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- ItemPrussian blue and its analogues as functional template materials: control of derived structure compositions and morphologies(London [u.a.] : RSC, 2023) Bornamehr, Behnoosh; Presser, Volker; Zarbin, Aldo J. G.; Yamauchi, Yusuke; Husmann, SamanthaHexacyanometallates, known as Prussian blue (PB) and its analogues (PBAs), are a class of coordination compounds with a regular and porous open structure. The PBAs are formed by the self-assembly of metallic species and cyanide groups. A uniform distribution of each element makes the PBAs robust templates to prepare hollow and highly porous (hetero)nanostructures of metal oxides, sulfides, carbides, nitrides, phosphides, and (N-doped) carbon, among other compositions. In this review, we examine methods to derive materials from PBAs focusing on the correlation between synthesis steps and derivative morphologies and composition. Insights into catalytic and electrochemical properties resulting from different derivatization strategies are also presented. We discuss challenges in manipulating the derivatives' properties, give perspectives of synthetic approaches for the target applications and present an outlook on less investigated grounds in Prussian blue derivatives.
- ItemInvestigating the electrochemical stability of Li7La3Zr2O12 solid electrolytes using field stress experiments(London [u.a.] : RSC, 2021) Smetaczek, Stefan; Pycha, Eva; Ring, Joseph; Siebenhofer, Matthäus; Ganschow, Steffen; Berendts, Stefan; Nenning, Andreas; Kubicek, Markus; Rettenwander, Daniel; Limbeck, Andreas; Fleig, JürgenCubic Li7La3Zr2O12 (LLZO) garnets are among the most promising solid electrolytes for solid-state batteries with the potential to exceed conventional battery concepts in terms of energy density and safety. The electrochemical stability of LLZO is crucial for its application, however, controversial reports in the literature show that it is still an unsettled matter. Here, we investigate the electrochemical stability of LLZO single crystals by applying electric field stress via macro- and microscopic ionically blocking Au electrodes in ambient air. Induced material changes are subsequently probed using various locally resolved analysis techniques, including microelectrode electrochemical impedance spectroscopy (EIS), laser induced breakdown spectroscopy (LIBS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and microfocus X-ray diffraction (XRD). Our experiments indicate that LLZO decomposes at 4.1–4.3 V vs. Li+/Li, leading to the formation of Li-poor phases like La2Zr2O7 beneath the positively polarized electrode. The reaction is still on-going even after several days of polarization, indicating that no blocking interfacial layer is formed. The decomposition can be observed at elevated as well as room temperature and suggests that LLZO is truly not compatible with high voltage cathode materials.
- ItemNiobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes(London [u.a.] : RSC, 2016) Tolosa, Aura; Krüner, Benjamin; Fleischmann, Simon; Jäckel, Nicolas; Zeiger, Marco; Aslan, Mesut; Grobelsek, Ingrid; Presser, VolkerThis study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m2 g−1. These nanofibers show a maximum specific energy of 19.5 W h kg−1 at low power and 7.6 W h kg−1 at a high specific power of 30 kW kg−1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g−1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g−1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg−1 was obtained. The high specific power for both systems, NbC–CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.
- ItemOn the anomalous optical conductivity dispersion of electrically conducting polymers: Ultra-wide spectral range ellipsometry combined with a Drude-Lorentz model(London [u.a.] : RSC, 2019) Chen, Shangzhi; Kühne, Philipp; Stanishev, Vallery; Knight, Sean; Brooke, Robert; Petsagkourakis, Ioannis; Crispin, Xavier; Schubert, Mathias; Darakchieva, Vanya; Jonsson, Magnus P.Electrically conducting polymers (ECPs) are becoming increasingly important in areas such as optoelectronics, biomedical devices, and energy systems. Still, their detailed charge transport properties produce an anomalous optical conductivity dispersion that is not yet fully understood in terms of physical model equations for the broad range optical response. Several modifications to the classical Drude model have been proposed to account for a strong non-Drude behavior from terahertz (THz) to infrared (IR) ranges, typically by implementing negative amplitude oscillator functions to the model dielectric function that effectively reduce the conductivity in those ranges. Here we present an alternative description that modifies the Drude model via addition of positive-amplitude Lorentz oscillator functions. We evaluate this so-called Drude-Lorentz (DL) model based on the first ultra-wide spectral range ellipsometry study of ECPs, spanning over four orders of magnitude: from 0.41 meV in the THz range to 5.90 eV in the ultraviolet range, using thin films of poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos) as a model system. The model could accurately fit the experimental data in the whole ultrawide spectral range and provide the complex anisotropic optical conductivity of the material. Examining the resonance frequencies and widths of the Lorentz oscillators reveals that both spectrally narrow vibrational resonances and broader resonances due to localization processes contribute significantly to the deviation from the Drude optical conductivity dispersion. As verified by independent electrical measurements, the DL model accurately determines the electrical properties of the thin film, including DC conductivity, charge density, and (anisotropic) mobility. The ellipsometric method combined with the DL model may thereby become an effective and reliable tool in determining both optical and electrical properties of ECPs, indicating its future potential as a contact-free alternative to traditional electrical characterization. © The Royal Society of Chemistry 2019.
