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[EN] New insight into the timing and structure of the Last Interglacial Period (Eemian) was obtained through U-Th dating of four speleothems from Northern Spain and an analysis of their stable isotope records. The four stalagmites examined were collected from different levels of Cueva del Cobre, a cold high-mountain cave in the Cantabrian Ranges (N Spain), in which speleothem growth took place essentially during the warmer interestadials. Through 18 TIMS and ICPMS datings and 263 stable isotope analyses, the onset of the Eemian interglacial period was precisely dated at 150±2 ka, an age consistent with a few other palaeoclimatic records but notably younger than the age ascribed by the Milankovitch theory. We also date the Eemian–Weichselian transition (~115 ka) for the fi rst time in the Iberian Peninsula. U-Th ages revealed a consistent anomaly at ~105-100 ka BP, which could be related to a drastic environmental change during the MIS-5c interestadial. This event would have caused the resetting of the U-Th system at the base of the stalagmites during a short time interval. In addition, we propose a new simple geochemical test to ensure the lack of disturbance of this type of samples for dating purposes, [ES] En este artículo se aportan nuevos datos sobre la cronología y estructura del Último Periodo Interglaciar (Eemiense) mediante la datación por U-Th de cuatro espeleotemas procedentes del norte de España y el análisis de sus registros de isótopos estables. Las cuatro estalagmitas estudiadas proceden de distintos niveles de la Cueva del Cobre, una cueva de alta montaña, relativamente fría, situada en la Cordillera Cantábrica, y en la que el crecimiento de espeleotemas tuvo lugar principalmente durante los estadios cálidos. El comienzo del periodo interglaciar Eemiense se ha situado de manera precisa en ~150±2 ka mediante 18 edades de TIMS e ICPMS y 263 análisis de isotópicos estables de oxígeno de las estalagmitas. Esta edad es coherente con otros registros paleoclimáticos, notablemente más reciente que la edad calculada a partir de los ciclos de Milankovitch. También ha sido posible datar la transición Eemiense-Weichseliense (~115 ka) por primera vez en la Península Ibérica. Por otro lado, las dataciones de U-Th revelaron una anomalía consistente entre ~105-100 ka, que podría estar relacionada con un drástico cambio ambiental durante el interestadio MIS-5c. Este evento podría haber abierto el sistema de U-Th en las bases de las cuatro estalagmitas durante un corto intervalo de tiempo. Además, en este trabajo proponemos por primera vez una sencilla prueba geoquímica para comprobar la ausencia de alteraciones del sistema de U-Th en las muestras elegidas para obtener las dataciones., This study is a contribution to Projects REN2001-1409/ CLI and CGL2004-01866 of the Spanish Ministry of Education and Science. The authors thank the authorities of the Fuentes Carrionas-Fuente Cobre Natural Park (Junta de Castilla-León) for providing the facilities and permissions required for our work. We also thank Drs. Helena Hercman (Polish Academy of Science, Poland) and Mª Teresa Crespo (CIEMAT, Spain) for their help with the alpha spectrometry datings. We are also indebted to Adriano Cortel, Carmen Pino, Araceli Sariá and José Matas for help with the fi eldwork and collection of rock samples, and to Gilberto Herrero, Beatriz Moral and María Isabel Sevillano for help with preparing the samples and laboratory assistance. The manuscript benefi ted of comments and suggestions from two anonymous referees. The English was edited by A. Burton.

In this study, a new mechanism for doping of spiro-MeOTAD by Zn(TFSI)(2) is revealed, which is completely different from the mechanism induced by LiTFSI. The oxidation of spiro-MeOTAD is facilitated by complexation between the zinc cation and tert-butylpyridine (tBP) even in the absence of oxygen and light. The lone electron pair of nitrogen in tBP coordinates to the zinc cation, confirmed by the Fourier transform infrared spectroscopy peak at 1637 cm(-1) corresponding to a pyridine ring mode coupled with nitrogen coordinating to zinc as the Lewis site. The doping mechanism is also evidenced by computational calculations. The coordination of zinc to tBP and TFSI- provides a driving force and stabilizes the oxidized spiro-MeOTAD species, showing the most favorable reaction by forming a [Zn(tBP)(3)](+)(TFSI-) complex with a Delta E of -1.52 eV. Our discovery of the mechanism of doping by Zn(TFSI)(2) provides practical insight for the oxidation of spiro-MeOTAD by avoiding ambiguous aging processes in ambient or dry air at the risk of decomposition of other components.

