A family of platinum group metal-free catalysts for oxygen reduction in alkaline media

Abstract

In this work a series of platinum group metal-free catalysts based on iron, cobalt, copper, nickel, silver and their bimetallic combinations are synthesized and their behavior for oxygen reduction in alkaline media is tested. A phthalocyanine-like ligand supported on carbon black serves as the nitrogen source and carbon support, respectively, for the catalysts. The as-prepared materials are thermally activated by pyrolysis at temperatures ranging from 600 °C to 1000 °C. Oxygen reduction reaction (ORR) activity and stability in 0.1 M KOH are tested by rotating ring disk electrode (RRDE) experiments. Several of the catalysts show ORR activities in the RRDE experiment that are superior to Pt, with Co, Co/Fe and Ag/Co being the best. All catalysts show remarkable stability, even when they are tested under air for 5000 RRDE cycles. RRDE experiments are also used to study the effect of catalyst loading and to determine reaction order. A thorough study of the catalyst performance in a single cell fuel cell test is conducted; exploring different methods to prepare the electrodes and the effects of catalyst loading, the catalyst-to-binder ratio and the removal of excess metal on the cell performance. Different methods of preparation of membrane electrode assemblies are also studied.