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Co-precipitation was used for the preparation of delafossite CuCrO2 from nitrates under an inert N2 flow. The diffractograms show a pure phase, crystallizing in a rhombohedral delafossite structure (S G: R 3 ¯ m). Stability up to 900°C, indicating high electrostatic energy, is demonstrated by the thermogravimetric analysis (TGA). The formation of CuCrO2 is corroborated by x-ray photoelectron spectroscopy (XPS) analysis with valence states Cu+ and Cr3+. The forbidden band (2.49 eV) is assigned to the transition Cu+: dxz → hybridizedO2−: 2p/Cu+: dz2/s linearly bonded in CuO23− entities. The thermal dependence of the electrical conductivity follows an exponential law: {σ = σo exp(−0.13 eV/kT) (Ω-cm)− 1} where the electrical conductivity comes from low polaron hopping (LPH) among mixed states of Cu2+/+ in the basal (0 0 n) planes. The doping is due to Cu2O units, the conduction of which gives a hole mobility of ~ 10−4 cm2 V−1 s−1. The semiconductor behavior of CuCrO2 is supported by the interfacial capacitance versus potential (C−2− E); the negative slope indicates p-type conduction, with a flat band potential (Efb) of 0.16 VSCE. The valence band (5.03 eV/0.28 VSCE) is formed by O(2p)–Cr(3d) states. The electrochemical impedance spectroscopy plot shows an arc assigned to a capacitive comportment with a deviation from a pure capacitance and a dominant bulk contribution (Rb = 69 kΩ cm2). The center is positioned below the abscissa with a constant phase element. [ABSTRACT FROM AUTHOR]

The climate crisis necessitates the development of non-fossil energy sources. Harnessing solar energy for fuel production shows promise and offers the potential to utilize existing energy infrastructure. However, solar fuel production is in its early stages of development, constrained by low conversion efficiency and challenges in scaling up production. Concentrated solar energy (CSE) technology has matured alongside the rapid growth of solar thermal power plants. This review provides an overview of current CSE methods and solar fuel production, analyzes their integration compatibility, and delves into the theoretical mechanisms by which CSE impacts solar energy conversion efficiency and product selectivity in the context of photo-electrochemistry, thermochemistry, and photo-thermal co-catalysis for solar fuel production. The review also summarizes approaches to studying the photoelectric and photothermal effects of CSE. Lastly, it explores emerging novel CSE technology methods in the field of solar fuel production.

The aqueous photo‐assisted battery is considered an efficient means of converting and storing solar energy in one device. However, identifying a suitable photocathode with excellent iodine capture capabilities for photo‐assisted Zn‐iodine batteries still remains challenging. In this work, bifunctional BiOI is prepared as sole cathode material for a photo‐assisted Zn‐iodine battery while simultaneously realizing an iodine host and solar responsiveness. The as‐presented BiOI with abundant vacancies offers highly reversible photo‐assisted iodine redox reactions. Meanwhile, the dual reaction routes involving vacancy iodine storage and reversible two‐steps iodine redox are confirmed by in/ex situ characterization techniques during the energy storage process. Consequently, the assembled battery exhibits areal capacity of 0.24 mAh cm−2 at 1 mA cm−2 with coulombic efficiency exceeding 96.5%. More impressively, benefiting from the wide visible light absorption of the BiOI cathode, the battery demonstrates a much enhanced specific areal capacity of 0.4 mAh cm−2 at 1 mA cm−2 under sun illumination, representing a remarkable increment of 60% compared to that in the dark environment. This work expands the utility of cathode materials for a photo‐assisted Zn‐iodine battery. [ABSTRACT FROM AUTHOR]

The utilization of diverse energy storage devices is imperative in the contemporary society. Taking advantage of solar power, a significant environmentally friendly and sustainable energy resource, holds great appeal for future storage of energy because it can solve the dilemma of fossil energy depletion and the resulting environmental problems once and for all. Recently, photo‐assisted energy storage devices, especially photo‐assisted rechargeable metal batteries, are rapidly developed owing to the ability to efficiently convert and store solar energy and the simple configuration, as well as the fact that conventional Li/Zn‐ion batteries are widely commercialized. Considering many puzzles arising from the rapid development of photo‐assisted rechargeable metal batteries, this review commences by introducing the fundamental concepts of batteries and photo‐electrochemistry, followed by an exploration of the current advancements in photo‐assisted rechargeable metal batteries. Specifically, it delves into the elucidation of device components, operating principles, types, and practical applications. Furthermore, this paper categorizes, specifies, and summarizes several detailed examples of photo‐assisted energy storage devices. Lastly, it addresses the challenges and bottlenecks faced by these energy storage systems while providing future perspectives to facilitate their transition from laboratory research to industrial implementation. [ABSTRACT FROM AUTHOR]

The present work describes the colour removal of Rhodamine B (Rh B), a cationic dye by photo-electrocatalysis and sono-photo-electrocatalysis on MgFe2O4 as an anode. The spinel MgFe2O4 synthesized by sol–gel route was characterized by physical and electrochemical methods, a preamble of Rh B oxidation. The XRD pattern shows the formation of the single phase, which crystallizes in a face-centred cubic lattice (space group, Fd − 3 m), with spherical crystallites (0.42 nm). The Zeta-sizer analysis gives an average grain size of 0.46 µm and a zeta potential of − 30 mV. The SEM analysis revealed the porosity of the oxide and the Mg-O and Fe–O bonds were confirmed by the FT-IR analysis. The direct optical gap (2.16 eV) assigned to d − d internal transition comes from the crystal field splitting of Fe3+ octahedrally coordinated. The low electron mobility is assigned to a narrow conduction band of Fe3+—3d parentage with activation energy (0.12 eV) in conformity with a conduction mechanism by small lattice polaron hopping. The intensity potential J(E) profile in Na2SO4 (10−2 M) exhibits a small hysteresis similar to a chemical diode. The semi-logarithmic plot (logJ − E) indicates the chemical stability of MgFe2O4 in the working solution (Na2SO4). Curiously and unlike most spinels, the capacitance plot exhibits n-type conduction confirmed by chrono-amperometry, plotted at the free potential (+ 0.5 V) with a flat band potential (Efb) of 0.29 V, due to Fe3+ insertion. As an application, Rh B (20 mg L−1) was successfully oxidized by photo-electrocatalysis on MgFe2O4 with an abatement of 75% under solar irradiation and a direct current of 150 mA which has a bactericidal effect. An enhancement up to 97% has been reached by sono-photo-electrocatalysis at a frequency of 60 kHz; almost complete discoloration occurred within 90 min in the "US-Electric Current-Sunlight-MgFe2O4". The Rh B elimination follows a pseudo-first-order kinetic with a rate constant of 3.9 × 10−2 mn−1 (t1/2 = 18 min), and a reaction mechanism is suggested. [ABSTRACT FROM AUTHOR]

