This lecture is entirely dedicated to the oxygen electrochemistry, encompassing both the oxygen reduction reaction in fuel cells (ORR) and the oxygen evolution reaction (OER) in electrolyzers on wide range of well-characterized materials; ranging from metals, meta/metal-oxides, and complex oxides. Of central importance is to show how the knowledge gained from well-characterized single crystal materials can be used to design real-world nanoscale materials at the atomic and molecular level.
First we show that both reactions are structure sensitive processes and that the rates are strongly dependent on the pH environment. For the ORR we will argue that structure sensitivity arises via structure sensitive adsorption of spectator species rather than reaction intimidate. To demonstrate this we show a specific example for the ORR on platinum and gold single crystal surfaces first and then on the corresponding bimetallic surfaces that are obtained by alloying the host metal with 3d-TM elements. Then we introduce the OER, emphasizing that the most active materials are less stable - indicating that the active sites are defects which are created during the reaction. We will argue that instead of characterizing catalytic performance by (mass or specific) activity, which does not capture any information about the stability (and ultimate commercial viability) of a given material, the design of catalyst materials for the OER should instead be guided by a new, quantitative descriptor-the Activity- Stability Factor; ASF-whichis expressed as the ratio between activity and stability for a given catalyst. In closing the lecture, we will point out that the importance of oxygen electrochemistry goes well beyond the success of hydrogen economy. In fact, it serves as a unique bridge between electrochemistry in aqueous and organic environments.
