Fluorinated MAX Phases for Photoelectrochemical Hydrogen Evolution

Photoelectrochemical generation of hydrogen from water is considered to be the most appealing solution for the replacement of fossil fuels as a source of energy. For this reason, the study of novel and affordable materials with high energy conversion efficiencies is currently a crucial objective for the scientific community. Chemical modification of two-dimensional (2D) and layered materials, such as fluorination, can play a decisive role in tuning the properties for energy-related applications, as it was documented in the past by fluorination of graphite and graphene. MAX phases (MAX) are a class of layered ternary compounds that is well known for their interesting physical properties but still underexplored as a photoelectrocatalyst for energy conversion. Herein, a set of MAX, namely, Ta2AlC, Cr2AlC, Ti2AlC, and Ti3AlC2, was exposed to fluorine gas in a controlled environment and their photoelectrocatalytic properties were tested for the hydrogen evolution reaction with illumination by a visible light source of 660 nm wavelength. All of the mentioned compounds showed excellent hydrogen evolution performances under illumination, in particular after the fluorination process. Fluorinated Cr2AlC is the phase that showed the lowest overpotential, and fluorinated Ti2AlC and Ti3AlC2 showed the most prominent photoelectrocatalytic enhancement upon fluorination. The fluorinated MAX phases should find broad applications to photoelectrochemistry, as their fluorinated graphene counterparts did in the past.