Multinary Oxides Research Articles

Time Dependence of Kinetic Unmixing and Kinetic Decomposition of a Perovskite ABO3 under Applied Voltage—A Case Study for BaTiO3

AbstractIn multinary oxides such as perovskites ABO3, an applied voltage causes charged mobile species (ions, electrons) to move according to their electrochemical mobilities. For different electrochemical mobilities of the cations kinetic unmixing takes place, and after some time even kinetic decomposition may occur. Both kinetic effects are detrimental to the functional application of the oxide, for example, in electrochemical cells or in multilayer ceramic capacitors. Thus far, kinetic unmixing and decomposition are analyzed by treating ABO3 only as a quasi‐binary mixture of AO and BO2, acceptors are not considered, and only the steady state of kinetic unmixing is investigated, allowing no prediction of the lifetime until kinetic decomposition. Here, ABO3 is treated as a really ternary system with defects in all three sublattices and with electronic defects. The complete set of transport equations is derived, and the moving boundary problem with six mobile species is solved numerically to investigate the time‐dependence of kinetic unmixing. As a case study, BaTiO3 is used which has various applications as a functional oxide. The simulations yield the kinetic decomposition voltage of the oxide, below which no kinetic decomposition occurs. For voltages larger than this critical value the lifetime of the oxide until kinetic decomposition is predicted.

Dataset of theoretical multinary perovskite oxides

Perovskite oxides (ternary chemical formula ABO3) are a diverse class of materials with applications including heterogeneous catalysis, solid-oxide fuel cells, thermochemical conversion, and oxygen transport membranes. However, their multicomponent (chemical formula {A}_{x}{A}_{1-x}^{text{'}}{B}_{y}{B}_{1-y}^{text{'}}{O}_{3}) chemical space is underexplored due to the immense number of possible compositions. To expand the number of computed {A}_{x}{A}_{1-x}^{{prime} }{B}_{y}{B}_{1-y}^{{prime} }{O}_{3} compounds we report a dataset of 66,516 theoretical multinary oxides, 59,708 of which are perovskites. First, 69,407 {A}_{0.5}{A}_{0.5}^{{prime} }{B}_{0.5}{B}_{0.5}^{{prime} }{O}_{3} compositions were generated in the a−b+a− Glazer tilting mode using the computationally-inexpensive Structure Prediction and Diagnostic Software (SPuDS) program. Next, we optimized these structures with density functional theory (DFT) using parameters compatible with the Materials Project (MP) database. Our dataset contains these optimized structures and their formation (ΔHf) and decomposition enthalpies (ΔHd) computed relative to MP tabulated elemental references and competing phases, respectively. This dataset can be mined, used to train machine learning models, and rapidly and systematically expanded by optimizing more SPuDS-generated {A}_{0.5}{A}_{0.5}^{{prime} }{B}_{0.5}{B}_{0.5}^{{prime} }{O}_{3} perovskite structures using MP-compatible DFT calculations.

A robust rationally designed multinarydouble perovskites microplates as an efficient visible-light photocatalyst

Rationally designed perovskite structured, multinary oxides having two or more different cations combinations diversify its photocatalytic applications. In current study Rhombohedral structured rationally designed visible light-responsive double perovskites (DPOs) were produced by hydrothermal method. The synthesized perovskites were confirmed by various characterizations techniques. The average crystallite size of the DPOs was found 25 nm calculated from XRD data using Scherer's equation. The EDX images confirmed the elemental composition of the synthesized material. The morphology of the DPOs was smooth, uniform and well organized as regular microplate form as seen in the SEM images. The average length of DPOs was 5.52 μm and the band gap was 2.03 eV, lies in the visible range. The BET results showed that the DPOs had a high specific surface area of 389 m²/g . The point of zero charge of the synthesized materials lies in the basic region at pH 8. The DPOs microplates showed 97% degradation of crystal violet (CV) at optimum conditions of pH 12, 50 ppm initial dye concentration, 0.6 g/L DPOs dosage within 20 min of irradiation contact time, following 2nd order kinetics with 0.9822, R2 value. The ANOVA confirmed that the polynomial quadratic model is best fitted model having high R2, R2 adj, and R2 pred values. In conclusion, the DPOs (Na2FeCoSeNaO6) are the most suitable and efficient entrant as a photocatalyst for dyes eradications.

