Molecular Vanadium Oxides for Energy Conversion and Energy Storage: Current Trends and Emerging Opportunities

Molecular vanadium oxides, or polyoxovanadates (POVs), have recently emerged as a new class of molecular energy conversion/storage materials, which combine diverse, chemically tunable redox behavior and reversible multielectron storage capabilities. This Review explores current challenges, major breakthroughs, and future opportunities in the use of POVs for energy conversion and storage. The reactivity, advantages, and limitations of POVs are explored, with a focus on their use in lithium and post‐lithium‐ion batteries, redox‐flow batteries, and light‐driven energy conversion. Finally, emerging themes and new research directions are critically assessed to provide inspiration for how this promising materials class can advance research in sustainable energy technologies

Covalent Linkage of BODIPY-Photosensitizers to Anderson-Type Polyoxometalates Using CLICK Chemistry

The covalent attachment of molecular photosensitizers (PS) to polyoxometalates (POMs) opens new pathways to PS-POM dyads for light-driven charge-transfer and charge-storage. Here, we report a synthetic route for the covalent linkage of BODIPY-dyes to Anderson-type polyoxomolybdates by using CLICK chemistry (i. e. copper-catalyzed azide-alkyne cycloaddition, CuAAC). Photophysical properties of the dyad were investigated by combined experimental and theoretical methods and highlight the role of both sub-components for the charge-separation properties. The study demonstrates how CLICK chemistry can be used for the versatile linkage of organic functional units to molecular metal oxide clusters. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

Covalent Linkage of BODIPY‐Photosensitizers to Anderson‐Type Polyoxometalates Using CLICK Chemistry

The covalent attachment of molecular photosensitizers (PS) to polyoxometalates (POMs) opens new pathways to PS-POM dyads for light-driven charge-transfer and charge-storage. Here, we report a synthetic route for the covalent linkage of BODIPY-dyes to Anderson-type polyoxomolybdates by using CLICK chemistry (i. e. copper-catalyzed azide-alkyne cycloaddition, CuAAC). Photophysical properties of the dyad were investigated by combined experimental and theoretical methods and highlight the role of both sub-components for the charge-separation properties. The study demonstrates how CLICK chemistry can be used for the versatile linkage of organic functional units to molecular metal oxide clusters

Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties through Heterometal Coordination Number

The rational control of the electrochemical properties of polyoxovanadate‐alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, the electronic consequences of ligand substitution at the heteroion in a heterometal‐functionalized cluster was examined. The redox properties of [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$FeCl] (1‐[V$_{5}$FeCl] ) and [V$_{5}$O$_{6}$(OCH$_{3}$)$_{12}$Fe]X (2‐[V5Fe]X ; X=ClO$_{4}$, OTf) were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal‐functionalized clusters reveals that differences in the redox profiles of 1‐[V$_{5}$FeCl] and 2‐[V$_{5}$Fe]X arise from changes in the number of ligands surrounding the iron center (e.g., 6‐coordinate vs. 5‐coordinate). Specifically, binding of the chloride to the sixth coordination site appears to change the orbital interaction between the iron and the delocalized electronic structure of the mixed‐valent polyoxovanadate core. Tuning the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster

Redox-inactive ions control the redox-activity of molecular vanadium oxides

Polyoxometalates are key materials for energy conversion and storage due to their unique chemical tunability and electrochemical reactivity. Herein, we report that functionalization of molecular vanadium oxides, polyoxovanadates, with redox-inert Ca$^{2+}$ cations leads to a significant increase in their electron storage capabilities. The electrochemical performance of the Ca$^{2+}$-functionalized dodecavanadate [Ca$_{2}$V$_{12}$O$_{32}$Cl(DMF) $_{3}$]$^{2-}$ (={Ca$_{2}$V$_{12}$}) was thus compared with that of the precursor compound (H$_{2}$NMe$_{2}$)$_{2}$ [V$_{12}$O$_{32}$Cl] $^{3-}$ (={V$_{12}$}). {Ca$_{2}$V$_{12}$} can store up to five electrons per cluster, while {V12} only shows one reversible redox transition. In initial studies, we demonstrated that {Ca$_{2}$V$_{12}$} can be used as an active material in lithium-ion cathodes. Our results show how redox-inert cations can be used as structural and electrostatic stabilizers, leading to major changes in the redox-chemistry of polyoxovanadates

Nanolithographic Top‐Down Patterning of Polyoxovanadate‐based Nanostructures with Switchable Electrical Resistivity