The present work deals with removing Rhodamine B (Rh B) from aqueous solution by Photo Sono-assisted catalytic process on CoFe2O4 elaborated by sol–gel method. The spinel identified by X-ray diffraction presents a face-centered cubic lattice with a grain size of 360 (± 2 nm) and a zeta potential of − 33 mV. The oxide is characterized by diffuse reflectance and photo-electrochemistry. The direct gap (1.42 eV) is assigned to the internal transition: F e oc 3 + : t 2 g → F e oc 4 + : e g in agreement with the red color. The narrow valence band deriving from Fe3+: 3d parentage induces a low hole mobility (µh = 8.91 × 10−6 cm2 V−1 s−1). The electrical conductivity of CoFe2O4 is characteristic of semiconducting comportment with activation energy (Ea) of 0.57 eV, where the electron jump occurs by small lattice polaron between mixed valences Fe3+/Fe4+. The intensity potential J(E) profile in Na2SO4 (10–2 M) exhibits a small hysteresis loop. The chrono-amperometry shows p-type conductivity due to metal insertion, a result confirmed by the capacitance measurement where a hole density (NA) of 0.176 × 1023 cm−3 and a flat band potential (Efb) equal to − 0.8 V are determined. As an application, Rh B (20 mg L−1) is successfully oxidized by photocatalysis on CoFe2O4 with a reduction of 53% under solar light. An enhancement up to 88% has been reached by sono-photocatalysis at an ultrasonic wave (USW) frequency (60 kHz, 550 W) within 105 min.; the Rh B elimination follows a pseudo-first-order kinetic with a rate constant of 1.23 × 10–2 mn−1 (t1/2 = 56 min), and a reaction mechanism is suggested, was entirely discolored in the USW/solar light/CoFe2O4 system. The Sono-photocatalytic degradation of Rh B depends on the initial Rh B concentration, acoustic power, and catalyst dose. At low ultrasound frequency, the results indicated a total chemical oxygen demand (COD) when applying the system USW/solar light/CoFe2O4, signifying its great potentiality for the treatment of water. [ABSTRACT FROM AUTHOR]

The hybrid material AlCo2P3O4·1/2H2O: DIMPPZ (AlCoP-DIMPPZ; 1, 4-Dimethyl piperazine: DIMPPZ) was synthesized hydrothermally at 453 K and characterized by X-ray diffraction (XRD), FT-IR and diffuse reflectance spectroscopies, SEM / EDX analysis. The crystal symmetry is rhombohedral and the XRD pattern is consistent with a single phase (S.G. R 3 -) isotypic to ACP-CHA9 (C4) AlCo2P3O4·1/2H2O with cell parameters in the hexagonal description: a = 13.5494 Å and c = 15.2795 Å. The optical study revealed a direct electronic transition at 1.82 eV, assigned to lift of degeneracy of CoII in a low spin configuration tetrahedrally bonded. The SEM image showed a more or less homogeneous morphology with similar grain sizes ranging from 3.5 to 6 μm whereas the FT-IR spectrum exhibits characteristic peaks of (PO4)3− units and C=C bonds. To our knowledge, no photo-electrochemistry has been reported to date and the low exchange current density (~ 2 mA cm−2) is consistent with the electrochemical stability in Na2SO4 (0.1 M) solution. The dependence of the interfacial capacitance (C−2) on the potential (E) is typical of n-type behaviour with an electron density (ND) of 2.14 × 1018 cm−3 and a flat band potential (Efb) of 0.59 VSCE. The valence band with an energy of 7.10 eV /vacuum (2.35 VSCE) derives from 3d wave function originating from Co2+ ion. The semicircle at high frequencies in the electrochemical spectroscopy with an impedance of 910 Ω cm2 is due to the intrinsic property, which decreases to 750 Ω cm2 under visible light, corroborating the semi conductivity of the material. As application, the hybrid material was tested for the first time for the oxidation of Methyl Violet (MV), with an abatement of 65% under visible light (15 mW cm−2) for 420 min while the adsorption of 33%. Based on the energy diagram, the title compound will be used as O2 photo electrode. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is one of the important chemicals for human life. The demand for ammonia is expected to increase every year. Conventionally, the fixation process of N2 to produce NH3 in the industrial sector is carried out through the Haber−Bosch process, which requires extreme temperature and pressure conditions that consume a high amount of energy and emit a considerable amount of CO2. Therefore, it is necessary to develop alternative technology to produce ammonia using environmentally friendly methods. Many studies have developed the photo-electrochemical conversion of nitrogen to ammonia in the presence of semiconductor materials, but the resulting efficiency is still not as expected. In this research, the development of the tandem system of Dye-Sensitized Solar Cell - Photoelectrochemistry (DSSC - PEC) was carried out for the conversion of nitrogen to ammonia. The DSSC cell was prepared using N719/TiO2 nanotubes as photoanode, Pt/FTO as cathode, and electrolyte I-/I3-. The DSSC efficiency produced in this research was 1.49%. PEC cell at the cathode and anode were prepared using BiOBr/TiO2 nanotubes synthesized by the SILAR (Successive Ionic Layer Adsorption and Reaction) method. The resulting ammonia levels were analyzed using the phenate method. In this study, ammonia levels were obtained at 0.1272 µmol for 6 hours of irradiation with an SCC (Solar to Chemical Conversion) percentage of 0.0021%.

