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7010432 
Journal Article 
The Determination of Electrochemical Active Surface Area and Specific Capacity Revisited for the System MnOx as an Oxygen Evolution Catalyst 
Connor, P; Schuch, J; Kaiser, B; Jaegermann, W; , 
2020 
1 
Zeitschrift fur Physikalische Chemie
ISSN: 0942-9352 
WALTER DE GRUYTER GMBH 
BERLIN 
234 
5 
979-994 
WOS:000534258100010 
In the last decades several different catalysts for the electrochemical water splitting reaction have been designed and tested. In so-called benchmark papers they are compared with respect to their efficiency and activity. In order to relate the different catalyst to each other the definition of well-defined procedures is required. Two different methods are mainly used: Either the normalization with respect to the geometric surface area or to the catalyst loading. Most often only one of these values is available for a sample and the other one cannot be estimated easily. One approach in electrocatalysis is to determine the Helmholtz double layer capacitance (DLC) and deduce the electrochemical active surface area (ECSA). The DLC can be obtained from two different methods, either using differential capacitance measurement (DCM) or impedance spectroscopy (EIS). The second value needed for the calculation of the ECSA is the specific capacitance, which is the capacitance for a perfectly flat surface of given catalyst material. Here, we present the determination of the different capacitance values using manganese oxide as the exemplary model for the oxygen evolution reaction (OER). We determine the capacitance by DCM and EIS to calculate the EC SA using literature values for the specific capacitance. The obtained values are comparable from the two methods, but are much larger than the surface areas obtained by atomic force microscopy. Therefore, we consider the possibility of using the measured AFM area together with the Helmholtz capacitance to determine the specific capacitances for this material class. The comparison of these results with literature values illustrates the actual limits of the ECSA method, which will be discussed in this paper. 
double layer capacitance; ECSA; electrochemical active surface area; manganese oxide; Helmholtz capacitance; MnO; MnO2