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The CO : H2 ratio in syngas is found to be controllable from 1 : 1 to 1 : 20 by the combined use of a pristine and a CoP-py-anchored mesoporous TiO2 electrode by simply tuning the applied potential.

In a Rh/CrOx core–shell cocatalyst for water-splitting photocatalysts, CrOx serves as an electron pathway, transfers the photoexcited electrons from photocatalysts to Rh (reduction site), and improves the H2 evolution activity.

Photoexcited charge manipulation was demonstrated by molecular engineering in conjugated polymers, bearing a Ru(ii) complex as the CO2 reduction photocatalyst.

Because the majority of Z-scheme water splitting systems employ a shuttle redox mediator that allows electron transfer between two photocatalyst materials, the development of an effective redox mediator is crucial for improving the efficiency of Z-scheme systems toward the overall water splitting reaction. We recently revealed that some polyoxometalates (POMs) such as Manganese-substituted Keggin-type silicotungstate ([SiW11O39MnIII/II(H2O)]5–/6–) can function as stable redox mediators. However, the limited number of POMs available for the Z-scheme system hinders the understanding of the fundamental properties of the employed POM. Herein, a series of Vanadium-substituted POMs, i.e., [XVVW11O40]n–/[XVIVW11O40](n+1)– (X = B, Si, and P), and a Cobalt-substituted POM [SiW11O39CoIII(H2O)]5–/[SiW11O39CoII(H2O)]6– were synthesized. Moreover, the fundamental properties, such as redox potential and chemical stability, of the POMs and their impact on water splitting photocatalysis efficiency was evaluated to provide guidance for designing efficient POM redox mediators. The substitution of constituent elements was found to affect their redox potentials, chemical stability under varied pH conditions, light absorption, and photocatalytic activity. All V-substituted POMs were found to possess an appropriate redox potential (i.e., between the potentials of water reduction and oxidation); however, their relatively high absorption in the visible light region appeared to be a disadvantage in terms of light shielding. Among the V-substituted ones, the [SiVVW11O40]5–/[SiVIVW11O40]6– exhibited stability in repeated redox cycles over a wider pH range (2.5–6.5). In contrast, the redox potential of [SiW11O39CoIII(H2O)]5–/[SiW11O39CoII(H2O)]6– was more positive than the water oxidation potential, making it unsuitable for use as a redox mediator.

An efficient spatial separation of photoexcited carriers is demonstrated in a layered-oxyhalide nanoplate by controlling the direction of carrier flows upon Rh cocatalyst loading, which leads to drastic photocatalytic H2 evolution activity.

A Sillén SrBi3O4Cl3 is synthesized in pure and high-crystallinity form via a flux method with an appropriate molten salt, which leads to a higher photocatalytic activity than that of SrBi3O4Cl3 prepared by a conventional solid-state reaction method.

Incorporation of Ag into a crystalline lattice of kesterite Cu2ZnSnS4 thin film was found to be effective for improvements of its photoelectrochemical properties for water reduction.

Bismuth-based oxyhalides with layered Sillén(−Aurivillius) structures have attracted significant attention as photocatalysts. Recent studies have unveiled a part of the structure-property relationship of this material; however, it has not been...

Interfacial electron flow is crucial for an efficient two-step (Z-scheme) solar water-splitting reaction. Dye-sensitization of a wide-gap oxide semiconductor has attracted considerable attention for decades as a means of producing hydrogen from water; however, it suffers from back electron transfer reactions at solid-solid and solid-solution interfaces. Here, we demonstrate that a combination of two nano-architectures, Ru-dye double layering and Pt cocatalyst intercalation to layered niobate semiconductor, effectively suppresses the back electron transfers at interfaces, leading to the complete oxidation of the [Co(bpy)(3)]-type electron mediator (bpy = 2,2'-bipyridine) as a result of efficient photocatalytic hydrogen production. Our systematic study on the Ru-dye double layers revealed that the double layering of two different Ru dyes and surface modification with the Zr4+ cation not only suppress the back electron transfer from an electron-injected semiconductor to oxidized dye but also accelerate the electron injection from the mediator to the oxidized dye. In addition, the re-reduction of the oxidized Co(III) mediator at the Pt cocatalyst surface was effectively suppressed by intercalation of Pt to the layered niobate semiconductor. The present work clearly shows that double nano-architectures controlling the surfaces of the semiconductor and cocatalyst have great potential for photo-induced charge separation at the solid-solution interface and expands the possibilities of layered semiconductor materials toward Z-scheme water splitting.

