Publisher: American Chemical Society (ACS)

Issue: 5

License: [{"start"=>{"date-parts"=>[[2026, 4, 14]], "date-time"=>"2026-04-14T00:00:00Z", "timestamp"=>1776124800000}, "content-version"=>"vor", "delay-in-days"=>0, "URL"=>"https://creativecommons.org/licenses/by/4.0/"}]

Publication date(s): 2026/05/07 (print) 2026/04/14 (online)

Pages: 1190-1196

Volume: 2 Issue: {"issue"=>"5", "published-print"=>{"date-parts"=>[[2026, 5, 7]]}}

Journal: ACS Electrochemistry

Link: [{"URL"=>"https://pubs.acs.org/doi/pdf/10.1021/acselectrochem.5c00541", "content-type"=>"application/pdf", "content-version"=>"vor", "intended-application"=>"unspecified"}, {"URL"=>"https://pubs.acs.org/doi/pdf/10.1021/acselectrochem.5c00541", "content-type"=>"unspecified", "content-version"=>"vor", "intended-application"=>"similarity-checking"}]

Understanding the interplay between redox behavior and structural stability is crucial for the development of transition metal oxides in electrocatalysis. In this work, we use both X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) to investigate the electrochemical response of Mn-based perovskite oxides (La1–xCaxMnO3) under oxygen reduction reaction (ORR) conditions. This dual approach enables tracking of changes in both the oxidation state and local coordination environment. Mn Kβ XES data show that oxidation-state changes are reversible, despite a shift in transition potentials across a range of compositions, including CaMnO3. In contrast, Mn K-edge EXAFS analyses reveal that while LaMnO3 retains structural integrity, CaMnO3 undergoes irreversible structural changes at low potentials, associated with the collapse of the perovskite framework. Intermediate compositions show partially reversible structural behavior. This decoupling of redox reversibility and structural instability, a picture only accessible through the use of XAS and XES, provides critical insight into the complex behavior of these materials under operational conditions. Additionally, our analysis shows that Mn(II) formation is only detected in CaMnO3 at potentials more negative than 0.4 V (vs RHE). The ORR onset is associated with Mn(IV) reduction, while peroxide formation correlates with an increased Mn(III)/Mn(IV) ratio, supporting a 2e– + 2e– reduction pathway. This study demonstrates the power of XAS and XES analyses to disentangle electronic and structural dynamics, providing a more complete understanding of activity–stability relationships in perovskite electrocatalysts.

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