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Potassium manganese hexacianoferrate has been prepared by co-precipitation from manganese (II) chloride and potassium citrate, with chemical analysis yielding the formula K 1.72 Mn[Fe(CN) 6 ] 0.92 □ 0.08  ⋅ 1.1H 2 O (KMnHCF). Its X-ray diffraction pattern is consistent with a monoclinic structure (space group P 2 1 /n, no. 14) with cell parameters a=10.1202(6)Å, b=7.2890(5)Å, c=7.0193(4)Å, and β=89.90(1)°. Its redox behavior has been studied in magnesium containing electrolytes. Both K + ions deintercalated from the structure upon oxidation and contamination with Na + ions coming from the separator were found to interfere in the electrochemical response. In the absence of alkaline ions, pre-oxidized manganese hexacianoferrate showed reversible magnesium intercalation, and the process has been studied by operando synchrotron X-ray diffraction. The location of Mg 2+ ions in the crystal structure was not possible with the available experimental data. Still, density functional theory simulations indicated that the most favorable position for Mg 2+ intercalation is at 32f sites (considering a pseudo cubic F m-3m phase), which are located between 8c and Mn sites., (© 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Gel polymer electrolytes composed of deep eutectic solvent acetamide 4 :Zn(TFSI) 2 and poly(ethylene oxide) (PEO) are prepared by using a fast, solvent-free procedure. The effect of the PEO molecular weight and its concentration on the physicochemical and electrochemical properties of the electrolytes are studied. Gels prepared with ultrahigh molecular-weight PEO present pseudo-solid behavior and ionic conductivity even higher than that of the original liquid electrolyte. A decrease in the dendritic growth in soft gels with PEO contents up to 1 wt % is demonstrated. The changes in the chemical structure of the electrolyte produced by the strong interactions between ethylene oxide units and Zn 2+ have also been studied. The addition of PEO takes the electrolyte out of its original eutectic composition, producing blend crystallization. However, it is possible to retain the eutectic point of the electrolyte in a gel form if the addition of PEO is accompanied by the reduction of acetamide., (© 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Metal-air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal-air batteries, the Na-O 2 battery has gained much attention due to its low discharge/charge overpotentials (∼100 mV) at relatively high current densities (0.2 mA/cm 2 ), high electrical energy efficiency (90%), high theoretical energy density, and low cost. However, there is no information reported regarding the effect of CO 2 contamination in non-aqueous Na-air batteries. Density functional theory has, here, been applied to study the effect of low concentrations of CO 2 contamination on NaO 2 and Na 2 O 2 growth/depletion reaction pathways and overpotentials. This was done on step surfaces of discharge products in non-aqueous Na-air batteries. Adsorption energies of CO 2 at various nucleation sites for both step surfaces were determined, and results revealed that CO 2 preferentially binds at the step valley sites of (001) NaO 2 and 11¯00 Na 2 O 2 surfaces with binding energies of -0.65 eV and -2.67 eV, respectively. CO 2 blocks the step nucleation site and influences the reaction pathways and overpotentials due to carbonate formation. The discharge electrochemical overpotential increases remarkably from 0.14 V to 0.30 V and from 0.69 V to 1.26 V for NaO 2 and Na 2 O 2 surfaces, respectively. CO 2 contamination is thus drastically impeding the growth/depletion mechanism pathways and increases the overpotentials of the surface reaction mechanism, hampering the performance of the battery. Avoiding CO 2 contamination from intake of gas and electrolyte decomposition is thus critical in development of Na-air batteries.