Semiconducting Quantum Dots for Energy Conversion and Storage

AbstractSemiconducting quantum dots (QDs) have received huge attention for energy conversion and storage due to their unique characteristics, such as quantum size effect, multiple exciton generation effect, large surface‐to‐volume ratio, high density of active sites, and so on. However, the holistic and systematic understanding of the energy conversion and storage mechanism centering on QDs in specific application is still lacking. Herein, a comprehensive introduction of these extraordinary 0D materials, e.g., metal oxide, metal dichalcogenide, metal halides, multinary oxides, and nonmetal QDs, is presented. It starts with the synthetic strategies and unique properties of QDs. Highlights are focused on the rational design and development of advanced QDs‐based materials for the various applications in energy‐related fields, including photocatalytic H2 production, photocatalytic CO2 reduction, photocatalytic N2 reduction, electrocatalytic H2 evolution, electrocatalytic CO2 reduction, electrocatalytic N2 fixation, electrocatalytic O2 evolution, electrocatalytic O2 reduction, solar cells, metal‐ion batteries, lithium–sulfur batteries, metal–air batteries, and supercapacitors. At last, challenges and perspectives of semiconducting QDs for energy conversion and storage are detailedly proposed.

Surface Modulation Inducing Bismuth-Rich Surface Composition in BiVO4 for Efficient Photoelectrochemical Water Splitting

Surface engineering affects the photoelectrochemical properties of multinary oxide photoelectrodes. Here, we report a simple alkaline solution treatment of the (010) faceted bismuth vanadate (BiVO4) photoanode to increase the surface ratio of bismuth to vanadium, thus improving the performance of photoelectrochemical water oxidation. This study demonstrates that the preferential vanadium dissolution occurs in an alkaline solution, resulting in a bismuth-rich surface on the outer region of the pristine BiVO4 to afford the formation of homojunction within BiVO4. The homojunction promotes the charge separation efficiency of the treated BiVO4 photoanode to reach an almost ∼100% enhancement at 1.23 VRHE under simulated sunlight. Upon further loading NiFeOx cocatalyst, the maximum applied-bias photon-to-current conversion efficiency (ABPE) of treated BiVO4 photoanode also shows a further 100% enhancement in 0.1 M KPi electrolyte. This study sheds light on the critical role of surface termination/composition on the photoelectrochemical properties of the BiVO4 photoanode. This essential surface property can be modulated through a simple strategy to improve its charge transport for efficient water oxidation.

Alternate-Target Layer-By-Layer Pulsed Laser Deposition of Epitaxial BiVO4 Thin Films

