Unveiling facet engineering of ultrathin Pt overlayers for enhanced ammonia oxidation reaction.

[Display omitted] • Ultrathin Pt overlayer was fabricated on Ni substrate using an SED method. • Pt loading mass was precisely controlled at a microgram scale. • Electron-deficient Ni improved *OH adsorption, allowing NH 3 adsorption on Pt site. • Acid etching provided simple surface engineering method for Pt facet control. • E-HNO 3 -Pt5/Ni with high Pt(1 0 0) ratio showed high catalytic activity for AOR. Utilizing ammonia for hydrogen production via ammonia oxidation reaction (AOR) remains a challenge owing to insufficient electrode performance and high cost of noble metal. Herein, we performed repeated self-terminated electrodeposition (SED) of Pt on Ni substrate to obtain Pt/Ni electrodes. The electron-deficient Ni sites prefer *OH adsorption and serve as a reservoir for NH 3 dehydrogenation, thereby promoting NH 3 adsorption on Pt sites. Additionally, this iterative process enabled precise regulation of the Pt loading mass. Pt5/Ni electrode exhibited the highest catalytic activity for AOR. Subsequently, immersing this electrode in various acid solutions resulted in surface morphologies with numerous well-defined pits, driven by the adsorption of different electrolyte ions. Specifically, etching in HNO 3 led to a higher Pt(1 0 0) density, further enhancing the electrode's catalytic performance for AOR. Thus, this study offers a simple, fast, and spontaneous method for facet engineering ultrathin Pt overlayers on Ni substrate under ambient conditions. [ABSTRACT FROM AUTHOR]