Catalytic impact of alloyed Al on the corrosion behavior of Co₅₀Ni₂₃Ga₂₆Al₁.₀ magnetic shape memory alloy and catalysis applications for efficient electrochemical H₂ generation
2017
Amin, Mohammed. A. | El-Bagoury, Nader | Mahmoud, M. H. H. | Hessien, M. M. | Abd El-Rehim, Sayed S. | Wysocka, Joanna | Ryl, Jacek
The electrochemical and corrosion behaviour of Co₅₀Ni₂₃Ga₂₇₋ₓAlₓ (x = 0 and 1.0 wt%) magnetic shape memory alloys (MSMAs) was studied in 0.5 M NaCl solutions using various electrochemical techniques. Results showed remarkable activation of the tested MSMA toward pitting corrosion upon alloying it with Al. XPS examination confirmed the activation influence of alloyed Al. It proved that the presence of Al in the alloy's matrix weakens its passivity, as manifested by a lower amount of gallium oxides and Cl⁻ adsorption in the aluminium containing MSMA sample. Alloyed Al also activated significantly the tested MSMA for the hydrogen evolution reaction (HER), as indicated by cathodic polarization, electrochemical impedance spectroscopy (EIS), and faradaic efficiency (FE) measurements. Such measurements were performed in 0.1 M KOH solutions and showed that the Co₅₀Ni₂₃Ga₂₆Al₁.₀ alloy is much more active for the HER than Co, Ni, Co₅₀Ni₅₀, and Co₅₀Ni₂₃Ga₂₇ electrodes. The catalytic impact of pitting corrosion, proved to be catalyzed by Al, on the HER activity of the CoNiGaAl alloy was also studied. The pitted Co₅₀Ni₂₃Ga₂₆Al₁.₀ MSMA, the best catalyst here, exhibited high HER catalytic performance with an exchange current density (jₒ) of 0.2 mA cm⁻² and FE 96%, and thus approached Pt/C (jₒ = 0.6 mA cm⁻² and FE ∼ 100%). Our best catalyst also showed good stability and durability after 3000 cycles of cathodic polarization between the corrosion potential (Ecₒᵣᵣ) and −1.0 V vs. RHE, and 24 h of electrolysis at a high cathodic current density of 100 mA cm⁻². Microstructure changes made by Al, together with findings obtained from SEM/EDX mapping and XPS studies, were used to interpret its activation influence towards the HER.
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