Effect of High Surface Area Carbon Addition to the Performance of a Non-Precious Metal Catalyst in a PEM Fuel Cell

In Polymer Electrolyte Membrane Fuel Cells (PEMFCs) the structure and morphology of the electrode layer play an important role in the value of the electrochemical resistance, which has an impact in the cell performance. These effects become particularly relevant when the cathode catalyst is based on a non-precious metal due to the higher catalyst loadings required to compensate for the lower catalytic activity when compared to Pt based catalysts.  In previous experiments performed in our lab, a pyrolyzed iron (III) porphyrin framework (PCPF-Fe) material was characterized, exhibiting a good single cell performance. In this study, the addition of a high surface carbon to the PCPF-Fe was conducted in an attempt to increase the surface area and the electron conductivity and, consequently, improve the activity and stability. For this purpose, as-synthetized PCPF-Fe was mixed with Ketjenblack (KJB) carbon to four different ratios, pyrolyzed and its catalytic activity towards the ORR was evaluated using rotating ring disk electrode (RRDE) experiments. The structure and morphology of the catalyst layer were analyzed through scanning electron microscopy (SEM), and X-Ray Diffraction (XRD). The best performed mixture was 50% PCPF-Fe, and  exhibited a comparable onset potential and a higher limiting current density (-4.6mA/cm² in the 100% vs. -6.0mA/cm² in the 50%) to that of the pure material.  The material was then used as the cathode electrode in a single cell.  The maximum current density obtained in single cell test for the 50% PCPF-Fe was only a third of that obtained with a 100% PCPF-Fe (0.25A/cm² vs. 0.81A/cm²) cathode with the same catalyst loading, which could be associated to a lower density of catalytic centers in the mixture.