Abstract
Besides revealing excellent mechanical properties, compositionally complex alloys are also very promising candidates for applications in heterogeneous catalysis. The opportunity provided by the tremendously large composition phase space to explore new materials and tune the materials properties in the materials design cycle is, however, intrinsically coupled with the challenge of controlling surface segregation, which is generally more severe in multicomponent alloys as compared to simpler systems. We demonstrate this by computing the surface phase diagram of two candidate compositionally complex catalysts. Significant surface segregation is found even at very high temperature and this can strongly affect the catalytic properties of these alloys. We explain the observed phase stabilities in terms of segregation energies and rationalize the segregation trends with canonical models. Finally, we propose a set of descriptors accessible with first-principles calculations that allows to quickly incorporate the evaluation of the segregation during the alloy design process.
Highlights
Materials for electrocatalysis are traditionally based on simple metals or bimetallic alloys
Catalysts based on CCAs [8,9] were shown to outperform state-of-the-art metals for methanol oxidation [10e13], oxygen reduction [13e16], hydrogen evolution [13,17,18], ammonia splitting [19e21], oxygen evolution [16,22], and CO and CO2 reduction [23] reactions
The results show that surface segregation is very prominent in both CCAs and explain why the resultant surface composition is predicted to be considerably different from the nominal bulk composition even at high temperature
Summary
Materials for electrocatalysis are traditionally based on simple metals or bimetallic alloys. Catalysts based on CCAs [8,9] were shown to outperform state-of-the-art metals for methanol oxidation [10e13], oxygen reduction [13e16], hydrogen evolution [13,17,18], ammonia splitting [19e21], oxygen evolution [16,22], and CO and CO2 reduction [23] reactions. Possible explanations for this outstanding performance of CCAs are the possibility to better fine-tune the composition to obtain the optimal absorption energy, and the opportunity to perform this fine-tuning for more than one reaction step at once [8]. Segregation may enhance or reduce the rate of certain reactions or reaction steps; having control of this phenomenon may turn out to be beneficial to boost some processes, but unwanted segregation shifting the surface composition away from a predetermined optimum could lead to a strong, detrimental decrease in the catalytic activity
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