Influence of the Benzoquinone Sorption on the Structure and Electrochemical Performance of the MIL-53(Fe) Hybrid Porous Material in a Lithium-Ion Battery

Abstract

Among the metal-organic frameworks (MOFs), MIL-53(Fe) or Fe III (OH) 0.8 F 0.2 [O 2 C-C 6 H 4 -CO 2 ] was the first ever reported member to reversibly insert Li + electrochemically. A variety of electroactive sorbents has been investigated in an attempt to increase its electrochemical capacity vs Li + /Li 0 . Here, we describe the synthesis and characterization of a new composite hybrid material involving MIL-53(Fe) as the host for the guest electroactive 1,4-benzoquinone molecule in a 1:1 molar ratio, using complementary highresolution X-ray diffraction (XRD), differential scanning calorimetry (DSC), and magic angle spinning nuclear magnetic resonance (MAS NMR) measurements. Its room-temperature structure has been solved and shows that the quinone molecules are located within the channels nearly parallel to each other, and to the benzene rings of the skeleton, in order to maximize π-π interactions. When heated in a sealed container, a flip-flop reorganization of the quinone molecules occurred above 140 °C, whereas in an open environment, desorption of the quinone was shown near 120 °C giving rise to a new phase having solely 0.5 quinone molecules/MIL-53(Fe) formula unit. Enhancement of the electrochemical performances, due to the redox properties of the quinone molecules, was observed during the first 2 cycles. An exchange between both the quinone and the electrolyte molecules is proposed to account for the capacity decay in subsequent cycles.

Theoretical study of conformational disorder and selective adsorption of small organic molecules in the flexible metal-organic framework material MIL-53-Fe

“…Pleasingly, both configurations 1 and 4 are seen in the experiment, evidenced from XRD. 20 At 413 K, kT is of the order of 3.4 kJ mol -1 , which exceeds the 2.2 kJ mol -1 energy difference between configurations 1 and 2 and hence this explains the transition to configuration 2, as seen experimentally. In addition to these four adsorption configurations, in which quinone molecules in the channel are parallel to the organic linker of MIL-53-Fe, either along lattice vector a' or along lattice vector b', we consider a fifth adsorption configuration (configuration 5, see Figure 3e), in which none of the quinone molecules in the channel is parallel to the organic linker of MIL-53-Fe.…”

“…The initial structures that were optimized were taken from the observed crystal structures for different guest molecules in MIL-53-Fe. 11,17,20 All calculations were performed at 0 K, i.e. excluding any zero-point or thermal corrections to the energetics and structures.…”

“…19 These factors affect the configurations of small organic molecules adopted in the host, and consequently the predicted ground state adsorption configuration can deviate from what is actually observed in the experiment. In the case of single component adsorption quinone and pyridine in MIL-53-Fe, for example, for quinone, two ordered phases were identified at two different temperatures, 20 and for pyridine, one ordered phase was identified at room temperature, and there was evidence of another phase between 363~423 K which could not be indexed due to poor crystallinity. 17 To account for these metastable adsorption phases, which cannot be easily identified in experiments but are still important in relation to the applications being considered for MOF materials, in addition to the ground state adsorption configuration which has already been solved by experiment for each adsorbate molecule, we also consider several other possible adsorption configurations.…”

“…Combarieu et al showed that experimentally, that MIL-53-Fe, when fully loaded with one quinone molecule per Fe center, adopt a parallel arrangement (see Figure 3a) at room temperature and transform to a "flip-flop" arrangement (see Figure 3b) upon heating to 140 °C. 20 We have modelled these two configurations and calculated their relative stabilities and unit cell volumes, which are listed in Table 2. The main difference between configurations 1 and 2 is that in configuration 2, quinone molecules in half of the channels become orthogonal to quinone molecules in the other half of the channels, i.e.…”

MIL-53(Fe): a good example to illustrate the power of powder diffraction in the field of MOFs

“…Ab initio structural determinations of the two compounds obtained with and without fluorine will be presented, as well as dehydration/rehydration processes of MIL-53(Fe) followed by thermodiffractometry [2,8]. Lastly, in order to understand the nature of the host-guest interactions, sorption of four organic molecules (benzene, benzoquinone, pyridine and 2,6-lutidine) have been studied in MIL-53(Fe) [8,9]. The structures of the four corresponding compounds have been solved and refined from high-resolution X-ray powder diffraction data.…”