The stability of perovskite solar cells (PSCs) is greatly affected by the interface between the perovskite active layer and the hole transport material (HTM). The rational design of HTMs with effective anchoring to the perovskite surface is an emerging elegant strategy to promote compact and ordered interfaces that lead to highly efficient and stable PSCs. Herein, we propose two fluorene-based HTM molecular architectures (SCF1 and SCF2) derived from the popular yet expensive Spiro-OMeTAD. Their employment as dopant-free HTMs in standard triple-cation CsFAMA PSCs leads to superior device stability, with a T80 lifetime well above 1 year (431 days). Our combined theoretical and experimental study of the CsFAMA|HTM interface reveals that the improved adhesion of the SCF-HTMs to the perovskite layer is the key to minimize the non-radiative recombination, reduce the hole trap density, and enhance the long-term stability of the corresponding devices. The simplified structures of SCF1 and SCF2, obtained by removing the orthogonal fragment of the Spiro-OMeTAD scaffold, show a lower molecular distortion than Spiro-OMeTAD, thus promoting a favorable electronic interaction between the SCF-HTMs and the perovskite. This study provides useful design criteria for achieving highly stable PSCs including dopant-free HTMs with optimized adhesion to the perovskite surface.

Antimony-based perovskite-inspired materials (PIMs) are solution-processable halide absorbers with interesting optoelectronic properties, low toxicity, and good intrinsic stability. Their bandgaps around 2 eV make them particularly suited for indoor photovoltaics (IPVs). Yet, so far only the fully inorganic Cs3Sb2ClxI9−x composition has been employed as a light-harvesting layer in IPVs. Herein, the first triple-cation Sb-based PIM (CsMAFA-Sb) in which the A-site of the A3Sb2X9 structure consists of inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations is introduced. Simultaneously, the X-site is tuned to guarantee a 2D structure while keeping the bandgap nearly unchanged. The presence of three A-site cations is essential to reduce the trap-assisted recombination pathways and achieve high performance in both outdoor and indoor photovoltaics. The external quantum efficiency peak of 77% and the indoor power conversion efficiency of 6.4% are the highest values ever reported for pnictohalide-based photovoltaics. Upon doping of the P3HT hole-transport layer with F4-TCNQ, the power conversion efficiency of CsMAFA-Sb devices is fully retained compared to the initial value after nearly 150 days of storage in dry air. This work provides an effective compositional strategy to inspire new perspectives in the PIM design for IPVs with competitive performance and air stability. publishedVersion

Engineering a solid-electrolyte interphase (SEI) with purposely designed molecules represents a promising strategy to achieve durable and effective anodes for lithium metal batteries (LMBs). The use of vinylene carbonate (VC) as an additive in conventional electrolytes has been shown to promote the formation of a stable and protective SEI at the Li metal interface. The fine-tuning and control of the underlying reactions still represent a major issue, due to complex VC decomposition and polymerization processes that may occur upon battery cycling. To dissect the tangled VC reactivity, here we present new atomistic insights into VC-induced SEI formation at the Li(001) interface: Density Functional Embedding Theory (DFET) is employed to combine the best feasible computational approaches to treat molecular species with localized charge (i.e., VC derivatives upon the reductive decomposition process) and the Li metal surface by means of hybrid DFT and semi-local GGA-based methods, respectively. Exploring VC adsorption and dissociation paths, our DFET investigation reveals that the thermodynamically accessible mechanisms for the VC ring-opening reductive reaction on Li(001) feature energy barriers in the range of 0.29–0.34 eV. Dissociation via cleavage at vinylic sites (i.e., CV–OV) is more likely to occur and leads to a highly reactive intermediate that can undergo either further decomposition towards C2H2 and Li2CO3 formation or a polymerization process, in close agreement with experimental observations. By setting solid scientific foundations for advanced understanding of initial SEI formation, our theoretical results can drive future experimental efforts towards the rational design of Li/electrolyte interfaces with tailored properties for high-performing LMB devices.

Na-ion batteries are emerging as convenient energy-storage devices for large-scale applications. Enhanced energy density and cycling stability are key in the optimization of functional cathode materials such as P2-type layered transition metal oxides. High operating voltage can be achieved by enabling anionic reactions, but irreversibility of O2-/O2n-/O2 evolution still limits this chance, leading to extra capacity at first cycle that is not fully recovered. Here, we dissect this intriguing oxygen redox activity in Mn-deficient NaxNi0.25Mn0.68O2 from first-principles, by analyzing the formation of oxygen vacancies and dioxygen complexes at different stages of sodiation. We identify low-energy intermediates that release molecular O2 at high voltage, and we show how to improve the overall cathode stability by partial substitution of Ni with Fe. These new atomistic insights on O2 formation mechanism set solid scientific foundations for inhibition and control of this process toward the rational design of new anionic redox-active cathode materials.

