Reactivity of one-, two-, three- and four-electron reduced forms of α-[P2W18O62]6− generated by controlled potential electrolysis in water

Bernardini, Gianluca; Wedd, Anthony G.; Bond, Alan M.

doi:10.1016/j.ica.2011.02.049

Cited by 8 publications

(5 citation statements)

References 27 publications

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“…At pH 7, each of these waves is a simple one-electron process (black line in Figure 1B), as determined by controlled potential bulk electrolysis and by UV-vis titration, which agrees with literature reports for this compound (see Figures S2-4 to S2-6). 38 However, as the pH is lowered to 4, both peaks below 0 V become two-electron processes, as previously of polyoxometalate (Figure 1C and Figure S2-7). Such behaviour suggested to us that the storage of electrons in the polyoxometalate was protoncoupled, and that as the concentration of polyoxometalate in solution increased (and the pH decreased) it might be possible to store an increasing number of electrons in the polyoxometalate.…”

Section: Resultssupporting

confidence: 64%

Highly reduced and protonated aqueous solutions of [P2W18O62]6− for on-demand hydrogen generation and energy storage

2018

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As our reliance on renewable energy sources grows, so too does our need to store this energy to mitigate against troughs in supply. Energy storage in batteries or by conversion to chemical fuels are the two most flexible and scalable options, but are normally considered mutually exclusive. Energy storage solutions that can act as both batteries and fuel generation devices (depending on the requirements of the user) could therefore revolutionize the uptake and use of renewably generated energy. Here, we present a polyoxoanion, [PWO], that can be reversibly reduced and protonated by 18 electrons/H per anion in aqueous solution, and that can act either as a high-performance redox flow battery electrolyte (giving a practical discharged energy density of 225 Wh l with a theoretical energy density of more than 1,000 Wh l), or as a mediator in an electrolytic cell for the on-demand generation of hydrogen.

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Section: Resultssupporting

confidence: 64%

Highly reduced and protonated aqueous solutions of [P2W18O62]6− for on-demand hydrogen generation and energy storage

2018

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“…Compound 1 was converted to a singly reduced state (correlating well with spectroelectrochemical analysis, Figure S5 in the Supporting Information), whereas the {P 2 W 17 } anion showed no discernible photo‐reduction (up to 2 h irradiation). Interestingly, the properties of {P 2 W 18 } were found to be intermediate between the two other species, showing only partial (2 e − ) reduction during the course of the experiment . Given that the extinction of both 1 and {P 2 W 18 } at 390 nm is almost identical, the effective photoactivity of each compound is therefore clearly dependent upon both optical and redox properties (i.e., the energies of both the LUMO level and the HOMO–LUMO gap) …”

Section: Figurementioning

confidence: 99%

“…Interestingly,t he properties of {P 2 W 18 }w ere found to be intermediate between the two other species, showingo nly partial (2 e À )r eduction during the course of the experiment. [13,14] Given that the extinction of both 1 and {P 2 W 18 }a t3 90 nm is almosti dentical, the effective photoactivity of each compound is therefore clearly dependent upon both optical and redox properties (i.e.,t he energies of both the LUMO level and the HOMO-LUMO gap). [4a] To validate whether the enhanced photosensitivity of 1 was reflected in its catalytic activity,w ee xplored its photooxidative performance.…”

