Templated non-PGM cathode catalysts derived from iron and poly(ethyleneimine) precursors

A series of oxygen reduction catalysts derived from pyrolyzed iron-containing compounds and a nitrogen-containing polymeric precursor, poly(ethyleneimine), (Fe–PEI) were prepared using a sacrificial support method (SSM). The synthesis includes high-temperature pyrolysis in inert atmosphere of the precursor that has been deposited onto a highly dispersed silica support, followed by etching (dissolving) the oxide support, thus resulting in a templated, self-supported, highly porous material – the non-PGM electrocatalyst. The influence of experimental parameters on the catalytic activity of the oxygen reduction reaction (ORR) in acid media was studied, such as molecular weight of PEI, temperature of the heat treatment, duration of the heat treatment, and the ratio of metal to nitrogen precursor. This series of materials was analyzed and characterized by scanning electron microscopy (SEM), BET method (BET) and XPS in order to establish structural morphology and chemical moieties, which was then correlated to activity. Rotating ring disk electrode (RRDE) experiments were performed to evaluate catalytic activity, and the ring current data was used to conduct a mechanistic study of the material for the ORR. This work has determined that the most influential parameters on activity are the metal to nitrogen precursor ratio, and temperature of the heat treatment. Accelerated durability RDE tests (cycling between 0.2 and 1.1 V) revealed high stability of synthesized materials in acid media.

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► First report on templating a high-molecular weight precursor for non-PGM catalysts.
► Most critical parameters are the metal/nitrogen ratio and pyrolysis temperature.
► The role of the transition metal in oxygen reduction mechanism is discussed.