Bismuth vanadate (BiVO4) has emerged as one of the highest performing metal oxide photoelectrodes for solar energy-to-fuels applications [1, 2]. This achievement has been largely attributed to the development of high-quality synthesis techniques. Specifically, epitaxial synthetic routes to producing lattice-matched, near single-crystalline quality BiVO4 with minimal extrinsic defects have been essential to understand the fundamental and PEC properties of BiVO4 that are inaccessible by conventional bulk synthesis techniques. In addition, epitaxial synthesis may also be employed as a strategy to further improve the PEC properties of BiVO4 through, for instance, altering the band structure and enhancing the carrier dynamics by strain engineering. Hence, the ability to produce high-quality single-phase epitaxial BiVO4 films is desirable.To date, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) [3] have been used to fabricate epitaxial BiVO4 thin films, with PLD having the advantage of relatively simple experimental setup and material versatility. However, an oft-noted drawback in conventional PLD using single oxide targets is off-stoichiometry in the deposited films; this is especially so for BiVO4 which requires a Bi-rich compound target to achieve a stoichiometric BiVO4 film [4]. This problem is also expected in general for multinary oxides composed of elements with very different ablation properties. To alleviate the limitations of conventional PLD, we employ for the first time alternate-target layer-by-layer PLD as a more elegant approach to produce high quality epitaxial BiVO4 films. Briefly, constituent oxide targets are alternately ablated by an excimer laser (λ= 248 nm) to build the desired film one unit cell thick at a time. Stoichiometry is controlled by the number of shots corresponding to a specified laser fluence for the constituent oxide target.To demonstrate the method, we deposited epitaxial BiVO4 films onto (001)-oriented yttrium-stabilized zirconia (YSZ) using 4N-pure Bi2O3 and V2O5 targets. Films grown are single phase BiVO4 as shown by x-ray diffraction. Out-of-plane diffraction peaks indexed to BiVO4(00l) suggests epitaxy of the film onto the substrate; reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks further confirm the BiVO4(001) || YSZ(001) epitaxial relationship (top figure). Rocking curves of the BiVO4 (004) peak (FWHM ~ 0.015-0.041) indicate high crystalline perfection of the BiVO4 film, almost approaching that of the YSZ substrate (FWHM ~ 0.010). Thickness dependent-rocking curve studies reveal that BiVO4 films are strained to the substrate for film thicknesses under 22 nm; above this critical thickness, film relaxation ensues. In turn, the resulting optoelectronic properties of the BiVO4 film is dictated by its relaxation state. The optical band gap narrows with film relaxation as observed with spectroscopic ellipsometry. Moreover, steady-state photoluminescence emission spectroscopy reveals a sub-bandgap state (A 2, bottom figure) associated with strained BiVO4 films, on top of a state consistent with band-to-band recombination (B1 ). A higher energy sub-bandgap state (A 1, bottom figure) develops as the film relaxes. The implications of the relaxation state on the charge carrier dynamics and photoelectrochemical properties of BiVO4 will be discussed. Figure: (top) reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks; (bottom) photoluminescence emission spectra of strained and relaxed BiVO4 films.

High-throughput exploration of activity and stability for identifying photoelectrochemical water splitting materials.

The experimental high-throughput (HT) exploration for a suitable solar water splitting photoanode has greatly relied on photoactivity as the sole descriptor to identify a promising region within the searched composition space. Although activity is essential, it is not sufficient for describing the overall performance and excludes other pertinent criteria for photoelectrochemical (PEC) water splitting. Photostability in the form of (photo)electrocatalyst dissolution must be tracked to illustrate the intricate relation between activity and stability for multinary photoelectrocatalysts. To access these two important metrics simultaneously, an automated PEC scanning flow cell coupled to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) was used to study an Fe-Ti-W-O thin film materials library. The results reveal an interrelation between composition, photocurrent density, and element-specific dissolution. These structure-activity-stability correlations can be represented using data science tools like principal component analysis (PCA) in addition to common data visualization approaches. This study demonstrates the importance of addressing two of the most important catalyst metrics (activity and stability) in a rapid and parallel fashion during HT experiments to adequately discover high-performing compositions in the multidimensional search space.

Copper Oxide-Based Photocatalysts and Photocathodes: Fundamentals and Recent Advances.

This work aims at reviewing the most impactful results obtained on the development of Cu-based photocathodes. The need of a sustainable exploitation of renewable energy sources and the parallel request of reducing pollutant emissions in airborne streams and in waters call for new technologies based on the use of efficient, abundant, low-toxicity and low-cost materials. Photoelectrochemical devices that adopts abundant element-based photoelectrodes might respond to these requests being an enabling technology for the direct use of sunlight to the production of energy fuels form water electrolysis (H2) and CO2 reduction (to alcohols, light hydrocarbons), as well as for the degradation of pollutants. This review analyses the physical chemical properties of Cu2O (and CuO) and the possible strategies to tune them (doping, lattice strain). Combining Cu with other elements in multinary oxides or in composite photoelectrodes is also discussed in detail. Finally, a short overview on the possible applications of these materials is presented.

