How well did it work?
Physical and chemical characterisation of the material determined a highly porous, crystalline material as desired. Theoretical modelling was employed to attempt to uncover the modified sulfur environment, though evidence for this formation could not be obtained through traditional methods. Cyclic voltammetry determined the improvement imparted via sulfurization towards degradation processes compared with unmodified DUT-177. Finally application of these materials within a coin cell system revealed highly promising results.
Synthesis
Synthetic route to Thianthrene model compound and DUT-177 COF (A/B). XRD and Gas adsorption characterisation indicates desired, porous structure (C-F).
Structure Modelling
Proposed structures were theoretically modelled to investigate S linkages in sulfurized COFs
Sulfurization improvements
CV plots show irreversible oxidation of standard DUT-177 (A), while sulfurized sample reports a reversible change (B).
Coin cell performance
Nyquist plots of S-DUT-177 coin cell indicating low diffusivity resistance after a soaking treatment, while B-E report charge-discharge cycles, rate efficiency and cycle stability.
How did XPS help?
Analysis of the S LMM augers to obtain the modified auger parameter (a') enabled insights into the structure which were not found by any other technique.
Auger parameter (a')
The addition of binding energy of the S 2p core level to the kinetic energy of the S LMM auger peak gives us an calibration independent probe into chemical structure
Energy changes to a'
The energy of a' is sensitive to changes in core-hole screening and various final state effects which can give information regarding chemical environment
a' in DUT-177
In both the model compound and final COF structure, sulfurization increased the auger parameter
What does this mean?
Enhanced core-hole screening was attributed to an increased density of valence electrons around S atoms, due to the formation of C-S-S-C bonds!