- ItemTowards low-temperature processing of efficient γ-CsPbI3 perovskite solar cells(London [u.a.] : RSC, 2023) Zhang, Zongbao; Ji, Ran; Hofstetter, Yvonne J.; Deconinck, Marielle; Brunner, Julius; Li, Yanxiu; An, Qingzhi; Vaynzof, YanaInorganic cesium lead iodide (CsPbI3) perovskite solar cells (PSCs) have attracted enormous attention due to their excellent thermal stability and optical bandgap (∼1.73 eV), well-suited for tandem device applications. However, achieving high-performance photovoltaic devices processed at low temperatures is still challenging. Here we reported a new method for the fabrication of high-efficiency and stable γ-CsPbI3 PSCs at lower temperatures than was previously possible by introducing the long-chain organic cation salt ethane-1,2-diammonium iodide (EDAI2) and regulating the content of lead acetate (Pb(OAc)2) in the perovskite precursor solution. We find that EDAI2 acts as an intermediate that can promote the formation of γ-CsPbI3, while excess Pb(OAc)2 can further stabilize the γ-phase of CsPbI3 perovskite. Consequently, improved crystallinity and morphology and reduced carrier recombination are observed in the CsPbI3 films fabricated by the new method. By optimizing the hole transport layer of CsPbI3 inverted architecture solar cells, we demonstrate efficiencies of up to 16.6%, surpassing previous reports examining γ-CsPbI3 in inverted PSCs. Notably, the encapsulated solar cells maintain 97% of their initial efficiency at room temperature and under dim light for 25 days, demonstrating the synergistic effect of EDAI2 and Pb(OAc)2 in stabilizing γ-CsPbI3 PSCs.
- ItemVoltage hysteresis loop as a fingerprint of slow kinetics Co2+-to-Co3+ transition in layered NaxCox/2Ti1−x/2O2 cathodes for sodium batteries(London [u.a.] : RSC, 2022) Mikhailova, Daria; Gorbunov, Mikhail V.; An Nguyen, Hoang Bao; Pohle, Björn; Maletti, Sebastian; Heubner, ChristianSodium transition metal oxides are one of the most promising cathode materials for future sodium ion batteries. Chemical flexibility of layered Na-oxides including cobalt enables its partial substitution by other redox-active or non-active metals, often leading to structural stabilization. Sharing the same structural positions with other transition metals in layered oxides, Co can be double- or triple-charged, and as Co3+ can adopt a low-spin (LS), intermediate-spin (IS), high-spin (HS) state, or a combination of them. Using Ti4+ in the structure together with Co2+ results in a reduced number of phase transformations compared to Ti-free compositions. However, a large potential hysteresis of about 1.5-2.5 V between battery charge and discharge is observed, pointing a first-order cooperative phase transition. Based on several examples, we found that Na extraction from NaxCox/2Ti1−x/2O2 materials with high-spin HS-Co2+, crystallizing in the P2 or O3 structure, mostly results in valence and spin-state transition of Co, leading to the formation of a second phase with a low-spin LS-Co3+, and a much smaller unit cell volume. We elucidated a kinetic origin of the potential hysteresis, which can be minimized by increasing temperature or reduction of the current density during battery cycling with P2- and O3-Na0.67Co0.33Ti0.67O2 materials. The slow kinetics of the structural phase transition, especially upon Na-insertion, hampers the application of classical methods of electrochemical thermodynamics, such as determining the entropic potential dE/dT. We showed that the entropic potential depends only on the Na-content in NaxCo0.33Ti0.67O2 during battery charge or discharge, what additionally confirms a kinetic nature of the potential hysteresis.
- ItemA general approach for all-visible-light switching of diarylethenes through triplet sensitization using semiconducting nanocrystals(London [u.a.] : RSC, 2022) Hou, Lili; Larsson, Wera; Hecht, Stefan; Andréasson, Joakim; Albinsson, BoCoupling semiconducting nanocrystals (NCs) with organic molecules provides an efficient route to generate and transfer triplet excitons. These excitons can be used to power photochemical transformations such as photoisomerization reactions using low energy radiation. Thus, it is desirable to develop a general approach that can efficiently be used to control photoswitches using all-visible-light aiming at future applications in life- and materials sciences. Here, we demonstrate a simple ‘cocktail’ strategy that can achieve all-visible-light switchable diarylethenes (DAEs) through triplet energy transfer from the hybrid of CdS NCs and phenanthrene-3-carboxylic acid, with high photoisomerization efficiency and improved fatigue resistance. The size-tunable excitation energies of CdS NCs make it possible to precisely match the clear spectral window of the relevant DAE photoswitch. We demonstrate reversible all-visible-light photoisomerization of a series of DAE derivatives both in the liquid and solid state, even in the presence of oxygen. Our general strategy is promising for fabrication of all-visible-light activated optoelectronic devices as well as memories, and should in principle be adaptable to photopharmacology.