Layered oxyhalides containing double or triple fluorite layers are promising visible-light-responsive water-splitting photocatalysts with unique band structures. Herein, we report on the synthesis, structure, and photocatalytic property of Bi4BaO6Cl2 (I4/mmm) with alternating double (Bi2O2) and triple (Bi2BaO4) fluorite layers, which was extracted from the crystallographic database on the basis of Madelung potential calculations. Rietveld refinements from powder X-ray and neutron diffraction data revealed the presence of cationic disorder between Bi2O2 and Bi2BaO4 layers, leading to electrostatic stabilization. DFT calculations suggested that photogenerated electrons and holes flow through the double and triple layers, respectively, which may suppress electron-hole recombination. We expanded this double-triple system to include Bi4CaO6Cl2 and Bi4SrO6Cl2 with orthorhombic distortions and different degrees of cationic disorder, which allow band gap tuning. All the double-triple compounds Bi4AO6Cl2 showed stable water-splitting photocatalysis in the presence of a sacrificial reagent.

The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H₁₀.₇Sb₃₂.₁O₄₄][H₂.₁Sb₂.₁I₈O₆][Sb₀.₇₆I₆]₂·25H₂O (HSbOI), forming a face-centered cubic structure with cationic Sb₃₂O₄₄ clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb3+ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements., 正電荷の酸化物クラスターの発見 酸触媒としての高い可能性. 京都大学プレスリリース. 2022-06-18., Scientists serendipitously discover rare cluster compound. 京都大学プレスリリース. 2022-06-18.

Photocatalytic reduction of CO2 using water as a reductant and visible light as the energy source is an important target in artificial photosynthesis. In this study, we report a highly stable photoelectrochemical CO2 reduction involving a new molecular photocathode comprising a NiO electrode and polymerized complexes of the Ru(II) photosensitizer and Ru(II) catalyst (NiO/PRu-poly-Ru-RuCAT1). CO and HCOOH were stably and selectively produced for over 100 h under visible light irradiation and a low bias. The turnover number of CO2 reduction products exceeded 1200, which represents the highest durability reported for photoelectrochemical reactions using molecular photocathodes. Moreover, a connected system of the NiO/PRu-poly-Ru-RuCAT1 molecular photocathode and a CoOx/BiVO4 photoanode suitable for water oxidation facilitated stable CO2 reduction with water as an electron donor and visible light as the energy source, with no bias for over 24 h. An energy conversion efficiency of 1.7 × 10−2% was obtained, which is the highest value reported for visible light driven systems utilizing a molecular photocatalyst for CO2 reduction with water as the reductant.

Sillen–Aurivillius layered oxyhalides with single-, double- and triple-perovskite slabs (n = 1–3) are promising visible-light-driven photocatalysts for water splitting with different behaviors observed depending on n. However, there was no report on the photocatalytic activity of n ≥ 4 phases. Here, we report three new oxychlorides BaBi5Ti3O14Cl, Ba2Bi5Ti4O17Cl and Ba3Bi5Ti5O20Cl, respectively, with triple-, quadruple- and quintuple-perovskite layers. The synthesis of these phases involves a “bricklaying” synthesis, where a plain perovskite, BaTiO3, a Sillen phase, BaBiO2Cl, and Aurivillius phases Bi4Ti3O12, BaBi4Ti4O15, and Ba2Bi4Ti5O18 were used as building blocks. The present Sillen–Aurivillius oxychlorides have appropriate valence and conduction band levels for visible-light-induced water splitting. DFT calculation for BaBi5Ti3O14Cl (n = 3) and Ba3Bi5Ti5O20Cl (n = 5) indicates that their valence and conduction bands are separated spatially on the perovskite and fluorite layers, respectively. The photocatalytic activity of the three Sillen–Aurivillius oxychlorides is enhanced with increasing the number of the perovskite layers.

