Low loading ORR selectivity evaluation of Pt-free catalysts with scanning electrochemical microscopy

Abstract

The challenges associated to oxygen reduction reaction (ORR) electrocatalysis are undoubtedly the most intricate impediments to solve regarding fuel cell vehicle (FCV) commercialization, mainly due to the complexity of this reaction and the scarcity of the required electrocatalysts. The synthesis of non-precious electrocatalysts with high intrinsic selectivity is indeed crucial in this field, but the methodology utilized to come to selectivity conclusions is undeniably equally important. In this work, we demonstrate how the higher required electrode loadings of a Fe-N-MWCNT catalyst in a rotating ring disc electrode (RRDE) prevent access to all of the peroxide produced by the catalyst during ORR. Via a spraying technique, much smaller amounts of the same catalyst were deposited on a flat boron-doped diamond (BDD) and their loading was determined meticulously by atomic force microscopy (AFM). These ultra-low loadings were investigated using scanning electrochemical microscopy (SECM), which revealed higher peroxide production and lower selectivity. This finding may have crucial implications for future ORR investigations in the laboratory, considering the harmful effect peroxide has on the catalyst.