An absolute evaluation of MA and electrochemically active surface area (ECSA) is ultimately the key to characterize a NC. MA and ECSA were evaluated in two different ways. The present approach focuses on as-prepared catalysts, the conversion of Au III to Au 0 is first assumed to be 100% for the synthesis and the MA and ECSA are first estimated using the nominal loading (synthesis-to-catalysis). To propose a relative, yet more accurate, picture of the performance of the Au NPs, the absorbance at 400 nm retrieved from UV-vis spectroscopy was also used to normalize the MA (MAA400) and ECSA (ECSAA400), since the absorbance at 400 nm in UV-vis characterization (A400) gives a relative indication of the conversion of Au III to Au 0 . This allows a more detailed comparison of the samples, without the need for more advanced methods such as mass spectroscopy (MS) based methods or X-ray absorption spectroscopy (XAS), at least in a screening phase to optimize a higher throughput.