Fluorinated MAX Phases for Photoelectrochemical Hydrogen Evolution

Abstract

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.

The unexpected photoelectrochemical activity of MAX phases: the role of oxide impurities

“…Recent studies have taken one step back, looking into the fundamental electrochemical properties of MAX phases and the possible application of these compounds as (photo)electrocatalysts for energy conversion. 22,31,32 In previous studies, 33,34 MAX showed better catalytic performances when exposed to different light sources. Ta 2 AlC, Cr 2 AlC, Ti 2 AlC and Ti 3 AlC 2 demonstrated improved photoelectrocatalytic H 2 production when illuminated by a 660 nm light source.…”

Sun, heat and electricity. A comprehensive study of non‐pollutant alternatives to produce green hydrogen

“…In each case, authors achieve, respectively, photocurrent values above 7 mAcm −2 (7% efficiency) and 10 mAcm −2 (12.82% efficiency). Currently stand out layered selenophosphites photocatalysts and improved Ag‐sensitized TiO 2 119‐125 . Photoelectrocatalysis report typical photoanodes of BiVO 4 and Ta 3 N 5 , with still low efficiency, and real pilot implementations with a short‐term 100 kg/day H 2 production 126‐128 …”

“…Currently stand out layered selenophosphites photocatalysts and improved Ag-sensitized TiO 2 . [119][120][121][122][123][124][125] Photoelectrocatalysis report typical photoanodes of BiVO 4 and Ta 3 N 5 , with still low efficiency, and real pilot implementations with a short-term 100 kg/day H 2 production. [126][127][128]…”

Fluorinated Transition Metal Carbides for Flexible Supercapacitors

“…However, halogenation of graphite (such as fluorination) is a unique approach that has been demonstrated to improve the electrochemical performance of graphite base electrodes , but yet to be examined in MAX phase materials. In light of this, our group have been demonstrated that many properties of graphene were triggered by fluorine doing including conductivity, specific capacity, electrochemical performance, and mechanical properties. ,, This diverse property allows fluorinated graphite in a wide range of applications such as sensors, , photocatalysts, energy storage, , photodetectors, field effect transistors, and so on.…”

“…In light of this, our group have been demonstrated that many properties of graphene were triggered by fluorine doing including conductivity, specific capacity, electrochemical performance, and mechanical properties. 21,23,24 This diverse property allows fluorinated graphite in a wide range of applications such as sensors, 21,25 photocatalysts, 26 energy storage, 27,28 photodetectors, 29 field effect transistors, 30 and so on.…”