Elucidation of Performance Recovery for Fe‐Based Catalyst Cathodes in Fuel Cells

Abstract

Platinum group metal (PGM)‐free oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) continue to demonstrate significant advances in catalytic activity. Unfortunately, the most promising catalysts exhibit initial rapid activity loss as well as significant sustained activity decay. Herein, it is shown that PGM‐free cathode fuel cell performance can be partially recovered by an in situ electrochemical method by restoring a percentage of the original active sites or activating originally inactive sites. The same approach is also shown to increase the initial activity if applied to a pristine PGM‐free cathode. This is achieved by applying low constant potential holds to the cathode in the absence of oxygen in the cathode, by either flowing nitrogen or blocking the delivery of air and removing the residual oxygen by the ORR. Two types of active sites are further differentiated with degradation mechanisms characterized by different populations and timescales. It is hypothesized that the recovery of sites is due to the reduction of Fe3+ to Fe2+, restoring a percentage of the original active sites or activating originally inactive sites. This reduction has additionally shown to generate the removal of oxygen adsorbates at the catalyst surface.

Bypassing Formation of Oxide Intermediate via Chemical Vapor Deposition for the Synthesis of an Mn-N-C Catalyst with Improved ORR Activity

“…Currently, catalysts composed of single transition metal atoms embedded in a nitrogen-carbon matrix (TM-N-C where TM = Mn, Fe, or Co) formed through pyrolysis of TM, N, and C precursor compounds show the highest ORR activity in acidic media among PGM-free catalysts. − In particular, the ORR activity of state-of-the-art Fe-N-C catalysts approaches that of Pt in PEMFCs. , However, the durability of Fe-N-C needs to be significantly improved for viable applications . While improvements in recovery procedures have the potential to increase the lifetime of the Fe-N-C electrode, the fundamental lack of stability remains a primary concern . One proposed mechanism of the performance decay of Fe-N-C catalysts is the possible formation of radicals by the Fenton reaction between Fe ions and peroxide in the acidic PEMFC environment. − Alternative transition metals such as Mn and Co have been investigated to increase the stability of these single-atom sites. , First-principle density functional theory (DFT) calculations have shown the Co-N 4 sites and Mn-N 4 sites have higher intrinsic resistance to acid leaching of the metal center over their Fe counterpart, suggesting enhanced stability of these active site. , This hypothesis led us to develop Mn-N-C catalysts.…”

“…10 While improvements in recovery procedures have the potential to increase the lifetime of the Fe-N-C electrode, the fundamental lack of stability remains a primary concern. 11 One proposed mechanism of the performance decay of Fe-N-C catalysts is the possible formation of radicals by the Fenton reaction between Fe ions and peroxide in the acidic PEMFC environment. 12−14 Alternative transition metals such as Mn and Co have been investigated to increase the stability of these single-atom sites.…”

The Effect of Arsenic on the Photocatalytic Removal of Methyl Tet Butyl Ether (MTBE) Using Fe2O3/MgO Catalyst, Modeling, and Process Optimization

“…In this study, Fe 2 O 3 /MgO was used as a catalyst because it is a porous structure with a high capacity for adsorbing organic matter [24,25] and generating free radicals [26]. Moreover, its band gap is 5.4-5.45 ev, so the electron in the band layer excites the current layer [24].…”

Investigation into MnNC synthesis pathway for improved oxygen reduction reaction activity, and, examination the electron transfer and degradation processes for nonaqueous redox flow batteries

“…24 While improvements in recovery procedures have the potential to increase the lifetime of the Fe-N-C electrode, the fundamental lack of stability remains a primary concern. 25 One proposed mechanism of the performance decay of Fe-N-C catalysts is the formation of radicals by the Fenton reaction between Fe ions and peroxide in acid. [26][27][28] .…”