W<sup>VI</sup>–OH functionality on polyoxometalates for water reduction to molecular hydrogen

Mulkapuri, Sateesh; Ravi, Athira; Mukhopadhyay, Subhabrata; Kurapati, Sathish Kumar; Siby, Vinaya; Das, Samar K.

doi:10.1039/d2qi00421f

Cited by 8 publications

(14 citation statements)

References 59 publications

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“…Thus, compound 1 is stable up to 100 CV cycles in the HER catalytic action at neutral pH (Figure a), whereas it is durable enough for 500 CV cycles (Figure b) when subjected to multiple CV cycles in an aqueous acidic pH 3 electrolyte. As shown in Figure c,d, this CV cycling stability at operating pH values (at neutral pH and in acidic pH 3) is interpreted by the plots of specific current densities vs the number of CV cycles, where the specific current density data points have been collected as the last data of the catalytic HER current densities. − The relevant observations highlight the fact that the stability of POMs increases while moving down to the lower pH solutions. Further, the chronoamperometry (CA) measurements were performed on compound 1 -coated carbon paper (CP) electrodes at the catalytic HER region of −1.1 V vs Ag/AgCl (3 M), and it is found that stable and steady-state cathodic current is maintained for a period of 2 and 6 h at neutral pH and in acidic pH 3, respectively, (Figure e,f) which is an almost equivalent timing to the cycling stability time for both the cases.…”

Section: Resultsmentioning

confidence: 87%

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Mulkapuri,

Siddikha,

Ravi

et al. 2023

Inorg. Chem.

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The uranyl ion (UO 2 ) 2+ , a uranium nuclear waste, is one of the serious contaminants in our ecosystem because of its radioactivity, relevant human activities, and highly mobile and complex nature of living cells. In this article, we have reported the synthesis and structural characterization of an uranyl cationi n c o r p o r a t e d p o l y o x o m e t a l a t e ( P O M ) c o m p o u n d , K 10 [{K 4 (H 2 O) 6 }{UO 2 } 2 (α-PW 9 O 34 ) 2 ]•13H 2 O (1), in which the uranyl cations are complexed with an in situ generated [α-PW 9 O 34 ] 9− cluster. Single-crystal X-ray diffraction (SCXRD) analysis of compound 1 reveals that the uranyl−potassium complex cationic species, [{K 4 (H 2 O) 6 }{UO 2 } 2 ] 8+ , is sandwiched by two [α-PW 9 O 34 ] 9− clusters resulting in a Dawson type of POM.Compound 1 was further characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis and infrared (IR), Raman, electronic absorption, and solid-state photoluminescence spectral studies. IR stretching vibrations at 895 and 856 cm −1 and the Raman signature peak at 792 cm −1 in the IR and Raman spectra of compound 1 primarily confirm the presence of a trans-[O�U�O] 2+ ion. The solid-state photoluminescence spectrum of 1 exhibits a typical vibronic structure, resulting from symmetrical vibrations of [O�U�O] 2+ bands, corresponding to the electronic transitions of S 11 → S 10 and S 10 → S 0 υ (υ = 0−3). Interestingly, title compound 1 shows efficient electrocatalytic hydrogen evolution by water reduction with low Tafel slope values of 186.59 and 114.83 mV dec −1 at 1 mA cm −2 along with optimal Faradaic efficiency values of 82 and 87% at neutral pH and in acidic pH 3, respectively. Detailed electrochemical analyses reveal that the catalytic hydrogen evolution reaction (HER) activity mediated by compound 1 is associated with the U VI /U V redox couple of the POM. The microscopic as well as routine spectral analyses of postelectrode samples and controlled experiments have confirmed that compound 1 behaves like a true molecular electrocatalyst for the HER. To our knowledge, this is the first paradigm of a uranium-containing polyoxometalate that exhibits electrocatalytic water reduction to molecular H 2 . In a nutshell, an environmental toxin (a uranium-oxo compound) has been demonstrated to be utilized as an efficient electrocatalyst for hydrogen generation from water, a green approach of sustainable energy production.

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Section: Resultsmentioning

confidence: 87%

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Mulkapuri,

Siddikha,

Ravi

et al. 2023

Inorg. Chem.

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“…In our very recent report, we have shown the catalytic HER activity by a tungsten POM cluster, which is synergistically activated by a redox-active copper wheel . We have also demonstrated that if a transition metal aqua species is confined in a constrained space or put on the POM cluster surface by a coordinate covalent bond, it drives electrocatalytic water oxidation. , Our other report has shown that if the −W(OH) 2 moiety is grafted on a POM cluster surface, this moiety acts as a functional group for electrocatalytic water reduction to molecular hydrogen . These two important facts inspired us to explore a POM-based compound that has a W–OH moiety (referring to water reduction) and a −M(H 2 O) n group (referring to electrocatalytic water oxidation) so that it would act as a bifunctional catalyst for HER as well as for OER.…”

Section: Introductionmentioning

confidence: 75%

“…34,35 Our other report has shown that if the −W(OH) 2 moiety is grafted on a POM cluster surface, this moiety acts as a functional group for electrocatalytic water reduction to molecular hydrogen. 39 These two important facts inspired us to explore a POM-based compound that has a W−OH moiety (referring to water reduction) and a −M(H 2 O) n group (referring to electrocatalytic water oxidation) so that it would act as a bifunctional catalyst for HER as well as for OER. Thus, in the present work, we have reported the synthesis and crystal structure of a three-dimensional-framework-containing polyoxometalate…”