- ItemRhodamine 6G and 800 intermolecular heteroaggregates embedded in PMMA for near-infrared wavelength shifting(London [u.a.] : RSC, 2022) Castillo-Seoane, Javier; Gonzalez-Garcia, Lola; Obrero-Perez, José M.; Aparicio, Francisco J.; Borrás, Ana; González-Elipe, Agustín R.; Barranco, Ángel; Sanchez-Valencia, Juan R.The opto-electronic properties of small-molecules and functional dyes usually differ when incorporated into solid matrices with respect to their isolated form due to an aggregation phenomenon that alters their optical and fluorescent properties. These spectroscopic modifications are studied in the framework of the exciton theory of aggregates, which has been extensively applied in the literature for the study of molecular aggregates of the same type of molecules (homoaggregation). Despite the demonstrated potential of the control of the heteroaggregation process (aggregation of different types of molecules), most of the reported works are devoted to intramolecular aggregates, complex molecules formed by several chromophores attached by organic linkers. The intramolecular aggregates are specifically designed to hold a certain molecular structure that, on the basis of the exciton theory, modifies their optical and fluorescent properties with respect to the isolated chromophores that form the molecule. The present article describes in detail the incorporation of Rhodamine 6G (Rh6G) and 800 (Rh800) into polymeric matrices of poly-(methyl methacrylate), PMMA. The simultaneous incorporation of both dyes results in an enhanced fluorescent emission in the near-infrared (NIR), originating from the formation of ground-state Rh6G–Rh800 intermolecular heteroaggregates. The systematic control of the concentration of both rhodamines provides a model system for the elucidation of the heteroaggregate formation. The efficient energy transfer between Rh6G and Rh800 molecules can be used as wavelength shifters to convert effectively the light from visible to NIR, a very convenient wavelength range for many practical applications which make use of inexpensive commercial detectors and systems.
- ItemChoosing the right carbon additive is of vital importance for high-performance Sb-based Na-ion batteries(London [u.a.] : RSC, 2020) Pfeifer, Kristina; Arnold, Stefanie; Budak, Öznil; Luo, Xianlin; Presser, Volker; Ehrenberg, Helmut; Dsoke, SoniaElectrodes based on alloying reactions for sodium-ion batteries (NIB) offer high specific capacity but require bespoken electrode material design to enable high performance stability. This work addresses that issue by systematically exploring the impact of carbon properties on antimony/carbon composite electrodes for NIBs. Since the Sb surface is covered by an insulating oxide layer, carbon additives are crucial for the percolation and electrochemical activity of Sb based anodes. Instead of using complex hybridization strategies, the ability of mechanical mixing to yield stable high-performance Sb/C sodium-ion battery (NIB) electrodes is shown. This is only possible by considering the physical, chemical, and structural features of the carbon phase. A comparison of carbon nanohorns, onion-like carbon, carbon black, and graphite as conductive additives is given in this work. The best performance is not triggered by the highest or lowest surface area, and not by highest or lowest heteroatom content, but by the best ability to homogenously distribute within the Sb matrix. The latter provides an optimum interaction between carbon and Sb and is best enabled by onion-like carbon. A remarkable rate performance is attained, electrode cracking caused by volume expansion is successfully prevented, and the homogeneity of the solid/electrolyte interphase is significantly improved as a result of it. With this composite electrode, a reversible capacity of 490 mA h g-1 at 0.1 A g-1 and even 300 mA g-1 at 8 A g-1 is obtained. Additionally, high stability with a capacity retention of 73% over 100 cycles is achieved at charge/discharge rates of 0.2 A g-1 This journal is © The Royal Society of Chemistry.
- ItemPolysulfide driven degradation in lithium–sulfur batteries during cycling – quantitative and high time-resolution operando X-ray absorption study for dissolved polysulfides probed at both electrode sides(London [u.a.] : RSC, 2021) Zech, Claudia; Hönicke, Philipp; Kayser, Yves; Risse, Sebastian; Grätz, Olga; Stamm, Manfred; Beckhoff, BurkhardThe development of operando characterization techniques on realistic batteries is essential for an advanced mechanistic understanding in battery chemistry and, therefore, contributes to their further performance improvement. This manuscript presents operando Near-Edge X-ray Absorption Spectroscopy (NEXAFS) traceable to the SI units (SI is the abbreviation for the International System of Units) during multiple charge–discharge cycles on both electrodes of lithium–sulfur (Li/S) coin cells which enables an absolute quantification of dissolved polysulfides with no need for calibration samples or reference material. We could reveal that during the charging process, polysulfide (PS) movement from the negative to the positive electrode is inhibited. This leads to a steady increase of dissolved polysulfides at the anode side and, therefore, is one of the key points for capacity fading. We quantitatively track the polysulfides dissolved in the electrolyte and correlate for the first time their evolution with the capacity fading of the cell. We analyze the appearance of PS during cell operation at the cathode and anode side to characterize the transport mechanisms of the polysulfide shuttle phenomena and to reveal quantitative information about their evolution at different states of charge and states of health. Our cell design suppresses the contribution of cathodic sulfur, which is mandatory for reference-sample-free quantification in X-ray spectrometry and allows us to use only slightly modified standard coin cell batteries.
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