Deciphering the Synergistic Effect in Strong Metal–Support\nInteraction toward Surface Reconstruction of Prussian Blue Analogue-Based\nPre-Catalysts for Boosted Bifunctional Oxygen Electrocatalysis via\nOperando Raman Spectroscopy

The strong metal–support interaction\n(SMSI) effect in Prussian\nblue analogues (PBAs) has been widely investigated and is credited\nfor the enhanced activity, selectivity, and durability for electrocatalysis\nreactions. However, deciphering the contribution of individual components\nand identifying the active sites in PBA-based pre-catalysts for electrocatalysts\nare seldom realized. Herein, we report the unraveling of the synergism\nin a cobalt hexacyanoferrate (CoHCF) PBA pre-catalyst-decorated three-dimensional\n(3D) network of interlinked graphene oxide and functionalized carbon\nnanotubes (GO/f-CNT) for the boosted bifunctional oxygen reduction\nreaction (ORR) and oxygen evolution reaction (OER). We find that the\nSMSI between CoHCF and GO/f-CNT modulates the surface reconstruction\nof the PBA pre-catalyst for boosted activity and durability. Besides,\nthe SMSI effect leads to a change in the rate-determining step (RDS)\nfrom surface-adsorption-limited over CoHCF to charge-transfer-controlled\nover CoHCF/GO/f-CNT during the ORR. Operando Raman spectroscopy confirms\nthis finding and demonstrates the lowered overpotential for the ORR\nover GO/f-CNT predominantly due to efficient adsorption of <i>O</i><sub>2</sub><sup>–</sup> (an ORR intermediate), while CoHCF provides a 4-electron ORR pathway.\nIn the OER, the leaching of Fe(CN)<sub>6</sub> species from the CoHCF\npre-catalyst under alkaline conditions generates OER-active CoOOH/FeOOH\non the surface.