In this study, performance and transport properties of electrodes based on the cyanamide-polyaniline-iron (CM-PANI-Fe) catalyst developed by Los Alamos National Laboratory were investigated. The electrode microstructure was characterized by use of the nano-scale X-ray tomography (nano-CT) technique. After ion exchanging the protons in Nafion® with cesium (Cs+), the samples were scanned in absorption contrast mode to visualize Cs+intensity, and thus the ionomer, while pore morphology was obtained using Zernike phase contrast scans, as in . Ionomer volume fraction distribution and pores larger than the nano-CT resolution (~20 nm) were obtained as shown in Fig. 1. By running transport simulations, the effective transport properties were calculated for various sub-volumes extracted from the nano-CT data, as illustrated in Fig. 1. Using the effective ion conductivities in a simple performance model, ORR kinetic parameters () were calculated and sources of voltage losses were identified depending on the experimental polarization data. Finally, the mass transport resistances were quantified by using the calculated kinetic ORR and effective transport parameters within a detailed cathode model that accounts for the charge, reactant and liquid water transport. It was concluded that the flooded pores are the major source of mass transport resistances for the thick PGM-free electrodes whereas the film resistance becomes dominant for thinner electrodes, as shown in Figs. 2a and 2b.
 G. Wu, K.L. More, C.M. Johnston, P. Zelenay, Science, 332 (2011) 443
 S.K. Babu, H.T. Chung, P. Zelenay and S. Litster, ACS Applied Materials and Interfaces, 8 (2016) 32764
This work was supported under the auspices of the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office’s Electrocatalyst Consortium (ElectroCat). This research also used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. Special thanks to Iryna Zenyuk for sharing her beamtime.
Figure 1. Nano-CT image showing PGM-free catalyst distribution (in solid gray-blue color) and ionomer distribution (green)