This research investigated the anodic degradation of perfluorooctanesulfonate (PFOS) and perfluorobutanesulfonate (PFBS) on Magnéli phase titanium suboxide (Ti4O7) surface via Density Functional Theory (DFT) simulations. It indicates a gradual loss of one electron from PFOS and PFBS ions (e.g. C8F17SO3– and C4F9SO3–) adsorbed on Ti3+-ion sites as the background charges increases on the model of Ti4O7 surface. This results in the elongation of the C−S bond in C8F17SO3– and C4F9SO3– and eventually their breakage. This confirms that direct electron transfer (DET) is determinant in the degradation of C8F17SO3– and C4F9SO3– on Ti4O7 anode, consistent with reports by previous experiments. When comparing adsorption energies, the adsorption on Ti4O7 surface follow the order OH– &gt; C8F17SO3– &gt; H2O. The degradation mechanism of C8F17SO3– and C4F9SO3– on Ti4O7 surface with adsorbed OH– appeared to be the same as that without OH– adsorbed but requiring more background charges to break the C−S bond. On the Ti4O7 surface with or without OH–, the radical of C4F9SO3* has a shorter C−S bond length than that in C8F17SO3*, leading to a greater activation energy with respect to C−S breakage. This is the primary reason why PFBS is harder to degrade than PFOS on Ti4O7 anode.

First principle study on the degradation of perfluorooctanesulfonate and perfluorobutanesulfonate on Magnéli phase Ti4O7 anode

ACS Fall 2020 Virtual Meeting

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