Section: ■ Introductionmentioning

confidence: 99%

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH

2023

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A sole inorganic framework material [Li(H2O)4][{CuI(H2O)1.5} {CuII(H2O)3}2{WVI 12O36(OH)6}]·N2·H2S·3H2O (1) consisting of a hydroxylated polyoxometalate (POM) anion, {WVI 12O36(OH)6}6–, a mixed-valent Cu(II)– and Cu(I)–aqua cationic complex species, [{CuI(H2O)1.5}{CuII(H2O)3}2]5+, a Li(I)-aqua complex cation, and three solvent molecules, has been synthesized and structurally characterized. During its synthesis, the POM cluster anion gets functionalized with six hydroxyl groups, i.e., six WVI–OH groups per cluster unit. Moreover, structural and spectral analyses have shown the presence of H2S and N2 molecules in the concerned crystal lattice, formed from “sulfate-reducing ammonium oxidation (SRAO)”. Compound 1 functions as a bifunctional electrocatalyst exhibiting oxygen evolution reaction (OER) by water oxidation and hydrogen evolution reaction (HER) by water reduction at the neutral pH. We could identify that the hydroxylated POM anion and copper-aqua complex cations are the functional sites for HER and OER, respectively. The overpotential, required to achieve a current density of 1 mA/cm2 in the case of HER (water reduction), is found to be 443 mV with a Faradaic efficiency of 92% and a turnover frequency of 4.66 s–1. In the case of OER (water oxidation), the overpotential needed to achieve a current density of 1 mA/cm2 is obtained to be 418 mV with a Faradaic efficiency of 88% and turnover frequency of 2.81 s–1. Diverse electrochemical controlled experiments have been performed to conclude that the title POM-based material functions as a true bifunctional catalyst for electrocatalytic HER as well as OER at the neutral pH without catalyst reconstruction.

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“…Polyanion 1 contains two tri-lacunary building blocks {β-SbW 9 O 33 }, three tungsten units of two {WO 2 (OH)} + and one {WO 2 } 2+ , and a {RuC 7 H 3 NO 4 } 2+ centre (Figure a). Based on the bond valence-sum (BVS) calculation, , the values of the O55 and O63 are 1.000 and 0.875, respectively (Table S2), indicating that these two oxygens linked to W are monoprotonated (Figure b), that is the W–OH groups. , Naturally, the intact details of bond distances and angles are given in the crystallographic tables (Tables S3 and S4). Three W atoms and one Ru atom in the linking groups form an irregular quadrilateral middle-banded structure and present at the sandwiched positions.…”

Section: Resultsmentioning

confidence: 99%

Organic Hybrid Antimoniotungstate Layered Ionic Crystal: Synthesis, Structure, and Interlayer-Confined Proton Conduction

Yang

Zhang

et al. 2023

Inorg. Chem.

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A synchronous crystal- and microstructure-dependent strategy was implemented to synthesize the organic hybrid antimoniotungstate layered ionic crystal Na5.5H6.5[(SbW9O33)2{WO2(OH)}2{WO2}RuC7H3NO4]·36H2O, and the layered structure was constructed through the Na+ bridged sheet and the hydrogen-bonded layers. It displayed an effective proton conductivity of 2.97 × 10–2 S cm–1 at 348 K and 75% RH, owing to the complete interlayer confined hydrogen-bond network formed by the hydrogens of interlayer crystal waters, organic ligands ({RuC7H3NO4}2+, {C7H3NO4} is formed by the hydrolysis of pyridine 2,5-dicarboxylic acid (C7H5NO4)), and acidic protons (H+), along with the interlayer domain as a transport channel. Furthermore, the hydrogen-bond network originating from interlayer organic ligands and acidic protons was more stable at a higher temperature of 423 K, preserving a high conductivity of 1.99 × 10–2 S cm–1.

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W^VI–OH functionality on polyoxometalates for water reduction to molecular hydrogen

Abstract: When a polyoxometalate cluster surface is grafted with WVI–(OH)2 functionality, the surface-modified POM turns into an efficient & stable electrocatalyst for hydrogen evolution reaction by water reduction. We performed detailed kinetic studies for this electrocatalysis.

Cited by 8 publications

References 59 publications

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH

Organic Hybrid Antimoniotungstate Layered Ionic Crystal: Synthesis, Structure, and Interlayer-Confined Proton Conduction

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WVI–OH functionality on polyoxometalates for water reduction to molecular hydrogen

Abstract: When a polyoxometalate cluster surface is grafted with WVI–(OH)2 functionality, the surface-modified POM turns into an efficient & stable electrocatalyst for hydrogen evolution reaction by water reduction. We performed detailed kinetic studies for this electrocatalysis.

Cited by 8 publications

References 59 publications

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH

Organic Hybrid Antimoniotungstate Layered Ionic Crystal: Synthesis, Structure, and Interlayer-Confined Proton Conduction

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W^VI–OH functionality on polyoxometalates for water reduction to molecular hydrogen