Microwave-Assisted Synthesis of Platinum-free High-Entropy Alloy Catalysts on Reduced Graphene Oxide Sheets for Enhanced Oxygen Reduction and Evolution Reactions

Nano-sized high-entropy materials (HEMs) recently received more attention to researchers due to their superior electrochemical catalytic properties. HEMs comprise at least five elements with or without metals and are synthesized through solid-state reactions and solution-mediated techniques. The presence of many elements in these HEMs result in a high mixing entropy and facilitates the formation of stable solid solutions in fundamental crystal structures. Herein, Pt-free high-entropy alloys (HEAs) were synthesized through facile and straightforward pulse microwave (PM) synthesis technique, which serve as efficient electrochemical catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The PM synthesis method was conducted at an extremely low temperature (100 °C) without any external catalytic reagents. Using this PM technique, Cr_18.2Zr_13.5Ti_5.3Co_17.8Ni_8.4Cu_8.5Fe_28.3 and Al_15.3Mn_18.2Ti_3.7Co_23.2Ni_5.9Cu_5.9Fe_27.8 HEAs catalysts were synthesized with superior catalytic activity towards OER and ORR and compare its activities with pure Pt catalysts. The as-prepared HEAs also display an anti-CO poisoning effect and long-term durability, as compared to pure Pt catalysts. The low-temperature PM approach not only confirms the feasibility of synthesis of noble metal-free HEAs but also validates their superior catalytic activity towards OER and ORR, which is beneficial for the development of proton exchange membrane fuel cells and proton exchange membrane water electrolysis.