Na-ion batteries (NIBs) are emerging as promising energy storage devices for large-scale applications. Great research efforts are devoted to design new effective NIB electrode materials, especially for the anode side. A hybrid 2D heterojunction with graphene and MoS2 has been recently proposed for this purpose: while MoS2 has shown good reversible capacity as a NIB anode, graphene is expected to improve conductivity and resistance to mechanical stress upon cycling. The most relevant processes for the anode are the intercalation and diffusion of the large Na ion, whose complex mechanisms are determined by the structural and electronic features of the MoS2/graphene interface. Understanding these processes and mechanisms is crucial for developing new nanoscale anodes for NIBs with high performances. To this end, here we report a state-of-the-art DFT study to address (a) the structural and electronic properties of heterointerfaces between the MoS2 monolayers and graphene, (b) the most convenient insertion sites for Na, and (c) the possible diffusion paths along the interface and the corresponding energy barrier heights. We considered two MoS2 polymorphs: 1T and 3R. Our results show that 1T-MoS2 interacts more strongly with graphene than 3R-MoS2. In both cases, the best Na host site is found at the MoS2 side of the interface, and the band structure reveals a proper n-type character of the graphene moiety, which is responsible for electronic conduction. Minimum-energy paths for Na diffusion show very low barrier heights for the 3R-MoS2/graphene interface (

Recently, great research efforts have been devoted to perovskite solar cells (PSCs) leading to sunlight-to-power conversion efficiencies above 25%. However, several barriers still hinder the full deployment of these devices. Critical issues are related to PCE stability and device lifetimes, which could be improved by targeted engineering of the hole transport material (HTM). Indeed, the HTM is not only responsible for transporting holes and preventing direct contact between the photo-active perovskite and the charge collector layer, but it plays important structural and protective roles too. As alternatives to the widely used yet expensive and unstable Spiro-OMeTAD, organic HTMs based on triphenylamine (TPA) and phenothiazine (PTZ) moieties have been proposed. However, their performances in PSC devices, and in particular their interfacial properties with the most popular methylammonium lead iodide perovskite (MAPI) still need investigations to be fully determined. In this framework, here we report a first-principles study on the structural and the electronic properties of a recently designed TPA and PTZ-based HTM (HTM1) and its interface with the MAPI (001) surface, considering both the PbI2- and the MAI-terminations. We also addressed already known HTM molecular systems to allow for a direct comparison with the recently proposed HTM1: we characterized the molecular parameters and the MAPI/HTM interfacial properties for Spiro-OMeTAD, PTZ1, and PTZ2. Our results suggest that good adhesion properties do not ensure effective and efficient MAPI-HTM hole injection. Despite the theoretical good alignment between HTM1 HOMO and MAPI valence band edge, our results for the mutually polarized interface point out the lack of a sufficient driving force for hole transport. While the hole mobility of HTM1 outperforms those of the other HTM molecules, for this HTM molecule, our findings suggest the application of lead halide perovskite compositions other than MAPI, with substituents that lower its valence band maximum potential value.

An example of breaking "Ewen's symmetry rule" for olefin catalysis polymerization is proposed by DFT calculations. Catalyst precursors with Cs symmetry are suggested to promote the isotactic propene polymerization by a modification of the active site geometry obtained via coordination with AlH-alkyl species in solution. The origin of stereocontrol in olefin polymerization is due to a dual mechanism dictated by the chiral catalyst. These findings may expand the toolbox for promoting stereoselective olefin polymerization by transition metal catalysts.

In this study, a new mechanism for doping of spiro-MeOTAD by Zn(TFSI)2 is revealed, which is completely different from the mechanism induced by LiTFSI. The oxidation of spiro-MeOTAD is facilitated by complexation between the zinc cation and tert-butylpyridine (tBP) even in the absence of oxygen and light. The lone electron pair of nitrogen in tBP coordinates to the zinc cation, confirmed by the Fourier transform infrared spectroscopy peak at 1637 cm-1 corresponding to a pyridine ring mode coupled with nitrogen coordinating to zinc as the Lewis site. The doping mechanism is also evidenced by computational calculations. The coordination of zinc to tBP and TFSI- provides a driving force and stabilizes the oxidized spiro-MeOTAD species, showing the most favorable reaction by forming a [Zn(tBP)3]+(TFSI-) complex with a ΔE of -1.52 eV. Our discovery of the mechanism of doping by Zn(TFSI)2 provides practical insight for the oxidation of spiro-MeOTAD by avoiding ambiguous aging processes in ambient or dry air at the risk of decomposition of other components.