Integrating Computation and Experiment to Investigate Photoelectrodes for Solar Water Splitting at the Microscopic Scale.

ConspectusPhotoelectrochemical water-splitting is a promising and sustainable way to store the energy of the sun in chemical bonds and use it to produce hydrogen gas, a clean fuel. The key components in photoelectrochemical cells (PECs) are photoelectrodes, including a photocathode that reduces water to hydrogen gas and a photoanode that oxidizes water to oxygen gas. Materials used in photoelectrodes for PECs must effectively absorb sunlight, yield photogenerated carriers, and exhibit electronic properties that enable the efficient shuttling of carriers to the surface to participate in relevant water-splitting reactions. Discovering and understanding the key characteristics of optimal photoelectrode materials is paramount to the realization of PEC technologies.Oxide-based photoelectrodes can satisfy many of these materials requirements, including stability in aqueous environments, band edges with reasonable alignment with the redox potentials for water splitting, and ease of synthesis. However, oxide photoelectrodes generally suffer from poor charge transport properties and considerable bulk electron–hole separation, and they have relatively large band gaps. Numerous strategies have been proposed to improve these aspects and understand how these improvements are reflected in the photoelectrochemical performance. Unfortunately, the structural and compositional complexity of multinary oxides accompanied by the inherent complexity of photoelectrochemical processes makes it challenging to understand the individual effects of composition, structure, and defects in the bulk and on the surface on a material’s photoelectrochemical properties. The integration of experiment and theory has great potential to increase our atomic-level understanding of structure–composition–property relationships in oxide photoelectrodes.In this Account, we describe how integrating experiment and theory is beneficial for achieving scientific insights at the microscopic scale. We highlight studies focused on understanding the role of (i) bulk composition via solid-state solutions, intercalation, and comparison with isoelectronic compounds, (ii) dopants for both the anion and cation and their interactions with oxygen vacancies, and (iii) surface/interface structure in the photocurrent generation and photoelectrochemical performance in oxide photoelectrodes. In each instance, we outline strategies and considerations for integrating experiment and theory and describe how this integration led to valuable insights and new directions in uncovering structure–composition–property relationships. Our aim is to demonstrate the unique value of combining experiment and theory in studying photoelectrodes and to encourage the continued effort to bring experiment and theory in closer step with each other.

Combining Electrosynthesis with Thermolysis: A Safe/Scalable Route to Multinary Oxide Semiconductor Films

AbstractAdding a thermolysis step to electrosynthesis (as in “electrothermosynthesis”) considerably enhances the scope of electrochemical film deposition and affords multinary compositions previously inaccessible by this otherwise versatile and mild synthetic approach. Copper pyrovanadate (β−Cu2V2O7), a member of the Cu−V−O family of ternary oxide semiconductors that are of considerable interest to the solar fuel community, is shown herein to be an exemplar of this approach. Finally, the generality of the hybrid approach is discussed for a variety of ternary metal oxides.

The impact of surface composition on the interfacial energetics and photoelectrochemical properties of BiVO4

The ability to engineer a photoelectrode surface is pivotal for optimizing the properties of any photoelectrode used for solar fuel production. Altering crystal facets exposed on the surface of photoelectrodes has been a major strategy to modify their surface structure. However, there exist numerous ways to terminate the surface even for the same facet, which can considerably alter the photoelectrode properties. Here we report tightly integrated experimental and computational investigations of epitaxial BiVO4 photoelectrodes with vanadium- and bismuth-rich (010) facets. Our study demonstrates that even for the same facet the surface Bi:V ratio has a remarkable impact on the interfacial energetics and photoelectrochemical properties. We also elucidate the microscopic origins of how the surface composition can affect the photoelectrochemical properties. This study opens an unexplored path for understanding and engineering surface energetics via tuning the surface termination/composition of multinary oxide photoelectrodes. Surface facets are known to influence the behaviour of photoelectrodes for solar fuel production; however, the role of surface composition, which can vary even for the same facet, is less well understood. Here the authors find that the surface Bi:V ratio is a key factor that affects properties of BiVO4 photoanodes.

