Non-Equilibrium Construction of Layered Ruddlesden–Popper La₂NiO₄ Porous Nanosheets for Efficient Urea Electrooxidation

Abstract

Urea electrooxidation offers a low-voltage pathway for hydrogen production while simultaneously addressing nitrogen-cycle remediation, yet its multi-step mechanism is kinetically hindered by sluggish C–N bond cleavage and the accumulation of strongly adsorbed intermediates. Conventional nickel-based oxides suffer from limited exposure of Ni–O active sites and slow charge redistribution, restricting overall catalytic turnover. In this study, a microwave shock strategy was developed to construct two-dimensional porous La₂NiO₄ nanosheets with a well-defined Ruddlesden–Popper (n = 2) layered structure. The ultrafast non-equilibrium synthesis generates transient supersaturation and controlled gas evolution, promoting the formation of open interlayer channels and abundant oxygen vacancies. This architecture enhances mixed ionic–electronic transport and facilitates rapid proton-coupled electron transfer during urea oxidation, yielding a low onset potential, high mass activity, and excellent durability. Mechanistic analysis reveals that the coexistence of Ni²⁺/Ni³⁺ redox couples and oxygen defects strengthens Ni 3d–O 2p hybridization, narrows the band gap, and accelerates charge redistribution. The results establish a structure–defect–activity correlation for layered nickelates and show that microwave-induced non-equilibrium synthesis provides a versatile route for designing metastable oxides. This work advances the understanding of structure-driven electrocatalysis and offers a strategic framework for future energy–environment catalytic technologies.

Keywords

2D materials / Layered Ruddlesden–Popper / microwave shock / perovskite oxide / urea oxidation

References

[1] G. Zhan, L. Hu, H. Li, et al., “Highly Selective Urea Electrooxidation Coupled With Efficient Hydrogen Evolution,” Nature Communications 15 (2024): 5918.

[2] J. Liu, S. C. Smith, Y. Gu, and L. Kou, “C─N Coupling Enabled by N─N Bond Breaking for Electrochemical Urea Production,” Advanced Functional Materials 33 (2023): 2305894.

[3] S. Fletcher, “Butler–Volmer Meets Microscopic Reversibility,” Current Opinion in Electrochemistry 37 (2023): 101199.

[4] B. Gao, X. Mu, J. Feng, et al., “Proton-Coupled Electron Transfer in Photoelectrochemical Alcohol Oxidation Enhanced by Nickel-Based Cocatalysts,” Angewandte Chemie International Edition 64 (2025): e202413298.

[5] X. Xu, H. Ullah, M. Humayun, et al., “Fluorinated Ni-O-C Heterogeneous Catalyst for Efficient Urea-Assisted Hydrogen Production,” Advanced Functional Materials 33 (2023): 2303986.

[6] T. Zhao, S. Wang, D. Ye, J. Xu, and J. Zhao, “Oxygen-Vacancy-Engineered Cr₂CO₂ Electrocatalysts for Efficient Urea Synthesis From Nitrite and Carbon Monoxide,” Applied Catalysis B: Environment and Energy 372 (2025): 125327.

[7] G. Long, L. Chen, X. Chen, et al., “Interface Engineering in Ni(OH)₂/NiOOH Heterojunction to Enhance Energy-Efficient Hydrogen Production via Urea Electrolysis,” Journal of Colloid and Interface Science 680 (2025): 880–889.

[8] C. Ji, H. Duan, C. Wang, et al., “Pairing N-Vacancy and Adjacent Ni-Sites in the Local Microenvironment to Regulate the Urea Oxidation Reaction Pathway With Enhanced Kinetics,” Advanced Materials 37 (2025): e2503879.

[9] J. Cheng, “A Nickel for Your Superconductivity,” Nature Materials 24 (2025): 1160–1161.

