Electrochemical studies on the corrosion protection of aluminum metal in acid media by unsubstituted and 4-tetranitro substituted nickel(II) phthalocyanine inhibitors for hydrogen fuel cells

• K.D. Modibane¹, T. Pesha¹, T.C. Maponya¹, K.E. Ramohlola¹, G.R. Monama¹, M.E. Makhatha², E. Makhado¹ and M.J. Hato¹

¹ Nanotechnology Research Group, Department of Chemistry, School of Physical and Mineral Sciences, University of Limpopo (Turfloop), Sovenga 0727, Polokwane, South Africa
² Department of Metallurgy, School of Mining, Metallurgy and Chemical Engineering, Faculty of Engineering and Built Environment, University of Johannesburg (Doorfontein Campus), Johannesburg 2001, South Africa

Abstract: One of the ways to protect aluminum metal from corrosion in polymer electrolyte membrane (PEM) hydrogen fuel cells is through the use of the chemical inhibition method. In this work, we present unsubstituted (NiPc) and tetrasubstituted nickel phthalocyanines (TNNiPc) as corrosion inhibitors for aluminum (Al) metal in 1 mol·L^–1 hydrochloric acid (HCl) solution. The synthesized inhibitors were characterized using several techniques. The XRD patterns demonstrated that NiPc was more crystalline than TNNiPc (a nitro group at a peripheral position). The FTIR spectra for all the inhibitors showed a similar vibration band at around 730 cm^–1, which was due to C–H deformations. The TNNiPc inhibitor showed additional asymmetric and symmetric NO₂ vibrations around 1336 and 1525 cm^–1, respectively. The UV-vis spectrum of NiPc showed an intense Q-band at around 774 nm in 1 mol·L^–1 H₂SO₄, whereas TNNiPc resulted in a blue shift of the Q-band due to the electron-withdrawing properties of the NO₂ group. The TGA supported the presence of NO₂ by the degradation step as indicative of decomposition of NO₂ group in the TNNiPc inhibitor. Electrochemical studies showed that the inhibitors prevent Al metal sheet corrosion by adsorbing on Al surface to form a pseudo-capacitive interface. The inhibitive effect of NiPc and TNNiPc inhibitors increased with increasing concentration. Furthermore, potentiodynamic polarization measurements revealed that the dyes are mixed-type corrosion inhibitors.

Keywords: phthalocyanines inhibitor, aluminum metal, corrosion rate, electrochemical analysis

Int. J. Corros. Scale Inhib., 2021, 10, no. 1, 314-330 PDF (773 K)
doi: 10.17675/2305-6894-2021-10-1-18

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