The objective of this work is to investigate the somewhat edged out fundamental knowledge gained from single crystal model systems and link certain aspects to the features of high-surface area catalysts, in order to demonstrate the importance of fundamental research and create a connection to practical applications. This is achieved by treating the ideal systems not as "one-to-one" models, but rather rationalize the effects that can be correlated to real catalysts, while always keeping the structural and electronic differences in mind. In this regard important fuel cell reactions such as the CO oxidation and oxygen reduction are investigated, and novel insights into the origin of the particle size effects are demonstrated. Based on this information from Pt systems more complicated catalysts like the promising Pt-alloys can be analyzed unambiguously. With the variety of systems discussed in this work, it can be considered as a benchmark for the further development of novel catalysts. Moreover the presented perception resulting from the applied "surface science approach" reflects the state of the art for the complex electrocatalysis of fuel cell reactions, and can consequently be supportive for everybody in the field, to researchers in industry as well as at university.