Colloidal Nanocrystals as Precursors and Intermediates in Solid State Reactions for Multinary Oxide Nanomaterials.

ConspectusPolyelemental compounds with dimensions in the nanosized regime are desirable in a large variety of applications, yet their synthesis remains a general challenge in chemistry. One of the major bottlenecks to obtaining multinary systems is the complexity of the synthesis itself. As the number of elements to include in one single nano-object increases, different chemical interactions arise during nucleation and growth, thus challenging the formation of the targeted product. Choosing the reaction conditions and identifying the parameters which ensure the desired reaction pathway are of the uttermost importance. When, in addition to composition, the simultaneous control of size and shape is sought after, the development of new synthetic strategies guided by the fundamental understanding of the formation mechanisms becomes crucial.In this Account we discuss the use of colloidal chemistry to target multinary oxide nanomaterials, with focus on light absorbers which can drive chemical reactions. We propose the combination of soft and solid-state chemistries as one successful strategy to target this family of polyelemental compounds with control on composition and morphological features. To start with, we highlight studies where in situ forming nanoparticles act as reaction intermediates, which we found in both oxide (i.e., Bi-V-O) and sulfide (Cu-M-S, with M = V, Cr, Mn) nanocrystals (NCs). Examples of ternary sulfides are mentioned only with the purpose of showing that similar mechanisms can apply to different families of multinary nanomaterials. Using this new knowledge, we demonstrate that reacting pre-synthesized NCs with well-defined composition and size with molecular precursors allows significant control of these same property-dictating features (i.e., composition and grain size) in the resulting ternary and quaternary compounds. For example, nanostructured BiV1-xSbxO4 thin films with tunable composition and nanostructured β-Cu2V2O7 with tunable grain size were accessed from colloidally synthesized Bi1-xSbx NCs (0 < x < 1) and size-controlled Cu NCs reacted with a vanadium molecular precursor, respectively. The analysis of reaction aliquots revealed that the formation of these materials occurs via a solid-state reaction between the NC precursors and V-containing amorphous nanoparticles, which form in situ from the molecular precursors. With the aim to achieve better control on the reaction product, we finally propose the use of colloidally synthesized NCs as reactants in solid state reactions. As the first proof of concept, ternary metal oxide NCs, including CuFe2O4, CuMn2O4, and CuGa2O4 with defined size and shape regulated by the NC precursors were obtained. Considering the huge library of single component and binary NCs accessible by colloidal chemistry, the extension of this synthetic concept, which combines soft and solid-state chemistries, to a larger variety of polyelemental nanomaterials is foreseen. Such an approach will contribute to facilitate a more rapid translation of design principles to materials with the desired composition and structural features.

Electrochemically Grown Sodium Transition Metal Oxides NaxMO2 (M=Co, Mn, Fe, Ni)

Electrochemically grown ceramic oxide films have exhibited improved electrochemical, photovoltaic, and catalytic performance. However, product library accessible through conventional aqueous anodic electrolytic deposition of oxides is limited primarily to binary systems and rare examples exist for air and moisture sensitive ternary oxides. Moreover, growth rate, thickness, and functionality of the electrodeposited oxide films are hindered by the solvent of choice, poor reaction kinetics and low temperature of synthesis. Here, we introduce, an intermediate temperature (350oC), dry molten sodium hydroxide mediated binder-free electrodeposition process to grow air and moisture sensitive layered sodium transition metal oxides, NaxMO2 (M=Co, Mn, Ni, Fe), which are conventionally synthesized by solid state reactions at temperatures ≥ 700oC. Albeit the lowest reported synthesis temperature and reaction times, our electrodeposited oxides retain the key structural and electrochemical performance observed in the high temperature bulk synthesized analogues. We demonstrate that tens of microns thick, >75% dense O3 NaxCoO2 and O'3 NaxMnO2 can be deposited at a growth rate of ~5-20 mg/cm2/hr, with near theoretical gravimetric capacity, chemical diffusion coefficient of Na+ ions, and reversible areal capacity in the range ~0.25-0.76 mAh/cm2, which are significantly higher than those reported for binder free sodium cathodes deposited by other techniques. Our method resolves longstanding intrinsic challenges associated with traditional aqueous solution-based electrodeposition of ceramic oxides and opens a general solution chemistry approach for electrochemical processing of hitherto unexplored air and moisture sensitive high valent multinary oxides.