The mononuclear ruthenium 1-Cl and dinuclear ruthenium 2-Cl complexes undergo a photo-induced ligand exchange in water, affording the corresponding 1-H2O and 2-H2O complexes. The use of indium tin oxide nanoparticles (nanoITOs) to explore the photo-electrochemistry of the in situ-generated 1-H2O and 2-H2O in solution revealed greater photocurrents produced by these two complexes when compared with an experiment using a buffer only. Interestingly, the high photocurrent shown by the dinuclear complex 2-H2O was accompanied by the deposition of its higher oxidation state (H2O)RuII–RuIII(OH), as evidenced with cyclic voltammetry, SEM and XPS. The IPCE and spectro-electrochemistry studies supported by TD-DFT calculations revealed the visible light harvesting ability of 1-H2O and 2-H2O in solution and the subsequent electron injection into the conduction band of the nanoITOs, enhanced in 2-H2O via a plausible chelating effect. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is one of the important chemicals for human life. The demand for ammonia is expected to increase every year. Conventionally, the fixation process of N2 to produce NH3 in the industrial sector is carried out through the Haber-Bosch process, which requires extreme temperature and pressure conditions that consume a high amount of energy and emit a considerable amount of CO2. Therefore, it is necessary to develop alternative technology to produce ammonia using environmentally friendly methods. Many studies have developed the photoelectrochemical conversion of nitrogen to ammonia in the presence of semiconductor materials, but the resulting efficiency is still not as expected. In this research, the development of the tandem system of Dye-Sensitized Solar Cell - Photoelectrochemistry (DSSC - PEC) was carried out for the conversion of nitrogen to ammonia. The DSSC cell was prepared using N719/TiO2 nanotubes as photoanode, Pt/FTO as cathode, and electrolyte I-/I3 -. The DSSC efficiency produced in this research was 1.49%. PEC cell at the cathode and anode were prepared using BiOBr/TiO2 nanotubes synthesized by the SILAR (Successive Ionic Layer Adsorption and Reaction) method. The resulting ammonia levels were analyzed using the phenate method. In this study, ammonia levels were obtained at 0.1272 µmol for 6 hours of irradiation with an SCC (Solar to Chemical Conversion) percentage of 0.0021%. [ABSTRACT FROM AUTHOR]

Nanocrystalline CaTiO3 materials with controlled particle size were prepared using spray-freezing/freeze-drying approach utilizing gelatine as a structure-directing agent. The resulting materials show characteristic particle size between 19 and 60 nm. The shape of the nanocrystals changes from cube-like single crystal containing particles into less regular isometric particles. Prepared materials as identified by X-ray diffraction analysis are formed by orthorhombic perovskite with small admixture of cubic phase. The ratio of both perovskite phases is independent of the particle size or prevailing crystal shape. All prepared materials show n-semiconducting character with band gap of ca 3.6 eV. They also show photo-electrochemical activity in water oxidation in acid media if a bias greater than 400 mV with respect to the flat band potential is applied. The specific photo-electrochemical activity decreases with increasing specific surface area. This behavior is attributed to increased probability of the electron transfer at the illuminated CaTiO3 surface facilitated by the surface states. The CaTiO3 materials also generate significant amount of ozone upon illumination in oxygen saturated solutions. The tendency to form ozone increases with increasing particle size suggesting that the ozone formation is hindered on materials with large number of low dimensionality states (crystal edges and vertices). [ABSTRACT FROM AUTHOR]

Active and stable materials that utilize solar radiation for promoting different reactions are critical for emerging technologies. Two of the most common polymeric carbon nitrides were prepared by the thermal polycondensation of melamine. The scope of this work is to investigate possible structural degradation before and after photoelectrochemical testing. The materials were characterized using synchrotron radiation and lab-based techniques, and subsequently degraded photoelectrochemically, followed by post-mortem analysis. Post-mortem investigations reveal: (1) carbon atoms bonded to three nitrogen atoms change into carbon atoms bonded to two nitrogen atoms and (2) the presence of methylene terminals in post-mortem materials. The study concludes that polymeric carbon nitrides are susceptible to photoelectrochemical degradation via ring opening. [ABSTRACT FROM AUTHOR]

The spinel NiFe 2 O 4 , 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 NiFe 2 O 4 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 NiFe 2 O 4 (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 H 2 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 H 2 level (−0.8 V SCE), enabled the use of NiFe 2 O 4 for the water reduction into hydrogen. The H 2 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 SO 3 2− (10−3 M) as hole scavenger under visible light flux of 23 mW cm−2. A deactivation effect of only 1% was obtained. • The spinel NiFe 2 O 4 is elaborated by nitrate route was used for H 2 production. • The optical band gap of NiFe 2 O 4 is directly allowed with a value of 1.78 eV. • H 2 evolution rate of 46.5 μmol g−1 min−1 was obtained under visible light irradiation. [ABSTRACT FROM AUTHOR]

Pt and its alloys are commonly used as catalysts for electrochemical methanol oxidation reaction (MOR), owing to their high efficiencies. However, the high cost and instability of these catalysts due to poisoning from intermediates restrict their large-scale applications. Here we study plasmonic porous Au–Ag nanoparticles toward electrochemical and photoelectrochemical MOR. We synthesized Au–Ag@Au nanostructures that consist of the Au nanorod core and Au–Ag shell, where nanopores were created via selectively etching Ag atoms. The porous Au–Ag@Au nanostructures demonstrated significantly better MOR activity compared to their nonporous counterpart. Importantly, the presence of pores drastically suppressed the poisoning from the intermediate species, leading to a large improvement of their electrochemical stability. Furthermore, the porous Au–Ag@Au constructs showed strong enhancement of their catalytic activity under visible as well as near-infrared (NIR) excitations with generation of photocurrents of 1.23 and 0.45 mA mg–1 cm2, and with incident photon to current conversion efficiencies of 1.43 and 0.34% for visible and NIR wavelengths, respectively. Generation of photocurrents was shown to be predominantly due to the plasmonic hot-hole-assisted MOR. [ABSTRACT FROM AUTHOR]

Photo‐electrochemical production of solar fuels from carbon dioxide, water, and sunlight is an appealing approach. Nevertheless, it remains challenging to scale despite encouraging demonstrations at low power input. Higher current densities require notable voltage input as ohmic losses and activation overpotentials become more significant, resulting in lower solar‐to‐CO conversion efficiencies. A concentrated photovoltaic cell is integrated into a custom‐made heat managed photo‐electrochemical device. The heat is transferred from the photovoltaic module to the zero‐gap electrolyzer cell by the stream of anodic reactant and produce synergetic effects on both sides. With solar concentrations up to 450 suns (i.e., 450 kW m−2) applied for the first time to photo‐electrochemical reduction of CO2, a partial current for CO production of 4 A is achieved. At optimal conditions, the solar‐to‐CO conversion efficiency reaches 17% while maintaining a current density of 150 mA cm−2 in the electrolyzer and a CO selectivity above 90%, representing an overall 19% solar‐to‐fuel conversion efficiency. This study represents a first demonstration of photo‐electrochemical CO2 reduction under highly concentrated light, paving the way for resource efficient solar fuel production at high power input. [ABSTRACT FROM AUTHOR]

In the present work, we investigate the photo-electrochemical properties of β′-Mn3(PO4)2 prepared by hydrothermal route at 453 K for the first time. The phosphate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR spectroscopy, and UV–Visible diffuse reflectance. The XRD pattern indicates a single phase crystallizing in a monoclinic structure with unit cell constants: a = 8.961(3) Å, b = 9.961(4) Å, and c = 24.138(1) Å, and β = 120.419°, due to the lifting of degeneracy of the Jahn–Teller effect of Mn2+ penta-coordinated. The SEM analysis shows a homogeneous morphology with similar grain sizes in the range 3–13 µm. Optical transitions are determined from diffuse reflectance which indicates direct (2.38 eV) and indirect (2.88 eV) optical transitions; assigned to Mn2+: d-d transition. To our knowledge, the photo-electrochemical characterization of β′-Mn3(PO4)2 is reported for the first time. The exchange current density (29 µA cm−2) is characteristic of good electrochemical stability. The dependence of the interfacial capacitance on the potential (C−2 − E) displays n-type conduction with electrons as majority carriers, a behavior supported by the chrono-amperometry. A flat band potential (Efb) of 0.29 VSCE and an electron mobility (µe) of 1.6 × 10−6 cm2 V−1 s−1 have been determined. The semicircle in the electrochemical impedance spectroscopy (EIS) is due the charge transfer (24.6 kΩ cm2) which falls down to 3.25 kΩ cm2 under visible irradiation, corroborating a semiconducting behavior. The phosphate is stable at neutral pH and is successfully tested for the oxidation of methyl violet (MV). The valence band deriving from O2−: 2p character (2.65 VSCE/7.40 eV) has a strong oxidizing power, able to mineralize the dye radicals. The integrated intensity of the visible light (23 mW cm−2) shows a total MV photodegradation in the presence of β′-Mn3(PO4)2 within 5 h. A first-order model is successfully used with a half-photocatalytic life of 113 min. As expected, the COD removal yield increases, with illumination time, and reaches 4.26% after 5 h while the total organic carbon (TOC) removal rate reached 9%. According to the inhibitor study, the holes (h+) were found to be the main active radicals in the photocatalytic process, followed by the •OH. [ABSTRACT FROM AUTHOR]

In the large field of research on nanoplatelets (NPLs), their strong tendency to self‐assemble into ordered stacks and the resulting changes in their properties are of great interest. The assembly reveals new characteristics such as the charge carrier transport through the NPL assembly or altered optical properties. In particular, a reduced distance should enhance the charge carrier transport due to higher electronic coupling of neighboring NPLs, and therefore, is the focus of this work. To modify the inter‐particle distances, the straightforward method of ligand exchange is applied. Various CdSe and CdSe/CdX (hetero‐) NPLs serve as building blocks, which not only display different material combinations but also different types of heterostructures. The surface‐to‐surface distance between the stacked NPLs can be reduced to below 1 nm, thus, to less than the half compared to assemblies of pristine NPLs. Moreover, for certain NPLs stacking is only enabled by the ligand exchange. To characterize the ligand exchanges and to investigate the influences of the reduced distances, photo‐electrochemical measurements, fluorescence spectroscopy, energy dispersive X‐ray spectroscopy, nuclear magnetic resonance, and X‐ray photoelectron spectroscopy are performed. It is possible to show higher photocurrents for smaller distances, indicating enhanced charge transport ability within those stacks. [ABSTRACT FROM AUTHOR]

The attempts to develop efficient methods of solar energy conversion into chemical fuel are ongoing amid climate changes associated with global warming. Photo-electrocatalytic (PEC) water splitting and CO2 reduction reactions show high potential to tackle this challenge. However, the development of economically feasible solutions of PEC solar energy conversion requires novel efficient and stable earth-abundant nanostructured materials. The latter are hardly available without detailed understanding of the local atomic and electronic structure dynamics and mechanisms of the processes occurring during chemical reactions on the catalyst–electrolyte interface. This review considers recent efforts to study photo-electrocatalytic reactions using in situ and operando synchrotron spectroscopies. Particular attention is paid to the operando reaction mechanisms, which were established using X-ray Absorption (XAS) and X-ray Photoelectron (XPS) Spectroscopies. Operando cells that are needed to perform such experiments on synchrotron are covered. Classical and modern theoretical approaches to extract structural information from X-ray Absorption Near-Edge Structure (XANES) spectra are discussed. [ABSTRACT FROM AUTHOR]

Boron- and cerium-doped titania (Anatase) were prepared via sol-gel method. Phase composition and morphology were assessed by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET, diffuse reflectance spectra (DRS), and XPS. Photo-electrochemistry of these materials, deposited onto fluorine-doped SnO2 (FTO), was investigated in acid and acid-containing methanol. The boron-doped sample showed the best opto-electronic properties among the investigated samples. On the other hand, the cerium-doped titania samples annihilate to a certain extent the titania surface states, however, photogenerated charge separation was limited, and certainly associated to surface Ce3+/Ce4+ species. The substitutional effect of boron ions for O sites and interstitial sites was confirmed by XRD and XPS analyses.

Solar energy is considered the most promising renewable energy source. Solar cells can harvest and convert solar energy into electrical energy, which needs to be stored as chemical energy, thereby realizing a balanced supply and demand for energy. As energy storage devices for this purpose, newly developed photo-enhanced rechargeable metal batteries, through the internal integration of photovoltaic technology and high-energy-density metal batteries in a single device, can simplify device configuration, lower costs, and reduce external energy loss. This review focuses on recent progress regarding the working principles, device architectures, and performances of various closed-type and open-type photo-enhanced rechargeable devices based on metal batteries, including Li/Zn-ion, Li-S, and Li/Zn-I2, and Li/Zn-O2/air, Li-CO2, and Na-O2 batteries. In addition to provide a fundamental understanding of photo-enhanced rechargeable devices, key challenges and possible strategies are also discussed. Finally, some perspectives are provided for further enhancing the overall performance of the proposed devices.

