Electrospinning Machine | One-dimensional porous MnCo2O4/CF nanofibers prepared by electrospinning as efficient bifunctional electrocatalyst for Li–O2 batteries

Amid the global energy crisis and increasing environmental pressures, developing high-energy-density, long-life energy storage technologies has become a core task for the scientific research community. Li–O2 batteries, with their ultra-high theoretical energy density of 3500 Wh·kg‒1, are regarded as a "potential candidate" in the next generation of energy storage.However, their commercialization is hindered by the slow kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).

Recently, a team led by Teacher Wu Haitao and Professor Dong Yanmao from the School of Chemistry and Life Sciences at Suzhou University of Science and Technology published important research findings titled "One-dimensional porous MnCo2O4/CF nanofibers prepared by electrospinning as efficient bifunctional electrocatalyst for Li–O2 batteries" in the "Journal of Energy Storage". The researchers prepared one-dimensional porous MnCo2O4/carbon nanofiber (MnCo2O4/CF) composite material by combining carbon nanofibers (CF) with MnCo2O4 spinel via electrospinning technology, achieving dual regulation of structure and composition. Its core advantage lies in the uniform distribution of MnCo2O4 nanoparticles within the carbon nanofibers, where the interfacial coupling interaction between the two synergistically enhances their catalytic activity for ORR/OER, demonstrating good bifunctional catalytic activity. The innovative value of this research lies not only in the performance breakthrough but also in proposing a catalyst design concept of "in-situ composite of spinel oxide-carbon material" – achieving dual regulation of structure and composition through electrospinning technology, maximizing the synergistic effect between active sites (MnCo2O4) and the conductive network (CF), effectively addressing the inherent defects of single-component catalysts.

Figure 1: Morphology of MnCo2O4 electrospun precursor before and after calcination.

The MnCo2O4/CF electrospun precursor before calcination exhibits slender and uniform fibrous morphology (Figure 1a-b), with a diameter of approximately 300-500 nm; after calcination at 400 °C in an air atmosphere, the fibers shrink due to the rapid carbonization of the polyvinylpyrrolidone (PVP) template, resulting in a final diameter reduced to 150-200 nm, while maintaining a complete fibrous structure without significant breakage or agglomeration.

Figure 2: Physical performance characterization of MnCo2O4

TEM characterization (Figure 2a-b) further reveals the microstructural features of the MnCo2O4/CF nanofibers: the average fiber diameter is approximately 181 nm, and variations in surface brightness indicate the presence of an internal mesoporous structure. This structure originates from the escape of gases generated during the carbonization of PVP in the calcination process, which can provide channels for subsequent ion diffusion and oxygen transport.

Figure 3: Crystal structure, pore structure and surface chemical state characterization of MnCo2O4/CF nanofibers

As shown in Figure 3a, the characteristic peaks of MnCo₂O₄ in MnCo₂O₄/CF show a significant shift to higher angles compared to the standard JCPDS card (No. 23-1237). This is due to the interfacial interaction between MnCo₂O₄/CF and CF, which induces a lattice compression effect. This effect enhances atomic binding force, suppresses dislocation movement, not only improves the structural strength and stability of the material, but also modulates the surface electronic structure, laying the foundation for subsequent enhancement of catalytic activity.

Figure 4: Catalytic performance characterization of MnCo2O4/CF electrode and its comparison electrodes in 0.1 M KOH solution

In an aqueous electrolyte (0.1 M KOH), MnCo₂O₄/CF showed a reduction peak potential of 0.696 V in CV tests. Furthermore, the ORR polarization curve (Figure 4b) exhibited a large limiting current density (–5.30 mA cm⁻²), and the OER LSV polarization curve showed a low overpotential (460 mV), which are superior to those of the individual MnCo₂O₄ NP and CF electrodes (Figure 4e), demonstrating that MnCo₂O₄/CF possesses good bifunctional catalytic activity.

Figure 5: Electrochemical performance characterization of MnCo2O4/CF cathode in Li–O2 battery

As an oxygen cathode catalyst for Li–O₂ batteries, MnCo₂O₄/CF exhibits excellent electrochemical performance. At a current density of 200 mA g⁻¹, its maximum discharge capacity reaches 6611.2 mAh g⁻¹ with an overpotential as low as 1.24 V; at 400 mA g⁻¹, it can stably cycle for 251 cycles, and after 300 cycles, the discharge terminal voltage remains above 2.34 V. The excellent electrochemical performance of the MnCo₂O₄/CF nanofibers originates from the synergistic effect of structure and composition: the one-dimensional porous structure provides efficient transport channels for O₂ and Li⁺, while maximizing the exposure of active sites; simultaneously, the interfacial coupling between MnCo₂O₄ and CF reduces electron/ion transport resistance, inhibits the agglomeration of MnCo₂O₄ particles, and enhances the catalytic activity of the composite material.

Figure 6: Surface morphology changes of MnCo2O4/CF cathode before and after initial cycle

Furthermore, after the initial discharge, disc-shaped Li₂O₂ discharge products appeared on the surface of the MnCo₂O₄/CF cathode (Figure 6c). This disc-like morphology not only benefits the increase of discharge capacity but also provides a clear reaction interface for subsequent charging decomposition. After charging, the surface disc-shaped discharge products almost completely decompose, demonstrating good electrode reversibility.

In summary, the in-situ coupling between manganese-cobalt spinel (MnCo₂O₄) and carbon nanofibers (CF) constructs continuous ion/electron transport pathways, effectively combining the bifunctional catalytic activity of MnCo₂O₄ with the excellent conductivity of carbon nanofibers. The prepared material exhibits good ORR and OER bifunctional catalytic activity, while also demonstrating excellent electrode reversibility and lithium-oxygen battery performance. This study, through dual regulation of the material's structure and compositional elements, provides a new paradigm for the in-situ composite of spinel oxides and carbon materials, and also opens a new path for preparing high-performance bifunctional catalytic electrode materials for lithium-oxygen batteries.

Paper link: https://doi.org/10.1016/j.est.2025.118082