A versatile and powerful method in the assessment of electrocatalysts is scanning electrochemical microscopy (SECM). The spatial activity and selectivity of a catalytic material is immediately visualized by analyzing the current response of a movable probe electrode . Recently, Rodríguez-López et al.  described a surface interrogation mode of SECM that allows the detection of adsorbates depending on time and substrate potential. This method is based on a transient feedback of a redox mediator with which a coulometric titration is performed. By integrating the current response at the tip electrode the quantification of active catalytic sites is accessible.
In this study, we apply the surface interrogation mode to detect the amount of active sites at spinel type metal oxide catalyst under alkaline fuel cell conditions. Therefore, the catalyst powder is supplied in cavity-microelectrodes which were prepared by electrochemical etching of a metal wire . Through the quantification of active sites and the examination of their reactivity new insights to the ORR of alkaline fuel cells are achieved. The results will be compared to a commercial carbon-supported platinum fuel cell catalyst.
1. X. Deng and H. Tüysüz, ACS Catal., 4, 3701 (2014).
2. I. Katsounaros, S. Cherevko, A. R. Zeradjanin and K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 53, 102 (2014).
3. G. Wittstock, M. Burchardt, S. E. Pust, Y. Shen and C. Zhao, Angew. Chem. Int. Ed., 46, 1584 (2007).
4. J. Rodríguez-López, M. A. Alpuche-Avilés and A. J. Bard, J. Am. Chem. Soc., 130, 16985 (2008).
5. A. Minguzzi, C. Locatelli, O. Lugaresi, A. Vertova and S. Rondinini, Electrochim. Acta, 114, 637 (2013).