Prediction of the catalytic mechanism of hydrogen evolution reaction enhanced by surface oxidation on FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 multi-principal element alloys based on site preference

Figure Catalytic schematic of hydrogen evolution reaction (HER) on the surface of multi-principal-element alloys (MPEAs) established by combing the predicted site occupying fractions (SOFs) and the FCC_L12_AuCu3 prototype. This figure depicted ordered FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEAs with the L12_AuCu3 sublattice model as a prototype, where CoCrFeNi MPEA/Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEA was supposed to be obtained by heat treatment equilibrated at 1273K/1420K, and then subjected to water quenching to keep the ordered configurations at 1273K/1420K. For FCC_CoCrFeNi MPEA, Ni atoms tend to occupy the 1a sublattice at all temperatures, while Co, Cr, and Fe atoms preferentially occupy the 3c sublattice. For FCC_Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEA, Co and Fe always occupy the 3c sublattice at all temperatures, and Mo always occupy the 1a sublattice at all temperatures. Surface catalytic models for HER were obtained through relaxation and cross-sectional analysis. Upon oxidation of the surface model segment, it was observed that oxygen facilitated the departure of hydrogen from the alloy surface, ultimately resulting in the formation of hydrogen gas. [Display omitted] •The ordered configurations of two selective FCC MPEAs were constructed based on the predicted site occupying fractions (SOFs).•The catalytic activity of single intermediate *H at top or bridge adsorption sites surpassed that at the hollow site.•The catalytic models based on SOFs are more reasonable than those based on the speical qusirandom structure (SQS).•The HER performances of two MPEAs were enhanced by surface oxidation behavior. Some multi-principal element alloy (MPEA) catalysts may exhibit the ability to promote the hydrogen evolution reaction (HER) and maintain stability under acidic conditions. Here, we investigated the impact of ordered behavior and surface oxidation of FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEAs on HER performance through first-principles calculations. The ordering behaviors of MPEAs were described using L12_AuCu3 sublattice model and the predicted site occupying fractions (SOFs). And we found that the catalytic activity of single intermediate *H at top or bridge adsorption sites surpassed that at the hollow site. However, the hollow site exhibits strong adsorption towards *H, resulting in the transfer of *H from other sites to hollow site. Meanwhile, compared to those containing only hydrogen, MPEAs with both hydrogen and oxygen exhibit lower over