Although niobium oxynitrides such as BaNbO2N possess desirable properties for solar energy conversion (e.g., narrower band gaps compared to their tantalum counterparts), their photoelectrode performance is generally inferior, probably because of the excessively high donor density derived from the reduced species (e.g., Nb4+) generated during their synthesis via nitridation with NH3. In this study, a series of BaNbO2N particles doped with various cations were synthesized to improve the photoelectrochemical (PEC) water splitting performance of porous BaNbO2N photoanodes via donor density control in the semiconductor bulk. Doping lower-valent cations (Ti4+, Zr4+) into Nb5+ sites decreased the donor density, as indicated by the Mott–Schottky plots, and also suppressed the generation of Nb4+ species to some extent. In contrast, doping with higher-valent cations (W6+, Mo6+) increased the donor density and accelerated Nb4+ generation. The porous photoanodes of BaNbO2N doped with lower-valent cations showed a larger photocurrent density than that of the undoped photoanodes, whereas those fabricated with higher-valent cations exhibited smaller values over the entire applied potential range. The optimized Ti4+-doped BaNbO2N photoanodes exhibited superior performance compared to their tantalum counterparts, demonstrating PEC water splitting with a relatively high quantum efficiency under visible light after appropriate loading of a cocatalyst. These results strongly suggest that the donor density of undoped BaNbO2N was excessively high because of the inevitable reduction of Nb5+ during the nitridation process, and the appropriate reduction of donor density by lower-valent cation doping can provide both a suitable electron conductivity and a sufficient hole diffusion length, thus substantially improving the performance.

Z-scheme water splitting has exhibited significant potential for practical water splitting under visible light irradiation. This system comprises two photocatalysts for O2 and H2 evolution, along with a redox shuttle for transporting electrons between these photocatalysts. Therefore, the promotion of redox reaction of the shuttle play a crucial role in efficient water splitting. In particular, for multielectron redox reactions (e.g., IO3−/I−), a cocatalyst is indispensable, where only noble metals may contribute thus far. Herein, we demonstrate that FeOx catalyzes the multielectron IO3− reduction on the Bi4TaO8Cl photocatalyst. While bare Bi4TaO8Cl does not show O2 evolution from an aqueous IO3− solution because of the lack of multielectron reduction ability, FeOx loading enables O2 evolution. Based on a series of experimental investigations, such as time-resolved spectroscopy, we elucidated that the O2 evolution enhancement stems from the promotion of multielectron reduction of IO3− by FeOx. The FeIII/FeII redox couple in the loaded FeOx facilitates both electron carrier capture from Bi4TaO8Cl and reduction of the redox mediator. In addition, FeOx is effective for other photocatalysts and redox mediators. To the best of our knowledge, the developed cocatalysts is the first earth-abundant cocatalyst for multielectron redox mediators.

The performance of photoelectrodes is hugely affected by the preparation method. Although a flux synthesis is useful to endow semiconductor particles with the desired properties such as high crystallinity, there are only a few reports on its application to photoelectrode fabrication, probably because relatively high temperatures are necessary. In the present study, we introduce a new concept for on-site flux synthesis of semiconductor crystals on a commonly used fluorine-doped tin oxide (FTO) substrate; a seed layer is predeposited and then treated with an appropriate flux containing other required elements at a right temperature lower than the limit temperature of FTO but sufficiently high to transform the seed layer to the target material with the aid of flux. Here, an oxyhalide PbBiO2Cl, one of the promising semiconductors for achieving visible-light water splitting, is selected as a target material. Combination of a BiOCl seed layer and the NaCl-PbCl2 flux containing other precursors enables the seed layer to transform into PbBiO2Cl crystals even at 450 °C. The thickness of the PbBiO2Cl layer can be controlled by changing the thickness of the BiOCl seed layer for efficient photon-to-current conversion. Owing to a good contact at the semiconductor-substrate interfaces as well as the high quality of PbBiO2Cl crystals, the flux-synthesized PbBiO2Cl photoelectrode shows a significantly improved PEC performance compared with those prepared from the particulate PbBiO2Cl samples via the conventional squeegee method. In addition, the present PbBiO2Cl photoelectrodes exhibit both anodic and cathodic photoresponses with substantially high current values depending on the applied potentials; the unusual phenomenon is affected by the conditions in flux-assisted synthesis. The present study provides a new and effective way for fabricating efficient photoelectrodes of various semiconductors on various substrates and a possible option to control their morphologies and p/n types for further improvement in performance.