Perovskite solar cells (PSCs) represent a promising technology for highly efficient sunlight harvesting and its conversion to electricity at convenient costs. However, a few flaws of current devices undermine the long-term stability of PSCs. Some of them concern the interface between the photoactive perovskite and the hole transport layer (HTL), e.g. undesired charge recombination, polarization barriers and oxidation processes. A strategy to solve this problem is to replace the standard organic HTL (e.g. Spiro-OMeTAD) with a solid-state inorganic layer. Being extensively used in p-type dye sensitized solar cells (DSSCs), nickel oxide (NiO) has been the first choice as an inorganic HTL. Despite the great interests in the application of NiO and other p-type oxides in PSCs, there is no available atomistic model of their interface with a halide perovskite. Here, we address this knowledge gap via a thorough first-principles study of the prototypical PSC perovskite methyl-ammonium lead iodide (MAPI) and two inorganic p-type oxides: NiO and CuGaO2. This copper-gallium delafossite oxide is one of the most promising alternatives to NiO in p-type DSSCs, thanks to its wide optical bandgap and low valence band edge. Here, we characterize the properties of both isolated surface slabs and MAPI/HTL heterostructure models. Besides considering MAPI/NiO and MAPI/CuGaO2 interfaces from the pristine materials, we also address the effects of intrinsic and extrinsic p-type defects in both NiO (Ni vacancy, Ni vacancy with Li and Ag doping) and CuGaO2 (Cu vacancy) using more realistic models. Our study reveals the most convenient interfaces in terms of structural affinities and adhesion energies. From the electronic perspective, we present a detailed analysis on band edge alignments, with direct insights into the key functional parameters of PSCs: hole injection driving force and open circuit potential. Our data show how the presence of defects/dopants is crucial for a convenient hole injection in NiO and CuGaO2. These results provide new science-based design principles for further development of p-type oxides in PSC devices.

Na-ion batteries (NIBs) are attracting widespread interest as a potentially more convenient alternative to current state-of-the-art Li-ion batteries (LIBs), chiefly for large-scale energy storage from renewables. Developing novel active materials is essential for the deployment of NIBs, especially in terms of negative electrodes that can accommodate the larger sodium ions. We focus on TiO2 anatase, which has been proposed as a promising anode material for the overall balance of performance, stability and cost. As the exposed crystal facets in different morphologies of nanostructured anatase can affect the electrochemical performances, here we report a theoretical investigation of Na+ adsorption and migration through (101), (100) and (001) surface terminations, thus explaining the different activities toward sodiation reported in the literature. Energy barriers computed by means of the CI-NEB method at the DFT+U level of theory show that the (001) surface is the most effective termination for Na+ insertion. We also provide a detailed analysis to elucidate that the energy barriers are due to structural modifications of the lattice upon sodiation. From these results we derive new design directions for the development of cheap and effective oxide-based nanostructured electrode materials for advanced NIBs.

X-ray diffraction data demonstrate that the adduct formed upon the reaction of dirhodium(II,II) tetraacetate with RNase A reacts with imidazole, leading to the formation of an unexpected product with the imidazole that binds the dirhodium center at an equatorial site rather than an axial site. The origin of this result has been dissected using quantum-chemical calculations.

The first-principles investigation of M-doped BiVO4-based materials (M = Mo, W) provides a comprehensive understanding of the dopant role in enhancing the photocatalytic properties for Oxygen Evolution Reaction (OER), which is the key-process for water splitting. We found that the beneficial effect of Mo/W doping on bismuth vanadate stems from structural surface re-organizations with the formation of a peculiar site (Biopp), which stabilizes both hydration and catalytic capabilities. Water adsorption is more favourable on Biopp site rather than on top of the dopant Mo/W atoms. Also, the catalytic performances for OER are significantly improved at Biopp site thanks to a stabilization of the crucial intermediate along the OER mechanism. Therefore, the Mo/W dopants exert a non-innocent indirect effect on the catalysis by activating the under-coordinated Biopp site via a long-range pull-back mechanism. These findings pave the route to new design strategies based on doping and defect engineering to push further the development of new photocatalysts for water splitting.

