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. 2024 Dec 5;15(48):11919-11926.
doi: 10.1021/acs.jpclett.4c01674. Epub 2024 Nov 21.

Reaction-Type-Dependent Behavior of Redox-Hopping in MOFs─Does Charge Transport Have a Preferred Direction?

Minliang Yan  1 , Zaya Bowman  2 , Zachary J Knepp  3 , Aiden Peterson  4 , Lisa A Fredin  3 , Amanda J Morris  1   4
Affiliations

Reaction-Type-Dependent Behavior of Redox-Hopping in MOFs─Does Charge Transport Have a Preferred Direction?

Minliang Yan et al. J Phys Chem Lett. .

Abstract

Redox hopping is the primary method of electron transport through redox-active metal-organic frameworks (MOFs). While redox hopping adequately supports the electrocatalytic application of MOFs, the fundamental understandings guiding the design of redox hopping MOFs remain nascent. In this study, we probe the rate of electron and hole transport through a singular MOF scaffold to determine whether the properties of the MOF promote the transport of one carrier over the other. A redox center, [RuII(bpy)2(bpy-COOH)]2+, where bpy = 2,2'-bipyridine and bpy-COOH = 4-carboxy-2,2'-bipyridine, was anchored within NU-1000. The electron hopping coefficients (De) and ion diffusion coefficients (Di) were calculated via chronoamperometry and application of the Scholz model. We found that electrons transport more rapidly than holes in the studied MOF. Interestingly, the correlation between De and self-exchange rate built in previous research predicted reversely. The contradicting result indicates that spacing between the molecular moieties involved in a particular hopping process dominates the response.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Molecular structures and simplified molecular orbital diagrams of [RuII(bpy)2(bpy-COOH•–)]+ (left), [RuII(bpy)2(bpy-COOH)]2+ (middle), and [RuIII(bpy)2(bpy-COOH)]3+ (right).
Figure 2
Figure 2
(Left) PXRD pattern of NU-1000 (red), Ru-NU-1000 (blue), and simulated PXRD pattern of NU-1000 (black). (Right) The SEM image of Ru-NU-1000 film prepared by EPD on the FTO slide shows a near particle-thick film distribution.
Figure 3
Figure 3
DPV plot of Ru-NU-1000 (a) oxidation and (b) reduction side, in a 0.1 M TBAPF6 in acetonitrile solution. Period = 30 ms, width = 50 ms, height = 50 mV, increment = 5 mV.
Figure 4
Figure 4
(a,b) Chronoamperograms (black line) and the Stage A Scholz model fits (red line) for (a) reduction and (b) oxidation of Ru-NU-1000. (c,d) The formula image vs formula image Scholz plots for reduction (c) and oxidation (d) used to determine tref.
Figure 5
Figure 5
Distribution of Di and De in (a) stage A and (b) stage B. Black crosses (×) and black circles (●) represent the data points of the oxidation and reduction on independently measured MOF samples, respectively.
Figure 6
Figure 6
Predicted distribution of [RuII(bpy)2(bpy-COOH)]2+ centers in the hexagonal tunnel of NU-1000, with arrows showing the estimated distances between (red) Ru centers, (orange) bpy ligands and bpy-COOH ligands (blue).
Figure 7
Figure 7
Computational electron configuration of [RuII(bpy)2(bpy-COOH)]2+ in acetonitrile.
See this image and copyright information in PMC

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