[10] Y. H. Wu, M. Janák, P. M. Abdala, et al., “Probing Surface Transformations of Lanthanum Nickelate Electrocatalysts During Oxygen Evolution Reaction,” Journal of the American Chemical Society 146 (2024): 11887–11896.

[11] Y. Huan, S. Chen, R. Zeng, et al., “Intrinsic Effects of Ruddlesden-Popper-Based Bifunctional Catalysts for High-Temperature Oxygen Reduction and Evolution,” Advanced Energy Materials 9 (2019): 1901573.

[12] Y. Chen, C. Lin, X. Chen, et al., “Modulating the Structure of Interlayer/Layer Matrix on δ-MnO₂ via Cerium Doping-Engineering Toward High-Performance Aqueous Zinc Ion Batteries,” Advanced Energy Materials 14 (2024): 2304303.

[13] P. Guo, S. Cao, W. Huang, et al., “Heterojunction-Induced Rapid Transformation of Ni³⁺/Ni²⁺ Sites Which Mediates Urea Oxidation for Energy-Efficient Hydrogen Production,” Advanced Materials 36 (2024): e2311766.

[14] D. Parfitt, A. Chroneos, J. A. Kilner, and R. W. Grimes, “Molecular Dynamics Study of Oxygen Diffusion in Pr₂NiO_4+δ,” Physical Chemistry Chemical Physics 12 (2010): 6834–6836.

[15] L. Wang, H. Su, G. Tan, et al., “Boosting Efficient and Sustainable Alkaline Water Oxidation on a W-CoOOH-TT Pair-Sites Catalyst Synthesized via Topochemical Transformation,” Advanced Materials 36 (2024): e2302642.

[16] Y. Li, H. Kong, J. Yan, et al., “Large-Scale Conformal Synthesis of One-Dimensional MAX Phases,” Nature Communications 9275 (2024): 15.

[17] R. Nandan, H. N. Nam, Q. M. Phung, H. Nara, J. Henzie, and Y. Yamauchi, “Mesoporous Single-Crystal High-Entropy Alloy,” Journal of the American Chemical Society 147 (2025): 18651–18661.

[18] H. Jiang, J. Xian, R. Hu, et al., “Microwave Discharge for Rapid Introduction of Bimetallic-Synergistic Configuration to Conductive Catecholate Toward Long-Term Supercapacitor,” Chemical Engineering Journal 455 (2023): 140804.

[19] G. Fang, K. Liu, M. Fan, et al., “Unveiling the Electron Configuration-Dependent Oxygen Evolution Activity of 2D Porous Sr-Substituted LaFeO₃ Perovskite Through Microwave Shock,” Carbon Neutralization 2 (2023): 709–720.

[20] M. Fan, H. Tian, Z. Wu, et al., “Microwave Shock Synthesis of Porous 2D Non-Layered Transition Metal Carbides for Efficient Hydrogen Evolution,” SusMat 5 (2025): e252.

[21] S. Xu, G. Zhong, C. Chen, et al., “Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis Through Defect Engineering,” Matter 1 (2019): 759–769.

[22] R. Hu, H. Jiang, J. Xian, et al., “Microwave-Pulse Sugar-Blowing Assisted Synthesis of 2D Transition Metal Carbides for Sustainable Hydrogen Evolution,” Applied Catalysis, B: Environmental 317 (2022): 121728.

[23] S. Liu, C. Sun, J. Chen, J. Xiao, and J.-L. Luo, “A High-Performance Ruddlesden–Popper Perovskite for Bifunctional Oxygen Electrocatalysis,” ACS Catalysis 10 (2020): 13437–13444.

[24] M. Zhang, X. Deng, M. Fu, and Z. Tao, “Sn-Doped Ruddlesden-Popper Structured LNO Oxide as an Effective Cathode for Proton-Conducting Solid Oxide Fuel Cells,” International Journal of Hydrogen Energy 92 (2024): 748–754.

