DFT Study of Hydrogen-Evolution Reaction on Mo-Based Alloys

Electrochemical hydrogen evolution reaction (HER) through water splitting is one of the most effective mechanism among the various hydrogen productions. Although Pt-based catalysts are at present the most active HER catalysts [1], the high cost and scarcity of Pt essentially limit their large-scale practical applications. Therefore, the development of cost-effective and earth-abundant catalysts as alternatives to noble Pt has devoted significant research interest. Among the various materials, intermetallic compounds formed by non-precious transition metals are promising cost-effective and robust catalysts for electrochemical hydrogen production [2]. Using the current theoretical methods it is now possible to study surface chemical reactions in detail and to understand variations in catalytic activity from one catalyst to another as well as compare with available experimental data [3].<br/>Here, we have studied the HER catalytic activity of μ-Co₇Mo₆, μ-Fe₇Mo₆, Mo, Cr₅₀Mo₅₀heterogeneous catalysts and compared with HER catalytic activity of Pt. The geometry optimization of the selected surface structures, the evaluation of the electronic and thermodynamic properties of the selected compounds and the detailed analysis of their catalytic activities toward hydrogen evolution reaction (HER) through water splitting were performed using the density functional theory calculations implemented in the Vienna Ab initio Simulation Package [4]. The activation barriers have been calculated with the nudged elastic band (NEB) method [5].<br/>The most active catalytic sides toward H₂O, OH and H adsorption have been evaluated for the studied catalysts. The values of the adsorption energies have been calculated and the surface effect on these values have been analyzed based on the geometry of top layers and the electronic structures (Partial density of states) of catalytic surfaces and the charge transfer between surface atoms and adsorbed species. The obtained results showed that the dissociative adsorption of water is demonstrated to be thermodynamically favorable (exothermic) for μ-Co₇Mo₆, μ-Fe₇Mo₆, Mo, Cr₅₀Mo₅₀catalysts and the lowest activation barrier is found in the case of μ-Fe₇Mo₆one. Based on the calculated DG_H* values, the catalytic activity trend of the order of μ-Co₇Mo₆ &gt; Mo &gt; Cr₅₀Mo₅₀ &gt; μ-Fe₇Mo_6.In the case of μ-Co₇Mo₆, this value is comparable with the DG_H* value calculated for H adsorption on Pt(111) surface. Thus it can be suggested that Mo-based alloys, especially Co₇Mo₆may be the good candidates for electrolyte fuel cell as substitution of Pt.<br/><br/>REFERENCES<br/>R. Subbaraman <i>et al.</i> <i>Science</i>, 2011, <i>334</i>, 1256-1260.<br/>H. Shi <i>et al.</i> <i>Nat. Commun.,</i> 2020, <i>11</i>, 1-10.<br/>G. Kresse and J. Furthmüller, J. <i>Comput. Mater. Sci.,</i> 1996, <i>6</i>, 15-50.<br/>G. Henkelman and H. Jonsson <i>J. Chem. Phys.</i>, 2000, <i>113</i>, 9978-9985.