Materials exhibiting a substitutional disorder such as multicomponent alloys and mixed metal oxides/oxyfluorides are of great importance in many scientific and technological sectors. Disordered materials constitute an overwhelmingly large configurational space, which makes it practically impossible to be explored manually using first-principles calculations such as density functional theory due to the high computational costs. Consequently, the use of methods such as cluster expansion (CE) is vital in enhancing our understanding of the disordered materials. CE dramatically reduces the computational cost by mapping the first-principles calculation results on to a Hamiltonian which is much faster to evaluate. In this work, we present our implementation of the CE method, which is integrated as a part of the atomic simulation environment (ASE) open-source package. The versatile and user-friendly code automates the complex set up and construction procedure of CE while giving the users the flexibility to tweak the settings and to import their own structures and previous calculation results. Recent advancements such as regularization techniques from machine learning are implemented in the developed code. The code allows the users to construct CE on any bulk lattice structure, which makes it useful for a wide range of applications involving complex materials. We demonstrate the capabilities of our implementation by analyzing the two example materials with varying complexities: a binary metal alloy and a disordered lithium chromium oxyfluoride.

The Na-O 2 system holds great potential as a low-cost, high-energy-density battery, but under normal operating conditions, the discharge is limited to sodium superoxide (NaO 2 ), whereas the high-capacity peroxide state (Na 2 O 2 ) remains elusive. Here, we apply density functional theory calculations with an improved error-correction scheme to determine equilibrium potentials and free energies as a function of temperature for the different phases of NaO 2 and Na 2 O 2 , identifying NaO 2 as the thermodynamically preferred discharge product up to ∼120 K, after which Na 2 O 2 is thermodynamically preferred. We also investigate the reaction mechanisms and resulting electrochemical overpotentials on stepped surfaces of the NaO 2 and Na 2 O 2 systems, showing low overpotentials for NaO 2 formation (η dis = 0.14 V) and depletion (η cha = 0.19 V), whereas the overpotentials for Na 2 O 2 formation (η dis = 0.69 V) and depletion (η cha = 0.68 V) are found to be prohibitively high. These findings are in good agreement with experimental data on the thermodynamic properties of the Na x O 2 species and provide a kinetic explanation for why NaO 2 is the main discharge product in Na-O 2 batteries under normal operating conditions.

We report the interface energetics of decacyclene trianhydride (DTA) monolayers on top of two distinct model surfaces, namely, Au(111) and Ag(111). On the latter, combined valence band photoemission and X-ray absorption measurements that access the occupied and unoccupied molecular orbitals, respectively, reveal that electron transfer from substrate to surface sets in. Density functional theory calculations confirm our experimental findings and provide an understanding not only of the photoemission and X-ray absorption spectral features of this promising organic semiconductor but also of the fingerprints associated with the interface charge transfer.

An extensive database of spectroscopic properties of molecules from ab initio calculations is used to design molecular complexes for use in tandem solar cells that convert two photons into a single electron-hole pair, thereby increasing the output voltage while covering a wider spectral range. Three different architectures are considered: the first two involve a complex consisting of two dye molecules with appropriately matched frontier orbitals, connected by a molecular diode. Optimized combinations of dye molecules are determined by taking advantage of our computational database of the structural and energetic properties of several thousand porphyrin dyes. The third design is a molecular analogy of the intermediate band solar cell, and involves a single dye molecule with strong intersystem crossing to ensure a long lifetime of the intermediate state. Based on the calculated energy levels and molecular orbitals, energy diagrams are presented for the individual steps in the operation of such tandem solar cells. We find that theoretical open circuit voltages of up to 1.8 V can be achieved using these tandem designs. Questions about the practical implementation of prototypical devices, such as the synthesis of the tandem molecules and potential loss mechanisms, are addressed.

In the search for sustainable energy sources, dye sensitized solar cells (DSSCs) represent an attractive solution due to their low cost, relatively high efficiencies, and flexible design. Porphyrin-based dyes are characterized by strong absorption in the visible part of the spectrum and easy customization allowing their electronic properties to be controlled by structural variations. Here we present a computational screening study of more than 5000 porphyrin-based dyes obtained by modifying the porphyrin backbone (metal center and axial ligands), substituting hydrogen by fluorine, and adding different side and anchoring groups. Based on the calculated frontier orbital energies and optical gaps we quantify the energy level alignment with the TiO2 conduction band and different redox mediators. An analysis of the energy level-structure relationship reveals a significant structural diversity among the dyes with the highest level alignment quality, demonstrating the large degree of flexibility in porphyrin dye design. As a specific example of dye optimization, we show that the level alignment of the high efficiency record dye YD2-o-C8 [Yella et al., Science, 2011, 334, 629-634] can be significantly improved by modest structural variations. All the presented data have been stored in a publicly available database.