The ever-growing demands for energy supply have put great stress on environment protections. Photo-electrochemistry (PEC) is a repaid developing technique which can directly transform solar energy into chemical compounds and have been regarded as a promising strategy to solve the energy and environmental problems. However, the biggest restriction is the fast recombination of photo-generated charge carriers which greatly limits the PEC efficiency. In recent years, introducing external-field into PEC system have been proved to be a powerful method to enhance the PEC performance and attracted more and more attentions. In this review, we summarized the remarkable progresses in external-field enhanced PEC reactions including mechanical stress field, thermal field, electrical field, magnetic field and muti-field coupling. The enhancing principles of different external-fields have also been systemically discussed. Furthermore, the challenges and outlook of the external-field enhanced PEC reactions are presented., (© 2024 Wiley-VCH GmbH.)

Green hydrogen production is a key area of importance for advancing into a completely sustainable world, not only for its use in industry and ammonia production, but also for its potential as a new fuel. One promising method for generating green hydrogen is light-driven water splitting using photoelectrodes. Here, a bismuth vanadate (BiVO 4 ) photoanode deposition process was developed using new, bespoke dual-source precursors, tailored for use in aerosol-assisted chemical vapour deposition (AACVD). The resulting thin films were highly nanostructured and consisted of phase-pure monoclinic BiVO 4 . Pristine films under 1 sun solar irradiation yielded photocurrent densities of 1.23 mA cm -2 at 1.23 V vs RHE and a peak incident photon-electron conversion efficiency (IPCE) of 82 % at 674 nm, the highest performance of any CVD-grown BiVO 4 film to date. A new, AACVD-compatible WO 3 precursor was subsequently designed and synthesised for the deposition of W-doped BiVO 4 within the same single deposition step., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Solar energy conversion plays a very important role in the transition to a more sustainable energy system. In this sense, so many systems have been proposed to drive artificial photosynthesis, most of them based on inorganic semiconductors, and the achievements performed continue every day. However, most of these systems present well‐known shortcomings as low light absorption, fast charge recombination, and lack of tunability, thus limiting their efficiency. The use of organic polymers in general and conjugated porous polymers (CPPs) in particular, opens the door to a multitude of new possibilities when it comes to design and selection of a suitable photocatalyst. CPPs exhibit improved light harvesting, charge conduction properties, high photochemical stability, and high surface area that make them ideal for photocatalytic applications. Here, the use of CPPs and hybrids as photocatalysts for solar energy conversion in the hydrogen evolution reaction and the CO2 reduction reaction and its use as a photoelectrode are reviewed. The photocatalytic properties are focused upon here. The photophysics related to these applications is also discussed. Finally, a perspective is provided, proposing an in situ and operando characterization methodology that is expected to allow improvements to their optoelectronic properties and thereby their future design and applicability. [ABSTRACT FROM AUTHOR]

The efficiency of photo‐electrochemistry is jointly determined by multiple factors such as light absorption, charge separation, and carrier transportation. It is essential to maximize all of them but has proved challenging especially for photoelectrodes made from wide‐bandgap semiconductors. Here, a conceptually new strategy noted as semiconductive‐ferroelectric‐enhanced photo‐electrochemistry (SF‐PEC) is reported based on a doped TiO2‐BaxSr1−xTiO3 (BST) core–shell nanowire array. Through an in situ surface conversion and an electron/nitrogen codoping process, a self‐polarized, surface‐amorphized, and doped BST thin layer is created on the surface of TiO2, resulting in a semiconductive‐ferroelectric‐enhanced TiO2 (SF‐TiO2) photoelectrode. Compared with pristine TiO2 and ferroelectric‐enhanced TiO2 (F‐TiO2), the SF‐TiO2 has stronger light absorption, greater charge separation, and faster carrier transportation, which is identified to be a synergistic outcome of the reduced bandgap, moderate ferroelectric polarization, and high carrier density and mobility. The photocurrent density of SF‐TiO2 reaches 1.87 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE), 1.39 and 2.46 times higher than that of F‐TiO2 and TiO2, respectively. The SF‐TiO2 maintains over 90% of its photocurrent density after being aged in air for 11 months. This work provides new insights to extend the efficiency limit of photo‐electrochemistry. [ABSTRACT FROM AUTHOR]

Photo‐electrochemical cathodic protection (CP) technology is considered to be a green metallic corrosion protection technology that uses solar energy to protect from corrosion and does not consume any anode materials. In this work, a CdIn2S4/WO3 nanocomposite photoelectrode was prepared, and its photo‐electrochemical CP performance and mechanism were studied and analyzed. WO3 has a well band matching with CdIn2S4, leading to a significantly enhanced photo‐electrochemical CP performance of the nanocomposite. Meanwhile, as confirmed in this work, the CdIn2S4/WO3 nanocomposite can store photoinduced electrons under light illumination through intercalation reactions and changing the valence state of tungsten. Moreover, it can discharge in the dark state to provide continuous CP for the coupled metals. This research will promote the practical application process of the photo‐electrochemical CP technology. [ABSTRACT FROM AUTHOR]

Surface states strongly affect charge transfer at the semiconductor/electrolyte interface and thus the total power conversion efficiency of photoelectrochemical CO 2 reduction. In this study, we report surface states modulation of ZnTe via ultrathin ZnO layer formed with a one-step hydrothermal method. The resulting photocathode achieved an impressive performance (−7.70 mA cm−2, 93.88 % CO selectivity at −2.58 V vs. Fc+/Fc) and stability (10 h) in CO 2 -saturated acetonitrile with 0.1 M TBAPF 6 electrolyte. Detailed investigation including electrochemical impedance spectroscopy and DFT calculation reveals the surface modification of ZnTe with ultrathin ZnO layer reduces the energy disorder, thereby increasing the electron utilization involved in the CO 2 reduction reaction. This work provides an in-depth analysis of the charge transfer process at the semiconductor/electrolyte interface from the perspective of surface states and has the potential to stimulate further excellent research in this area. [Display omitted] • Surface states modulation of ZnTe via ultrathin ZnO layer formed with a one-step hydrothermal method. • ZnO effectively saturates the Te dangling bonds on the ZnTe surface. • Modulating the surface states to improve electron utilization by reducing energy disorder. [ABSTRACT FROM AUTHOR]