[25] Z. Wu, M. Fan, H. Jiang, et al., “Harnessing the Unconventional Cubic Phase in 2D LaNiO₃ Perovskite for Highly Efficient Urea Oxidation,” Angewandte Chemie International Edition 64 (2024): e202413932.

[26] J. W. Zhao, K. Yue, L. Wu, et al., “Surface Transformation in Lanthanum Nickelate for Enhanced Oxygen Evolution Catalysis,” Angewandte Chemie-international Edition in English 64 (2025): e202507144.

[27] J. Song, D. He, X. Ma, et al., “Magnetic Field-Enhanced Acidic CO₂ Electroreduction Reaction on Single Nickel-Site Catalysts,” Journal of the American Chemical Society 147 (2025): 16198–16206.

[28] J. Wan, Z. Wu, G. Fang, et al., “Microwave-Assisted Exploration of the Electron Configuration-Dependent Electrocatalytic Urea Oxidation Activity of 2D Porous NiCo₂O₄ Spinel,” Journal of Energy Chemistry 91 (2024): 226–235.

[29] Y. Zhang, L.-F. Lin, A. Moreo, S. Okamoto, T. A. Maier, and E. Dagotto, “Electronic Structure, and Magnetic and Superconducting Pairing Tendencies of the Alternating Single Layer–Bilayer Stacking Nickelate La₅Ni₃O₁₁ Under Pressure,” Physical Review B 112 (2025): 094515.

[30] C. Zhou, W. Guo, J. Fan, et al., “Recent Advances and Future Perspectives of Ruddlesden–Popper Perovskite Oxides Electrolytes for All-Solid-State Batteries,” InfoMat 6 (2024): e12563.

[31] Z. Liu, C. Zhang, H. Liu, and L. Feng, “Efficient Synergism of NiSe2 Nanoparticle/NiO Nanosheet for Energy-Relevant Water and Urea Electrocatalysis,” Applied Catalysis, B: Environmental 276 (2020): 119165.

[32] P. Babar, A. Lokhande, V. Karade, et al., “Trifunctional Layered Electrodeposited Nickel Iron Hydroxide Electrocatalyst With Enhanced Performance Towards the Oxidation of Water, Urea and Hydrazine,” Journal of Colloid and Interface Science 557 (2019): 10–17.

[33] X. Jia, H. Kang, X. Yang, et al., “Amorphous Ni(Ⅲ)-Based Sulfides as Bifunctional Water and Urea Oxidation Anode Electrocatalysts for Hydrogen Generation From Urea-Containing Water,” Applied Catalysis, B: Environmental 312 (2022): 121389.

[34] J. Tang, Z. Li, H. Jang, et al., “Local Charge Modulation Induced the Formation of High-Valent Nickel Sites for Enhanced Urea Electrolysis,” Advanced Energy Materials 14 (2024): 2403004.

[35] S. Lu, M. Hummel, Z. Gu, et al., “Highly Efficient Urea Oxidation via Nesting Nano-Nickel Oxide in Eggshell Membrane-Derived Carbon,” ACS Sustainable Chemistry & Engineering 9 (2021): 1703–1713.

[36] Q. Xu, G. Qian, S. Yin, et al., “Design and Synthesis of Highly Performing Bifunctional Ni-NiO-MoNi Hybrid Catalysts for Enhanced Urea Oxidation and Hydrogen Evolution Reactions,” ACS Sustainable Chemistry & Engineering 8 (2020): 7174–7181.

[37] Q. N. Bian, B. S. Guo, D. X. Tan, et al., “Constructing CoNi-LDH/Fe MOF/NF Heterostructure Catalyst for Energy-Efficient OER and UOR at High Current Density,” ACS Applied Materials & Interfaces 16 (2024): 14742–14749.

[38] S. L. Fereja, Z. Zhang, Z. Fang, et al., “High-Entropy Oxide Derived From Metal-Organic Framework as a Bifunctional Electrocatalyst for Efficient Urea Oxidation and Oxygen Evolution Reactions,” ACS Applied Materials & Interfaces 14 (2022): 38727–38738.

