Subnanometer control and electrochemical mapping of a Pt monolayer catalyst for boosting ethanol oxidation.

Strain engineering with atomical precision is considered the ultimate strategy for enhancing nanocatalyst activity. Although methods for strain modulation, such as elemental doping, core-shell structures, and defect engineering, have achieved substantial success, they inevitably alter catalyst composition, complicating the interpretation of strain effects. Herein, we developed a combined mechanically controlled break junction (MCBJ) and scanning electrochemical microscopy (SECM) method, enabling subnanometer control on the nanocatalyst structure and visual monitoring of electrochemical activity under continuous strain modulation without altering the material's composition. As proof of principle, we prepared a monolayer of platinum (Pt) catalyst on a gold surface and applied continuous tensile strain to it using the MCBJ module. In situ x-ray diffraction and finite element simulations confirmed that the lattice spacing of the Pt monolayer catalyst was controlled with atomic precision. Electrochemical mapping using SECM revealed that the catalytic activity of the Pt monolayer catalyst follows a volcano-type trend with increasing strain, with optimal electrocatalytic activity for ethanol oxidation at 1.0% tensile strain. Density functional theory calculations and quasi-in situ x-ray photoelectron spectroscopy analysis indicate that tensile strain elevates the d-band center of Pt, enhancing the adsorption of both reactants and intermediates while facilitating charge transfer processes, resulting in enhanced performance in the final. This work provides an experimental method for studying the independent impact of strain engineering on the material performance, with both atomic precision and dynamic visualization, offering insights for the design of advanced electrocatalysts.