Metal Monolayers on Command: Underpotential Deposition at Nanocrystal Surfaces: A Quantitative Operando Electrochemical Transmission Electron Microscopy Study br

Underpotential deposition (UPD) enables the generation of metal monolayers whoseelectronic properties can be significantly different from the bulk. While studied extensively for bulkelectrodes, UPD kinetics for individual nanoparticles can deviate from their bulk counterparts due tothe distinct differences in the distribution of local electricfields. UPD's nature remains largelyunexplored due to the lack of nanoscale time-resolvedoperando/in situtechniques at interfaces. Thisstudy presents an investigation on a model system, the UPD of monolayer Cu at single-crystal Aunanocube surfaces, based on a correlative analysis of electrochemical results and high-resolutionchemical mapping.Operandoelectrochemical liquid-cell scanning transmission electron microscopy(EC-STEM) directly visualizes the potential-dependent and spatially resolved Cu electrodepositionkinetics, classified as planar, island-shaped, or dendritic growth.OperandoEC-STEM reveals the well-defined diffusion-controlled processes during Cu electrodeposition in sub-mu m thick liquid with bothquantitative electrochemistry and quantitative imaging analysis. 4D-STEM shows that the Cuelectrodeposition is guided by the crystallographic orientation of the Au substrate. This methodologyofoperandoEC-STEM for quantitative electrochemistry can serve as a generalized platform to advance fundamentalunderstanding of (electro)chemical reaction dynamics.