Perovskite solar cells (PSCs) and dye-sensitized solar cells (DSCs) both represent promising strategies for the sustainable conversion of sunlight into electricity and fuels. However, a few flaws of current devices hinder the large-scale establishment of such technologies. On one hand, PSCs suffer from instabilities and undesired phenomena mostly linked to the perovskite/hole transport layer (HTL) interface. Most of the currently employed organic HTL (e.g., Spiro-OMeTAD) are supposed to contribute to the perovskite decomposition and to be responsible for charge recombination processes and polarization barriers. On the other hand, power conversion efficiencies (PCEs) of DSCs are still too low to compete with other conversion technologies. Tandem cells are built by assembling p-type and n-type DSCs in a cascade architecture and, since each dye absorbs on a different portion of the solar spectrum, the harvesting window is increased and the theoretical efficiency limit for a single chromophore (i.e., the Shockley–Queisser limit) is overcome. However, such a strategy is hindered by the lack of a p-type semiconductor with optimal photocathode features. Nickel oxide has been, by far, the first-choice inorganic p-type semiconductor for both PV technologies, but its toxicity and non-optimal features (e.g., too low open circuit voltage and the presence of trap states) call for alternatives. Herein, we study of three p-type semiconductors as possible alternative to NiO, namely CuI, CuSCN and Cu2O. To this aim, we compare the structural and electronic features of the three materials by means of a unified theoretical approach based on the state-of-the art density functional theory (DFT). We focus on the calculation of their valence band edge energies and compare such values with those of two widely employed photo-absorbers, i.e., methylammonium lead iodide (MAPI) and the triple cation MAFACsPbBrI in PSCs and P1 and Y123 dyes in DSCs, given that the band alignment and the energy offset are crucial for the charge transport at the interfaces and have direct implications on the final efficiency. We dissect the effect a copper vacancy (i.e., intrinsic p-type doping) on the alignment pattern and rationalize it from both a structural and an electronic perspective. Our data show how defects can represent a crucial degree of freedom to control the driving force for hole injection in these devices.

Na-ion batteries (NIBs) are promising devices for large-scale energy-storage facilities. Nanostructured TiO2 is an efficient NIB negative electrode, showing good cycling performance and rate capability, but its activity depends on the crystalline facets exposed by anatase nanoparticles. Hence, we propose here a DFT+U study of Na+ adsorption and insertion at (101), (100) and (001)-TiO2 surfaces under the influence of external electric fields, which are simulated by adding a sawtooth-like electrostatic potential to the bare ionic potential. We find that field polarization affects Na+ uptake as well as titania electronic features, promoting redox processes within Ti sublattice, as in battery charge/discharge cycling. Our results highlight the high-energy (001) surface to be the most active, for both directions of external fields, proving its activity to be exerted reversibly. Besides further insights, these outcomes pave the route for further exploration and design of electrode materials by simulation of battery in operando conditions. Graphical Abstract

CsPbBr3 nanocrystals (NCs) passivated by conventional lipophilic capping ligands suffer from colloidal and optical instability under ambient conditions, commonly due to the surface rearrangements induced by the polar solvents used for the NC purification steps. To avoid onerous postsynthetic approaches, ascertained as the only viable stability-improvement strategy, the surface passivation paradigms of as-prepared CsPbBr3 NCs should be revisited. In this work, the addition of an extra halide source (8-bromooctanoic acid) to the typical CsPbBr3 synthesis precursors and surfactants leads to the in situ formation of a zwitterionic ligand already before cesium injection. As a result, CsPbBr3 NCs become insoluble in nonpolar hexane, with which they can be washed and purified, and form stable colloidal solutions in a relatively polar medium (dichloromethane), even when longly exposed to ambient conditions. The improved NC stability stems from the effective bidentate adsorption of the zwitterionic ligand on the perovskite surfaces, as supported by theoretical investigations. Furthermore, the bidentate functionalization of the zwitterionic ligand enables the obtainment of blue-emitting perovskite NCs with high PLQYs by UV-irradiation in dichloromethane, functioning as the photoinduced chlorine source. publishedVersion

Improving morphological and electronic properties of the electron transport layer (ETL) is a critical issue to fabricate highly efficient perovskite solar cells. Tin dioxide is used as an ETL for its peculiarities such as low-temperature solution-process and high electron mobility and several handlings have been tested to increase its performances. Herein, SnO2:ZnO and SnO2:In2O3 composites are studied as ETL in planar n-i-p CH3NH3PbI3 solar cells fabricated in ambient air, starting from glass/ITO substrates. Morphological, electrical and optical properties of zinc- and indium-oxide nanoparticles (NPs) are investigated. First-principle calculations are also reported and help to further explain the experimental evidences. Photovoltaic performances of full devices show an improvement in efficiency for SnO2:In2O3–based solar cells with respect to pristine SnO2, probably due to a suppression of interfacial charge recombination between ITO/ETL and ETL/perovskite. Moreover, a better homogeneity of SnO2:In2O3 deposition with respect to SnO2:ZnO composites, conducts an increase in perovskite grain size and, consequently, the device performances.

