What is the Crystal Structure of Molybdenum Carbide?

Transition metal carbides (TMCs) possess fascinating physical and chemical properties, especially when the structure is scaled down to the nanoscale. The temperature and chemical flexibility of this family of materials make them ideal for electrochemical applications in harsh environments. In the TMC series, molybdenum carbide has proven as an effective catalyst for the hydrogen evolution reaction (HER). This article will introduce a research paper, which investigate the performance of molybdenum carbide as catalyst^[1].

Crystal Structure

This paper focused on two phases of molybdenum carbide α-MoC and β-Mo2C, structures of which are illustrated in the figure above. β-Mo2C has been reported as excellent catalyst for HER in acidic solution, while the α-MoC has not been well investigated due to the synthesis difficulty. 

The 3 × 3 × 3 generated structures were relaxed using the Vienna Ab Initio Simulation Package to ensure all the forces on the ions were smaller than 0.01 eV Å−1. All surface geometries were optimized before placing any adsorbate. The initial guesses for adsorbate geometries were obtained by placing the adsorbate at different sites. Such optimized geometries were characterized as minima on the potential energy surface by appropriate frequency analysis involving diagonalization of the corresponding block of the Hessian matrix with elements obtained through finite differences of analytic gradients of 0,03 Å length. The necessary numerical integrations in the reciprocal space were carried out using an optimal 3 × 3 × 1 k-point mesh selected following the Monkhorst-Pack scheme for the molybdenum carbide (α-MoC and β-Mo2C).

Reference

[1] Investigation of molybdenum carbides as catalyst for hydrogen evolution in PH universal environment using density functional theory simulation. METALURGIJA 59 (2020) 3, 355-357.