RECENT PROGRESS IN SURFACE NMR-ELECTROCHEMISTRY

NMR spectroscopy is one of the newer spectroscopic techniques for inve stigating the static, dynamic and electronic structures of molecules a dsorbed onto metal catalyst surfaces. We review recent progress in the application of solid-state NMR methods to the investigation of molecu les adsorbed onto metal surfaces in an electrochemical environment: in the presence of electrolyte, and at an electrified interface under ex ternal potentiostatic control. While at a very early stage of developm ent, the NMR-electrochemistry approach has considerable potential for investigating otherwise inaccessible aspects of electrode and adsorbat e structure, and should enable a comparison of results obtained from d ifferent spectroscopies, in particular from IR spectroscopy. We presen t a brief review of the development of the subject, followed by detail s of the instrumentation necessary for NMR-electrochemistry studies. W e show how spin-spin relaxation can give information on surface struct ure and surface diffusion, how spin-lattice relaxation can give inform ation on the presence of conduction electron spillover onto the adsorb ate, and how the NMR of surface species responds to an externally appl ied electric held. The C-13-NMR of CO on Pt in an electrochemical envi ronment is compared with the C-13-NMR of CO on Pt catalysts in vacuum, which are well characterized. In the case of CN on Pt, we show large spectral shifts of the resonance as the electrode potential is varied, providing an independent measurement of the effects of the electrifie d interface on the chemisorption bond. Spectral sensitivity is also no w adequate to observe nuclei which produce even weaker signals than C- 13, such as N-15. The NMR-electrochemistry method thus opens up a broa d new array of possibilities for probing static structures (from T-2), surface diffusion (from the temperature dependence of T-2) as well as electronic properties of the chemisorption bond (from T-1, and from e lectrode potential effects) at electrochemical interfaces, and for stu dying reactive intermediates and poisons on high-surface-area catalyst s, such as those utilized in hydrogen and organic fuel cells.