Abstract Nanocrystalline BaTiO3 photocatalysts were prepared by spray‐freeze/freeze‐drying procedure in presence of structure directing gelatin. The synthetic approach yields materials with particle sizes ranging between 20 and 60 nm conforming to cubic perovskite structure. Regardless of the structural differences, the materials show particle size independent bandgap energy of ca. 3.27 eV. All prepared materials are photo‐electrochemically active in water oxidation with intrinsic activity decreasing with decreasing particle size. The photo‐electrochemical activity of BaTiO3 in water oxidation is pH dependent with the hole charge transfer processes being significantly suppressed in alkaline media. Such a behavior can be ascribed to deprotonation of surface OH groups encountered in alkaline media that promotes surface state catalyzed electron transfer reactions at the illuminated BaTiO3 surface. The barium titanate shows the ability to oxidize water with formation of oxygen and ozone. The ozone formation is pronounced on large nanocrystals particularly in acid media. No ozone formation was observed in alkaline solutions.

Well dispersed Cu2FeSnSe4 (CFTSe) nanofilms were synthesized by hot-injection method. The structural and morphological measurements were characterized using XRD (X-ray diffraction), Raman spectroscopy, SEM (scanning electron microscopy), and TEM (transmission electron microscopy). Chemical composition and optical properties of as-synthesized CFTSe nanoparticles were characterized using EDS (energy dispersive spectroscopy) and UV-Vis spectrophotometry. The average particle size of the nanoparticles was about 7-10 nm. The UV-Vis absorption spectra showed that the synthesized CFTS nanofilms have a band gap (Eg) of about 1.16 eV. Photo-electrochemical characteristics of CFTSe nanoparticles were studied and indicated their potential application in photovoltaic applications. [ABSTRACT FROM AUTHOR]

Photocatalysts are part of key strategies to enable green fuel. Photocatalysis and water splitting could be a promising solution to challenges associated with the intermittent nature of sunlight as a huge energy source on Earth. In this study, photo-electrochemical performance and behavior of mixed-phase titanium oxide and iron oxide heterojunction (Ti-TiO x (High-voltage)-FeO x electrode) are compared to the photo-electrochemical performance and behavior of titanium oxide nanotubes with the rutile phase and iron oxide heterojunction (TiO x -nanotubes (H 2 SO 4 /KF)-FeO x electrode). The results of photo-electrochemical experiments show that the application of stabilization potential and the presence/absence of dissolved oxygen could not be considered as significant factors affecting the photo-electrochemical properties of the Ti-TiO x (High-voltage)-FeO x and TiO x -nanotubes (H 2 SO 4 /KF)-FeO x electrodes. The Ti-TiO x (High-voltage)-FeO x electrode shows an anodic photo-electrochemical response in wavelengths shorter than 530 nm and cathodic photo-electrochemical response in wavelengths longer than 530 nm. However, the Ti-nanotubes (H 2 SO 4 /KF)-FeO x electrode consistently exhibits the anodic photo-electrochemical response. Both of the prepared heterojunctions are further characterized through Scanning Electron Microscopy, Energy-dispersive X-ray Spectroscopy, Diffuse Reflectance UV–Vis Spectroscopy, X-ray Diffraction, and Attenuated Total Reflectance Spectroscopy methods. These experiments show that despite different morphologies observed in SEM imaging data, the deposited iron oxide layers on both mixed-phase titanium oxide and titanium oxide nanotubes share the same hematite phase structure. However, only iron oxide electro-deposited on the surface of the mixed-phase titanium oxide, which contains both anatase and rutile phases, with vacant sites of oxygen, exhibits un-expected anodic and cathodic photo-electrochemical responses. Furthermore, according to the results of the characterization and photo-electrochemical investigations, the different chemical environment of mixed-phase titanium oxide, and the possible formation of different types of heterojunction structures in mixed-phase titanium oxide and iron oxide, in contrast to the titanium oxide nanotubes and iron oxide, might be considered the possible discernible reasons for the observed different photo-electrochemical responses. This paper sheds new light on photo-electrochemistry of iron oxide/mixed-phase titanium oxide heterojunction for possible solar energy conversion. In this study, photo-electrochemical performance and behavior of mixed-phase titanium oxide and iron oxide heterojunction were investigated. Image 1 • Photo-electrochemical studies conducted on mixed-phase titanium oxide and iron oxide. • The photocatalysts showed a cathodic response contrary to n-type nature of hematite. • Mixed-phase TiO 2 imposes different chemical conditions on iron oxide photocatalyst. • Photo-electrochemistry of the compound confirms the energy band level. [ABSTRACT FROM AUTHOR]

Covalently tethering photosensitizers to catalytically active 1T‐MoS2 surfaces holds great promise for the solar‐driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new RuII‐complex‐functionalized MoS2 hybrids [RuII(bpy)2(phen)]‐MoS2 and [RuII(bpy)2(py)Cl]‐MoS2. The influence of covalent functionalization of chemically exfoliated 1T‐MoS2 with coordinating ligands and RuII complexes on the HER activity and photo‐electrochemical performance of this dye‐sensitized system was studied systematically. We find that the photo‐electrochemical performance of this RuII‐complex‐sensitized MoS2 system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS2. The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye‐sensitized MoS2 system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye‐sensitized MoS2 hydrogen production devices towards improved the photofuel conversion efficiency. [ABSTRACT FROM AUTHOR]

Covalently tethering photosensitizers to catalytically active 1T‐MoS2 surfaces holds great promise for the solar‐driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new RuII‐complex‐functionalized MoS2 hybrids [RuII(bpy)2(phen)]‐MoS2 and [RuII(bpy)2(py)Cl]‐MoS2. The influence of covalent functionalization of chemically exfoliated 1T‐MoS2 with coordinating ligands and RuII complexes on the HER activity and photo‐electrochemical performance of this dye‐sensitized system was studied systematically. We find that the photo‐electrochemical performance of this RuII‐complex‐sensitized MoS2 system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS2. The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye‐sensitized MoS2 system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye‐sensitized MoS2 hydrogen production devices towards improved the photofuel conversion efficiency. [ABSTRACT FROM AUTHOR]

