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Pulsed cathodic arc-plasma deposition was employed to create a few nanometre-thick Pt overlayer on a 50 μm-thick Fe-Cr-Al metal (SUS) foil, resulting in an effective NH 3 oxidation catalyst fabrication. This catalyst exhibited a turnover frequency (TOF) exceeding 100 times that of Pt nanoparticles. In this study, Pt overlayer catalysts with varying degrees of surface roughness were fabricated using different metal foil substrates: mirror-polished (Pt/p-SUS), unpolished (Pt/SUS) and roughened by the formation of a surface oxide layer (Pt/Al 2 O 3 /SUS). The nanoscale roughness was comprehensively analysed using electron microscopy, laser scanning confocal microscopy and chemisorption techniques. NH 3 oxidation activity, measured at 200 °C, followed an increasing trend in the order of Pt/Al 2 O 3 /SUS < Pt/SUS < Pt/p-SUS, despite a decrease in the apparent Pt surface area in the same order. Consequently, the calculated TOF was markedly higher for Pt/p-SUS (267 min -1 ) compared to Pt/SUS (107 min -1 ) and Pt/Al 2 O 3 /SUS (≤22 min -1 ). The smooth Pt overlayer surface also favoured N 2 yield over N 2 O at this temperature. This discovery enhances our fundamental understanding of high-TOF NH 3 oxidation over Pt overlayer catalysts, which holds significance for the advancement and industrial implementation of selective NH 3 oxidation processes.