We show that oxyhalide Bi5PbTi3O14Cl is a potential photocatalyst for visible-light-induced water splitting owing to the appropriate band levels for both water reduction and oxidation. The present ...

Owing to the rapid advancement in computer hardware and quantum chemical software, chemists can relatively easily calculate the electronic properties of semiconducting photocatalysts. However, thes...

The atificial Z-scheme is a promising and rational strategy for solar-to-chemical energy conversion such as water-splitting. In the Z-scheme, backward redox processes are an essential drawback that should be overcome to increase its efficiency. Here, we demonstrate that the simple co-loading of Fe/Ru oxide, (Fe,Ru)O

Kesterite Cu

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Separation of photoexcited charge carriers in semiconductors is important for efficient solar energy conversion and yet the control strategies and underlying mechanisms are not fully established. Although layered compounds have been widely studied as photocatalysts, spatial separation between oxidation and reduction reaction sites is a challenging issue due to the parallel flow of photoexcited carriers along the layers. Here we demonstrate orthogonal carrier flow in layered Bi

Layered oxyhalides containing double or triple fluorite layers are promising visible-light-responsive water-splitting photocatalysts with unique band structures. Herein, we report on the synthesis, structure, and photocatalytic property of Bi

The development of systems for photocatalytic CO2 reduction with water as a reductant and solar light as an energy source is one of the most important milestones on the way to artificial photosynthesis. Although such reduction can be performed using dye-sensitized molecular photocathodes comprising metal complexes as redox photosensitizers and catalyst units fixed on a p-type semiconductor electrode, the performance of the corresponding photoelectrochemical cells remains low, e.g., their highest incident photon-to-current conversion efficiency (IPCE) equals 1.2%. Herein, we report a novel dye-sensitized molecular photocathode for photocatalytic CO2 reduction in water featuring a polypyrrole layer, [Ru(diimine)3]2+ as a redox photosensitizer unit, and Ru(diimine)(CO)2Cl2 as the catalyst unit and reveal that the incorporation of the polypyrrole network significantly improves reactivity and durability relative to those of previously reported dye-sensitized molecular photocathodes. The irradiation of the novel photocathode with visible light under low applied bias stably induces the photocatalytic reduction of CO2 to CO and HCOOH with high faradaic efficiency and selectivity (even in aqueous solution), and the highest IPCE is determined as 4.7%. The novel photocathode is coupled with n-type semiconductor photoanodes (CoOx/BiVO4 and RhOx/TaON) to construct full cells that photocatalytically reduce CO2 using water as the reductant upon visible light irradiation as the only energy input at zero bias. The artificial Z-scheme photoelectrochemical cell with the dye-sensitized molecular photocathode achieves the highest energy conversion efficiency of 8.3 × 10−2% under the irradiation of both electrodes with visible light, while a solar to chemical conversion efficiency of 4.2 × 10−2% is achieved for a tandem-type cell using a solar light simulator (AM 1.5, 100 mW cm−2)., A novel dye-sensitized molecular photocathode with polypyrrole networks exhibits high efficiency and durability for photocatalytic CO2 reduction by using water as reductant and visible light as energy.

