Atomically Dispersed Zn and Ir Synergistic Modulation of Substrate and Active Sites for High-Performance Ammonia Oxidation.

A rationally designed, bifunctional ammonia-oxidation catalyst spatially decouples NH3 activation and *OH adsorption to overcome the intrinsic trade-off of single-component systems. Atomically dispersed Zn single atoms in an N,O-doped carbon support (Zn1/NOC) serve as dedicated *OH-adsorption sites, while Ir-modulated Pt(100) nanocubes selectively activate NH3. Comprehensive structural characterization (AC HAADF-STEM, XPS, XANES, EXAFS) confirms Zn-N3O3 coordination and atomically isolated Zn centers. Electrochemical-kinetic analysis, mechanistic spectroscopy, and DFT calculations reveal that Zn1/NOC lowers the *OH-adsorption energy by 0.84 eV (to -0.98 eV versus -0.14 eV on Pt), facilitating the dehydrogenation steps and reducing surface poisoning. Simultaneously, traces of stabilized Ir4+-decorated Pt cubes enhance NH3 dissociation kinetics to form N2. The catalyst demonstrates a specific activity of 3.80 mA cm-2 PGMs, exceeding the state-of-the-art benchmarks. When deployed in a membrane-electrode-assembly direct ammonia fuel cell, the catalyst achieves a maximum current density of 200 mA cm-2 and a peak power density of 18 mW cm-2, representing a significant improvement over previously reported systems, with ∼250% increase over Ptnp-C || Pt/C and more than double monofunctional systems. This work demonstrates a generalizable strategy for engineering spatially decoupled active sites in multistep electrochemical reactions, paving the way for high-performance ammonia fuel cells and beyond.