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Metal oxide libraries for photoanodes for the oxygen evolution reaction (OER) were generated by printing a metal salt solution in an array layout, followed by calcination to yield 22 ternary metal oxide systems. The libraries included a ternary metal cation system based on CuWO

To enhance the safety of lithium-ion batteries (LIBs), alternatives to liquid electrolytes are widely studied. One of them is the plastic-crystal succinonitrile (SN) which is able to solvate various Li salts. This system can be further extended by inserting polymers, bringing additional advantages such as higher melting points and the possibility of adjusting thermo-mechanical and electrochemical properties. The plastic-crystalline electrolyte consisting of the Li salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in SN was extended by adding various thermoplastic polymers, namely, polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polyethylene carbonate (PEC), and polyvinylpyrrolidone (PVP). Even small amounts (10 wt %) of added polymer to the SN-base were found to impact the Li-ion mobility. Variable temperature investigations on structure and ion dynamics were performed using static and magic angle spinning (MAS) solid-state NMR and various relaxometry measurements. Influence of the Li concentration and the polymers’ functional groups on the structure of SN and the resulting Li-ion mobility was elaborated. Activation energies and jump rates of the Li ions were determined. As a result, the PAN-containing system stands out to be a promising candidate for application in future LIBs as it shows high ion mobility, low activation energy, and a high potential for further modifications. Solid-state NMR turned out to be a reliable method and a good alternative to impedance spectroscopy measurements for investigating ion mobility behavior providing even more information.

The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [Mo

International audience; Co3O4/CoFe2O4 decorated on nickel foam (NF/Co3O4/CoFe2O4) was synthesized from a metal–organic framework by a solvothermal approach using nicotinic acid as an organic linker followed by annealing at 500 °C. The electrochemical activity of NF/Co3O4/CoFe2O4 for the oxygen evolution reaction (OER) was assessed in alkaline medium. Under basic conditions (pH > 10), the composite electrode revealed enhanced electrocatalytic OER activity requiring an overpotential of 215 mV versus RHE to reach 10 mA cm–2 with a Tafel slope of 90 mV dec–1. The enhanced OER activity was ascribed to the presence of Co3+ and Fe3+ in the octahedral sites of Co3O4 and CoFe2O4, respectively, and their synergic effect in Co3O4/CoFe2O4. This anode showed a stable current density of about 160 mA cm–2 for 20 h; the same Co3O4/CoFe2O4/NF anode was applied for several OER experiments without loss of activity.

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium‐oxo clusters (POCs). The 16‐palladium(II)‐oxo cluster [Pd16O24(OH)8((CH3)2As)8] (Pd16) comprises a cyclic palladium‐oxo unit capped by eight dimethylarsinate groups. The chloro‐derivative [Pd16Na2O26(OH)3 Cl3 ((CH3)2 As)8] (Pd16Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24‐palladium(II)‐oxo cluster [Pd24O44(OH)8((CH3)2As)16] (Pd24) can be considered as a bicapped derivative of Pd16 with a tetra‐palladium‐oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single‐crystal and powder XRD, IR, TGA, and solid‐state 1H and 13C NMR spectroscopy, 2) in solution by 1H, 13C NMR and 1H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI‐MS)., The first three examples of neutral palladium‐oxo clusters (POCs), Pd16, Pd16Cl, and Pd24, were prepared by simple open‐pot, room‐temperature reactions of palladium(II) salts in sodium dimethylarsinate aqueous solutions. The dimethylarsinate capping groups act as bidentate, monoanionic ligands for the various palladium‐oxo cores. The three POCs were fully characterized in the solid, solution, and gaseous states by a multitude of physicochemical techniques.

Films of conductive coordination network compounds are interesting as functional materials for charge storage, electrocatalysis, electrochromic switching, or conversion of light. The electrical con...

