Au(111)-Supported Pt Monolayer as the Most Active Electrocatalyst toward Hydrogen Oxidation and Evolution Reactions in Sulfuric Acid

As a subnanometer thick platinum (Pt) film can have catalytic properties different from those of the Pt bulk, the research on the preparation and characterization of a Pt monolayer is fundamentally intriguing and may lead to cost-effective fuel cells. We devise an electroless deposition method to fabricate a Pt monolayer and use scanning tunneling microscopy (STM) to characterize its atomic structures. This method involves the use of carbon monoxide (CO) molecules as the reducing agent for PtCl6 2– complexes, yielding a CO-capped Pt film on an Au(111) substrate. The deposition of the Pt film stops at one atom thick. To expose the Pt film, the CO adlayer is stripped off by pulsing the potential to 0.96 V (vs hydrogen reversible electrode) for 3 s in H2-saturated 0.1 M H2SO4. Atomic resolution STM imaging shows that the Pt adatoms arrange in two hexagonal arrays with different atomic corrugation patterns and a notable difference (5.5%) in the Pt–Pt distance at 0.1 V. The Pt film with a larger interatomic spacing of 0.287 nm is 2× more active than that of Pt(111), and may be the most active catalyst toward hydrogen evolution and oxidation reactions (HER and HOR) reported thus far.