The replacement of cobalt in the lattice of lithium-rich layered oxides (LRLO) is mandatory to improve their environmental benignity and reduce costs. In this study, we analyze the impact of the cobalt removal from the trigonal LRLO lattice on the structural, thermodynamic, and electronic properties of this material through density functional theory calculations. To mimic disorder in the transition metal layers, we exploited the special quasi-random structure approach on selected supercells. The cobalt removal was modeled by the simultaneous substitution with Mn/Ni, thus leading to a p-doping in the lattice. Our results show that cobalt removal induces (a) larger cell volumes, originating from expanded distances among stacked planes, (b) a parallel increase of the layer buckling, (c) an increase of the electronic disorder and of the concentration of Jahn–Teller defects, and (d) an increase of the thermodynamic stability of the phase. Overall p-doping appears as a balanced strategy to remove cobalt from LRLO without massively deteriorating the structural integrity and the electronic properties of LRLO.

Titanium dioxide (TiO2) has been extensively studied as a suitable material for a wide range of fields including catalysis and sensing. For example, TiO2-based nanoparticles are active in the catalytic conversion of glucose into value-added chemicals, while the good biocompatibility of titania allows for its application in innovative biosensing devices for glucose detection. A key process for efficient and selective biosensors and catalysts is the interaction and binding mode between the analyte and the sensor/catalyst surface. The relevant features regard both the molecular recognition event and its effects on the nanoparticle electronic structure. In this work, we address both these features by combining two first-principles methods based on periodic boundary conditions and cluster approaches (CAs). While the former allows for the investigation of extended materials and surfaces, CAs focus only on a local region of the surface but allow for using hybrid functionals with low computational cost, leading to a highly accurate description of electronic properties. Moreover, the CA is suitable for the study of reaction mechanisms and charged systems, which can be cumbersome with PBC. Here, a direct and detailed comparison of the two computational methodologies is applied for the investigation of d-glucose on the TiO2 (100) anatase surface. As an alternative to the commonly used PBC calculations, the CA is successfully exploited to characterize the formation of surface and subsurface oxygen vacancies and to determine their decisive role in d-glucose adsorption. The results of such direct comparison allow for the selection of an efficient, finite-size structural model that is suitable for future investigations of biosensor electrocatalytic processes and biomass conversion catalysis.

In this contribution, we demonstrate the presence of high-spin Fe3+ in Fe-substituted ZrO2 (FexZr1−xO2−δ), as deduced from X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and 57Fe Mössbauer spectroscopy measurements. The activity of this carbon-supported FexZr1−xO2−δ catalyst toward the oxygen reduction reaction (ORR) was examined by both rotating (ring) disk electrode (R(R)DE) method and single-cell proton exchange membrane fuel cells (PEMFCs). DFT calculations suggest that the much higher ORR mass activity of FexZr1−xO2−δ compared to Fe-free ZrO2 is due to the enhanced formation of oxygen vacancies: their formation is favored after Zr4+ substitution with Fe3+ and the oxygen vacancies create potential adsorption sites, which act as active centers for the ORR. H2O and/or H2O2 production observed in RRDE measurements for the Fe0.07Zr0.93O1.97 is also in agreement with the most likely reaction paths from DFT calculations. In addition, Tafel and Arrhenius analyses are performed on Fe0.07Zr0.93O1.97 using both RRDE and PEMFC data at various temperatures.

In this manuscript, we report a detailed physico-chemical comparison between the α- and β-polymorphs of the NaMnO2 compound, a promising material for application in positive electrodes for secondary aprotic sodium batteries. In particular, the structure and vibrational properties, as well as electrochemical performance in sodium batteries, are compared to highlight differences and similarities. We exploit both laboratory techniques (Raman spectroscopy, electrochemical methods) and synchrotron radiation experiments (Fast-Fourier Transform Infrared spectroscopy, and X-ray diffraction). Notably the vibrational spectra of these phases are here reported for the first time in the literature as well as the detailed structural analysis from diffraction data. DFT+U calculations predict both phases to have similar electronic features, with structural parameters consistent with the experimental counterparts. The experimental evidence of antisite defects in the beta-phase between sodium and manganese ions is noticeable. Both polymorphs have been also tested in aprotic batteries by comparing the impact of different liquid electrolytes on the ability to de-intercalated/intercalate sodium ions. Overall, the monoclinic α-NaMnO2 shows larger reversible capacity exceeding 175 mAhg−1 at 10 mAg−1.

