Dual modulation of Fe–N–C catalysts via axial and in-plane heteroatoms for oxygen reduction: A combined DFT and machine learning study

Abstract

The Fe–N–C single-atom catalyst represents a promising candidate for promoting the oxygen reduction reaction (ORR), which is crucial for fuel cell applications; yet, identifying optimal modification strategies to enhance its activity and stability remains challenging. Herein, the modulation of Fe–N–C catalysts via in-plane heteroatom doping and axial coordination is systematically investigated using integrated density functional theory (DFT) and machine learning (ML) approaches. The analysis reveals that axial ligands have a more profound influence on ORR performance than in-plane dopants, primarily by modulating the Fe d_z2 orbital and weakening *OH adsorption. Through interpretable descriptors extracted from ML models, the key electronic and geometric properties governing catalyst behavior are identified, and several novel dual-modified candidates with enhanced activity relative to pristine Fe–N–C are subsequently predicted and validated by DFT calculations. This work provides a unified mechanistic and data-driven framework for accelerating the design of high-performance Fe–N–C ORR electrocatalysts.

Graphical abstract

Keywords

Fe–N–C single-atom catalyst / oxygen reduction reaction (ORR) / axial ligands / density functional theory (DFT)

References

[1] Chen N J , Wang H H , Kim S P . et al. Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells. Nature Communications, 2021, 12(1): 2367

[2] Jiao K , Xuan J , Du Q . et al. Designing the next generation of proton-exchange membrane fuel cells. Nature, 2021, 595(7867): 361–369

[3] Nørskov J K , Rossmeisl J , Logadottir A . et al. Origin of the overpotential for oxygen reduction at a fuel-cell cathode. The Journal of Physical Chemistry B, 2004, 108(46): 17886–17892

[4] Qiao B T , Wang A Q , Yang X F . et al. Single-atom catalysis of CO oxidation using Pt₁/FeO_x. Nature Chemistry, 2011, 3(8): 634–641

[5] Huang B Y , Huang S H , Lu C B . et al. Decrypting the influence of axial coordination on the electronic microenvironment of Co–N₅ site for enhanced electrocatalytic reaction. CCS Chemistry, 2023, 5(8): 1876–1887

[6] Liu M H , Zhang J , Su H . et al. In situ modulating coordination fields of single-atom cobalt catalyst for enhanced oxygen reduction reaction. Nature Communications, 2024, 15(1): 1675

[7] Liu W G , Zhang L L , Liu X . et al. Discriminating catalytically active FeN_x species of atomically dispersed Fe–N–C catalyst for selective oxidation of the C–H bond. Journal of the American Chemical Society, 2017, 139(31): 10790–10798

[8] Liu S W , Li C Z , Zachman M J . et al. Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells. Nature Energy, 2022, 7(7): 652–663

[9] Huang S Q , Qiao Z L , Sun P P . et al. The strain induced synergistic catalysis of FeN₄ and MnN₃ dual-site catalysts for oxygen reduction in proton-/anion-exchange membrane fuel cells. Applied Catalysis B: Environmental, 2022, 317: 121770

[10] Shang N Z , Wang C , Zhang X Y . et al. Atomically dispersed iron on nitrogen-decorated carbon for high-performance oxygen reduction and zinc–air batteries. Chemical Engineering Journal, 2021, 426: 127345

[11] He T , Lu B Z , Chen Y . et al. Nanowrinkled carbon aerogels embedded with FeN_x sites as effective oxygen electrodes for rechargeable zinc–air battery. Research, 2019, 2019: 6813585

[12] Xia T , Wang X F , Wan J W . et al. Asymmetrically coordinated single-atom catalysts: From synthetic strategy to structure–activity relationship. Chemical Synthesis, 2025, 5: 74

[13] Mao Z L , Fu Y , Long X Y . et al. Carbon-based materials for electrocatalytic energy conversion: From understanding to designing. Chemical Synthesis, 2025, 5: 68

[14] Lin X Y , Lin D L , Zhang W W . et al. Molecular iron phthalocyanines anchoring onto ZIF-67-derived cobalt-carbon nanomaterials as bifunctional oxygen catalysts. Frontiers in Energy, 2025, 19(6): 1037–1044

[15] Chang H , Guo Y F , Liu X . et al. Dual MOF-derived Fe/N/P-tridoped carbon nanotube as high-performance oxygen reduction catalysts for zinc–air batteries. Applied Catalysis B: Environmental, 2023, 327: 122469

[16] Liu J , Zhu J Q , Xu H X . et al. Rational design of heteroatom-doped Fe–N–C single-atom catalysts for oxygen reduction reaction via simple descriptor. ACS Catalysis, 2024, 14(9): 6952–6964

