ULTRA-HIGH VACUUM TECHNIQUES IN THE STUDY OF SINGLE-CRYSTAL ELECTRODE SURFACES

The development of powerful, surface-sensitive analytical methods has led to spectacular advances in the field of gas-solid interfacial science over the past two decades. Earlier research had been based upon thermodynamic and kinetic methods that portrayed only the macroscopic properties of the interfacial ensemble. The dearth of atomic-level information at that time is remarkably similar to what presently handicaps classical electrochemistry. In search of a more fundamental, microscopic view of electrode processes, research in modern electrochemistry has incorporated non-traditional approaches to the study of the electrode-solution interface. One approach, motivated by the overwhelming successes in vacuum-metal surface science, is the adaptation of ultra-high vacuum (UHV) surface spectroscopic techniques; such approach is the subject of the present review. This article describes the capabilities and limitations of coupled UHV-electrochemistry (UHV-EC) as a means to extract an atomic-level picture of the solid-electrolyte interface. After a brief introduction that outlines the experimental and theoretical obstacles in electrochemical surface science, this review presents a detailed discussion on experimental protocols (sample preparation, surface analytical techniques, instrument design) and critical processes (emersion, evacuation, surface characterization) inherent in the UHV-EC methodology. The final segment of this article summarizes selected studies with single-crystal electrode surfaces that showcase the power and elegance of the UHV-EC strategy; a more extensive bibliography of published investigations is provided in the Appendix. This review is concluded with a commentary on the future prospects of the UHV-EC approach.