Nickel-based nanostructured materials have gained widespread attention, particularly for energy-related applications. Employing chemical vapor deposition (CVD) for NiO necessitates suitable nickel precursors that are volatile and stable. Herein, we report the synthesis and characterization of a series of new nickel β-ketoiminato complexes with different aliphatic and etheric side chain substitutions, namely, bis(4-(isopropylamino)-pent-3-en-2-onato)nickel(II) ([Ni(ipki)2], 1), bis(4-(2-methoxyethylamino)pent-3-en-2-onato)nickel(II) ([Ni(meki)2], 2), bis(4-(2-ethoxyethylamino)pent-3-en-2-onato)nickel(II) ([Ni(eeki)2], 3), bis(4-(3-methoxy-propylamino)-pent-3-en-2-onato)nickel(II) ([Ni(mpki)2], 4), and bis(4-(3-ethoxypropylamino)pent-3-en-2-onato)nickel(II) ([Ni(epki)2], 5). These compounds have been thoroughly characterized with regard to their purity and identity by means of nuclear magnetic resonance spectroscopy (NMR) and electron impact mass spectrometry (EI-MS). Contrary to other transition metal β-ketoiminates, the imino side chain strongly influences the structural geometry of the complexes, which was ascertained via single-crystal X-ray diffraction (XRD). As a result, the magnetic momenta of the molecules also differ significantly as evidenced by the magnetic susceptibility measurements employing Evan's NMR method in solution. Thermal analysis revealed the suitability of these compounds as new class of precursors for CVD of Ni containing materials. As a representative precursor, compound 2 was evaluated for the CVD of NiO thin films on Si(100) and conductive glass substrates. The as-deposited nanostructured layers were stoichiometric and phase pure NiO as confirmed by XRD, Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). X-ray photoelectron spectroscopy (XPS) indicated the formation of slightly oxygen-rich surfaces. The assessment of NiO films in electrocatalysis revealed promising activity for the oxygen evolution reactions (OER). The current densities of 10 mA cm-2 achieved at overpotentials ranging between 0.48 and 0.52 V highlight the suitability of the new Ni complexes in CVD processes for the fabrication of thin film electrocatalysts.

Proton exchange membrane water electrolysis is technically the most suitable technology for the production of green hydrogen on a large scale. Although it is still more expensive than hydrogen produced from fossil sources, it has already been commercialized. Novel components with cost-effective materials and efficient manufacturing processes are being rapidly developed. However, these components must endure durability tests that can guarantee a lifetime of at least 50,000 operation hours. Consequently, there is an urgent need to develop accelerated stress test protocols based on a deep understanding of degradation mechanisms of stack components. Recent reports show that the main degradation mechanisms are associated to anode catalyst dissolution, membrane chemical decomposition, and formation of semiconducting oxides on the metal components. These mechanisms can be accelerated by stressors such as high current density, dynamic operation, and shutdown modes. On the basis of these reports and knowledge of the operational requirements for large-scale proton exchange membrane water electrolysis, we propose an accelerated stress test protocol for the fast evaluation of newly developed cost efficient and durable components.

Herein, we report a semiconductive, proton-conductive, microporous hydrogen-bonded organic framework (HOF) derived from phenylphosphonic acid and 5,10,15,20‐tetrakis[p‐phenylphosphonic acid] porphyrin (GTUB5). The structure of GTUB5 was characterized using single crystal X-ray diffraction. A narrow band gap of 1.56 eV was extracted from a UV-Vis spectrum of pure GTUB5 crystals, in excellent agreement with the 1.65 eV band gap obtained from DFT calculations. The same band gap was also measured for GTUB5 in DMSO. The proton conductivity of GTUB5 was measured to be 3.00 × 10−6 S cm−1 at 75 °C and 75% relative humidity. The surface area was estimated to be 422 m2 g−1 from grand canonical Monte Carlo simulations. XRD showed that GTUB5 is thermally stable under relative humidities of up to 90% at 90 °C. These findings pave the way for a new family of organic, microporous, and semiconducting materials with high surface areas and high thermal stabilities., Research in hydrogen-bonded organic frameworks (HOFs) has gained interest in recent years due to their facile design and synthesis but no semiconducting HOF has been reported to date. Here the authors report a thermally stable and proton-conductive organic semiconductor based on a porphyrin HOF.

This paper gives an overview about recent theoretical and experimental work on electronic and optical properties of spinel ferrites MFe2O4. These compounds have come into focus of research due to their possible application as photocatalyst material for photoelectrochemical water splitting. The theoretical background of state-of-the-art quantum-chemical approaches applied for predicting electronic and optical band gaps, absolute band positions, optical absorption spectra, dielectric functions and Raman spectra, is briefly reviewed. Recent applications of first-principles methods on magnetic and electronic properties of ferrites with M = Mg and the first row of subgroup elements Sc to Zn are presented, where it is shown that the fundamental band gap is strongly dependent on the spin state and the degree of inversion of the spinel structure. The observed variation of electronic properties may serve as an explanation for the large scattering of experimental results. The exchange of M and Fe cations has also a pronounced effect on the Raman spectra of ferrites, which is analyzed at atomic scale from first principles. Calculated optical absorption spectra of ferrites are compared to experimental spectra. The electronic nature of the first excitations and the role of oxygen vacancies are discussed. For the calculation of absolute band positions, which have a significant impact on the photoelectrochemical activity of the ferrites, models of the most stable ferrite surfaces are developed that take into account their polar nature and the interaction with the solvent. Theoretically predicted valence and conduction band edges are compared to results from electrochemical measurements. The role of cation exchange on the surface electronic structure is investigated both theoretically and experimentally.

