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Figure 1. 

Schematic diagram of the synthesis of NiO/Fe₃O₄@LCFs.

Figure 2. 

Structural and elemental characterization of NiO/Fe₃O₄@LCFs: (a), (b) Low and high magnification SEM images of NiO/Fe₃O₄@LCFs; (c)–(g) TEM image, HRTEM image of NiO/Fe₃O₄@LCFs; (h) Electron diffraction pattern of NiO/Fe₃O₄@LCFs; (i) EDS elemental mapping images of C, N, O, Fe, and Ni elements.

Figure 3. 

Structural and physicochemical properties of the catalysts: (a) XRD patterns; (b) Raman spectra; (c) Specific surface area of Fe₃O₄@LCFs, NiO/Fe₃O₄@LCFs; (d) Pore size distribution of Fe₃O₄@LCFs, NiO/Fe₃O₄@LCFs.

Figure 4. 

XPS analysis of the surface composition and chemical states of NiO@LCFs, Fe₃O₄@LCFs, and NiO/Fe₃O₄@LCFs: (a) survey scan spectra; (b) Fe 2p; (c) Ni 2p; (d) C 1s; (e) N 1s; (f) O 1s.

Figure 5. 

Electrochemical properties of NiO@LCFs, Fe₃O₄@LCFs, and NiO/Fe₃O₄@LCFs: (a) LSV curves; (b) Overpotential required at j = 10, 50, and 100 mA cm⁻²; (c) Tafel plots; (d) Nyquist plots; (e) Scan rate as a function of ECSA of bilayer capacitance; (f) Stability of Fe₃O₄@LCFs and NiO/Fe₃O₄@LCFs at a current density of 100 mA cm⁻².

Figure 6. 

Mechanistic insights into the enhanced OER activity via in situ spectroscopy and DFT calculations. (a) In situ Raman spectrum of the OER on NiO/Fe3O4@LCFs in 1.0 M KOH; (b) Density of states onto Fe and Ni 3d orbitals for NiO/Fe₃O₄@LCFs; (c) Adsorption energies of H₂O and O₂ on Fe₃O₄@LCFs and NiO/Fe₃O₄@LCFs; (d) Gibbs free energy change diagram of Fe₃O₄@LCFs, and NiO/Fe₃O₄@LCFs during the OER process; (e) The pCOHP plot of the O–OH bond after OOH adsorbs on Fe₃O₄@LCFs and NiO/Fe₃O₄@LCFs; (f) Interface configuration of NiO/Fe₃O₄@LCFs at four different stages during the OER.