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.