This Review reports recent advances in the field of nanoscale electrochemistry. We specifically focus on new electrochemical phenomena, properties, and technological capabilities essential to reducing the dimensions of an electrochemical probe to the nanometer scale, as well as electrochemical properties of new nanoscale electrode materials. Here, we adopt the conventional definition of nanoscale to refer to lengths between 1 and 100 nm. Nanoscale electrochemistry is critically important for modern electrochemical science as well as many other key research areas, such as energy conversion and storage, catalysis, sensor development, and environmental science. Nanoscale electrochemical investigations have provided unique information unattainable using traditional methods. For example, nano-electrodes can measure ultrafast electron-transfer kinetics that are often too fast to investigate with conventional electrodes. Nanoscale electrochemical materials, such as metal/semiconductor nanoparticles, have unique chemical and physical properties, and nanoscale electrochemical methods can be used to prepare advanced electrocatalytic materials. In addition, the use of nanoscale electrode probes has enabled electrochemical imaging with nanoscale spatial resolution, yielding unique information for better understanding heterogeneous electrode/solution interfaces. Nanoscale electrochemistry is a rather broad topic, as electrochemistry deals with electron- and charge-transfer processes at solid/liquid and liquid/liquid interfaces. These processes are inherently nanoscale by nature. Here, we restrict the scope of this Review and choose to focus on the following aspects: (1) preparation, characterization, and use of nanometer scale electrochemical probes including nanoelectrodes and nanopores; (2) theory and experiments for better understanding electron and mass transfer at nanoelectrodes; (3) faradaic processes of nanoscale redox species, e.g., metal nanoparticles and single redox molecules; (4) electrochemical techniques to prepare nanomaterials; (5) electrochemical imaging to achieve nanoscale spatial resolution. The field of nanoscale electrochemistry began about three decades ago shortly after the fast development and widespread application of microelectrodes. Since then, this field has generated enormous excitement and has seen a dramatic increase in popularity in the last two decades. This growth is largely due to rapid developments in nanofabrication and characterization and the introduction of numerous bottom-up and top-down processes capable of preparing well-defined nanoelectrodes and materials.
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