Fuel cells, and in particular solid oxide fuel cells, enable high-efficiency conversion of chemical fuels into useful electrical energy and, as such, are expected to play a major role in a sustainable energy future. Essential to the fuel cell energy conversion process are the electrochemical reactions at the electrodes - oxygen reduction at the cathode and fuel oxidation at the anode. Despite recognition of the importance of the electrochemical reactions and extensive research efforts towards their elucidation, the reaction pathways and rate-limiting steps remain largely unknown. Progress has been impeded by a number of factors including the morphological complexity of the electrode and of the electrode-electrolyte interface in typical structures, evolution of the surface chemistry during measurement and/or operating, and poor knowledge of the inherent defect and transport properties of the material under electrochemical investigation.
Here, we address these factors through micro/nano-fabrication of simplified, well-defined structures and evaluation of materials with well-known bulk defect and transport properties. We employ physical vapor deposition and micro/nano-patterning methods to prepare oxide-metal composite electrode structures with good impurity control. This geometry, in combination with selected in-situ and ex-situ characterization techniques, enables identification of the reaction pathways, facilitates measurement of the site-specific electro-catalytic activity, and reveals critical factors governing the overall electrode reaction rates. The observations give guidance for achieving fuel cell electrodes with exceptional performance.