Boosting the High Working Voltage of an Aqueous Symmetric Supercapacitor by a Phosphotungstic Acid-Based Coordination Polymer Coating with Polypyrrole

The low working voltage limits the energy density and feasibility of practical applications of aqueous supercapacitors (SCs) to some extent. Herein, new CuPW12@PPy (n, n = 1, 2, 3) nanocomposites were designed and fabricated by involving the hydrothermal synthesis of crystalline H4[Cu2(bix)4][PW12O40]2·8H2O (CuPW12) and subsequently pyrrole in situ oxidation polymerization on the CuPW12 surface. These were then used as electrode materials to widen the working voltage of SC. As expected, CuPW12@PPy (n, n = 1, 2, 3) can operate stably within −0.6 to 1.0 V while inhibiting the hydrogen evolution reaction, which exhibits higher specific capacitance in 2 M H3PO4. Specifically, CuPW12@PPy (2) shows a 711.2 F g–1 specific capacitance at 1.5 A g–1, attributed to the high ion/electron transportation and their synergy from the conductive PPy covering the CuPW12 surfaces. Finally, the assembled symmetric SC cell can operate at 1.6 V and deliver a 43.67 Wh kg–1 energy density and 1280 W kg–1 power density at 1.0 A g–1 and a 91.3% capacitance retention at 5 A g–1 after 10,000 cycles

Isomeric organic ligand dominating polyoxometalate-based hybrid compounds: synthesis and as electrocatalysts and pH-sensitive probes

<p>By introducing isomeric organic ligands into polyoxometalate (POM) systems, two new POM-based hybrid compounds, [Cu₆(<i>m</i>-pyttz)₂(H₂O)][HPMo₁₂O₄₀] (<b>1</b>) and [Ag₃(<i>p</i>-H₂pyttz)(<i>p</i>-Hpyttz)Cl][H₂PMo₁₂O₄₀]·6H₂O (<b>2</b>) (<i>m</i>-/<i>p</i>-H₂pyttz = 3-(pyrid-3/4-yl)-5(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), have been hydrothermally synthesized and characterized. Single-crystal structural analysis shows the <i>m</i>-pyttz ligands link Cu^I ions to generate a two-dimensional layer with hanger-like rhombus, which is pillared by the PMo₁₂ anions in <b>1</b>. Compound <b>2</b> exhibits a three-dimensional supramolecular framework, in which PMo₁₂ anions are building blocks facilitating the extension of the whole structure. The influence of the coordination modes of <i>m</i>-/<i>p</i>-H₂pyttz on the structures is discussed in detail. Furthermore, electrochemical properties of <b>1</b> and <b>2</b> have been studied and they display excellent electrocatalytic activities toward the reduction of nitrite and hydrogen peroxide and pH-dependent electrochemical behaviors.</p

Polyoxometalates Templated Metal Ag–Carbene Frameworks Anodic Material for Lithium-Ion Batteries

A POMs templated 3D Ag–carbene framework with <i>lvt-a</i> topology was hydrothermally synthesized. The POMs templated MCF combining the advantages of POMs, MOFs, and carbene not only shows excellent thermal and chemical stabilities but also possesses a good discharge capacity of 481 mAh·g^–1 after 100 cycles applied as anode material in LIBs

Acidity Considerations in the Self-Assembly of POM/Ag/trz-Based Compounds with Efficient Electrochemical Activities in LIBs

Controlled self-assembly of the inorganic–organic hybrid compounds based on polyoxometalates (POMs) is hampered by the wide range of oxo and hydroxo units on the peripheries of POMs and many chemical parameters. In this work, aiming to understand the pH value influence on the POM/Ag/trz assembly (trz = 1,2,3-triazole), two new hybrid compounds based on POMs combining with metal–organic frameworks (MOFs), H­[Ag₂₇(trz)₁₆(H₂O)₄]­[(AsW₁₂O₄₀)₂] (<b>1</b>), and [Ag₁₅(trz)₈]­[AsW₁₂O₄₀] (<b>2</b>), were isolated under different pH value. The structural analysis reveals that the [Ag₇(trz)₄]³⁺ subunits and Keggin-type arsenotungstate are assembled into a complicated three-dimensional framework containing two distinct types of channels in compound <b>1</b>. And the [Ag₅(trz)₄]⁺ subunits and Keggin-type arsenotungstate are assembled into a three-dimensional framework containing the single channel under the aid of Ag–Ag bonds in compound <b>2</b>. In addition, compounds <b>1</b> and <b>2</b> were employed as anode materials of lithium-ion batteries (LIBs) and exhibited the promising electrochemical performances