Search for: All records

This tutorial-review describes a systematic framework for selecting suitable electrolytes to improve the efficiency of resulting non-aqueous redox flow batteries. 

The mechanism of proton-coupled electron transfer at the surface of titanium-substituted polyoxovanadate-alkoxide clusters can be tuned by judicious selection of substrate. 

Actinide doping enhances redox chemistry of polyoxomolybdate-alkoxide clusters; the first isolable U(v) polyoxometalate cluster is reported. 

“Goldilocks” affinity of K⁺for the POV surface stabilizes reduced form of assembly for improved cycling stability! 

We report the reduction of O₂to H₂O₂viaconcerted proton–electron transfer from the terminal V(iii)–OH₂moiety of a reduced polyoxovanadate-alkoxide cluster. 

Exposing consequences of ligand sterics on H-atom uptake at surfaces with POV-alkoxide clusters. 

A series of pyridine dipyrrolide actinide(IV) complexes, (MesPDPPh)AnCl2(THF) and An(MesPDPPh)2 (An = U, Th, where (MesPDPPh) is the doubly deprotonated form of 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine), have been prepared. Characterization of all four complexes has been performed through a combination of solid- and solution-state methods, including elemental analysis, single crystal X-ray diffraction, and electronic absorption and nuclear magnetic resonance spectroscopies. Collectively, these data confirm the formation of the mono- and bis-ligated species. Time-dependent density functional theory has been performed on all four An(IV) complexes, providing insight into the nature of electronic transitions that are observed in the electronic absorption spectra of these compounds. Room temperature, solution-state luminescence of the actinide complexes is presented. Both Th(IV) derivatives exhibit strong photoluminescence; in contrast, theU(IV) species are nonemissive. 

Non-aqueous redox flow batteries constitute a promising solution for grid-scale energy storage due to the ability to achieve larger cell voltages than can be readily accessed in water. 

Emergent, flowable electrochemical energy storage technologies suitable for grid-scale applications are often limited by sluggish electron transfer kinetics that impede overall energy conversion efficiencies. To improve our understanding of these kinetic limitations in heterometallic charge carriers, we study the role of solvent in influencing the rates of heterogeneous electron transfer, demonstrating its impact on the kinetics of di-titanium substituted polyoxovanadate-alkoxide cluster, [Ti 2 V 4 O 5 (OMe) 14 ]. Our studies also illustrate that the one electron reduction and oxidation processes exhibit characteristically different rates, suggesting that different mechanisms of electron transfer are operative. We report that a 1 : 4 v/v mixture of propylene carbonate and acetonitrile can lead to a three-fold increase in the rate of electron transfer for one electron oxidation, and a two-fold increase in the one electron reduction process as compared to pure acetonitrile. We attribute this behavior to solvent–solvent interactions that lead to a deviation from ideal solution behavior. Coulombic efficiencies ≥90% are maintained in MeCN–PC mixtures over 20 charge/discharge cycles, greater than the efficiencies that are obtained for individual solvents. The results provide insight into the role of solvent in improving the rate of charge transfer and paves a way to systematically tune solvent composition to yield faster electron transfer kinetics. 

Anionic dopants, such as O-atom vacancies, alter the thermochemical and kinetic parameters of proton coupled electron transfer (PCET) at metal oxide surfaces; understanding their impact(s) is essential for informed material design for efficient energy conversion processes. To circumvent challenges associated with studying extended solids, we employ polyoxovanadate–alkoxide clusters as atomically precise models of reducible metal oxide surfaces. In this work, we examine net hydrogen atom (H-atom) uptake to an oxygen deficient vanadium oxide assembly, [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 . Addition of two H-atom equivalents to [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 results in formation of [V 6 O 5 (MeCN)(OH 2 )(OCH 3 ) 12 ] 0 . Assessment of the bond dissociation free energy of the O–H bonds of the resultant aquo moiety reveals that the presence of an O-atom defect weakens the O–H bond strength. Despite a decreased thermodynamic driving force for the reduction of [V 6 O 6 (MeCN)(OCH 3 ) 12 ] 0 , kinetic investigations show the rate of H-atom uptake at the cluster surface is ∼100× faster than its oxidized congener, [V 6 O 7 (OCH 3 ) 12 ] 0 . Electron density derived from the O-atom vacancy is shown to play an important role in influencing H-atom uptake at the cluster surface, lowering activation barriers for H-atom transfer.