On the Stability of Perfluoroisobutyronitrile in High-Voltage Circuit Breaker: A Computational Study

2,3,3,3-Tetrafluoro-2-(trifluoromethyl) propanenitrile, also known as perfluoroisobutyronitrile (CF4-CN), is the main component of the so-called g³ gas mixture (C₃F₇CN-CO₂-O₂), a proven alternative to SF₆ as an insulating gas in high-voltage circuit breakers. In recent years, numerous experimental investigations have been conducted to identify the principal reactions that this mixture undergoes before and during the electric arcing processes. While thanks to these efforts, several products have already been characterized in different possible experimental conditions, a full picture of CF4-CN reactivity in the high-voltage conditions of circuit breakers has yet to be reached. In this paper, we present a computational study based on density functional theory (DFT) that further expands the mapping of the possible chemical reactions of CF4-CN before (hydrolysis) and during (decomposition) electric arcing. Through a careful analysis of all possible reactions paths that includes the structural and energy characterization of reaction intermediates and products, the decomposition of C₃F₇CN in the presence of oxygen is evidenced, together with the formation of stable amide derivatives upon hydrolysis. This work allows the unambiguous identification of the most probable reaction paths, in terms of energy, leading to the decomposition products reported experimentally, such as CF₄, COF₂, or C₂F₅CN, as well as the reactions leading to the amide species that have been observed to form crystals in experimental conditions.