Understanding the Structure-Property Relationship in Bio-Enabled High Entropy Nanocatalysts

High entropy alloy nanocatalysts (HEAs) are an emerging class of materials that presents a paradigm shift in the discovery of functional electrocatalysts. The distinct structural features of HEAs enables these materials with reactive electronic transitions, facilitating them to be optimal materials in emerging electrocatalytic reactions. However, to leverage the catalytic opportunities in HEAs, it is essential to increase their synthetic accessibility with precise atomic-scale structure characterization. On the synthesis front, research efforts have largely focused on the use of joule-heating processes, which requires sophisticated equipment and/or harsh operating conditions, necessitating the need for novel synthesis techniques that offer atomic-scale structure control. In addition to that, our present understanding about the structure-property relationship in HEAs is hindered by the increased structural and compositional complexities of HEAs that are inherently difficult to decouple. As such, it is essential to utilize characterization tools that can uncover the atomic insights in HEAs such that the origin of performance enhancement in HEAs is accurately discerned. Ultimately, we need to be able to overcome the limitations of trial-and-error experimental design protocols for HEA development and instead focus on progressing towards rational engineering of HEAs with desired properties, where the establishment of structure-property relationships providing a means forward in this regard.<br/>Here, using a combination of electrocatalytic reactions, advanced structural characterization, and computational modelling, we explore the structure-property relationship of peptide-enabled HEAs. Peptides have been implemented as capping ligands for HEA synthesis due to its ability to induce controlled nucleation and growth of sub-5 nm HEAs in water with tuneable non-covalent binding affinities, achieved through sequence manipulation. The local and extended atomic structure of the multimetallic systems were probed and characterized using a combination of high-resolution transmission electron microscopy (HR-TEM), extended x-ray absorption fine structure spectroscopy (EXAFS) and high-energy x-ray diffraction coupled with pair distribution function analysis (HE-XRD/PDF). Using experimental structural characterization and reverse Monte Carlo (RMC) simulation of PDF, atomic models over the length-scale of HEAs were constructed, revealing a sequence dependent structure difference in both surface structure and composition. Furthermore, our catalytic results unveiled a structure-property relationship, where enhanced catalytic performance is achieved through the formation of optimal surface atomic ensemble. Taken together, our results present an experimental platform to study a wide range of functional HEA structures. More broadly, we have demonstrated the viability of using stochastic modelling of atomic PDFs to study the structure-property relationship in HEAs, facilitating rapid screening and rational design of HEAs possible.