A Facile Route to Large‐Area 2D Pt

Abstract Platinum (Pt) is a popular hydrogen‐evolution reaction (HER) catalyst, yet its high‐cost limits industrial deployment. This is addressed by incorporating an oxygen‐deficient, gallium (Ga)‐rich gallium oxide (GaO x ) adhesion layer that reverses the dewetting thermodynamics, yielding continuous 2D Pt at sub‐nanometer thickness by simple direct current (DC) sputtering. Alloy anchoring and vacancy chemisorption produce mechanically robust, transparent, conductive films with high thermal stability. During HER, 2D Pt/GaO x reduces, forming a Ga‐Pt that further smoothens. The 1 nm film matches bulk Pt electrocatalytic activity while sustaining 1A cm −2 for 100 h without decay. Revealing the wetting mechanism including the effect of adhesion layer, and the depositing metals, the strategy generalizes to other noble metals with adhesion layers, offering a scalable route to ultrathin catalytic and electronic platforms.