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 R-2 values of 0.83 (Delta G(*OOH) vs Delta G*OH) and 0.31 (Delta G(*O)vs Delta G(*OH)), which are lower compared to a single metal atom supported by defective BN, 0.99 (Delta G(*OOH) vs Delta G(*OH)) and 0.81 (Delta G(*O)vs Delta G(*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 electro-chemical-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.