Dual Atom Catalysts for the Oxygen Reduction Reaction: The Undisputable, the Controversial, and the Misleading

Electrocatalysis of the oxygen reduction reaction (ORR) is critical for energy generation in the scheme of the hydrogen economy. Scientists have been trying to replace platinum group metal (PGM) catalysts for this reaction with PGM-free catalysts to lower the cost of fuel cells. In the past decade, significant attention has been given to the design and synthesis of dual atom catalysts (DACs), designed to break the linear scaling relations (LSRs) observed with single atom catalysts. Breaking the LSR allows fine-tuning of the catalyst properties and theoretically reaches the best performance possible for ORR electrocatalysis. In the effort to develop DACs, several categories and various synthesis approaches have been created, which eventually result in DACs, controversial DACs, and those that cannot be regarded as DACs. In this perspective, we distinguish between the three categories.