Electrochemical Oxidation of Metal-Catechol Complexes as a New Synthesis Route to the High-Quality Ternary Photoelectrodes: A Case Study of Fe2TiO5 Photoanodes.

A new electrochemical, solution-based synthesis method to prepare uniform multinary oxide photoelectrodes was developed. This method involves solubilizing multiple metal ions as metal-catechol complexes in a pH condition where they are otherwise insoluble. When some of the catechol ligands are electrochemically oxidized, the remaining metal complexes become insoluble and are deposited as metal-catechol films on the working electrode. The resulting films are then annealed to form crystalline multinary oxide electrodes. Because catechol can serve as a complexing agent for a variety of metal ions, the newly developed method can be used to prepare a variety of multinary oxide films. In the present study, we used this method to prepare n-type Fe2TiO5 photoanodes and investigated their photoelectrochemical properties for use in a photoelectrochemical water-splitting cell. We also performed a computational investigation with two goals. The first goal was to investigate small electron polaron formation in Fe2TiO5. Charge transport in most oxide photoelectrodes involves small polaron hopping, but small polaron formation in Fe2TiO5 has not been examined prior to this work. The second goal was to investigate the effect of substitutional Sn doping at the Fe site on the electronic band structure and the carrier concentration of Fe2TiO5. The combined experimental and theoretical results presented in this study greatly improve our understanding of Fe2TiO5 for use as a photoanode.

18O(p,p′γ)18O nuclear reaction in the determination of oxygen by proton induced γ-ray emission

A particle induced γ-ray emission methodology employing the 18O(p,p′γ)18O (E γ = 1982 keV) nuclear reaction is described for the non-destructive determination of bulk oxygen in materials. The development of the methodology follows a comprehensive measurement of the thick target yields of the 1982 keV prompt γ-rays in the 3.0–4.2 MeV proton energy region and a systematic assessment of such analytical features as the limit of detection, probing depth, precision and accuracy. The methodology is validated by analyzing binary, ternary and multinary oxides. It is simple and rapid, and in combination with prompt γ-ray producing reactions involving the other constituents, enables the complete compositional analysis of oxygen bearing materials.

Crystal structure of monoclinic samarium and cubic europium sesquioxides and bound coherent neutron scattering lengths of the isotopes 154Sm and 153Eu

Abstract The crystal structures of monoclinic samarium and cubic europium sesquioxide, Sm2O3 and Eu2O3, were reinvestigated by powder diffraction methods (laboratory X-ray, synchrotron, neutron). Rietveld analysis yields more precise structural parameters than previously known, especially for oxygen atoms. Interatomic distances d(Sm–O) in Sm2O3 range from 226.3(4) to 275.9(2) pm [average 241.6(3) pm] for the monoclinic B type Sm2O3 [space group C2/m, a = 1418.04(3) pm, b = 362.660(7) pm, c = 885.48(2) pm, β = 100.028(1)°], d(Eu–O) in Eu2O3 from 229.9(2) to 238.8(2) pm for the cubic bixbyite (C) type [space group Ia3̅, a = 1086.87(1) pm]. Neutron diffraction at 50 K and 2 K did not show any sign for magnetic ordering in Sm2O3. Isotopically enriched 154Sm2O3 and 153Eu2O3 were used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. The isotopic purity was determined by inductively coupled plasma – mass spectrometry to be 98.9% for 154Sm and 99.8% for 153Eu. Advanced analysis of the neutron diffraction data suggest that the bound coherent scattering lengths of 154Sm and 153Eu need to be revised. We tentatively propose b c(154Sm) = 8.97(6) fm and b c(153Eu) = 8.85(3) fm for a neutron wavelength of 186.6 pm to be better values for these isotopes, showing up to 8% deviation from accepted literature values. It is shown that inaccurate scattering lengths may result in severe problems in crystal structure refinements causing erroneous structural details such as occupation parameters, which might be critically linked to physical properties like superconductivity in multinary oxides.

