Functionalization of Carbon Surfaces Tunes the Redox Stability of Polyoxometalate@Carbon Electrodes

Abstract

The use of redox-active polyoxometalates (POMs) offers unique opportunities for the development of advanced functional materials, but the use of such systems is often limited by their instability in operando. To enhance the functional stability of POMs they are often immobilized onto solid supports, though complex POM-hybridization strategies are usually required. Herein we describe a simple and scalable method for the fabrication of POM-based redox materials. Our method involves functionalizing inexpensive carbon black (Vulcan XC-72R) support with oxygenic groups, which act as stabilizing anchor points for the Wells-Dawson POM K6[P2W18O62]. X-ray photoelectron spectroscopy and electron microscopy confirm that oxidation of the carbon surfaces promotes interactions between the POMs and the carbon surface. Scanning electron microscopy shows that the surface area of the Vulcan decreases upon oxidation and this is confirmed by Brunauer-Emmett-Teller analysis, where the specific surface area of the carbon decreases from 234 m 2 g -1 to 108 m 2 g -1 . Solid-state voltammetry shows that the electrochemical properties of the POMs are retained by the hybrid material. Four successive, reversible reductions of the attached POMs are observed when the composite is in contact with 1.0 mol dm -3 H2SO4, corresponding to theIn contrast, formation of a composite using unoxidized carbon only shows the [P2W18O62] 6-/[P2W18O62] 8-, [P2W18O62] 8-/[H2P2W18O62] 8-, and [H2P2W18O62] 8-/[H4P2W18O62] 8-couples. Finally, voltammetric analysis shows that the composite formed using the oxidized carbon shows very little degradation in any of its 4 redox process over 500 charging/discharging cycles, whereas that formed using unoxidized carbon almost completely loses its redox activity after 250 cycles. These observations have significant implications for the sustainable synthesis of functional molecular redox materials for future energy-storage technologies.

Polyoxometalates-Functionalized Electrodes for (Photo)Electrocatalytic Applications: Recent Advances and Prospects

“…This is an important drawback for the development of electrodes based exclusively on POMs. This is why most electrodes used for (photo)-(electro)-catalysis required the use of conductive additives (e.g., carbon black) . So far, only few investigations have been engaged to study the electron-transport properties in the solid state and to improve their electrical conductivity.…”

Redox-active hierarchical assemblies of hybrid polyoxometalate nanostructures at carbon surfaces

“…This method confirms both that: (a) the micellar species spontaneously and rapidly adhere to the GC surface in the presence of acid, and; (b) the micelles are not electrodeposited but rather, chemically adsorbed to the surface. The importance of acid in the deposition process suggests that H 2 SO 4 is either promoting surface oxidation of the carbon in order to produce functional groups which facilitate favourable non-covalent interactions between {W 17 C 20 } and the GC surface (a phenomenon recently observed in POM-activated carbon composites), 22 or that the protons otherwise act as bridging agents between the carbon and metal-oxide surfaces to facilitate deposition. We discuss these hypotheses in more detail below.…”

“…18,19 Similarly, the deposition of POMs onto electrode materials has been achieved through non-covalent strategies including electrostatic interactions, 20 π-π interactions, 21 and oxidation of electrode surfaces to promote weak interactions. 22 A particular advantage offered by hybrid POMs is their capacity to act as amphiphiles and form ordered superstructures such as micelles and vesicles in solution. [23][24][25] Recent work in our group has demonstrated that the redox properties of molecular hybrid POMs are translated to solution-phase supramolecular assemblies.…”

POM-derived MoO3/CoMoO4mixed oxides directed by glucose for high-performance supercapacitors

“…[24][25][26] Carbon materials are widely utilized as sacrificial templates to assemble porous materials on account of convenient acquisition, regular morphology and easy removal. [27][28][29] In this procedure, carbon sphere precursors could be obtained via hydrothermal treatment of glucose, which could be decomposed under high temperature annealing.…”