[17] Zhang H W , Chen H C , Feizpoor S . et al. Tailoring oxygen reduction reaction kinetics of Fe–N–C catalyst via spin manipulation for efficient zinc–air batteries. Advanced Materials, 2024, 36(25): 2400523

[18] Tian H , Song A L , Zhang P . et al. High durability of Fe–N–C single-atom catalysts with carbon vacancies toward the oxygen reduction reaction in alkaline media. Advanced Materials, 2023, 35: 2210714

[19] Wu Y J , Wang X Y , Tian B B . et al. Optimizing reaction intermediate adsorption by engineering the coordination structure of single-atom Fe–N₅–C electrocatalysts for efficient oxygen reduction. Inorganic Chemistry Frontiers, 2023, 10(14): 4209–4220

[20] Hu L Y , Dai C L , Chen L W . et al. Metal-triazolate-framework-derived FeN₄ Cl₁ single-atom catalysts with hierarchical porosity for the oxygen reduction reaction. Angewandte Chemie International Edition, 2021, 60(52): 27324–27329

[21] Liu J , Ye Q , Wu Y . et al. Short-range electronic engineering by coupling Fe phthalocyanines with MOF-derived N,S-doped carbon nanorods for oxygen reduction. Science China Chemistry, 2025, 68(5): 1859–1868

[22] Sun J , Fang Y H , Liu Z P . Electrocatalytic oxygen reduction kinetics on Fe-center of nitrogen-doped graphene. Physical Chemistry Chemical Physics, 2014, 16(27): 13733–13740

[23] Hu X , Chen S Y , Chen L T . et al. What is the real origin of the activity of Fe–N–C electrocatalysts in the O₂ reduction reaction? Critical roles of coordinating pyrrolic N and axially adsorbing species. Journal of the American Chemical Society, 2022, 144(39): 18144–18152

[24] Yan H M , Wang G , Lv X M . et al. Revealing the potential-dependent rate-determining step of oxygen reduction reaction on single-atom catalysts. Journal of the American Chemical Society, 2025, 147(4): 3724–3730

[25] Qiao J Y , Lu C J , Kong L Q . et al. Spin Engineering of Fe─N─C by axial ligand modulation for enhanced bifunctional oxygen catalysis. Advanced Functional Materials, 2024, 34(51): 2409794

[26] Zhang W L , Meeus E J , Wang L . et al. Boosting electrochemical oxygen reduction performance of iron phthalocyanine through axial coordination sphere interaction. ChemSusChem, 2022, 15(3): e202102379

[27] Peng L S , Yang J , Yang Y Q . et al. Mesopore-rich Fe–N–C catalyst with FeN₄-O-NC single-atom sites delivers remarkable oxygen reduction reaction performance in alkaline media. Advanced Materials, 2022, 34(29): 2202544

[28] Liu J Q , Chen W B , Yuan S . et al. High-coordination Fe–N₄SP single-atom catalysts via the multi-shell synergistic effect for the enhanced oxygen reduction reaction of rechargeable Zn–air battery cathodes. Energy & Environmental Science, 2024, 17(1): 249–259

[29] Li L B , Huang S H , Cao R . et al. Optimizing microenvironment of asymmetric N,S-coordinated single-atom Fe via axial fifth coordination toward efficient oxygen electroreduction. Small, 2022, 18(2): 2105387

[30] Li B , Shi C S , Zhao N Q . et al. Hydrogen-bond-promoted ORR mechanism in P-doped Fe–N–C materials. The Journal of Physical Chemistry C, 2023, 127(2): 1023–1031

[31] Liu Y R , Liu X J , Lv Z H . et al. Tuning the spin state of the iron center by bridge-bonded Fe–O–Ti ligands for enhanced oxygen reduction. Angewandte Chemie, 2022, 134(21): e202117617

[32] Fung V , Hu G X , Wu Z L . et al. Descriptors for hydrogen evolution on single atom catalysts in nitrogen-doped graphene. The Journal of Physical Chemistry C, 2020, 124(36): 19571–19578

[33] Ding R , Ma M , Chen Y W . et al. Inspecting design rules of metal-nitrogen-carbon catalysts for electrochemical CO₂ reduction reaction: From a data science perspective. Nano Research, 2023, 16(1): 264–280

[34] Sun H , Li Y Z , Gao L Y . et al. High throughput screening of single atomic catalysts with optimized local structures for the electrochemical oxygen reduction by machine learning. Journal of Energy Chemistry, 2023, 81: 349–357

[35] Minotaki M G , Geiger J , Ruiz-Ferrando A . et al. A generalized model for estimating adsorption energies of single atoms on doped carbon materials. Journal of Materials Chemistry A, 2024, 12(18): 11049–11061

