^?2. Moreover, NOC-6M possessed the high H₂O₂ production rate of 548.8 mmol g_cat^?1 h^?1 with faradaic efficiency of 92.4% in a two-chamber H-cell. Further mechanistic analysis revealed that the introduction of pyrrolic-N and ether C–O are likely to improve the binding energy of the defect sites toward 1OOH intermediate, resulting in a more favorable 2e^? ORR pathway for H₂O₂ production.     

Evaluation of in-situ formed La2O3–TiO2–La2O2CO3 nanocomposite photocatalyst for H2 production

The photocatalytic evolution of H₂ over La₂O₃ decorated TiO₂ catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La₂O₃/TiO₂ into La₂O₃–TiO₂–La₂O₂CO₃ occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H₂ yield. The 2 wt%La₂O₃/TiO₂ nanocomposite demonstrated better H₂ yield (～8.76 mmol (g_cat)^?1) than the bare TiO₂ (～1.1 mmol (g_cat)^?1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H₂ rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H₂-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy.     

Highly efficient Bi2O3/MoS2 p-n heterojunction photocatalyst for H2 evolution from water splitting

The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi₂O₃/MoS₂ p-n heterojunction photocatalysts with tunable loading amount of Bi₂O₃ (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi₂O₃ and MoS_2, the Bi₂O₃/MoS₂ heterostructures displayed significantly superior performance for photocatalytic hydrogen (H₂) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi₂O₃/MoS₂ photocatalyst (10 μmol h⁻¹g⁻¹) with Bi₂O₃ content of 11 wt%, which was approximately ten times higher than pure Bi₂O₃ (1.1 μmol h⁻¹g⁻¹) and MoS₂ (1.2 μmol h⁻¹g⁻¹) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi₂O₃/MoS₂ heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.     

Catalyst support effect on ammonia decomposition over Ni/MgAl2O4 towards hydrogen production

Ammonia is a prospective fuel for hydrogen storage and production, but its application is limited by the high cost of the catalysts (Ru, etc.) to decompose NH₃. Decomposing ammonia using non-precious Ni as catalysts can therefore improve its prospects to produce hydrogen. This work proposes several Ni/MgAl₂O₄ with the support properties tuned and investigates the support effect on the catalytic performance. Ni/MgAl₂O₄-LDH shows high NH₃ conversion (～88.7%) and H₂ production rate (～1782.6 mmol g^?1 h^?1) at 30,000 L. kg^?1 h^?1 and 600 °C, which is 1.68 times as large as that of Ni/MgAl₂O₄-MM. The performance remains stable over 30 h. The characterizations manifest that the high specific surface area of Ni/MgAl₂O₄-LDH can introduce highly dispersed Ni on the surface. Kinetics analysis implies promoted NH₃ decomposition reaction and alleviated H₂ poisoning for Ni/MgAl₂O₄-LDH. A roughly linear relationship is obtained by fitting the curves of dispersed Ni on the surface vs the reaction orders regarding H₂ and NH₃. This indicates that enhanced NH₃ decomposition performance can be ascribed to the strengthened NH₃ decomposition reaction and weakened H₂ poisoning by the highly dispersed Ni on the MgAl₂O₄-LDH surface. This work provides an opportunity to develop highly active and cost-effective catalysts to produce hydrogen via NH₃ decomposition.     

Enhanced photocatalytic performance of NiFe2O4 nanoparticle spinel for hydrogen production

The spinel NiFe₂O₄, prepared from nitrates precursors, was characterized by thermal analyses, X-Ray Diffraction, UV-Vis diffuse reflectance, Scanning electron microscopy, X-Ray Fluorescence spectrometry, X-ray photoelectron spectroscopy and photo-electrochemistry measurements. The X-ray diffrcation analysis of the powder indicates a cubic phase with a lattice constant of 8.327(8) Å and crystallite size of 19 nm. The X-Ray Fluorescence spectrometry indicates a stoichiometry, very close to NiFe₂O₄ catalyst calcined at 900 °C The X-ray photoelectron spectroscopy analysis confirmed the valences and crystallographic sites of the transition elements. The direct optical gap of NiFe₂O₄ (1.78 eV), due to the crystal field splitting of the 3d orbital in the octahedral site, is well suited for the solar spectrum and attractive for photo-electrochemical H₂ production. The flat band potential (E_fb = 0.47 V_SCE) was obtained from the capacitance-potential (C^?2 - E) characteristic in NaOH (0.1 M) electrolyte. A conduction band of ?1.11 V_SCE, more cathodic than the H₂ level (?0.8 V_SCE), enabled the use of NiFe₂O₄ for the water reduction into hydrogen. The H₂ evolution rate of 46.5 μmol g^?1 min^?1 was obtained under optimal conditions (1 mg of catalyst/mL, NaOH and 50 °C) in the presence of SO₃^2? (10^?3 M) as hole scavenger under visible light flux of 23 mW cm^?2. A deactivation effect of only 1% was obtained.     

Photocatalytic hydrogen evolution of nanoporous CoFe2O4 and NiFe2O4 for water splitting

The spinels CoFe₂O₄ and NiFe₂O₄ of nanoporous photocatalysts were prepared by dealloying and calcination. The photocatalytic performance for the hydrogen generation rate via water splitting was measured. The results revealed that CoFe₂O₄ exhibits a sheet-like nanoporous structure and that abundant mesopores are distributed in the nanosheets. NiFe₂O₄ shows a typical pore-ligament structure. The measurements show that hydrogen generation is exhibited by both oxides because the bandgap of CoFe₂O₄ and NiFe₂O₄ is higher than the water oxidization potential. The hydrogen generation rate is approximately 0.088 mmol h^?1g^?1 for CoFe₂O₄ and 0.026 mmol h^?1g^?1 for NiFe₂O₄ when the TEOA (10 vol%) sacrificial agent is adopted. This performance is significantly higher than that of methanol as the scavenger because TEOA increases the pH value of the solution, changes the negative shift in the conduction band energy level and improves the electron transport efficiency. The higher performance of CoFe₂O₄ is attributed to its larger specific surface area, ample unimpeded penetration diffusion paths and higher electron transfer rate.     

One step synthesis of self-doped F–Ta2O5 nanoshuttles photocatalyst and enhanced photocatalytic hydrogen evolution

Tantalic oxide (Ta₂O₅), as an excellent transition metal oxide photocatalyst, has been extensively studied on fluorination or self-doped for hydrogen production, while there is little research to combine the two modifications. In this work, surface fluorination self-doped Ta₂O₅ nanoshuttles (FTNSs) photocatalyst is synthesized successfully by a modified one-step hydrothermal method. The test results show the presence of surface fluorine ions, Ta⁴⁺ and oxygen vacancies in the sample. The FTNSs prepared by hydrothermal method under 180 °C for 24 h exhibits the highest hydrogen evolution rate (HER). The HER is 179.2 and 19.78 μmol h^?1 g^?1 in the absence of any co-catalyst under full-spectrum and simulated solar light, respectively, which is higher than that of the Ta₂O₅ nanoshuttles without fluoride and the commercial Ta₂O₅. The higher HER can attribute to the existence of F, Ta⁴⁺ and oxygen vacancies, which enhance the photogenerated carrier mobility and reduce the recombination.