Ballmilling of Carbon Supports to Enhance the Performance of Fe-based Electrocatalysts for Oxygen Reduction in PEM Fuel Cells

摘要

The effect of ballmilling three carbon black supports on the ORR activity of Fe-based electrocatalysts was investigated. Catalysts were prepared by acid-washing these ballmilled carbon supports, then impregnating them with iron(II) acetate and pyrolyzing in NH3 at 950℃. It was found that ballmilling the carbon support improved the ORR activity for catalysts made with Black Pearls 2000 (Cabot), but decreased it for those made with N650 and left it relatively unchanged for those made with N234 (both low surface area commercial furnace carbon blacks from Sid Richardson Carbon Corporation). For catalysts made with ballmilled Black Pearls 2000, it was found that ORR activity increases as ⅰ) degree of disorder increases, ⅱ) the change in micropore surface area due to pyrolysis increases, ⅲ) nitrogen content increases and ⅳ) crystallite size (L_a) approaches 24 A. No compelling trends were found for catalysts made with ballmilled N234 and N650. Interestingly, despite the wide ranging catalytic activities of catalysts produced from these carbon blacks without ballmilling, almost identical activity for ORR is obtained when the carbon blacks are ballmilled for 2 hours prior to acid-washing, FeAc impregnation and pyrolysis.