Progress, challenges, and prospects with electrocatalyst (From transition metal oxides to dual-atom catalysts) for oxygen reduction reaction

Electrocatalytic oxygen reduction reaction (ORR) is essential in fuel cells and metal-air batteries for converting and storing energy. Nevertheless, these devices suffer from ORR's slow kinetics at cathode surfaces, necessitating effective electrocatalysts. To meet the practical application of these devices, various ORR electrocatalysts, including transition metal oxides (TMOs), sulfides (TMSs), phosphides (TMPs), and single-atom catalysts (SACs), have been developed, each with its issues related to limited activity, selectivity, and durability. Although TMOs possessed promise towards ORR, their limited conductivity and poor selectivity motivated the researcher to perform their sulfurization and phosphorization, resulting in TMSs, TMPs, and SACs, which displayed good ORR. However, at a practical level, these catalysts still exhibited poor selectivity and durability, introducing a novel class of electrocatalysts, 'dual-atom catalysts (DACs)'. DACs have many advantages, including maximum atomic utilization in catalysis and a well-established activity descriptor, over other electrocatalysts. However, an assessment of DAC's evolution, their promise towards ORR, and the learned concepts to design efficient ORR catalysts is required. The purpose of this review is to provide a road map of the transition of electrocatalysts from TMOs to DACs with recent advancements in chemistry, structural-functional relationships, advantages, and disadvantages. In addition, the challenges, and relative prospects of various critical parameters of ORR electrocatalysts are also covered systematically.