Understanding and Breaking the Scaling Relations in the Oxygen Reduction Reaction on Pd_xCu_4–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 Pd_xCu_4–x subnanoclusters supported by defective two-dimensional boron nitride materials (Pd_xCu_4–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 Pd_xCu_4–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 Pd_xCu_4–x/BN materials are good candidates for optimization. These results are expected to stimulate the exploration of novel subnanocluster catalysts for the ORR.