Semiconducting materials for photoelectrochemical energy conversion

To achieve a sustainable society with an energy mix primarily based on solar energy, we need methods of storing energy from sunlight as chemical fuels. Photoelectrochemical (PEC) devices offer the promise of solar fuel production through artificial photosynthesis. Although the idea of a carbon-neutral energy economy powered by such ‘artificial leaves’ is intriguing, viable PEC energy conversion on a global scale requires the development of devices that are highly efficient, stable and simple in design. In this Review, recently developed semiconductor materials for the direct conversion of light into fuels are scrutinized with respect to their atomic constitution, electronic structure and potential for practical performance as photoelectrodes in PEC cells. The processes of light absorption, charge separation and transport, and suitable energetics for energy conversion in PEC devices are emphasized. Both the advantageous and unfavourable aspects of multinary oxides, oxynitrides, chalcogenides, classic semiconductors and carbon-based semiconductors are critically considered on the basis of their experimentally demonstrated performance and predicted properties. Photoelectrochemical (PEC) devices offer the promise of efficient artificial photosynthesis. In this Review, recently developed light-harvesting materials for PEC application are scrutinized with respect to their atomic constitution, electronic structure and potential for practical performance in PEC cells.

Hydrothermal Synthesis of CoSb2O4: In Situ Powder X-ray Diffraction, Crystal Structure, and Electrochemical Properties

MSb2O4 constitutes a relatively unexplored class of multinary oxides that is traditionally synthesized by high-temperature solid-state methods. Here, we report a facile synthesis of CoSb2O4 under hydrothermal conditions (T = 135–300 °C, 256 bar). Using in situ synchrotron powder X-ray diffraction (PXRD), the formation and growth of CoSb2O4 nanoparticles are followed in real time using different precursor stoichiometries. Phase-pure CoSb2O4 can be formed at 135 °C, although the formation mechanism changes with precursor stoichiometry. The crystallite size can be fine-tuned between 14 and 17.5 nm under nonstoichiometric conditions, but crystallites twice as large are found in the stoichiometric case. An activation energy of 65(12) kJ/mol is obtained for the crystallization from a nonstoichiometric precursor. Modeling of atomic displacement parameters obtained from Rietveld refinement of multi-temperature high-resolution synchrotron PXRD data gives a Debye temperature of 331(11) K. The thermal expansion coef...

On the path-dependence of the open-cell voltage of a galvanic cell involving a ternary or multinary compound with multiple mobile ionic species under multiple chemical potential gradients

It is well known that the open-cell voltage (U) of a galvanic cell involving a binary compound, or a multinary compound with a single kind of mobile ionic species, is a state property under a gradient of chemical potential of the mobile component. It is not so transparent, however, whether U is still a state property when involving a ternary or multinary compound with two or more kinds of mobile ions under multiple chemical potential gradients of those mobile components. We clarify this issue with a multinary oxide that conducts oxide ions, protons and electron holes and is exposed to the chemical potential gradients of both water and oxygen. We show that U is path- and history-dependent, and manifests itself along the diffusion paths of the two mobile components H and O under given boundary conditions.

Mechanism of gel-to-crystallite conversion process in the synthesis of nanocrystalline multinary oxides

Description of gel-to-crystallite conversion process is made towards the synthesis of nanocrystalline titanates and aluminates. Thermodynamic and kinetic factors governing the conversion of a gel to meta-stable and stable nanocrystalline products(s) are discussed. Correlations between these factors and the preparative conditions employed for the syntheses of titanates and aluminates are arrived at.