In situ determination of electronic structure at solid/liquid interfaces

Various important processes take place at solid/liquid interfaces. Understanding of structural changes accompanying with those interfacial processes is important not only for fundamental science but also for a wide range of applications, especially electrocatalysis. In the last several decades, a variety of microscopic and spectroscopic techniques have been developed to observe geometric/molecular/electronic structures at the solid/liquid interfaces in situ. However, techniques to probe the electronic structure of electrocatalysts are still limited because of the complexity of the experimental setup and the interpretation of results. Since the 1980s, our groups have developed and utilized various techniques which enable to investigate those structural changes under electrochemical potential control. In the present paper, our recent research progress on the electronic structure at solid/liquid interfaces, (1) in situ XAFS studies on molecular catalysts confined within molecular layers and electrocatalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells, (2) development of an in situ electrochemical XPS apparatus for the solid/liquid interfaces and (3) investigation of the electronic structure of metal surfaces modulated by adsorbed species by in situ DR-SFG is briefly reviewed.