Understanding and Breaking the Scaling Relations in the Oxygen Reduction Reaction on PdxCu4–x Subnanoclusters Supported by Defective Two-Dimensional Boron Nitride Materials

Scaling relations in the oxygen reduction reaction (ORR) impose an intrinsic limitation on the maximum performance of a catalyst. To gain a high ORR activity, great efforts have been made to break these scaling relations. We showed that on PdxCu4–x subnanoclusters supported by defective two-dimensional boron nitride materials (PdxCu4–x/BN), scaling relations can be broken with R2 values of 0.83 (ΔG*OOH vs ΔG*OH) and 0.31 (ΔG*Ovs ΔG*OH), which are lower compared to a single metal atom supported by defective BN, 0.99 (ΔG*OOH vs ΔG*OH) and 0.81 (ΔG*Ovs ΔG*OH). The poor correlations can be explained by the variation in binding sites and the fluxional behavior of PdxCu4–x in its geometry shape during intermediate binding. The ORR occurs via the 4e– mechanism with large overpotentials, implying that breaking the scaling relation does not necessarily guarantee a high ORR activity. Through electrochemical-step symmetry index (ESSI) analysis, we further showed that PdxCu4–x/BN materials are good candidates for optimization. These results are expected to stimulate the exploration of novel subnanocluster catalysts for the ORR.