Toward expanding the realm of high entropy materials to platinum group metals: A review

Highlights:• Recent advances in PGM-based high entropy materials is reviewed.• The current state and challenges of the synthesis of HEM-NPs are reported.• Catalytic/electrocatalytic properties of HEM-NPs are reviewed considering their intrinsic multicomponent nature.• Mechanical and shape memory properties of PGM-based HEAs are discussed.• The realm of PGM-based HEAs has been expanded to superconductivity and magnetocaloric effects. -- Abstract: High entropy materials (HEMs) have emerged as a new class of materials with exceptional scientific and technological potential. Since discovery of high entropy alloys (HEAs) in 2004, the concept of high entropy has been enlarged to ceramic, sulfide, fluoride, and phosphide materials. Correspondingly, their nearly infinite compositional space has been expanded to refractories, lanthanides, and recently platinum group metals (PGMs). Among these types of alloys, PGM-based HEM nanoparticles (HEM-NPs) are of great scientific interest because of the ability to continuously tailor their properties by tuning the ratio of noble to non-noble metal species. Besides, the functional properties of bulk HEAs such as shape memory effect, magnetocaloric, and superconductivity are attracting more and more attentions. In this review, we discuss the progress in the PGM-based HEMs focusing on catalytic performance of nanoparticles and functional properties of bulk materials. We begin with the synthesis of HEM-NPs emphasizing on the ability of alloying immiscible elements into single phase NPs. Then, we summarize the reported catalytic/electrocatalytic applications of HEM-NPs for different types of reactions, including CO₂/CO reduction reactions, CO oxidation, methanol oxidation, oxygen reduction reaction and electrochemical water splitting. We present a case-by-case discussion to clarify how various metal species can play distinct role in chemically complex structure of HEM-NPs under different reaction conditions. We further try to give a picture of the current state of shape memory, magnetocaloric, and superconductivity effects in the bulk PGM-based HEAs.