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confidence: 99%

Orbital Engineering: Photoactivation of an Organofunctionalized Polyoxotungstate

Cameron

Fujimoto

Kastner

et al. 2016

Chemistry A European J

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Tungsten-based polyoxometalates( POMs) have been employeda sU V-driven photo-catalysts for ar ange of organic transformations. Their photoactivityi sd ependent on electronic transitionsb etween frontier orbitals and thus manipulation of orbital energy levels provides ap romising meanso fe xtending their utility into the visible regime. Herein, an organic-inorganic hybrid polyoxometalate, K 6 [P 2 W 17 O 57 (PO 5 H 5 C 7 ) 2 ]·6C 4 H 9 NO, was foundt o exhibite nhanced redox behaviour andp hotochemistry compared to its purely inorganicc ounterparts. Hybridization with electron-withdrawingm oieties was shownt o tune the frontier orbitale nergy levels and reduce the HOMO-LUMO gap, leading to direct visible-lightp hotoactivationof the hybrid and establishing as imple, cheap and effective approacht ot he generation of visible-lightactivated hybrid nanomaterials.Systemst hat harness energy from visible light are among the most prized targets in modern materials design.[1] Ap romising group of photoactive materials, polyoxometalates (POMs), are discrete early transition-metal-oxide clusters that exhibite xcellent stability,s olubility in both aqueous and organic mediaa nd aw ide range of potentialc ompositions and structures.[2] These nanoscopic clusters are characterized in large part by their rich redox chemistry,l eadingt op otentiala pplicationsi nm ulti-electron transfer and charge-storaget echnologies.[3] Most importantly,t heir capacity to form highly active photo-excited states (oxo-centred radicals) upon excitation of the O!Ml igand-tometal charge transfer (LMCT) band [4] has led to sustainedi nterest in their use as both heterogeneous and homogeneous photocatalysts for ar ange of transformations.[5] In particular, tungstate-based POMs have been successfully employed in ar ange of UV-light-driven photooxidationr eactions. [4a, 6] In their native state, POMs typically exhibit negligible visible light absorption, with the broad LMCT band located almostentirely within in the UV region of the spectrum.P OMs have thus had limited application in visible-light-driven catalysis and while the absorption profiles of molybdate-and vanadatebased POMs often tail into the near-visible/blue range, [4, 7] they do not generally exhibit the stability or easeo ff unctionalization seen in tungstate-baseda nalogues.Mizuno and co-workersr ecently reported two examples of polyoxotungstate photoactivation in systemsb ased on the lacunary POM [g-SiW 10 O 36 ] 8À ,i nw hich charget ransferf rom secondary components (Ce III or bound substrates) facilitated photo-reduction of the POMcorea nd allowedo xidative catalysis on the appended moieties.[8] Another approach to the visible-lighta ctivation of POMs is through functionalization with (typically, preciousm etal-based) visible-light-activec hromophores or 'photosensitizers' (PS), throughe ither supramolecular or covalenta pproaches.[9] Subsequentp hoto-excitation can lead to PS!POMc harge transfer.[10] Indeed, to the best of our knowledge,a ll previous reports of polyoxot...

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“…However, photoreduction again occurred preferentially at the interface with initial diffusion of ½P 2 W 18 O 62 7− into the aqueous phase followed by subsequent extraction into the IL phase. 5− in wet acetonitrile, confirming that the role of reversible potential also is significant (8,28). In general terms the overall reaction is represented by Eq.…”

Section: − Ilmentioning

confidence: 53%

Photochemical oxidation of water and reduction of polyoxometalate anions at interfaces of water with ionic liquids or diethylether

Bernardini

Wedd

Zhao

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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DEAP ¼ diethanolamine hydrogen phosphate). Photochemical formation of reduced POMs at both thermodynamically stable and unstable water-IL interfaces led to their initial diffusion into the aqueous phase and subsequent extraction into the IL phase. The mass transport was monitored visually by color change and by steady-state voltammetry at microelectrodes placed near the interface and in the bulk solution phases. However, no diffusion into the organic phase was observed when ½P 2 W 18 O 62 6− was photo-reduced at the water-diethylether interface. In all cases, water acted as the electron donor to give the overall process:However, more highly reduced POM species are likely to be generated as intermediates. The rate of diffusion of photo-generated POM − was dependent on the initial concentration of oxidized POM and the viscosity of the IL (or mixed phase system produced in cases in which the interface is thermodynamically unstable). In the water-DEAS system, the evolution of dioxygen was monitored in situ in the aqueous phase by using a Clark-type oxygen sensor. Differences in the structures of bulk and interfacial water are implicated in the activation of water. An analogous series of reactions occurred upon irradiation of solid POM salts in the presence of water vapor.electrochemistry | water oxidation I t has been known for some time that photochemical reduction of polyoxometalate anions (POMs) in molecular solvents may occur in the presence of an efficient electron donor such as 2-propanol or benzyl alcohol (1-6). In recent studies, we have found that photoreduction of tetracyanoquinodimethane (TCNQ) to TCNQ − and ½P 2 W 18 O 62 6− to ½P 2 W 18 O 62 7− or more extensively reduced POMs occurs in "wet" ionic liquids (ILs) where water acts as an electron donor and is photo-oxidized to dioxygen (7,8). Intriguingly, these processes do not occur in wet molecular organic solvents or in neat water itself. The net reactions that describe the photo-irradiation of ½P 2 W 18 O 62 6− in wet 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF 4 ] (Fig. S1) are summarized in Eqs. 1 and 2:However, while ½P 2 W 18 O 62 7− is the detected product it is probable that more extensively reduced POMs are generated (8) as intermediates in the overall water oxidation reaction [Eq. 3]:[3]

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Reactivity of one-, two-, three- and four-electron reduced forms of α-[P2W18O62]6− generated by controlled potential electrolysis in water

Cited by 8 publications

References 27 publications

Highly reduced and protonated aqueous solutions of [P2W18O62]6− for on-demand hydrogen generation and energy storage

Highly reduced and protonated aqueous solutions of [P2W18O62]6− for on-demand hydrogen generation and energy storage

Orbital Engineering: Photoactivation of an Organofunctionalized Polyoxotungstate

Photochemical oxidation of water and reduction of polyoxometalate anions at interfaces of water with ionic liquids or diethylether

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