# Theoretical Guidelines for Electrochemical C–F Bond Cleavage in Perfluorobutanoic Acid Using Transition Metal Catalysts

## TL;DR

This paper presents a theoretical framework to evaluate transition metal catalysts for breaking stable C–F bonds in perfluorobutanoic acid, a common persistent pollutant.

## Contribution

The study introduces a systematic theoretical screening protocol that incorporates electrochemical constraints to identify viable catalysts for PFAS degradation.

## Key findings

- A theoretical screening protocol was developed and applied to 27 transition metals and 81 surface facets.
- Fourteen promising TM surface facets were identified that meet electrochemical criteria for PFBA degradation.
- C–F cleavage difficulty correlates with electron density accumulation on the reacting carbon site.

## Abstract

Per- and polyfluoroalkyl
substances (PFAS) are persistent
pollutants
with highly stable carbon–fluorine bonds, which makes catalytic
degradation difficult. Among various catalytic strategies, electrochemical
reduction has emerged as a practical alternative because it promotes
C–F cleavage and H/F exchange. Transition metals (TMs) are
particularly attractive for this process, since their conductivity
and d-orbitals facilitate electron transfer into the C–F bond.
Yet many theoretical studies overlook essential electrochemical factors;
these include the hydrogen evolution reaction, surface oxidation,
fluorine poisoning, and physisorption exclusion, and neglecting them
limits realistic assessment of TM catalysts for PFAS degradation.
Consequently, no theoretical framework exists to systematically screen
catalysts under such rigorous constraints. To bridge this gap, we
developed a theoretical screening protocol and applied it to 27 TMs,
evaluating 81 surface facets. Specifically, this approach evaluates
the viability of each metal surface for the electrochemical C–F
cleavage in perfluorobutanoic acid (PFBA), chosen as a representative
short-chain PFAS. Our screening incorporates all four essential electrochemical
criteria, enabling the identification of 14 promising TM surface facets
that satisfy the demanding requirements for PFBA degradation. An interesting
trend emerging from this screening is that the difficulty of C–F
cleavage is closely tied to how effectively electron density accumulates
on the reacting carbon site. As defluorination progresses, later cleavage
steps show sharply reduced charge transfer and correspondingly higher
reaction free energies. This relationship suggests that a simple electronic
descriptor can anticipate when C–F cleavage becomes energetically
demanding.