A Facile Route to Large‐Area 2D Pt

This work demonstrates a simple route to form continuous 2D platinum (Pt) films only up to 0.3 nm thick using a gallium oxide (GaOx) adhesion layer. The oxygen‐deficient GaOx reverses wetting thermodynamics, enabling scalable sputtering of transparent, conductive, and robust 2D Pt. During hydrogen evolution, the films alloy with gallium (Ga), matching bulk Pt activity while sustaining long‐term stability. 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 (GaOx) 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/GaOx 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. This work demonstrates a simple route to form continuous 2D platinum (Pt) films only up to 0.3 nm thick using a gallium oxide (GaO x ) adhesion layer. The oxygen-deficient GaO x reverses wetting thermodynamics, enabling scalable sputtering of transparent, conductive, and robust 2D Pt. During hydrogen evolution, the films alloy with gallium (Ga), matching bulk Pt activity while sustaining long-term stability. 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. Advanced Science, EarlyView.