Abstract
Nanostructured electrochemical interfaces (electrodes) are found in diverse applications ranging from electrocatalysis and energy storage to biomedical and environmental sensing. These functional materials, which possess compositional and structural heterogeneity over a wide range of length scales, are usually characterized by classical macroscopic or "bulk" electrochemical techniques that are not well-suited to analyzing the nonuniform fluxes that govern the electrochemical response at complex interfaces. In this Perspective, we highlight new directions to studying fundamental electrochemical and electrocatalytic phenomena, whereby nanoscale-resolved information on activity is related to electrode structure and properties colocated and at a commensurate scale by using complementary high-resolution microscopy techniques. This correlative electrochemical multimicroscopy strategy aims to unambiguously resolve structure and activity by identifying and characterizing the structural features that constitute an active surface, ultimately facilitating the rational design of functional electromaterials. The discussion encompasses high-resolution correlative structure-activity investigations at well-defined surfaces such as metal single crystals and layered materials, extended structurally/compositionally heterogeneous surfaces such as polycrystalline metals, and ensemble-type electrodes exemplified by nanoparticles on an electrode support surface. This Perspective provides a roadmap for next-generation studies in electrochemistry and electrocatalysis, advocating that complex electrode surfaces and interfaces be broken down and studied as a set of simpler "single entities" (e.g., steps, terraces, defects, crystal facets, grain boundaries, single particles), from which the resulting nanoscale understanding of reactivity can be used to create rational models, underpinned by theory and surface physics, that are self-consistent across broader length scales and time scales.
Highlights
The structure of electrode surfaces has long been considered to have a profound effect on electrode kinetics and reaction mechanisms
In this Perspective we have highlighted recent approaches to studying fundamental electrochemistry and electrocatalysis, whereby colocated information on structure and activity is collected on commensurate scales, ranging from hundreds of nanometers all the way down to the atomic level
Some of the different techniques that we have discussed provide electrode topography and activity synchronously, and this alone may reveal a wealth of information, there is often the need to further employ complementary ex situ high-resolution microscopy/spectroscopy, which for some techniques (e.g., SECCM) is easier to implement due to the ease of obtaining a wide field optical view pre-/post-experiment but for others may require sample marking to assist in the use of colocation techniques
Summary
The structure of electrode surfaces has long been considered to have a profound effect on electrode kinetics and reaction mechanisms. Despite this acknowledged complexity, electrochemical measurements rely mainly on rather old macroscopic techniques that provide activity averaged over a wide range of interacting surface sites, thereby obscuring the nature of key elementary processes The aim of this Perspective is to highlight opportunities for fundamental electrochemistry and electrocatalysis studies, whereby electrode activity and dynamics (electrochemical fluxes) can be visualized at the nanoscale in the form of electrochemical “activity pictures” and “activity movies”, and further, where these high spatiotemporal resolution electrochemical data can be correlated directly with the underlying electrode structure and properties (electronic, chemical), obtained by using complementary high-resolution microscopy techniques in the same region of an electrode. These studies[11,13,15,16] and those discussed below clearly demonstrate how scanning probe techniques can go well beyond the capabilities of macroscopic electrochemical measurements to look at the heterogeneities within the surfaces of well-defined metal single crystals[11] and layered materials.[13,15,16] The techniques discussed collect electrochemical and topographical information synchronously (in situ and in real time) which, in conjunction with complementary structural information, reveal nanoscale structure−activity dynamics at functional electrochemical interfaces
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