Title: A Strategy for Increasing the Efficiency of the Oxygen Reduction Reaction in Mn-Doped Cobalt Ferrites

Abstract

Alkaline fuel cells have drawn increasing attention as next-generation energy-conversion devices for electrical vehicles, since high pH enables the use of non-precious-metal catalysts. Herein, we report on a family of rationally designed Mn-doped cobalt ferrite (MCF) spinel nanocrystals, with an optimal composition Mn_0.8(CoFe₂)_0.73O₄ (MCF-0.8), that are effective electrocatalysts for the oxygen reduction reaction. MCF-0.8 exhibits a half-wave potential (E_1/2) of 0.89 V vs RHE in 1 M NaOH, only 0.02 V less than that of commercial Pt/C under identical testing conditions and, to the best of our knowledge, one of the highest recorded values in the literature. Moreover, MCF-0.8 exhibits remarkable durability (ΔE_1/2 = 0.014 V) after 10 000 electrochemical cycles. In situ X-ray absorption spectroscopy (XAS) reveals that the superior performance of the trimetallic MCF-0.8 originates from the synergistic catalytic effect of Mn and Co, while Fe helps preserve the spinel structure during cycling. We employed in situ XAS to track the evolution of the oxidation states and the metal–oxygen distances not only under constant applied potentials (steady state) but also during dynamic cyclic voltammetry (CV) (nonsteady state). The periodic conversion between Mn(III, IV)/Co(III) and Mn(II, III)/Co(II) as well as the essentially constant oxidation state of Fe during themore » CV suggests collaboration efforts among Mn, Co, and Fe. Mn and Co serve as the synergistic coactive sites to catalyze the oxygen reduction, apparently resulting in the observed high activity, while Fe works to maintain the integrity of the spinel structure, likely contributing to the remarkable durability of the catalyst. Furthermore, these findings provide a mechanistic understanding of the electrocatalytic processes of trimetallic oxides under real-time fuel cell operating conditions. This approach provides a new strategy to design high-performance non-precious-metal electrocatalysts for alkaline fuel cells.« less

Authors:

Xiong, Yin ^[1]; Yang, Yao  ^[1];

• Search DOE PAGES for author "Yang, Yao"
• Search DOE PAGES for ORCID "0000-0003-0321-3792"

Feng, Xinran ^[1]; DiSalvo, Francis J. ^[1]; Abruña, Héctor D.  ^[1]

• Search DOE PAGES for author "Abruña, Héctor D."
• Search DOE PAGES for ORCID "0000-0002-3948-356X"

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+ Show Author Affiliations

1. Cornell Univ., Ithaca, NY (United States)

Publication Date:

Thu Feb 21 00:00:00 EST 2019

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Alkaline-Based Energy+B11:C29 Solutions (CABES); Cornell Univ., Ithaca, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); Center for Alkaline-Based Energy Solutions (CABES); Center for Energy Materials at Cornell (emc2); National Science Foundation Materials Research Science and Engineering Center (NSF MRSEC); National Science Foundation (NSF)

OSTI Identifier:

1566595

Grant/Contract Number:  

SC0019445; DMR-1719875; DMR-1332208

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Volume: 141; Journal Issue: 10; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (heterogeneous); electrocatalysis; hydrogen and fuel cells; charge transport; membranes; water; materials and chemistry by design; synthesis (novel materials); redox reactions; x-rays; spinel; oxides; transition metals