The development of semiconductors with narrow band gap and high stability is crucial for achieving solar to chemical energy conversion. Compounds with iodine, which has a high polarizability, have attracted attention because of their narrow band gap and long carrier lifetime, as typified by halide perovskite solar cells; however, they have been regarded as unsuitable for harsh photocatalytic water splitting because iodine is prone to self-oxidation. Here, we demonstrate that Ba2Bi3Nb2O11I, a layered Sillen-Aurivillius oxyiodide, not only has access to a wider range of visible light than its chloride and bromide counterparts, but also functions as a stable photocatalyst, efficiently oxidizing water. Density functional theory calculations reveal that the oxygen 2p orbitals in the perovskite block, rather than the fluorite Bi2O2 block as previously pointed out, anomalously push up the valence band maximum, which can be explained by a modified Madelung potential analysis that takes into account the high polarizability of iodine. In addition, the highly polarizable iodide contributes to longer carrier lifetime of Ba2Bi3Nb2O11I, allowing for a significantly higher quantum efficiency than its chloride and bromide counterparts. Visible-light-driven Z-scheme water splitting was achieved for the first time in an iodine-based system using Ba2Bi3Nb2O11I as an oxygen-evolution photocatalyst. The present study provides a novel approach for incorporating polarizable "soft" anions into building blocks of layered materials to manipulate the band structure and improve the carrier dynamics for visible-light responsive functions.

Owing to the shallow valence band maximum generated upon hybridization of Bi/Pb 6s and O 2p orbitals, layered oxyhalides of Bi4TaO8Cl and PbBiO2Cl are stable and promising O2-evolving photocatalyst...

Strontium titanate (SrTiO3) is a perovskite that is important in water-splitting photocatalytic chemistry. Although excess Sr is known to improve the photocatalytic activity, its effect on charge d...

In the present study, a conductive carbon microfiber felt (CMF) with three-dimensional structure of carbon fibers (CFs) was employed as a conductive substrate of visible light responsive WO3 photoanodes for oxidative decomposition of organic contaminants and oxidation of water to molecular oxygen (O2). Since the surface of original CFs in CMF are highly hydrophobic, the pretreatment of CMF and the composition of W-precursor solution significantly affected the morphology and the resulting performance of photoanodes. The preheating of CMF at optimal temperature (640 °C) in air make the surface of CFs hydrophilic substantially while maintaining the mechanical strength of CMF structure, enabling the better impregnation of a water-soluble tungsten precursor, ammonium metatungstate (AMT) solution. The addition of polyethylene glycol 300 (PEG) to the precursor solution further improved the affinity to the surface of CFs, resulting in homogeneous loading of fine WO3 particles preferentially on the surface of CFs as well as in the voids of CFs to some extent. The results on optimization of loaded amount of WO3 of CMF from various precursor solutions indicated that both the WO3 particles loaded on the surface of CFs and those in the voids contribute to the photocurrent generation, while the efficiency of electron injection from WO3 on the CFs seems higher. Consequently, the optimized WO3/CMF photoanode exhibited higher photocurrent compared to conventional porous WO3/FTO photoanodes. It was demonstrated that a WO3 photoanode prepared on CMF could efficiently oxidize water to O2 with considerably high stability under visible light, not only for oxidation of 2-propanol.

Recently, Bi4MO8X (M = Nb and Ta; X = Cl and Br), Sillen–Aurivillius-type single-layered perovskite oxyhalides, have been shown to be promising visible-light-responsive photocatalysts with unique v...

Loading an efficient cocatalyst that can selectively enhance favorable reactions is an effective way to improve the efficiency of Z-scheme water splitting with a redox mediator such as IO3−/I−. Given a recent finding on a highly active Ru(OH)xCly cocatalyst for IO3− reduction on the TaON photocatalyst, here we systematically investigate Rh, Co, and Ir-based cocatalysts for enhancing water oxidation thereby improving the total efficiency of O2 evolution on TaON with the help of the Ru(OH)xCly cocatalyst. The calcination temperature of metal cation (i.e., Rh, Co or Ir) species on TaON, which is co-loaded by Ru(OH)xCly species at a fixed temperature of 200 °C, significantly affected the rate of O2 evolution from aqueous solution containing IO3− under visible light irradiation. The rate of O2 evolution basically increased with increasing temperature at the cocatalyst loading up to 400 °C (for Ir) and 500 °C (for Rh and Co), while calcination at 600 °C drastically lowered the activity due to the detrimental effect on the TaON itself. The highest O2 evolution rate was obtained by the loading of Rh species at 500 °C, followed by co-loading of Ru(OH)xCly at 200 °C, on TaON. The results of both photocatalytic reactions and electrochemical measurements revealed that the Rh species loaded at 500 °C, which mainly consist of Rh oxides, promote water oxidation more effectively than conventional CoOx or IrOx species. The rates of H2 and O2 evolution in overall water splitting via the Z-scheme mechanism were significantly increased by the use of the TaON photocatalyst co-loaded with Rh and Ru species as the O2-evolving photocatalyst, in place of the TaON loaded with only conventional RuO2 species or previously reported TaON co-loaded with Ru(OH)xCly and Co-based species. These results indicate the effectiveness of co-loading of cocatalysts that are independently optimized for water oxidation and IO3− reduction for improving the efficiency of Z-scheme water splitting.