The first real examples of luminescent solar concentrators (LSCs) based on Ir(III) cyclometalates, are described herein. Two new Ir(III) tetrazole complexes, namely [Ir(ppy)2(iQTZ-PPG)]+ and [Ir(npy)2(iQTZ-PPG)]+, where (C^N) = ppy, 2 phenylpyridine or npy = 2-(naphthalen-2-yl)pyridine and iQTZ-PPG = 1-(2-(prop-2-yn-1-yl)-2H-tetrazol-5-yl)isoquinoline, were synthesized, fully characterized and tested as phosphors for colourless LSCs. Notably, increasing quantities (0.2–1.8 wt %) of the new Ir(III) based phosphors were dispersed in different acrylate polymers like poly(methyl methacrylate), PMMA, poly(benzyl methacrylate), PBzMA and poly(cyclohexyl methacrylate), PCHMA, leading to visible transparent polymeric films exhibiting excellent photostability and bright yellow to orange phosphorescent emissions. The performances as solar collectors of all the Ir(III)-doped polymers were investigated, providing results comparable, or superior, to those obtained from colourless LSC based on organic fluorophores. In fact, the best optical efficiency (ηopt up to 7%, combined to transmittance close to 80% at 390 nm) was displayed by the polymer film obtained from physical dispersion of [Ir(ppy)2(iQTZ-PPG)]+ (1.4 wt %) in PCHMA.

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies., Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. Righteous font designed by Astigmatic and licensed under the Open Font License.

We present a first-principles study on the structure-property relationships in MoS2 and WS2 monolayers and their vertically stacked hetero-bilayer, with and without Sulfur vacancies, in order to dissect the electronic features behind their photocatalytic water splitting capabilities. We also benchmark the accuracy of three different exchange-correlation density functionals for both minimum-energy geometries and electronic structure. The best compromise between computational cost and qualitative accuracy is achieved with the HSE06 density functional on top of Perdew-Burke-Ernzerhof minima, including dispersion with Grimme's D3 scheme. This computational approach predicts the presence of mid-gap states for defective monolayers, in accordance with the present literature. For the heterojunction, we find unexpected vacancy-position dependent electronic features: the location of the defects leads either to mid-gap trap states, detrimental for photocatalyst or to a modification of characteristic type II band alignment behavior, responsible for interlayer charge separation and low recombination rates.

The recycling of CO2 back into chemicals via photo-electrochemical cells represents a viable route to mitigate the global climate crisis of current days. In this paper we focus on the copper-iron delafossite oxide, CuFeO2, which has been proven to have suitable physico-chemical properties to photo-catalyze the carbon dioxide reduction to formic acid. The specific electronic and structural features that allow activating the highly stable CO2 molecule are dissected by exploiting state-of-the art first principles methods. The effects of surface oxygen vacancies as well as the different roles of copper and iron on the adsorption and the activation of carbon dioxide at the CuFeO2 most stable surface are analyzed. These results highlight the key role of oxygen defects in favoring the CO2 adsorption and in promoting the formation of a radical anion CO2 − or a carbonate-like adsorbate so providing the scientific grounds for implementing new rational design strategies and improving the performances of CuFeO2-based photoelectrodes for CO2 reduction.

In this study we address the Li-ion de-insertion/insertion mechanisms from/into the lattice of the mixed olivine LiCo1/3Fe1/3Mn1/3PO4 (LCFMP). This mechanism is driven by a subtle interplay of structural, electronic and thermodynamic features. We aim at dissecting this complex landscape that is tightly connected to the long-term electrochemical performance of this material as a positive electrode in lithium-ion cells. To this end, we report advanced structural characterization, based on ex situ synchrotronradiation diffraction on samples at different lithium contents. We couple this analysis with first-principles simulations, for a direct vis-a-vis comparison. Our results show that (1) the mixing of the three transition-metal (TM) cations in the olivine lattice leads to a solid solution, providing the olivine lattice with the necessary flexibility to retain its single-phase structure during cell operation; (2) the electronic features of the three TMs are responsible for the observed electrochemical performance; (3) the de-lithiation of the olivine lattice is a thermodynamically driven process. Last but not least, our integrated experimental and theoretical results reveal the subtle features behind the formation of antisite defects that selectively involve Li–Co couples. In conclusion, our study provides the necessary scientific foundations to understand the structure–property–function relationships in LCFMP olivines, paving the way for further development and optimization of this material for application in Li-ion batteries.

