DFT Study of MAX Phase Surfaces for Electrocatalyst Support Materials in Hydrogen Fuel Cells

Abstract

In moving towards a greener global energy supply, hydrogen fuel cells are expected to play an increasingly significant role. New catalyst support materials are being sought with increased durability. MAX phases show promise as support materials due to their unique properties. The layered structure gives rise to various potential (001) surfaces. DFT is used to determine the most stable (001) surface terminations of Ti2AlC, Ti3AlC2 and Ti3SiC2. The electrical resistivities calculated using BoltzTraP2 show good agreement with the experimental values, with resistivities of 0.460 µΩ m for Ti2AlC, 0.370 µΩ m for Ti3AlC2 and 0.268 µΩ m for Ti3SiC2. Surfaces with Al or Si at the surface and the corresponding Ti surface show the lowest cleavage energy of the different (001) surfaces. MAX phases could therefore be used as electrocatalyst support materials, with Ti3SiC2 showing the greatest potential.

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

“…The DOS and band structure results agree with previous works on theoretical studies of Nb 2 AlC, 57,58 Ta 2 AlC 36 and Ti 3 AlC 2 . 35,59 Having a basic understanding of the MAX, we proceeded with extensive experimental material characterisations. SEM was used to study the morphology of the three phases and the obtained micrographs are shown in Fig.…”

“…The DOS and band structure results agree with previous works on theoretical studies of Nb 2 AlC, 57,58 Ta 2 AlC 36 and Ti 3 AlC 2 . 35,59…”

“…33 In addition, Cr 2 AlC demonstrated huge potential in the photodegradation of various cationic and anionic dyes under the inuence of visible and UV light, showing an optical band gap of 1.28 eV. 34 These studies provided evidence that in contrast to the metallic nature of MAX, 35,36 some of them, if not all, possess band gaps and absorb light, as shown in Scheme 1, so they can be applied in solar-driven applications.…”

Surface Properties of Ti2AlV (100) and (110) Surfaces Using First-Principle Calculations

“…It was also reported elsewhere that the stoichiometric (100) surface is the most stable, and additionally that the Al terminated (110) surface becomes more stable as the Al chemical potential increases [13]. Gertzen et al [14] employed the DFT method to investigate MAX phase surfaces of (Ti2AlC, Ti3AlC2 and Ti3SiC) for electrocatalyst support material in hydrogen fuel cells. It was reported that the cleavage energy value for Ti2AlC is lower (1.924 to 5.254 eV/unit cell) than Ti3AlC2 (1.9-6.48 eV/unit cell) and Ti3SiC2 (2.8-6.47 eV/unit cell) surfaces.…”

Ti3AlC2/Pd Composites for Efficient Hydrogen Production from Alkaline Formaldehyde Solutions

“…The MAX phases are ternary transition metal carbide and/or nitride with a layered hexagonal crystal structure [26,27]. The unique structure endows them the dual properties of both metals and ceramics, that is, they are machinable and possess high electronic conductivities, are lightweight, and oxidation resistant [28,29]. Further studies by Ng et al showed the potential of Ti 3 AlC 2 as a catalyst in selective oxidation reactions, which was most likely derived from the non-stoichiometric oxide surface layer containing oxygen vacancies [30].…”