Polyoxometalate adsorbed in a metal–organic framework for electrocatalytic dopamine oxidation

Abstract

A redox-active vanadium-based polyoxometalate, V10O28, was post-synthetically immobilized into a water-stable zirconium-based metal–organic framework, NU-902. The adsorbed V10O28 in NU-902 renders charge hopping in the framework in aqueous electrolytes, and...

Probing the electronic and ionic transport in topologically distinct redox-active metal–organic frameworks in aqueous electrolytes

“…For electrochemical measurements, thin films of MOF-808, UiO-66, CAU-24, and manganese-decorated MOFs were fabricated using a drop-casting approach; similar procedures have been used to fabricate Zr-MOF thin films in our previous studies. 26,48,53 Briefly, a fluorine-doped tin oxide (FTO) conducting substrate (7 O sq. À1 ; 3 cm  1.5 cm in size) was sequentially cleaned with water, ethanol, and acetone for 5 min by sonicating.…”

“…[16][17][18][19] The most commonly reported category of group 4 metal-based MOFs consists of the frameworks constructed from zirconium-based clusters as their nodes (Zr-MOFs), and thin films of such water-stable Zr-MOFs deposited on underlying electrodes have been considered as attractive candidates for various aqueous electrochemical applications. 10,[20][21][22][23][24][25][26] The main challenge that hinders the direct use of pristine Zr-MOFs for practical electrochemical purposes is their low electrical conductivity. 20 In fact, the intrinsic electrically insulating nature of most MOFs has strongly limited the use of pristine MOFs for electrochemical and electronic applications; [27][28][29][30][31] the use of MOF-derived carbon and metal oxide for such applications is thus more common.…”

“…By utilizing such materialdesign strategies, researchers from different groups have investigated the redox-hopping charge transport in a range of Zr-MOFs, both in aqueous and organic electrolytes, and applied these MOFs for various electrochemical applications. 24,26,[39][40][41][42][43][44][45][46][47][48] The apparent diffusivity (D app ) of the MOF thin film, which can be measured electrochemically, usually serves as the benchmark to probe the redox-hopping process. However, it should be noted that this process requires the charge transport from the underlying electrode to the redox-active site as well as the ionic transport from the external electrolyte to the active site.…”

“…47 A model assuming that ions are transported through the direction perpendicular to that of electronic transport within isolated MOF crystals deposited on the electrode was used, and the findings revealed that the ionic transport within these MOFs is the rate-determining step during the redox-hopping processes in organic electrolytes. However, it has been reported in several studies that the redox-hopping process occurring in various Zr-MOFs could be much more sluggish in aqueous electrolytes compared to that in organic systems, 21,22,26,42,48 presumably because water is the trap for electrons. Thus, we reasoned that similar studies in aqueous electrolytes should be crucial since these redox-active Zr-MOFs have more opportunities for the use in aqueous electrochemical systems.…”

“…16–19 The most commonly reported category of group 4 metal-based MOFs consists of the frameworks constructed from zirconium-based clusters as their nodes (Zr-MOFs), and thin films of such water-stable Zr-MOFs deposited on underlying electrodes have been considered as attractive candidates for various aqueous electrochemical applications. 10,20–26…”