(182i) Density Functional Study for Atomically Dispersed Noble Metal on Mesoporous Carbide By Topotactic Conversion

The highly ordered mesoporous Mo_xC synthesized through the Kirkendall effect and the catalytic effect of nanomaterials is a key factor in the nanostructuring of Mo_xC. Catalytic effects have been observed with noble metals such as Pt, Ru, and Au. Notably, in the presence of noble metals, topotactic conversion is facilitated. Molybdenum carbide exists in two forms: α-MoC and β-MoC. The formation of α-MoC occurs via topotactic conversion induced by noble metal catalysis. Moreover, mesoporous Mo_xC predominantly exhibits the α-MoC phase. To elucidate the topotactic conversion mechanism and noble metal catalytic effect on two types of Mo_xC, density functional theory (DFT) calculations were conducted. Through investigation into defect formation mechanisms occurring via different pathways—α-MoC made from initial MoO3 through MoO_xC_y and β-MoC made from MoO₂—the process of topotactic conversion is elucidated. Identifying the preferred vacancy site and investigating the possibility of migration when generated in less favored locations, it focuses on analyzing the pore structure formed during MoC synthesis and the process of carbon substitution. Analyzing the entire process allows for the identification of defect formation locations and elucidation of the overall pore formation mechanism, enabling an explanation of the Kirkendall effect. Additionally, comparisons of electrochemical performance were made through calculations of the hydrogen evolution reaction, water dissociation, and hydrogen spillover. In the case of α-MoC, it was observed that there were better performances in HER and water dissociation. Additionally, it was confirmed that the performance was further enhanced with the addition of Pt. Finally, a comparison between Phosphomolybdic acid, utilized as the precursor for Mo, and H₂PtCl₆ or platinum acetylacetonate (Pt(acac)₂), employed as the precursor for platinum, is conducted to assess the interactions of these compounds. Through this comparison, the objective is to evaluate the two precursors. Specifically, Pt(acac)₂'s interaction with PMA results in a higher Pt dispersion, thereby preventing the formation of Pt agglomerates. Subsequently, interaction energy calculations are performed to highlight the differences between the precursors and compare the outcomes with calculations involving other noble metals instead of Pt. The findings of this study demonstrate the advantages of α-MoC's topotactic conversion and are expected to provide insights into the distinguishing features of α-MoC compared to other MoC forms.