Synergistic Doping Effects of Y3+ and Co3+ on the Electrochemical Hydrogen Storage Property of Nanosized La1–xYxFe0.80Co0.20O3 as the Anode in Ni-MH Batteries

Abstract

As one of the important ways to obtain electrochemical hydrogen storage, nickel–metal hydride batteries (Ni-MH) play an increasingly crucial role in the field of energy storage/conversion technology and will greatly enhance the strategic position of hydrogen energy in the energy market. However, with the development of modern society, the disadvantages of poor cycling stability and low discharge capacity at high temperatures that existed for the Ni-MH batteries have severely hindered their development. To solve these drawbacks, improving the stability and discharge capacity of the batteries has immense research values. In this work, Y³⁺ and Co³⁺ ions codoped nanosized La_1–xY_xFe_0.80Co_0.20O₃ (x = 0, 0.04, 0.08, 0.12, 0.16, 0.20) solid solutions were synthesized via the sol–gel method. X-ray diffraction pattern (XRD) indicates that the grain sizes and cell volumes of samples are reduced. Scanning and transmission electron microscopy (SEM, TEM) results reveal that the agglomeration degrees of the codoped samples are evidently alleviated, and the crystallite sizes are refined and distributed uniformly. Ultraviolet absorption spectra (UV–vis) indicate that the band gap energies of the doped samples are decreased. Raman spectra confirm that the addition of Y³⁺ ions enhances the content of the oxygen vacancies and defects in the lattices of samples. Electrochemical hydrogen storage results manifest that the electrochemical and the kinetic properties of the codoped samples are improved obviously. The maximum discharge capacity of the Y_0.12Co_0.20 sample reaches 464.7 mAh/g at 333 K and exhibits the most outstanding kinetic properties. H₂-TPR analysis illustrates that the catalyzed reaction activities of the codoped samples are significantly strengthened, and the hydrogen absorption capacity of the Y_0.12Co_0.20 sample is the highest. It is analyzed that the synergistic doping effects of the two ions, the concentrations of the oxygen vacancies and defects, the capabilities of the electron transition, and the grain sizes are the main factors that affect the hydrogen storage performance of the samples.