[39] V. Maheskumar, A. Min, C. J. Moon, R. A. Senthil, and M. Y. Choi, “Modulating the Electronic Structure of Ni/NiO Nanocomposite With High-Valence Mo Doping for Energy-Saving Hydrogen Production via Boosting Urea Oxidation Kinetics,” Small Structures 4 (2023): 2300212.

[40] Y. Wang, Y. Liu, M. Zhang, B. Liu, Z. Zhao, and K. Yan, “One-Step Architecture of Bifunctional Petal-Like Oxygen-Deficient NiAl-LDHs Nanosheets for High-Performance Hybrid Supercapacitors and Urea Oxidation,” Science China Materials 65 (2022): 1805–1813.

[41] S. Lu, X. Zheng, K. Jiang, et al., “Sub-3 nm Pt₃Ni Nanoparticles for Urea-Assisted Water Splitting,” Advanced Composites and Hybrid Materials 8 (2025): 182.

[42] X. Gu, D. Yang, Z. Liu, S. Wang, and L. Feng, “Iron Oxide Promoted Nickel/Nickel Oxide Rough Nanorods for Efficient Urea Assisted Water Splitting,” Electrochimica Acta 353 (2020): 136516.

[43] Y. Liu, Y. Wang, B. Liu, M. Amer, and K. Yan, “Cobalt-Vanadium Layered Double Hydroxides Nanosheets as High-Performance Electrocatalysts for Urea Oxidation Reaction,” Acta Physico Chimica Sinica 39 (2023): 2205020–2205028.

[44] W. Liu, W. Xu, G. Dong, and M. Fang, “Controlled Fabrication of Hierarchically Structured MnO₂@NiCo-LDH Nanoarrays for Efficient Electrocatalytic Urea Oxidization,” Nanomaterials 13 (2023): 2268.

[45] H. Ze, Z. L. Yang, M. L. Li, et al., “In Situ Probing the Structure Change and Interaction of Interfacial Water and Hydroxyl Intermediates on Ni(OH)₂ Surface Over Water Splitting,” Journal of the American Chemical Society 146 (2024): 12538–12546.

[46] W. Liang, Z. Dan, X. Gong, et al., “Activating Ni via Heterostructure-Induced Electron Deficiency and Spatial Intermediate Coupling for Enhanced Alkaline HER/HOR,” Applied Catalysis B: Environment and Energy 383 (2026): 126069.

[47] K. Ye, K. Li, Y. Lu, et al., “An Overview of Advanced Methods for the Characterization of Oxygen Vacancies in Materials,” Trends in Analytical Chemistry 116 (2019): 102–108.

[48] W. Zhong, Y. Chen, P. Chen, et al., “Balancing Hydrogen Evolution and Hydrogenation Reaction via Facet Engineering for Efficient Conversion of Nitrate to Ammonia in Actual Wastewater,” Angewandte Chemie International Edition 64 (2025): e202503117.

[49] X. Wang, W. Pi, Z. Li, et al., “Orbital-Level Band Gap Engineering of RuO₂ for Enhanced Acidic Water Oxidation,” Nature Communications 16 (2025): 4845.

[50] N. Sun, Z. Zheng, Z. Lai, et al., “Augmented Electrochemical Oxygen Evolution by d-p Orbital Electron Coupling,” Advanced Materials 36 (2024): e2404772.

[51] W. Chen, L. Xu, X. Zhu, et al., “Unveiling the Electrooxidation of Urea: Intramolecular Coupling of the N-N Bond,” Angewandte Chemie International Edition 60 (2021): 7297–7307.

RIGHTS & PERMISSIONS

2026 The Author(s). Carbon Neutralization published by Wenzhou University and John Wiley & Sons Australia, Ltd.