An efficient dye sensitized solar cell (DSSC) is one possible solution to meet the world's rapidly increasing energy demands and associated climate challenges. This requires inexpensive and stable dyes with well-positioned frontier energy levels for maximal solar absorption, efficient charge separation, and high output voltage. Here we demonstrate an extensive computational screening of zinc porphyrins functionalized with electron donating side groups and electron accepting anchoring groups. The trends in frontier energy levels versus side groups are analyzed and a no-loss DSSC level alignment quality is estimated. Out of the initial 1029 molecules, we find around 50 candidates with level alignment qualities within 5% of the optimal limit. We show that the level alignment of five zinc porphyrin dyes which were recently used in DSSCs with high efficiencies can be further improved by simple side group substitutions. All frontier energy levels, gaps and level alignment quality values are stored in a database publicly available.

The band structure and optical absorption spectrum of lithium peroxide (Li(2)O(2)) is calculated from first-principles using the G(0)W(0) approximation and the Bethe-Salpeter equation, respectively. A strongly localized (Frenkel type) exciton corresponding to the π(∗)→σ(∗) transition on the O(2)(-2) peroxide ion gives rise to a narrow absorption peak around 1.2 eV below the calculated bandgap of 4.8 eV. In the excited state, the internal O(2)(-2) bond is significantly weakened due to the population of the σ(∗) orbital. As a consequence, the bond is elongated by almost 0.5 Å leading to an extreme Stokes shift of 2.6 eV. The strong vibronic coupling entails significant broadening of the excitonic absorption peak in good agreement with diffuse reflectance data on Li(2)O(2) which shows a rather featureless spectrum with an absorption onset around 3.0 eV. These results should be important for understanding the origin of the high potential losses and low current densities, which are presently limiting the performance of Li-air batteries., (© 2011 American Institute of Physics)

The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation. The energy of the charge-transfer excitations obtained for the gas phase complexes are found to be around 10% lower than the experimental values. When the molecules are placed outside the surface, the enhanced screening from the metal reduces the exciton binding energies by several eVs and the transition energies by up to 1 eV depending on the size of the transition-generated dipole. As a striking consequence we find that close to the metal surface the optical gap of benzene can exceed its quasiparticle gap. A classical image charge model for the screened Coulomb interaction can account for all these effects which, on the other hand, are completely missed by standard time-dependent density functional theory.

Various phases of binary molecular assemblies of perfluorinated Cu-phthalocyanine (F₁₆CuPc) and pentacene were examined using scanning tunneling microscopy (STM). Alloying, solid solutions, phase separation, and segregation were observed in assemblies on monolayers according to the mixture ratios. The main driving force behind such molecular blending is CH-F hydrogen bonds. Lattice matching and molecular symmetry are other factors that determine the assembly configuration. A detailed understanding of such solid-state reactions provides a guideline to the construction of multilayered binary assemblies, where intermixing between molecules takes place when multiple layers are stacked.

Metal-organic interfaces based on copper-phthalocyanine monolayers are studied in dependence of the metal substrate (Au versus Cu), of its symmetry [hexagonal (111) surfaces versus fourfold (100) surfaces], as well as of the donor or acceptor semiconducting character associated with the nonfluorinated or perfluorinated molecules, respectively. Comparison of the properties of these systematically varied metal-organic interfaces provides new insight into the effect of each of the previously mentioned parameters on the molecule-substrate interactions.