Atomic-Level Engineering in Lattice Strain-Driven Pt3Ir-Skin@Pt6IrCo with Mesoscale Mass Transport Regulation for Ammonia Oxidation Reaction in Direct Ammonia Fuel Cells

Abstract Lattice-strained bimetallic-skin engineering with a defect-rich ternary core remains largely unexplored for ammonia oxidation reaction (AOR), mainly due to the challenges in probing and modeling its complex local coordination environments. Here, an integrated hierarchical system combines atomic-scale surface engineering (Pt3Ir-skin@Pt6IrCo) with mesoscale mass transport regulation by 3D-polydiaminopyridine-derived nanoporous carbon (3DPDPC), thereby enhancing active site accessibility and facilitating efficient ammonia oxidation in direct ammonia fuel cells (DAFCs). The optimum lattice strain (1.79%) and NH3 adsorption energy (−1.73 eV) in the Pt3Ir-skin@Pt6IrCo/3DPDPC modulate the position of the d-band center and mitigate the N* intermediate poisoning. Further, the local coordination environment was revealed by X-ray absorption spectroscopy, confirming that PtIr has a direct bonding nature with the heteroatom-N of the support (3DPDPC), whereas Co exists in the alloyed form due to the different coordination environment. Density functional theory calculations reveal a mechanistic switch: the strained Pt3Ir-skin@Pt6IrCo(111) favors the Oswin−Salomon (O-S) pathway, while the asymmetric Pt6IrCo(111) follows the Gerischer−Maurer (G-M) pathway. The temperature-variant kinetic analyses confirm a significantly reduced apparent activation energy (31.28 kJ mol−1) for the Pt3Ir-skin@Pt6IrCo/3DPDPC system compared to the commercial PtIr/C (58.5 kJ mol−1), reflecting the enhanced reaction kinetics and surface resilience. When employed in a membrane electrode assembly (MEA), the Pt3Ir-skin@Pt6IrCo/3DPDPC-based DAFC prototype (101.27 mW cm−2) outperforms the benchmark PtIr/C and Pt/C. This work demonstrates the synergistic benefits of the atomic-level skin design, strain-induced electronic tuning, and 3D carbon confinement for advancing the next-generation DAFC electrocatalysts.