Which is Best for ORR: Single Atoms, Nanoclusters, or Coexistence?

The commercialization of fuel cells necessitates achieving ultralow Pt loadings due to the scarcity of Pt. Single atoms (SAs) have emerged as a potential solution to enhance the atomic utilization of catalysts. Our density functional theory (DFT) calculations reveal that combining SAs with nanoclusters rather than using SAs alone in catalysts leads to optimized electronic structures. The coexistence of SAs and the nanoclusters significantly improves the adsorption and desorption behaviors of oxygen-containing intermediates during the oxygen reduction reaction (ORR). To experimentally validate this finding, we synthesized Pt SAs, Pt nanoclusters, and their mixture. The electrochemical performance of these catalysts in the ORR is consistent with the DFT calculations. This study answers the question, which is best for ORR: single atoms, nanoclusters, or coexistence?