| Autor: |
Celis-Salazar PJ; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Cai M; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Cucinell CA; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Ahrenholtz SR; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Epley CC; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Usov PM; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States., Morris AJ; Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24061 , United States. |
| Abstrakt: |
The chronoamperometric response ( I vs t ) of three metallocene-doped metal-organic frameworks (MOFs) thin films (M-NU-1000, M = Fe, Ru, Os) in two different electrolytes (tetrabutylammonium hexafluorophosphate [TBAPF 6 ] and tetrabutylammonium tetrakis(pentafluorophenyl)borate [TBATFAB]) was utilized to elucidate the diffusion coefficients of electrons and ions ( D e and D i , respectively) through the structure in response to an oxidizing applied bias. The application of a theoretical model for solid state voltammetry to the experimental data revealed that the diffusion of ions is the rate-determining step at the three different time stages of the electrochemical transformation: an initial stage characterized by rapid electron diffusion along the crystal-solution boundary (stage A), a second stage that represents the diffusion of electrons and ions into the bulk of the MOF crystallite (stage B), and a final period of the conversion dominated only by the diffusion of ions (stage C). Remarkably, electron diffusion ( D e ) increased in the order of Fe < Ru < Os using PF 6 1- as the counteranion in all the stages of the voltammogram, demonstrating the strategy to modulate the rate of electron transport through the incorporation of rapidly self-exchanging molecular moieties into the MOF structure. The D e values obtained with larger TFAB 1- counteranion were generally in agreement with the previous trend but were on average lower than those obtained with PF 6 1- . Similarly, the ion diffusion coefficient ( D i ) was generally higher for TFAB 1- than for PF 6 1- as the ions diffuse into the crystal bulk, due to the high degree of ion-pair association between PF 6 1- and the metallocenium ion, resulting in a faster penetration of the weakly associated TFAB 1- anion through the MOF pores. These structure-function relationships provide a foundation for the future design, control, and optimization of electron and ion transport properties in MOF thin films. |
