Epitaxial growth of hexagonal Pd on CoO/NC heterostructures for high-performance ORR electrocatalysis.

Multicomponent hybrid systems with engineered interfaces are promising candidates for enhancing electrocatalytic performance. Palladium, with an electronic structure similar to that of platinum but with a significantly lower cost, has emerged as a viable alternative to Pt-based catalysts in which the oxygenated intermediate coverage during the oxygen reduction reaction (ORR) limits the long-term performance of conventional Pt/C catalysts. This work introduces a strategically engineered multicomponent heterointerface comprising interstitially modified palladium (Pd-O) nanoparticles with a rare hexagonal crystal structure, spinel CoO, and nitrogen-doped porous carbon (NC). The formation of hexagonal palladium under ambient conditions using NaBH, rather than high-pressure or high-temperature routes, is exceptionally rare and represents a significant advancement in non-conventional phase stabilization. This unusual morphology, stabilized by the lattice strain and surface oxygen adsorption from CoO, modulates the d-band center of Pd, optimizing the adsorption energies of the oxygenated intermediates and accelerating ORR kinetics. Furthermore, the tight NC filling of the porous CoO matrix imparts high conductivity and structural robustness, even after calcination in air, which is itself a novel achievement. The synergistic interaction across these engineered interfaces enhances active site exposure, electronic conductivity, and stability, collectively driving the outstanding electrocatalytic ORR performance (onset potential () ≈ 0.99 V, half-wave potential () ≈ 0.89 V, mass activity ≈ 840 mA mg, electrochemical surface area (ECSA) ≈ 13.6 m g, and enhanced durability). This heterostructure thus serves as a powerful blueprint for the future catalyst designs, where lattice-strained phases and interfacial effects are deliberately exploited.