Proton Conduction Properties of Intrinsically Sulfonated Covalent Organic Framework Composites

Round 1

Reviewer 1 Report

In this manuscript, the authors report a series of COFs composites with increased proton conductivity. Two different materials are modified following two different strategies: loading of guest molecules or in-situ reaction to generate a coating. The proton conductivities of the materials are studied under different conditions of relative humidity and temperature. The work is well-organized and well written, and the experimental techniques are adequate for the intended studies. Therefore, I would like to recommend this work for publication after revision.

The main issue I find is in the characterization of the COFs. As the authors mention, both TpPa and TpPA-SO₃H have been reported previously, but the characterization provided in this manuscript does not agree with the literature. The authors claim that their materials are in the enol-imine form, based on the FTIR bands at 1582 and 1523 cm^-1. However, these systems should tautomerize to the keto-enamine form, and no explanations is given as to why they might not undergo this transformation. Moreover, the C=N bond in imine-based COFs usually appears at higher wavenumbers, around 1620 cm^-1. I believe the bands at 1582 and 1523 cm^-1 do not correspond to the C=N and C-O bonds in the enol-imine form, as the authors claim, but instead to the C=C and C-N bonds in the keto-enamine form. This would be consistent with previous reports of these COFs (Chem. Mater. 2016, 28, 1489; J. Am. Chem. Soc. 2019, 141, 5880) which have been confirmed with other techniques such as ¹³C-CP/MAS-NMR or XPS.

As to whether these materials are covalent organic frameworks or amorphous polymers, the crystallinity of TpPa is low, but enough to be considered a COF. However, no diffraction peaks are observed for TpPa-SO₃H. The authors assign this to a less effective π-π stacking due to the steric hinderance of the sulfonic acid groups, but this does not agree with the literature, where diffraction patterns with intense and well-defined peaks are obtained for this COF (see for instance Chem. Mater. 2016, 28, 1489; J. Am. Chem. Soc. 2019, 141, 5880; Adv. Sci. 2019, 6, 1900547). Additionally, the authors claim that this can also be observed in the SEM images, but that is not the case, as these images are taken with a scale bar of 400 microns and these crystalline defects would only be observable at much higher magnification, in the low nanometer scale. Also, the porosity of TpPa-SO₃H is also too low for a COF, with a BET surface area of only 78.9 m² g^-1. Thus, TpPA-SO₃H cannot be considered a COF, and instead other terms such as covalent organic polymer (COP) or porous organic framework (POF) should be used for this material.

Finally, I am curious as to whether the authors have tried to prepare PANa@TpPa and test its proton conductivity. It would be a nice addition and help to show the effect of the -SO₃H group as opposed to the PANa coating for the performance of PANa@TpPa-SO₃H.

Other minor points regarding the references:

-        Ref. 3 seems incorrect, as it relates to Aluminum MOFs and not to the sources of energy production.

-        Ref. 6 seems incorrect, as it relates to a MOF-801 derivative and not to new sources of energy.

-        Ref. 17 seems incorrect, as it relates to metal organic polyhedral (MOPs) and not to metal organic frameworks (MOFs).

-      Ref. 26 seems incorrect, as it related to the synthesis of azine-linked COFs and not to the synthesis of TpPa or TpPa-SO₃H.

-  Ref. 27 in line 266 seems incorrect, as it relates to a mechanochemical synthesis of the material and in this work solvothermal synthesis is employed.

 

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

see attached PDF

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf