Mn-O bond regulated Fe spin state in FePc/MnO2 heterojunction for efficient oxygen reduction reaction

Min Jiang; Yibo Wang; Yilin Han; Xichen Shao; Ruiqi Cheng; Jiao Zhang; Chaopeng Fu

doi:10.1016/j.cej.2026.174649

Mn-O bond regulated Fe spin state in FePc/MnO₂ heterojunction for efficient oxygen reduction reaction

Min Jiang
, Yibo Wang
, Yilin Han
, Xichen Shao
, Ruiqi Cheng
, Jiao Zhang
, Chaopeng Fu^*

^*Corresponding author for this work

Department of Physics

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

4 Citations (Scopus)

Abstract

Accelerating the sluggish kinetics of the electrocatalytic oxygen reduction reaction (ORR) is critical for enhancing the performance of fuel cells and metal-air batteries. Herein, we design FePc/MnO₂ heterojunctions supported on α-MnO₂ and β-MnO₂, aiming to modulate the spin state of Fe centers via the Mn-O framework to activate the synergy of electron delocalization and spin polarization.

EXAFS and Fe L-edge soft X-ray absorption spectroscopy (sXAS) reveal that β-MnO₂ shortens the Fe-N bond length, inducing a spin state transition of Fe from the intermediate-spin (MS) Fe(II) in pristine FePc (I_eg/I_t2g = 1.0) to low-spin (LS) Fe³⁺ (I_eg/I_t2g = 1.18, 0.29 eV blue shift of the Fe L3 edge). In contrast, α-MnO₂ only reduces the I_eg/I_t2g ratio to 0.89 without obvious spin transition. Electron spin resonance (ESR) confirms that FePc/β-MnO₂ loses the MS signature (g_ms = 4.28) observed in pristine FePc and FePc/α-MnO₂, instead exhibiting a prominent LS Fe³⁺ feature (g_z = 2.44).

Benefiting from the β-MnO₂-induced MS → LS transition and enhanced interfacial electronic coupling, FePc/β-MnO₂ delivers superior ORR activity with a half-wave potential of 0.87 V vs. RHE in alkaline media (outperforming commercial Pt/C at 0.86 V). Its aluminum-air battery achieves a peak power density of 151 mW cm⁻², demonstrating great practical potential. This work establishes a crystal-phase engineering strategy for modulating Fe spin states via Mn-O interactions, providing insights for developing high-performance iron-based electrocatalysts.

© 2026 Elsevier B.V.

Original language	English
Article number	174649
Number of pages	10
Journal	Chemical Engineering Journal
Volume	533
Online published	26 Feb 2026
DOIs	https://doi.org/10.1016/j.cej.2026.174649
Publication status	Published - 1 Apr 2026

Funding

This work was supported by the National Natural Science Foundation of China (No. 52304332), Shanghai Science and Technology Committee (No. 22ZR1429700), and project funded by China Postdoctoral Science Foundation (2022M712092). The authors thank the BL08U1A in the Shanghai Synchrotron Radiation Facility (SSRF) for help with characterization.

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 7 Affordable and Clean Energy

Research Keywords

Electronic structure
Iron phthalocyanine
Manganese dioxide
Oxygen reduction reaction
Single atom catalyst
Spin state regulation

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@article{1a243ca1608246d0916f47e94fe7ba4c,

title = "Mn-O bond regulated Fe spin state in FePc/MnO2 heterojunction for efficient oxygen reduction reaction",

abstract = "Accelerating the sluggish kinetics of the electrocatalytic oxygen reduction reaction (ORR) is critical for enhancing the performance of fuel cells and metal-air batteries. Herein, we design FePc/MnO2 heterojunctions supported on α-MnO2 and β-MnO2, aiming to modulate the spin state of Fe centers via the Mn-O framework to activate the synergy of electron delocalization and spin polarization. EXAFS and Fe L-edge soft X-ray absorption spectroscopy (sXAS) reveal that β-MnO2 shortens the Fe-N bond length, inducing a spin state transition of Fe from the intermediate-spin (MS) Fe(II) in pristine FePc (Ieg/It2g = 1.0) to low-spin (LS) Fe3+ (Ieg/It2g = 1.18, 0.29 eV blue shift of the Fe L3 edge). In contrast, α-MnO2 only reduces the Ieg/It2g ratio to 0.89 without obvious spin transition. Electron spin resonance (ESR) confirms that FePc/β-MnO₂ loses the MS signature (gms = 4.28) observed in pristine FePc and FePc/α-MnO₂, instead exhibiting a prominent LS Fe3+ feature (gz = 2.44). Benefiting from the β-MnO2-induced MS → LS transition and enhanced interfacial electronic coupling, FePc/β-MnO2 delivers superior ORR activity with a half-wave potential of 0.87 V vs. RHE in alkaline media (outperforming commercial Pt/C at 0.86 V). Its aluminum-air battery achieves a peak power density of 151 mW cm−2, demonstrating great practical potential. This work establishes a crystal-phase engineering strategy for modulating Fe spin states via Mn-O interactions, providing insights for developing high-performance iron-based electrocatalysts. {\textcopyright} 2026 Elsevier B.V.",

keywords = "Electronic structure, Iron phthalocyanine, Manganese dioxide, Oxygen reduction reaction, Single atom catalyst, Spin state regulation",

author = "Min Jiang and Yibo Wang and Yilin Han and Xichen Shao and Ruiqi Cheng and Jiao Zhang and Chaopeng Fu",

year = "2026",

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T1 - Mn-O bond regulated Fe spin state in FePc/MnO2 heterojunction for efficient oxygen reduction reaction

AU - Jiang, Min

AU - Wang, Yibo

AU - Han, Yilin

AU - Shao, Xichen

AU - Cheng, Ruiqi

AU - Zhang, Jiao

AU - Fu, Chaopeng

PY - 2026/4/1

Y1 - 2026/4/1

N2 - Accelerating the sluggish kinetics of the electrocatalytic oxygen reduction reaction (ORR) is critical for enhancing the performance of fuel cells and metal-air batteries. Herein, we design FePc/MnO2 heterojunctions supported on α-MnO2 and β-MnO2, aiming to modulate the spin state of Fe centers via the Mn-O framework to activate the synergy of electron delocalization and spin polarization. EXAFS and Fe L-edge soft X-ray absorption spectroscopy (sXAS) reveal that β-MnO2 shortens the Fe-N bond length, inducing a spin state transition of Fe from the intermediate-spin (MS) Fe(II) in pristine FePc (Ieg/It2g = 1.0) to low-spin (LS) Fe3+ (Ieg/It2g = 1.18, 0.29 eV blue shift of the Fe L3 edge). In contrast, α-MnO2 only reduces the Ieg/It2g ratio to 0.89 without obvious spin transition. Electron spin resonance (ESR) confirms that FePc/β-MnO₂ loses the MS signature (gms = 4.28) observed in pristine FePc and FePc/α-MnO₂, instead exhibiting a prominent LS Fe3+ feature (gz = 2.44). Benefiting from the β-MnO2-induced MS → LS transition and enhanced interfacial electronic coupling, FePc/β-MnO2 delivers superior ORR activity with a half-wave potential of 0.87 V vs. RHE in alkaline media (outperforming commercial Pt/C at 0.86 V). Its aluminum-air battery achieves a peak power density of 151 mW cm−2, demonstrating great practical potential. This work establishes a crystal-phase engineering strategy for modulating Fe spin states via Mn-O interactions, providing insights for developing high-performance iron-based electrocatalysts. © 2026 Elsevier B.V.

AB - Accelerating the sluggish kinetics of the electrocatalytic oxygen reduction reaction (ORR) is critical for enhancing the performance of fuel cells and metal-air batteries. Herein, we design FePc/MnO2 heterojunctions supported on α-MnO2 and β-MnO2, aiming to modulate the spin state of Fe centers via the Mn-O framework to activate the synergy of electron delocalization and spin polarization. EXAFS and Fe L-edge soft X-ray absorption spectroscopy (sXAS) reveal that β-MnO2 shortens the Fe-N bond length, inducing a spin state transition of Fe from the intermediate-spin (MS) Fe(II) in pristine FePc (Ieg/It2g = 1.0) to low-spin (LS) Fe3+ (Ieg/It2g = 1.18, 0.29 eV blue shift of the Fe L3 edge). In contrast, α-MnO2 only reduces the Ieg/It2g ratio to 0.89 without obvious spin transition. Electron spin resonance (ESR) confirms that FePc/β-MnO₂ loses the MS signature (gms = 4.28) observed in pristine FePc and FePc/α-MnO₂, instead exhibiting a prominent LS Fe3+ feature (gz = 2.44). Benefiting from the β-MnO2-induced MS → LS transition and enhanced interfacial electronic coupling, FePc/β-MnO2 delivers superior ORR activity with a half-wave potential of 0.87 V vs. RHE in alkaline media (outperforming commercial Pt/C at 0.86 V). Its aluminum-air battery achieves a peak power density of 151 mW cm−2, demonstrating great practical potential. This work establishes a crystal-phase engineering strategy for modulating Fe spin states via Mn-O interactions, providing insights for developing high-performance iron-based electrocatalysts. © 2026 Elsevier B.V.

KW - Electronic structure

KW - Iron phthalocyanine

KW - Manganese dioxide

KW - Oxygen reduction reaction

KW - Single atom catalyst

KW - Spin state regulation

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DO - 10.1016/j.cej.2026.174649

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