What is it about?
Iron-based electrocatalysts have emerged as promising, cost-effective alternatives to platinum for fuel-cell technologies; however, their advancement remains constrained by an incomplete understanding of the true catalytic sites, their electronic structures, and their dynamic evolution under operating conditions. This review provides a comprehensive overview of how in-situ/operando Mössbauer spectroscopy has transformed the study of Fe-based oxygen reduction catalysts by enabling direct observation of Fe species during catalysis. Through a series of representative case studies, we discuss how Mössbauer spectroscopy has been employed to identify catalytically active Fe configurations, distinguish different Fe phases and coordination environments, monitor oxidation-state and spin-state changes, evaluate catalyst stability and degradation pathways, and establish structure-activity relationships. By integrating insights from operando Mössbauer measurements with complementary electrochemical, spectroscopic, microscopic, and theoretical approaches, this review highlights Mössbauer spectroscopy's unique ability to reveal the dynamic nature of Fe active sites. It provides valuable guidance for the rational design of efficient, durable, platinum-group-metal-free ORR electrocatalysts.
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Why is it important?
The key importance of this work is that it addresses a major barrier in developing practical Fe-based ORR catalysts: knowing which Fe species remain active, how they transform during operation, and why performance declines over time. By bringing together evidence from in-situ/operando Mössbauer spectroscopy, the review highlights a route to connect Fe electronic and structural changes directly with catalytic behavior. This is timely because improving catalyst durability and reducing dependence on platinum are both central to advancing lower-cost fuel-cell technologies.
Perspectives
Writing this review has been a valuable opportunity to combine our expertise and long-standing collaborations in electrocatalysis and Mössbauer spectroscopy. Exploring how operando techniques reveal the hidden dynamics of iron active sites has strengthened our appreciation of the importance of real-time catalyst understanding. We hope this work will encourage broader application of advanced spectroscopy approaches and foster new collaborations toward the rational design of sustainable energy catalysts.
Sumbal Farid
Chinese Academy of Sciences Dalian Institute of Physics
Read the Original
This page is a summary of: Iron-Involved ORR Electrocatalysts under the Lens of <em>In-Situ/Operando</em> Mössbauer Spectroscopy, Journal of Electrochemistry, January 2026, Tsinghua University Press,
DOI: 10.61558/2993-074x.3578.
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