[36] Lu R H , Quan C X , Zhang C Y . et al. Establishing a theoretical insight for penta-coordinated iron-nitrogen-carbon catalysts toward oxygen reaction. Nano Research, 2022, 15(7): 6067–6075

[37] Wang J L , Zhang K N , Nga T T T . et al. Chalcogen heteroatoms doped nickel-nitrogen-carbon single-atom catalysts with asymmetric coordination for efficient electrochemical CO₂ reduction. Chinese Journal of Catalysis, 2024, 64: 54–65

[38] Zhu H Y , Gan X , McCreary A . et al. Heteroatom doping of two-dimensional materials: From graphene to chalcogenides. Nano Today, 2020, 30: 100829

[39] Liang W , Chen J X , Liu Y W . et al. Density-functional-theory calculation analysis of active sites for four-electron reduction of O₂ on Fe/N-doped graphene. ACS Catalysis, 2014, 4(11): 4170–4177

[40] Kresse G , Furthmüller J . Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Computational Materials Science, 1996, 6(1): 15–50

[41] Blöchl P E . Projector augmented-wave method. Physical Review B, 1994, 50(24): 17953–17979

[42] Perdew J P , Burke K , Ernzerhof M . Generalized gradient approximation made simple. Physical Review Letters, 1996, 77(18): 3865–3868

[43] Grimme S , Antony J , Ehrlich S . et al. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. The Journal of Chemical Physics, 2010, 132(15): 154104

[44] Grimme S , Ehrlich S , Goerigk L . Effect of the damping function in dispersion corrected density functional theory. Journal of Computational Chemistry, 2011, 32(7): 1456–1465

[45] Yang X , Xia D S , Kang Y Q . et al. Unveiling the axial hydroxyl ligand on Fe-N₄-C electrocatalysts and its impact on the pH-dependent oxygen reduction activities and poisoning kinetics. Advanced Science, 2020, 7(12): 2000176

[46] Mou Y M , Gao S R , Wang Y . et al. Axial coordination engineering on Fe–N–C materials for oxygen reduction: Insights from theory. Chemistry—A European Journal, 2024, 30(69): e202402869

[47] Umer M , Umer S , Zafari M . et al. Machine learning assisted high-throughput screening of transition metal single atom based superb hydrogen evolution electrocatalysts. Journal of Materials Chemistry A, 2022, 10(12): 6679–6689

[48] Pedregosa F , Varoquaux G , Gramfort A . et al. Scikit-learn: Machine learning in Python. The Journal of Machine Learning Research, 2011, 12: 2825–2830

[49] Ouyang R H , Curtarolo S , Ahmetcik E . et al. SISSO: A compressed-sensing method for identifying the best low-dimensional descriptor in an immensity of offered candidates. Physical Review Materials, 2018, 2(8): 083802

[50] Lundberg S M, Lee S I. A unified approach to interpreting model predictions. In: Proceedings of the 31st International Conference on Neural Information Processing Systems, Long Beach, USA, 2017, 4768–4777

[51] Zhou Y N , Sheng L , Chen L L . et al. Axial coordinated iron-nitrogen-carbon as efficient electrocatalysts for hydrogen evolution and oxygen redox reactions. Chinese Chemical Letters, 2025, 36(1): 109588

[52] Chen X , Zhang Y Z , Zhao X Y . et al. Effect of the axial halogen ligand on the oxygen reduction reaction performance of transition metal–nitrogen–carbon catalysts. The Journal of Physical Chemistry C, 2023, 127(29): 14107–14116

[53] Lu Y , Li Z , Cheng H . et al. d-band center regulation facilitated by asymmetrical ligand in the atomically dispersed iron site toward promoting oxygen electrocatalysis activities. ACS Applied Materials & Interfaces, 2025, 17(17): 25299–25311

[54] Sabatier P. La Catalyse en Chimie Organique. Paris et Liège: Béranger, 1913

[55] Tao X F , Lu R H , Ni L M . et al. Facilitating the acidic oxygen reduction of Fe–N–C catalysts by fluorine-doping. Materials Horizons, 2022, 9(1): 417–424

[56] Bai J S , Guan X , Qu H S . et al. Multiscale structure regulation induced by fluorine coordination enables high-performance and durable PEMFC. ACS Energy Letters, 2025, 10(6): 2743–2751

[57] Gao R , Qiu Z Y , Xu K . et al. Fluorine-decorated high loading Fe–N–C electrocatalysts for proton exchange membrane fuel cells. Journal of Materials Chemistry A, 2023, 11(47): 26044–26051

RIGHTS & PERMISSIONS

Higher Education Press