The relatively simple synthesis of SF Au NPs obtained at RT using 0.5 mM HAuCl4, 2 mM NaOH in water with 20 v.% ethanol is shown to be a suitable approach to efficiently study size effects at the nanoscale and in particular in catalysis. By inducing the synthesis in different ways including using sonochemistry, stirring or manual shaking, but also using different precursor types and grades, size control in the range 5 -22 nm is simply achieved. With the example of various alcohol-electro-oxidations, it is shown that the smallest NPs show the highest ECSAs and MAs. In particular, the smallest NPs of 5 nm prepared here using sonochemistry lead to the most active NPs reported to date for SF Au NPs for the EOR.