Surface modification of Mg₃MnNi₂ hydrogen storage electrode alloy with polyaniline

In this paper, polyaniline (PANI) has been adopted to modify the surface of Mg₃MnNi₂ hydrogen storage electrode alloy prepared by induction melting via chemical deposition. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) tests were performed to investigate the phase composition and microstructure. The comprehensive analysis based on the results of XRD, SEM, TEM and FT-IR indicates that PANI with a thickness of about 10 nm has been successfully polymerized on the surface of Mg₃MnNi₂ alloy. The discharge capacity retention (R₂₀) of the Mg₃MnNi₂ alloy has been increased from 13.5% to 36.2% after modification with PANI, indicating better cycling stability. The Tafel polarization curves reveal that the surface modification of Mg₃MnNi₂ alloy with PANI can enhance its anti-corrosion ability. The increase of the exchange current density (I_o) indicates that the surface activity of Mg₃MnNi₂ alloy can be improved through the surface modification with PANI. However, the high rate discharge ability (HRD) test shows that the kinetic property of Mg₃MnNi₂ alloy after the surface modification is declined, which is mainly due to the decline of the hydrogen diffusion in PANI, evidenced by the decreased limit current density (I_L) obtained from the anodic polarization curves.