Enhancing the Performance of Non-Noble Metal Catalysts for the Reduction of O(2) in PEM Fuel Cells:
The adsorption of iron II acetate over two microporous carbon blacks of different surface properties was studied in order to determine if this factor limits the activity of Fe/N/C catalysts for ORR made with these carbon supports. Whereas one of these carbons only had oxygen-derived functionalities over its surface, the other one contained both oxygen and nitrogen bearing functionalities. Their points of zero charge (PZC) were first determined to be 3.9 and 8.8, respectively. Adsorption curves showing the evolution of the metallic uptake with the pH revealed that both carbon supports are able to adsorb 100% of the positive Fe ions in solution at pH>4, and this up to 0.8 wt% Fe. Therefore, the adsorption of iron is not the factor responsible for the limited site density of Fe/N/C catalysts having a Fe content {less than or equal to} 0.8 wt% loaded either by adsorption or by wet-impregnation of the carbon supports.