A recent study on Bi4NbO8Cl and related Bi-based layered oxyhalide photocatalysts using a layer-by-layer Madelung potential (L2MP) analysis with a sphere model revealed that oxide anions in the fluorite-type slab of Bi4NbO8Cl are electrostatically destabilized by the 2nd nearest sublayer composed of the apical oxygen of the perovskite slab. Here we provide an extended L2MP analysis of Bi-based layered oxyhalides using a modified (square-prism) model and apply it to other layered compounds. It is found that consideration of up to the 3rd nearest sublayer is necessary to account for the nearly equal valence band maximum between Bi2GdO4X and Bi4NbO8Cl. Additionally, BiOX and Bi2GdO4X show a distinct X-dependence of the Madelung site potential of oxide anions. The L2MP analysis of Bi2WO6, Sr3Sc2Cu2S2O5 and Sr2ScCuSO3 revealed a sizable contribution of distant layers to their electrostatic potentials. This study demonstrates that this method can be applied to a wide range of layered materials and serves as a powerful guide toward finding composition and layer stacking sequences suitable for photocatalysis and other functions.

The development of systems for photocatalytic CO2 reduction with water as a reductant and solar light as an energy source is one of the most important milestones on the way to artificial photosynthesis. Although such reduction can be performed using dye-sensitized molecular photocathodes comprising metal complexes as redox photosensitizers and catalyst units fixed on a p-type semiconductor electrode, the performance of the corresponding photoelectrochemical cells remains low, e.g., their highest incident photon-to-current conversion efficiency (IPCE) equals 1.2%. Herein, we report a novel dye-sensitized molecular photocathode for photocatalytic CO2 reduction in water featuring a polypyrrole layer, [Ru(diimine)3]2+ as a redox photosensitizer unit, and Ru(diimine)(CO)2Cl2 as the catalyst unit and reveal that the incorporation of the polypyrrole network significantly improves reactivity and durability relative to those of previously reported dye-sensitized molecular photocathodes. The irradiation of the novel photocathode with visible light under low applied bias stably induces the photocatalytic reduction of CO2 to CO and HCOOH with high faradaic efficiency and selectivity (even in aqueous solution), and the highest IPCE is determined as 4.7%. The novel photocathode is coupled with n-type semiconductor photoanodes (CoOx/BiVO4 and RhOx/TaON) to construct full cells that photocatalytically reduce CO2 using water as the reductant upon visible light irradiation as the only energy input at zero bias. The artificial Z-scheme photoelectrochemical cell with the dye-sensitized molecular photocathode achieves the highest energy conversion efficiency of 8.3 × 10−2% under the irradiation of both electrodes with visible light, while a solar to chemical conversion efficiency of 4.2 × 10−2% is achieved for a tandem-type cell using a solar light simulator (AM 1.5, 100 mW cm−2).

The performance of photoelectrodes is hugely affected by the preparation method. Although a flux synthesis is useful to endow semiconductor particles with the desired properties such as high crystallinity, there are only a few reports on its application to photoelectrode fabrication, probably because relatively high temperatures are necessary. In the present study, we introduce a new concept for on-site flux synthesis of semiconductor crystals on a commonly used fluorine-doped tin oxide (FTO) substrate; a seed layer is predeposited and then treated with an appropriate flux containing other required elements at a right temperature lower than the limit temperature of FTO but sufficiently high to transform the seed layer to the target material with the aid of flux. Here, an oxyhalide PbBiO