In this investigation, the impact of electrodeposition time on the photoelectrochemical characteristics of a cuprous oxide (Cu2O) nanocube semiconductor photoelectrode is investigated. The Cu2O nanocube photoelectrode was synthesized electrochemically, utilizing underpotential deposition (UPD). Numerous techniques, including x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), ultraviolet–visible (UV–Vis) spectroscopy, linear sweep voltammetry (LSV) and chronoamperometry (CA), were utilized for characterization of the Cu2O nanocube photoelectrode. A highly crystalline structure of Cu2O nanocubes deposited on an indium tin oxide (ITO) substrate can be seen in the XRD results. SEM images revealed a cubic-shaped structure of Cu2O. However, EDX analysis and the optical bandgap confirmed the presence of uniform single-phase Cu2O nanocubes. Astonishingly, the Cu2O nanocube photoelectrode electrodeposited for 15 min possesses the highest photocurrent among all investigated films. Also, the Cu2O nanocubes displayed stable photocathodic performance as a result of the p-type nature. Moreover, the Cu2O nanocube photoelectrode is suggested to be a good candidate for progressive photoelectrochemical detection. Furthermore, it can be utilized for the expanded field of photoelectrochemical water splitting in addition to other solar photovoltaic devices. [ABSTRACT FROM AUTHOR]

Metal–insulator–semiconductor (MIS) photo‐electrocatalysts offer a pathway to stable and efficient solar water splitting. Initially motivated as a strategy to protect the underlying semiconductor photoabsorber from harsh operating conditions, the thickness of the insulator layer in MIS systems has recently been shown to be a critical design parameter which can be tuned to optimize the photovoltage. This study analyzes the underlying mechanism by which the thickness of the insulator layer impacts the performance of MIS photo‐electrocatalysts. A concrete example of an Ir/HfO2/n‐Si MIS system is investigated for the oxygen evolution reaction. The results of combined experiments and modeling suggest that the insulator thickness affects the photovoltage i) favorably by controlling the flux of charge carriers from the semiconductor to the metal electrocatalyst and ii) adversely by introducing nonidealities such as surface defect states which limit the generated photovoltage. It is important to quantify these different mechanisms and suggest avenues for addressing these nonidealities to enable the rational design of MIS systems that can approach the fundamental photovoltage limits. The analysis described in this contribution as well as the strategy toward optimizing the photovoltage are generalizable to other MIS systems. [ABSTRACT FROM AUTHOR]

Further to traditional corrosion monitoring techniques for rated deteriorations, nowadays modern electrochemical monitoring methods are promising for the control of non-rated damage mechanisms. Considering carbon steel as the most commonly used alloy in the oil and gas industry, there are special grades under NACE MR0175 standard which are immune to sour corrosion. However, according to the industry reports, their immunity can be terminated by upset conditions or on site repairs. This issue will impose either a high operational risk or exorbitant maintenance and inspection costs. Hence, in this paper, a new monitoring technology framework is discussed to lessen a catastrophic failure risk for carbon steel under wet H2S corrosion. In this regard, the application of a developed hybridized ZnO-graphene micro-electrode (ZnOG) with a mix band gap of 1.17 eV is studied. Under hydrogen sulfide attack and when ZnOG hybrids are excited by UV illumination, their photo-electrochemical responses are analyzed. ZnOG hybrids emanate informative impedance signals in a response to the formation of ZnO(1 – x)Sx nano-crystals. [ABSTRACT FROM AUTHOR]

The ilmenite CoTiO3 was synthesized by chemical route, and the decomposition of nitrates was followed by thermal analysis (TG/DTA). The intermediate products and single-phase were identified by X-ray diffraction (XRD). CoTiO3 was characterized by the Fourier transform infrared (FTIR) spectrum. The BET measurements indicated a small specific surface area (~ 2 m2 g−1). The microstructure, visualized by scanning electron microscopy (SEM), showed medium grains (200–300 nm diameter), and the crystallite size (~ 10 nm) was evaluated from the broadening of XRD peaks. The UV–Vis diffuse reflectance spectroscopy gave a direct optical transition at 1.88 eV, due to the crystal field splitting of Co3+ octahedrally coordinated. The electrical properties of CoTiO3 are characteristics of a semiconducting behavior with activation energy of 0.02 eV. The electrochemical characterization was undertaken to build the energy diagram of CoTiO3 which predicted the photocatalytic performance for the O2-evolution (~ 205 mmol h−1) upon visible light (27 mW cm−2). Indeed, the valence band (1.67 VREH) is more anodic than the O2 level, yielding spontaneous O2 evolution. [ABSTRACT FROM AUTHOR]

Photo-electrochemical cells (PECs) represent one of the most promising technologies today for storing sun energy as chemical bonds (solar fuels), exploiting carbon dioxide as a starting reagent. However, identifying suitable photoelectrodes remains a challenging and open issue. In this work, the possibility of using Aurivillius-type compounds to produce solar fuels was deeply investigated. Aurivillius-type perovskites, with general formula Bi (n+1) Fe (n-3) Ti 3 O (3n+3) (BFTO-n), were synthesized and fully characterized to study the influence of the number of perovskite layers and the synthesis parameters on their final properties. Specifically, eight different systems were considered increasing the amount of iron and, consequently, the number of perovskite layers. These compounds were synthesized through both a standard solid-state reaction method and a sol-gel technique. For each system, a screen printing ink was formulated to be deposited as photo-electrodes onto transparent conducting supports, and their morphological (XRD and SEM analysis) electrochemical and photo-electrochemical properties (cyclic and linear voltammetry, impedance, Mott-Schottky analysis) were determined. The obtained results demonstrate the potentiality of Aurivillius-type compounds as innovative materials for carbon dioxide photo-electrochemical reduction. • Aurivillius-type BFTO-n systems were synthesized by two different methods. • BFTO-n photo-electrodes on FTO-glass were produced by screen printing. • The films' structural, morphological, and (photo)-electrochemical properties were assessed. • Photo-electrochemical properties can be modulated tuning the perovskite layers number. • BFTO-n systems can be exploited as photo-electrodes for PEC applications. [ABSTRACT FROM AUTHOR]

