On the Challenge of Verifying Dual Atom Catalyst Presence and Their Superiority over Single Atom Catalysts

Dual atom catalysts (DACs) are emerging as a new frontier in electrocatalysis. Building on the success of single atom catalysts (SACs), they are believed to display remarkable activity and selectivity, especially in the electrochemical oxygen reduction and CO 2 reduction reactions (ORR and CO 2 RR). They are, however, difficult to selectively synthesize, and in most studies, there is an overlap with single atom catalysts in terms of both synthesis procedure and electrocatalytic activity. Indisputably determining their prevalence over single atom sites or even clusters and nanoparticles is a daunting task with the characterization methods that are available. In this Perspective, we argue that in many studies, the electrocatalytic activity could be explained simply through the presence of single atom catalysts. Still, some studies stand out as being notably superior to most single atom catalysts, nurturing a hopeful outlook for the field. In electrocatalysis, most studied DACs and SACs are carbon supported. In this Perspective, we go through the state of the field for these catalysts in the two electrochemical reactions ORR and CO 2 RR. We give an overview of synthesis procedures for carbon supported DACs and the two most used characterization methods, high-angle annular dark-field emission scanning transmission electron microscopy and extended X-ray absorption fine structure (HAADF-STEM and EXAFS). We also highlight common misinterpretations and recommend good practices in future studies.