Atomic-scale Ir decoration on Pt(100) via self-terminated electrodeposition for electrochemical ammonia oxidation

초록

The ammonia oxidation reaction (AOR) suffers from sluggish kinetics and poisoning by nitrogen intermediates, limiting its application in energy systems. Here, we present a self-terminated electrodeposition strategy to decorate Pt (100) nanosheets with ultra-trace Ir, enabling atomic-scale control of interfacial structure. Pulsed deposition directs Ir preferentially to step sites at low coverage, forming site-isolated Ir domains that maximize activity while suppressing poisoning. Under alkaline conditions, Ir decoration induced a volcano-type dependence of activity on Ir content. The Ir5/Pt NT electrode (5.67% surface Ir) achieved a specific activity of 0.772 mA/cm2 at 0.60 VRHE, while its integrated AOR charge density was nearly double that of pristine Pt NT, underscoring cumulative enhancement over the full potential window. X-ray photoelectron spectroscopy and electrochemical characterization confirm that this enhancement originates from isolated Ir at step sites, whereas extended Ir domains at higher coverages disrupt this configuration and diminish performance. Density functional theory calculations identify *NH2 coupling as the rate-determining step, with its free energy barrier decreasing from 1.45 eV on Pt to 1.30 eV at Ir-Pt step interfaces due to cooperative stabilization of intermediates. In addition, performance was evaluated in a membrane electrode assembly-type ammonia electrolyzer, where the Ir-decorated anode exhibited improved performance at low cell voltages. Collectively, these findings highlight the mechanistic and structural basis for optimizing AOR catalysts and provide a design principle for highperformance electrocatalystsin ammonia-based energy conversion.

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