The top-down fabrication of ∼10 nm vanadium oxide nanostructures by electron beam lithography based on a molecular vanadium oxide resist material is reported. The new material enables the large-scale deposition of electrically switchable nanostructures which can be directly incorporated in established e-beam lithography. The findings could in future enable the top-down fabrication of functional metal oxide nanostructures in the < 10 nm domain. The top-down lithographic fabrication of functional metal oxide nanostructures enables technologically important applications such as catalysis and electronics. Here, we report the use of molecular vanadium oxides, polyoxovanadates, as molecular precursors for electron beam lithography to obtain functional vanadium oxide nanostructures. The new resist class described gives access to nanostructures with minimum dimensions close to 10 nm. The lithographically prepared structures exhibit temperature-dependent switching behaviour of their electrical resistivity. The work could lay the foundation for accessing functional vanadium oxide nanostructures in the sub-10-nm domain using industrially established nanolithographic methods

O IVA nas prestações de serviços de construção civil: inversão do sujeito passivo e taxas reduzidas

O setor da Construção Civil apresenta um fator importante na economia nacional. Porém, é considerado pela Autoridade Tributária e pela Comissão Europeia como um setor de risco na fraude e evasão fiscal. Assim, no seguimento de medidas implementadas pela Comissão Europeia, Portugal aprovou o Decreto-Lei 21/2007 de 29 janeiro, com o intuito de combater a fraude e evasão fiscal em sede Imposto sobre o Valor Acrescentado. Apesar disso, têm sido implementados incentivos aos serviços de construção civil, dos quais destacamos a taxa reduzida de Imposto sobre Valor Acrescentado, nomeadamente para a reabilitação urbana e para os serviços com alta intensidade de fator de trabalho. Pretendemos analisar pormenorizadamente esta legislação com a finalidade de esclarecer dúvidas omissas, adotando-se uma metodologia assente na análise de jurisprudência, Informações Vinculativas e doutrina. Da análise efetuada ficou evidente que o conceito de serviços de construção civil é muito amplo e de difícil definição introduzindo dificuldades na aplicação da taxa reduzida de IVA prevista nas verbas 2.23 e 2.27. No mesmo sentido verificou-se não serem aplicados pela AT os mesmo critérios na definição de serviços de construção civil para a regra de inversão do sujeito passivo e para a aplicação da taxa reduzida de IVA

Experimental and theoretical reactivity studies of molecular metal oxides for energy conversion and storage

Nowadays, polyoxometalate attracting much attention in many applications such as energy conversion and storage, molecular magnetism and oxidative (photo-) catalysis. The incorporation of reactive metal sites into the polyoxometalate framework can lead to novel cluster properties, tuning the electronic structures and thus affects the reactivity in redox-mediated processes. To this end, the present thesis combined the experimental investigations with theoretical calculations to achieve a better understanding of the electronic structure, redox and catalytic activity of metal-functionalized polyoxometalates. The coordination of CoII to cyclic metavanadate [V4O12]4- via three terminal V=O oxo ligands results in the formation of a CoII-based coordination site for a series of anions, which suitable for both homogeneous and heterogeneous colorimetric anion sensing – even under harsh conditions – based on spectral response upon anion binding. Furthermore, tunable electrochemical properties of dodecavanadates via incorporation of redox active centers such as FeIII. Experimental and theoretical studies including electron paramagnetic resonance spectroscopy and density functional theory verify the formation of the low-valent iron (I) species in the high-valent vanadium (V) based molecular metal oxide cluster {FeV12}. Tuning of the electronic structure and catalytic activity of the Anderson anion was also achieved by incorporation of a series transition metals (e.g. Mn3+, Fe3+, Co3+) into the POM framework. Experimental investigations are combined with theoretical calculations to gain insight the electronic structure of the cluster framework and the role of the central transition metals for electrochemical and photocatalytic properties. Beyond the metal-functionalized POMs, organo-functionalization of POMs with phosphonates anchoring group as well as a reactive azide unit via covalent attachment was achieved. Subsequent “CLICK” chemistry via Cu(I)-catalyzed alkyne-azide cycloaddition was investigated to verify accessibility and reactivity of the azide. In the field of energy conversion and storage, colloidal manganese vanadium oxide particles with catalytic water oxidation activity were generated by the conversion of the manganese-based water oxidation catalyst {Mn4V4}. Recently, molecular vanadium oxide clusters mainly decavanadate have received enormous interest as molecular alternatives for solid-state vanadium oxide active materials in batteries. Here we investigated the molecular structural stability of decavanadate under typical electrode fabrication processes and pre-heat treatment for the removal of crystal water. XRD and Raman spectroscopy together with wet-chemical studies showed that the molecular vanadium oxide clusters are unstable under these conditions and undergo irreversible structural degradation and conversion to solid-state vanadium oxides. Furthermore, new strategy towards the fabrication of carbon conductive additives - and binder- free POMs-based electrode material for Li-ion batteries and post-Li-ion batteries was designed and successfully employed. To this end, the integration of POMs in conducting organic polymers (CPs) was achieved by in-situ chemical or electropolymerization of EDOT in the presence of POM