Unlocking d-p Orbital Coupling via Built-in Electric Fields for High-Performance Hydrazine Hydrate Fuel Cell.

Direct hydrazine fuel cells (DHzFCs) offer a promising carbon-free liquid-fuel route for power generation, yet progress is limited by sluggish hydrazine oxidation reaction (HzOR) kinetics and the high cost of Pt catalysts. In this work, we tune the built-in electric field (BIEF) at the Pt@MOF interface via linker-directed defect engineering. Partial substitution of 1,1'-ferrocenedicarboxylic acid (Fc) with ferrocene-carboxylic acid (Fc') generates graded ligand-defect and undercoordinated Ni─O environments, thereby regulating Pt anchoring and interfacial charge redistribution. The optimized Pt@NiFc0.95Fc'0.05-MOF delivers 1000 mA cm-2 for HER (180 mV, overpotential) and 2000 mA cm-2 for HzOR (346 mV, working potential), outperforming Pt/C while achieving 99% hydrazine conversion. The assembled direct hydrazine hydrate-hydrogen peroxide fuel cell (DHHPFC) delivers a peak power density of 441 mW cm-2 at 80°C. Density functional theory (DFT) calculations and experimental analyses reveal that the oxygen-mediated Pt─O─Ni interfacial electronic pathway, enhanced apparent BIEF, and accelerated interfacial charge transfer in Pt@NiFc0.95Fc'0.05-MOF, accounts for the improved catalytic and fuel-cell performance. This work establishes a linker-defect strategy for constructing Pt-utilization-efficient interfaces for hydrazine energy conversion.