This approach suggests a hybrid bimetallic organic frameworks (H-biMOF) as electrocatalyst for the oxygen evolution reaction (OER) under alkaline conditions. A H-biMOF including cobalt (II) and nickel (II) was synthesized with terephthalic acid (Tp) as a linker using one-pot solvothermal method. The morphological study with microscopy techniques shows hexagonal rod-like structures for pure cobalt MOF, wood-shaving-like structures for pure nickel MOF and hexagonal nanosheets coated by wood-shaving-like structures with for H-biMOF. The structure of H-biMOF was confirmed by XRD showing both pure Co and Ni MOFs in the pattern. The catalytic OER ability of all samples was evaluated using electrochemical methods. The best performance was achieved for a H-biMOF made from a 3:1 starting salt ratio of cobalt and nickel (CoTp 3:1(Ni)). The OER catalytic activity of CoTp 3:1(Ni) demonstrates a low overpotential of 371 mV and a Tafel slope of 53.6 mV dec−1 (at a current density of 10 mA cm−2). The high catalytic activity of the biMOF through OER is related to the high number of active sites and suitable mass transport properties providing reactatnts to increase the current density at a given potential.

Hydrochars from hydrothermal carbonization of different biowaste materials (dried dandelion, sawdust, coconut shell powder) formed in the presence of aqueous salt solutions were compared to those obtained by the common method in pure water. Hydrochars with increased carbon contents, pore volume and surface areas were specifically obtained from coconut shell powder in the presence of zinc chloride. Compositional and structural changes within the hydrochar products caused by the process conditions and/or the additive were characterized by solid state 13C NMR spectroscopy, proving that cellulose and, in particular, lignin units in the biomass are more easily attacked in the presence of the salt. Under saline conditions, a distinct particle break-up led to the creation of mesoporosity, as observable from hysteresis loops in nitrogen adsorption isotherms, which were indicative of the presence of pores with diameters of about 3 to 10 nm. The obtained hydrochars were still rich in functional groups which, together with the mesoporosity, indicates the compounds have a high potential for pollutant removal. This was documented by adsorption capacities for the methylene blue and methyl orange dyes, which exceeded the values obtained for other hydrochar-based adsorbers. A subsequent physical activation of the mesoporous hydrochars in steam at different temperatures and times resulted in a further drastic increase in the surface areas, of up to about 750 m2/g, however, this increase is mainly due to micropore formation coupled with a loss of surface functionality. Consequently, the adsorption capacity for the quite large dyes does not provide any further benefit, but the uptake of smaller gas molecules is favored.

We report on the synthesis and structural characterization of a giant, discrete, and neutral molecular disk, [Pd

Transition metal ferrites, such as CoFe2O4 (CFO) and NiFe2O4 (NFO), have gained increasing attention as potential materials for supercapacitors. Since chemical vapor deposition (CVD) offers advantages like interface quality to the underlying substrates and the possibility for coverage of 3D substrates, two CVD processes are reported for CFO and NFO. Growth rates amount to 150 to 200 nm h−1 and yield uniform, dense, and phase pure spinel ferrite films according to X-ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA) and scanning electron microscopy (SEM). Atom probe tomography (APT) and synchrotron X-ray photoelectron spectroscopy (XPS) give insights into the vertical homogeneity and oxidation states in the CFO films. Cation disorder of CFO is analyzed for the first time from synchrotron-based XPS. NFO is analyzed via lab-based XPS. Depositions on conducting Ni and Ti substrates result in electrodes with pseudocapacitive behavior, as evidenced by cyclovoltammetry (CV) experiments. The interfacial capacitances of the electrodes are up to 185 µF cm−2.