Transition-metal (TM) layered oxides have been attracting enormous interests in recent decades because of their excellent functional properties as positive electrode materials in lithium-ion batteries. In particular LiCoO2 (LCO), LiNiO2 (LNO) and LiMnO2 (LMO) are the structural prototypes of a large family of complex compounds with similar layered structures incorporating mixtures of transition metals. Here, we present a comparative study on the phase stability of LCO, LMO and LNO by means of first-principles calculations, considering three different lattices for all oxides, i.e., rhombohedral (hR12), monoclinic (mC8) and orthorhombic (oP8). We provide a detailed analysis&mdash, at the same level of theory&mdash, on geometry, electronic and magnetic structures for all the three systems in their competitive structural arrangements. In particular, we report the thermodynamics of formation for all ground state and metastable phases of the three compounds for the first time. The final Gibbs Energy of Formation values at 298 K from elements are: LCO(hR12) &minus, 672 &plusmn, 8 kJ mol&minus, 1, LCO(mC8) &minus, 655 &plusmn, LCO(oP8) &minus, 607 &plusmn, LNO(hR12) &minus, 548 &plusmn, LNO(mC8) &minus, 557 &plusmn, LNO(oP8) &minus, LMO(hR12) &minus, 765 &plusmn, 10 kJ mol&minus, LMO(mC8) &minus, 779 &plusmn, LMO(oP8) &minus, 780 &plusmn, 1. These values are of fundamental importance for the implementation of reliable multi-phase thermodynamic modelling of complex multi-TM layered oxide systems and for the understanding of thermodynamically driven structural phase degradations in real applications such as lithium-ion batteries.

International audience; Dye-sensitized photoelectrochemical cells form an emerging technology for the large-scale storage of solar energy in the form of (solar) fuels because of the low cost and easy processing of their constitutive photoelectrode materials. Such hybrid photoelectrodes consist of molecular dyes grafted onto transparent semiconducting metal oxides in combination with catalytic centers. The optimization of the performances of such hybrid photoelectrodes requires a detailed understanding of the light-driven electron transfer processes occurring first at the interface between the semiconducting material and the dye and then between the dye and the catalytic center. Here we address the first of these issues and use quantum chemistry to determine the structural and electronic features of the interfaces between a push-pull dye and the p-NiO (100) surface. We show that these calculations are in good agreement with transient absorption spectroscopic measurements on a prototypical dye-sensitized photocathode system able to evolve hydrogen in the presence of a cobaloxime catalyst in solution.

International audience; The development of NiO-based molecular photocathodes is attracting growing interest in thefield of dye-sensitized photoelectrochemical cells (DS-PEC) for efficient conversion of sunlightinto fuel. For this purpose different strategies are developed to assemble the molecularcomponents together in order to build functional devices. Here, an original dye-catalystsupramolecular assembly was designed and obtained via axial coordination of a cobalt-basedH2-evolving catalyst, i.e. a cobaloxime complex, to a pyridyl-functionalized rutheniumdiacetylide photosensitizer. The new supramolecular assembly was successfully employed forthe construction of efficient NiO-based photocathodes for solar hydrogen production. We reporta joint experimental and theoretical study of the new photocatalytic system, includingelectrochemical and XPS analyses. Photo-electrochemical generation of H2 under pertinentaqueous conditions eventually led to a faradaic efficiency of 27 %

Here we report the first theoretical characterization of the interface between the CuGaO2 delafossite oxide and the carboxylic (–COOH) and phosphonic acid (–PO3H2) anchoring groups. The promising use of delafossites as effective alternative to nickel oxide in p-type DSSC is still limited by practical difficulties in sensitizing the delafossite surface. Thus, this work provides atomistic insights on the structure and energetics of all the possible interactions between the anchoring functional groups and the CuGaO2 surface species, including the effects of the Mg doping and of the solvent medium. Our results highlight the presence of a strong selectivity toward the monodentate binding mode on surface Ga atoms for both the carboxylic and phosphonic acid groups. Since the binding modes have a strong influence on the hole injection thermodynamics, these findings have direct implications for further development of delafossite based p-type DSSCs.

In the quest for a sustainable society, energy storage technology is destined to play a central role in the future energy landscape. Breakthroughs in materials and methods involving sustainable resources are crucial to protect humankind from the most serious consequences of climate change. Rechargeable batteries of all forms will be required to follow the path. Elements that are eligible to harmonically contribute to the development of a sustainable ecosystem and fulfil the demands of high energy density batteries include Na, K, Ca, Mg, Zn, and Al. Numerous research efforts are underway to explore new battery chemistries based on these elements and, depending on the field of application, different elements inherit different advantages and challenges. Full sustainability implies that the environmental friendliness of these systems must be characterized by a “cradle-to-grave” approach. In this context, the pursuit of global environmental and economical sustainability from mass production, raw materials, and technical challenges is discussed herein for the most recent battery concepts based on monovalent and multivalent metal anodes. A perspective on strategies and opportunities particularly around the development of all-solid-state system configurations is provided, and the most important obstacles to overcome in search of a more sustainable future for electrochemical energy storage are addressed.