Photo-active heterojunctions were prepared by growing thin La 0.9 Sr 0.1 CrO 3-δ films on SrTiO 3 (STO) single crystals substrates via pulsed laser deposition. The photo-electrochemical characteristics of these heterojunctions under UV illumination were investigated by DC measurements and electrochemical impedance spectroscopy (EIS). Under UV illumination, the photo-current produced by these junctions increases over time by almost an order of magnitude to 1 to 2 mA cm-2 at 350 °C. Two effects governing this increase can be distinguished: A first process, independent of the surrounding atmosphere, is related to a stoichiometry polarization of the STO single crystal upon current flow. A second process is highly sensitive to contaminants in the surrounding atmosphere and is strongly accelerated in pure, synthetic atmospheres. We suggest that it is related to photo-oxidation of the STO single crystal. EIS revealed that both processes result in a decrease of both the electronic transport resistance through the STO single crystal and, to a lesser degree, the space charge resistance of the photo-active junction. Operando EIS under illumination and with DC bias was used to record the cells' photo-power characteristics and identify individual loss processes. Owing to the illumination induced strong increase of the STO single crystal conductivity, the photo-currents of such enhanced cells are limited by the space charge resistance. • The photo-current of SrTiO 3 |La 0.9 Sr 0.1 CrO 3 hetero-junctions continually increases under UV illumination. • Two mechanisms govern this effect: One is atmosphere independent and one strongly depends on atmosphere. • The atmosphere independent mechanism is caused by stoichiometry polarization in the SrTiO 3 crystal. • The atmosphere dependent mechanisms is related to photo-oxidation of the SrTiO 3 crystal. [ABSTRACT FROM AUTHOR]

The pulsed laser deposition (PLD) technique has been used to decorate TiO 2 nanotubes (NTs) with cobalt-nickel (CoNi) nanoparticles (NPs). The TiO 2 NTs were produced beforehand through the controlled anodic oxidation of titanium substrates. The effect of the nature of the PLD background gas (Vacuum, O 2 and He) on the microstructure, composition and chemical bondings of the CoNi-NPs deposited onto the TiO 2 -NTs has been investigated. We found that the PLD CoNi-NPs have a core/shell (oxide/metal) structure when deposited under vacuum, while they are fully oxidized when deposited under O 2. On the other hand, by varying the CoNi-NPs loading of the TiO 2 -NTs (through the increase of the number of laser ablation pulses (N LP)), we have systematically studied their photocatalytic effect by means of cyclic-voltammetry (CV) measurements under both AM1.5 simulated solar light and filtered visible light. We show that depositing CoNi-NPs on the substrate under vacuum and He increases the photo-electrochemical conversion effectiveness (PCE) by 600% (at N LP = 10,000) in the visible light domain, while their overall PCE degrades with N LP under solar illumination. In contrast, the fully oxidized CoNi-NPs (deposited under O 2) are found to be the most effective catalyst under sunlight with an overall increase of more than 50% of the PCE at the optimum loading around N LP ~1000. Such catalytic enhancement is believed to result from both an enhanced light absorption by CoO (of which bandgap is of ~2.4 eV) and the formation of a heterojunction between NiO/CoO nanoparticles and TiO 2 nanotubes. Image 1 • Pulsed laser deposition was used to decorate TiO 2 nanotubes with CoNi nanoparticles. • Photo-electrochemical activity is enhanced (~50%) by CoNi nanoparticles under sunlight. • Chemical composition and loading of CoNi nanoparticles can be easily adjusted. • Optimum catalyst loading was identified. [ABSTRACT FROM AUTHOR]

Abstract: Previously optimized anatase and nitrogen-doped anatase TiO2 coatings have been grown by low-frequency plasma-enhanced chemical vapor deposition (PECVD) on different kinds of substrates at low plasma power (64 W) and high plasma power (100 W) for photo-electrochemical studies. Nitrogen-doped TiO2 layers exhibit better photoactivity and also higher electronic conductivity under UV and visible irradiations than non-doped materials. The main reason is that nitrogen introduction induces TiO2 band gap tailoring towards higher wavelengths. In addition, films prepared at low plasma power present a 'typical photo-material' behavior (whose activity depends directly on the presence of light) while layers synthesized at higher plasma power contain an initial conductive phase giving them an activity that exists in the dark yet and can be slightly enhanced by illumination. Such conclusions are prominent in the field of photo-anodic thin films; indeed PECVD could constitute a promising approach for tailoring the efficiency of photo-electrochemical cells for hydrogen production under solar light.Graphical abstract: [ABSTRACT FROM AUTHOR]

(NH 4) 2.5 Co 0.25 PMo 12 O 40 , an insoluble heteropolysalt, was prepared from H 2.5 Co 0.25 PMo 12 O 40 and urea by a dry way. The physical characterizations showed that the compound crystallizes in a Keggin-type structure, with a cubic symmetry, a mesoporous nature and an homogeneous texture. The UV–Visible diffuse reflectance showed two allowed optical transitions, directly at 2.33 eV and indirectly at 1.90 eV. The compound is chemically stable in Na 2 SO 4 electrolyte (0.5 M), test with thiocyanate was negative. The intensity potential (J- E) characetristics showed an irreversible electrochemical system with a weak hysteresis loop. The n -type behavior was determined from the "capacitance−2 – potential" characteristic with a valence band positioned at 6.83 eV under vacuum (+0.18 V SCE), composed of O2−: 2p while the conduction band derives from the Mo6+: 5s wave functions. (NH 4) 2.5 Co 0.25 PMo 12 O 40 showed a good photoactivity for the degradation of Orange II (OII), a recalcitrant dye, by •OH radicals, under solar light (93 mW cm−2). Thus, a conversion of 58% was achieved in OII solution (10 mg L−1) in 80 min, under solar light and the kinetic obeys to a first order model with a rate constant of (30.776 ± 0.554) × 10−3 min−1 (t 1/2 = 23 min). • The synthesis and characterization of the Keggin type (NH 4) 2.5 Co 0.25 PMo 12 O 40 were investigated. • Semiconducting properties of (NH 4) 2.5 Co 0.25 PMo 12 O 40 are due to mixed valences MoVI/MoV. • The Rhodamine Boxidation follows a first order kinetic with a half-life of 23 min under solar light. [ABSTRACT FROM AUTHOR]