Supramolecular Host–Guest Assembly Based on Phosphotungstate Nanostructures for Pseudocapacitive and Electrochemical Sensing Applications

Abstract

Flexible ligands and multinuclear complexes were assembled into nanoscale {P2W18O62} polyoxometalates (POMs) to generate two phosphotungstate hybrid derivatives, (H2bip)2{H2P2 W18O62}·2H2O (1) and (bipy)0.5{Ag­(bipy)2}­{Ag4(bipy)7}­{NaP2W18O62}·H2O (2) (bip = 1,5-bis­(imidazole-1-yl)­pentane; bipy = 2,2′-bipy), via a precursor hydrothermal method. Compound 1 is a bip ligand modified 4,8-connected supramolecular net with {415;612;8}­{45;6}2 topology. In compound 2, the monocore complexes {Ag­(bipy)2} and tetranuclear complexes {Ag4(bipy)7} self-associate to generate two supramolecular chains A and B, respectively, which are further alternately joined together to form a unique metal–organic framework with irregular cavities via weak actions and π–π stacking. The Na-linked {P2W18O62} dipolymers as guest units were embedded into the holes, leading to a 3D supramolecular host–guest assemblies. The capacitive performance test reveals that 2-GCE/-CPE presents improved specific capacitance (802.4 and 752.1 F/g at 3 A/g), cycle efficiency (93.6 and 94.8% after the 5000th cycle), and electrical conductivity compared to the precursor and bip ligand modified compound 1. The electrocatalytic comparative data shows that 2-GCE has enhanced electrochemical redox capacity compared to the precursor and compound 1. Further sensing tests display that 2-GCE shows strong electrochemical responses to H2O2/AA at voltages of −0.41/0.36 V with a lower detection line of 0.33/0.05 μM, a wider linear range of 1.0 μM to 3.18 mM/0.15 μM to 2.33 mM, merit selectivity, and reproducibility. The excellent capacitive and sensing performances are related to increased redox centers, improved ion/electron conversion efficiency, and host–guest structural stability resulting from the introduction of multinuclear complexes, irregular holes, and abundant π–π stacking. This study not only enriches the variety of Dawson-type POMs but also provides a feasible idea for enhancing their electrochemical capacitance and sensing performance.

Solid-state supercapacitors based on polyoxometalate-based crystalline materials modified with polyaniline

“…The matched circuit appropriate to fit the EIS, which consists of a Faraday capacitor ( C f ) and electric double-layer capacitance ( C dl ), and three resistors ( R s = the Ohm resistance, R ct = the charge transfer resistance, Z w = the ion diffusion resistance). 50 The results show that complex 1 with three-dimensional structures possesses greater electrochemical performance than complex 2 .…”

“…According to eqn (1) and (2), the charge storage mechanism was investigated by analyzing the peak current values at different scanning rates. 48–50 i = av b Log ( i ) = b log ( v ) + log ( a )where i is the peak current of II–II′, v is the scan rate, and a and b are adjustable parameters, and the electrode reaction kinetics can be characterized. The slopes of the curves (fitted b value) were calculated to be 0.714 and 0.685, 0.668 and 0.608 (Fig.…”

“…According to eqn (1) and ( 2), the charge storage mechanism was investigated by analyzing the peak current values at different scanning rates. [48][49][50]…”

Nanomaterial with Core–Shell Structure Composed of {P2W18O62} and Cobalt Homobenzotrizoate for Supercapacitors and H2O2-Sensing Applications

“…The data in Table S1 show that Dawson POMs are widely used in photocatalysis and sensing, and the highly negatively charged, oxygen-rich surface of Dawson-type POMs can enhance the charge separation and electron transmission efficiency [ 24 , 25 , 26 ], which is beneficial for improving the performance of supercapacitors and H 2 O 2 sensors. In recent years, our group has reported several cases of Dawson-type POM compounds with an excellent supercapacitors performance synthesized using the hydrothermal method [ 27 , 28 , 29 , 30 , 31 ]. However, its large solubility in electrolytes or water and low intrinsic conductivity hinder its practical application as a solid electrode material in supercapacitors and sensing.…”

Hexnuclear, octanuclear, dodecanuclear, and hexadecnuclear polyoxomolybdenum(v)-based porous materials for selective adsorption of gases

“…4 Polyoxometalates as building blocks have specific topological and chemical information that can be transferred to the final products to achieve configurable and diverse architectures. 5 According to the different construction methods, polyoxometalate-based porous materials can be roughly divided into four categories: (a) porous materials formed by covalent bonds with polyoxometalates as building units; [6][7][8] (b) supramolecular porous materials composed of polyoxometalate anions and cations (clusters); [9][10][11] (c) porous materials as the main body of the hybrid materials loaded with polyoxometalates; 12,13 (d) porous materials directly constructed from polyoxometalates. 14,15 Most polyoxometalate-based porous complexes are limited to polyoxometalate anions with known structures such as Keggin, Anderson or Dawson type as "molecular adapters", which are obtained by non-covalent or covalent action.…”