Giant Redox Entropy in the Intercalation vs Surface Chemistry of Nanocrystal Frameworks with Confined Pores

Abstract

Redox intercalation involves coupled ion-electron motion within host materials, finding extensive application in energy storage, electrocatalysis, sensing, and optoelectronics. Monodisperse MOF nanocrystals, compared to their bulk phases, exhibit accelerated mass transport kinetics that promote redox intercalation inside nanoconfined pores. However, nanosizing MOFs significantly increases their external surface-to-volume ratios, making the intercalation redox chemistry into MOF nanocrystals difficult to understand due to the challenge of differentiating redox sites at the exterior of MOF particles from the internal nanoconfined pores. Here, we report that Fe(1,2,3triazolate) 2 possesses an intercalation-based redox process shifted ca. 1.2 V from redox at the particle surface. Such distinct chemical environments do not appear in idealized MOF crystal structures but become magnified in MOF nanoparticles. Quartz crystal microbalance and time-of-flight secondary ion mass spectrometry combined with electrochemical studies identify the existence of a distinct and highly reversible Fe 2+ /Fe 3+ redox event occurring within the MOF interior. Systematic manipulation of experimental parameters (e.g., film thickness, electrolyte species, solvent, and reaction temperature) reveals that this feature arises from the nanoconfined (4.54 Å) pores gating the entry of charge-compensating anions. Due to the requirement for full desolvation and reorganization of electrolyte outside the MOF particle, the anion-coupled oxidation of internal Fe 2+ sites involves a giant redox entropy change (i.e., 164 J K −1 mol −1 ). Taken together, this study establishes a microscopic picture of ion-intercalation redox chemistry in nanoconfined environments and demonstrates the synthetic possibility of tuning electrode potentials by over a volt, with profound implications for energy capture and storage technologies.

Why Ligand Doping Increases the Fluorescence of an Anthracene-Based Metal–Organic Framework

“…The difference between these peaks is 3.06 eV, which is higher than the excitation energy of Me 2 DCDPA (2.99 eV). It should be noted that differences in redox potentials of the ligands are not an accurate estimate of that in MOFs or ion pairs . Therefore, the excited-state charge transfer process in the MOF, DCDPA* + DCDPA → DCDPA + + DCDPA – , is still possible.…”

“…It should be noted that differences in redox potentials of the ligands are not an accurate estimate of that in MOFs or ion pairs. 30 Therefore, the excited-state charge transfer process in the MOF, DCDPA* + DCDPA → DCDPA + + DCDPA − , is still possible.…”

Ballistic electrolyte ion transport with undisturbed pathways for ultrahigh-rate electrochemical energy storage devices

“…In addition, a pair of distinct and separated redox peaks can be observed for the pristine Zn-CAT but not for Zn-CAT, which should be attributed to the long ion transport distance of the pristine Zn-CAT. [35][36][37] Shortening the synthesis time can effectively alleviate this phenomenon; however, too short a synthesis time can also lead to a decrease in the crystallinity of the sample, which greatly affects the electrochemical performance of the Zn-CAT electrode ground (Fig. S15, ESI †).…”

Electrochemical Anion Sensing Using Conductive Metal–Organic Framework Nanocrystals with Confined Pores

“…1.2 V vs Fc 0/+ , as reported previously. 52 Because solvated BF 4 − anions (diameter of ca. 10 Å) exceed the ca.…”