Iron(III) chloride-benzotriazole adduct for oxygen reduction reaction in alkaline medium

Abstract

Transition metal-nitrogen-carbon (MNC) based non-platinum metal catalysts obtained by pyrolysis of a transition metal, carbon and nitrogen sources were viewed as an inexpensive substitute for the platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Due to the pyrolysis step involved in synthesizing MNC catalysts, the exact active site structure responsible for ORR was not conclusively identified thereby limiting the efforts of scientists in identifying effective synthetic routes to achieve highly active MNC catalysts with required active site structure and site density. To alleviate the lack of clarity on the active site structure of MNC catalysts, as a substitute, copper, and cobalt-based metal-organic frameworks and complexes were synthesized recently and shown to be ORR active. In this study, we have synthesized an Iron(III) chloride-benzotriazole ([FeCl3(btaH)2]) adduct and demonstrated its ORR activity in alkaline medium, which primarily reduces oxygen by 4-electron reduction pathway. Single crystal XRD characterization revealed the crystal structure of [FeCl3(btaH)2] unambiguously. The ORR onset potential, Tafel slopes, and methanol tolerance ability of [FeCl3(btaH)2] were compared against commercial 20 wt% Pt/C. [FeCl3(btaH)2] adduct shows complete methanol tolerance and ORR onset potential of 0.89 V vs. RHE, which is highest among the unpyrolyzed metal-organic frameworks/complexes.