New Anderson‐Based Polyoxometalate Covalent Organic Frameworks as Electrodes for Energy Storage Boosted Through Keto‐Enol Tautomerization

Abstract

The unique electrochemical properties of polyoxometalates (POMs) render them ideal components for the fabrication of next‐generation high‐performance energy storage systems. However, their practical applications have been hindered by their high solubility in common electrolytes. This problem can be overcome by the effective hybridization of POMs with other materials. Here we present the design and synthesis of two novel polyoxometalate‐covalent organic frameworks (POCOF) via one‐pot solvothermal strategy between an amino‐functionalized Anderson‐type POM and a trialdehyde‐based building unit. We show that structural and functional complexity can be enriched by adding hydroxyl groups in the 2,4,6 position to the benzene‐1,3,5‐tricarbaldehyde allowing to exploit for the first time in POCOFs the keto‐enol tautomerization as additional feature to impart greater chemical stability to the COFs and enhanced properties leading to large specific surface area (347 m2/g) and superior electrochemical performance of the POCOF‐1 electrodes, when compared with POCOF‐2 electrodes that possess only imine‐type linkage and with pristine POM electrodes. Specifically, POCOF‐1 electrodes display remarkable specific, areal, and volumetric capacitance (125 F/g, 248 mF/cm2 and 41.9 mF/cm3, respectively) at a current density of 0.5 A/g, a maximum energy density (56.2 Wh/kg), a maximum power density (3.7 kW/kg) and an outstanding cyclability (90 % capacitance retention after 5000 cycles).

Recent progress on covalent organic frameworks for photocatalytic hydrogen generation via water splitting

“…Up to now, COFs have great potential for various applications, including gas adsorption and separation, sensing, heterogeneous catalysis, energy storage and other aspects. 32–39 Furthermore, numerous research findings have indicated that two-dimensional (2D) COFs possess excellent semiconductor properties and are a new type of superior photocatalysts, particularly for hydrogen generation via water splitting. As metal-free semiconductor photocatalysts, the advantages of 2D-COFs can be described as follows: first, one-dimensional nanopores with large surface area provide space for transport, action and transformation of matter, and also increase exciton utilization.…”

Combination of covalent organic frameworks (COFs) and polyoxometalates (POMs): the preparation strategy and potential application of COF–POM hybrids

“…108 Ciesielski and co-workers synthesized two polyoxometalate–covalent organic frameworks (POCOF) by condensation reaction between H 2 N–(CoMo 6 )–NH 2 and two different aldehyde building blocks (benzene-1,3,5-tricarbaldehyde (BTC) and 2,4,6-triformylphloroglucinol (TFP)) respectively through one-pot solvothermal strategy. 109…”

“…In addition, POCOF-1 and POCOF-2 presented greater cyclability with a capacitance retention of 90% and 74% 5000 GCD cycles. 109…”

Hydrogenation Catalysis by Hydrogen Spillover on Platinum‐Functionalized Heterogeneous Boronic Acid‐Polyoxometalates

“…One approach to this end is the use of organo‐functionalized POMs (organoPOMs) where the metal oxo cluster shell has been covalently functionalized with organic moieties [9–11] . Organo‐functionalization provides control over the physical and electronic structure of the POMs, making them ideal building blocks for supramolecular assemblies [12–14] .…”

“…One approach to this end is the use of organofunctionalized POMs (organoPOMs) where the metal oxo cluster shell has been covalently functionalized with organic moieties. [9][10][11] Organo-functionalization provides control over the physical and electronic structure of the POMs, making them ideal building blocks for supramolecular assemblies. [12][13][14] Thus organoPOMs have successfully been employed as molecular components in the assembly of functional supramolecular systems with unique functions.…”