Water electrolysis is a crucial technology for large-scale hydrogen generation, that is required for the transition to a fossil fuel-free energy system. Even though water electrolysis systems are already deployed in a limited capacity, the technology is largely constrained to liquid alkaline electrolysis. Proton exchange membrane (PEM) electrolysis could pose an alternative but it is still hindered by high investment costs, in-part due to its reliance on scarce noble-metal catalysts. Alternative structural designs of the anode catalyst layer (CL) could reduce Iridium loading of the whole system and thus accelerate its wide-spread application. In fuel cell research, it was already reported that a multi-layer design with varied ionomer content enhances performance of the CL and in-turn lowers required catalyst loading.[1,2,3] In this study, a gradient design for ionomer content is employed for anode CLs for the application in PEM water electrolysis. CLs are coated in a stacked multi-layer design via ultrasonic spray coating of Iridium/Nafion® suspensions. The target ionomer loadings (10 and 30 wt.%) are confirmed by a combination of thermo-gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The coating process yields homogenously loaded reference CLs as well as through-plane graded CLs with the desired ionomer loading. Additionally, scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS) shows equal CL thickness across all ionomer loadings and spatially differentiated Nafion® content throughout the CLs thickness. Electrochemical characterizations are carried out in an electrolysis-adapted gas diffusion electrode (GDE) half-cell setup to allow for quick examination and prototyping of produced layers. Differences in electrochemical performance of these layers can be observed with one gradient design CL showing reduced overpotential across all current densities compared to the homogenous CLs. In-particular a high ionomer loading near the membrane improves performance, most likely due to increased proton conduction to the membrane and higher available pore volume near the porous transport layer. Further analysis is performed on electrochemical studies to deepen the understanding of the role of ionomer in anodic PEM water electrolysis CLs. Particularly, the investigation of protonic and electric conductivity through the CL is of interest, because this parameter is most influenced by ionomer loading.[4] References: [1] Y. Wang, T. Liu, H. Sun, H. Wie, F. Yuanzhi, S. Wang, Electrochimica Acta 2020, 353, 136791. [2] R. Roshandel, F. Ahmadi, Renewable Energy 2013, 50, 921-931. [3] K.-H. Kim, H.-J. Kim, K.-Y. Lee, J.H. Jang, S.-Y. Lee, E. Cho, I.H. Oh, T.H. Lim, International Journal of Hydrogen Energy 2008, 33, 2783-2789. [4] M. Mandal, M. Moore, M. Secanell, ACS Applied Materials & Interfaces 2020, 13, 49549-49562. Figure 1

The preparation of compact and pinhole-free absorber layers is a major step towards device reproducibility and high performance for planar organic-inorganic perovskite solar cells. It is well known that the sequential deposition method exhibits some advantages over the common one-pot synthesis in terms of controlling the surface coverage. However, it still miscarries to produce pinhole-free layers from solution, mainly due to the occurrence of dissolution and recrystallisation processes. We show that by a careful choice of the permittivity of the alcoholic solvent in the conversion step the surface morphology can be finely modified, thereby yielding pinhole-free and compact absorber films comparable to that from vapour-assisted solution techniques. It is observed that the permittivity controls the intensity of the Ostwald ripening effect and that a low value of the former enables an in situ intercalation of precursor materials into the lead halide framework. We successfully prepared smooth and mirror-like perovskite surfaces that demonstrate enhanced optoelectronic properties and photovoltaic performance compared to films from the native two-step deposition in isopropanol. This strategy provides a facile approach for obtaining high-quality layers in the planar architecture by simple solution processing.

Hydrothermal carbonization (HTC) is a thermo-chemical process, which converts biomass into a coal-like product, referred to as hydrochar. Hydrochars have low pH and salinity, a high water holding capacity and cation exchange capacity, and thus are correlated to the requirements of horticultural substrates. However, germination- and growth-inhibiting effects were frequently observed in experiments using untreated fresh hydrochars. In this study we investigated the suitability of biological pretreated co-composted hydrochar substrates as growing media for horticultural crops. Hydrochars made from residue feedstocks, such as beer draff and green cuttings, were used to perform seed germination experiments with Chinese cabbage (Brassica rapa ssp. Pekinensis) on fresh, untreated and pretreated hydrochar-compost substrates and ii) pretreated hydrochar-compost substrates in a) different mixing ratios (10, 30 and 50% hydrochar), and b) using different hydrochars in a fixed mixing ratio of 50:50. Moreover, growth experiments with French marigold (Tagetes patula) for a growing season on the co-composted hydrochar substrates were performed. As reference substrates, a peat-based gardening substrate and a compost were used. Germination rate and plant growth were higher for co-composted substrates than on untreated freshly mixed substrates. Growth of French marigold increased with the amount of hydrochar in the mixtures up to equal growth quality compared to a peat-based gardening substrate. Substrate properties including salinity, density and pH value influenced the plant growth as well. The type of hydrochar had only a slight influence.

Here we report on the synthesis, structure, and characterization of the first example of a polyoxopalladate (POP)-based metal-organic framework (MOF). This novel class of materials comprises discrete polyoxo-13-palladate(II) nanocubes [Pd13O8(AsO4)8H6]8– decorated by four Ba2+ ions on each of two opposite faces. These secondary building units (SBUs) are linked to each other via rigid linear organic groups, resulting in a stable 3D POP-MOF framework, which exhibits interesting sorption as well as catalytic properties.