(453f) Canonical Surface Phase Diagrams for Disordered CoMo Alloys

The use of periodic DFT calculations and advanced synthesis techniques has accelerated the understanding and development of multimetallic alloy catalysts, including high-entropy alloys (HEAs). HEAs, composed of many elements with mixed atomic structures, offer attractive catalytic properties such as improved stability and tunable active site structures. Carbothermal shock synthesis enables the formation of such nanoparticles with many elements incorporated into a single solid-solution phase, with high-resolution STEM-based elemental mapping revealing a homogeneous distribution of the elements. However, uncertainty remains regarding the distribution of elements in the surface region, especially for elements with large miscibility gaps present in the phase diagram. In particular, fluctuations in local composition can lead to surface strain effects that alter catalytic performance. Understanding these effects in HEAs is crucial for designing effective catalysts and optimizing their activity and selectivity.

This study employs cutting-edge computational methods to elucidate the impact of strain and local surface compositional fluctuations of disordered CoMo bimetallic alloy surfaces, providing insights into the design of high-entropy alloy (HEA) catalysts. By analyzing canonical surface phase diagrams, we identify thermodynamically stable surface compositions that deviate from the bulk, emphasizing the importance of considering strain relaxation and corresponding Moiré pattern formation in random alloy surfaces. These local relaxations often occur when the local surface composition deviates from the bulk composition, in our case, Co₅₀Mo₅₀. The resulting stable surface structures are also used to calculate descriptors for NH₃ decomposition and to screen for reactivity properties. This work lays the foundation for understanding surface stability and strain effects in disordered alloys, facilitating the rational design of HEA catalysts with optimized surface properties for enhanced catalytic performance. The insights gained from this study can be extended to more intricate, multi-elemental systems, ultimately contributing to the development of efficient and sustainable catalytic processes.