Discover the Evolution: A Comprehensive Review of Transition and Rare Earth Metals for Oxygen Reduction Reaction, from Mono to High-Entropy Catalysts

Abstract

Green energy, including metal-air batteries and fuel cells, is the key solution to climate change. The efficiency of these energy technologies depends on the oxygen reduction reaction (ORR) at the cathode, which is a slow process requiring expensive noble metal catalysts, like platinum, for improvement. The high cost of this catalyst restricts its widespread use in producing metal-air batteries and fuel cells. An alternative approach is to utilize non-noble metals, such as transition and rare earth metal catalysts, which are more cost-effective and demonstrate comparable durability and effectiveness to noble metals. With their affordability and distinct electronic structure, these non-noble metals have the potential to revolutionize the industry. Transition and rare earth metals can enhance the effectiveness of ORR catalysts by manipulating the electronic and surface molecular makeup through ' doping ' and ' synergistic effects '. This article discusses the roles of various non-noble metals in the ORR process, covering fundamental to advanced levels, as well as the progression from mono to high-entropy systems (systems with increasing complexity and potential for improved performance), including bi-, tri-, and tetra-metallic catalysts in a comprehensive manner, and emphasizes opportunities for researchers to propose innovative strategies for optimizing the ORR process.