No abstract

This study has been conducted for investigating the contribution of polyaniline (PANI) to the electroactivity of nickel hydroxide (NH) by using a combination of electrochemical, structural and morphological characterization techniques. NH, PANI and nickel hydroxide/PANI composite (NHP) electrodes were produced on nickel foam substrates. Electrodeposition and chemical bath deposition methods were used for the preparation of NH and PANI, respectively. All the electrochemical experiments were conducted in alkaline solutions. NH and PANI were used as reference materials and exhibited properties in accordance with the literature. Namely, for NH electrode capacity decayed by cycling because of the phase transformation from α to β-Ni(OH) 2 , and particles growth from 350 to 850 nm. Also, flower-like structure of the as prepared Ni(OH) 2 faded after 2000 cycles. On the other hand, PANI electrode although exhibited a decrease in the conductivity because of its degradation retained its capacity over cycling because of swelling and shrinking that led to an increased surface area. Composite electrode consisting of PANI and NH resulted in an improvement of capacity retention. At the beginning of cycling capacitance of the composite electrode was 0.64 F/cm 2 , capacity decreased to 0.47 F/cm 2 after 500 cycles then, continuously increased and finally reached to 0.54 F/cm 2 after 2000 cycles. Presence of PANI in combination with NH, limited the particle growth and contributed to the preservation of flower like structure of NH. Contrary to both NH and PANI electrodes, charge transfer resistance of NHP exhibited a decrease with cycling indicating a synergy between NH and PANI in addition to morphological changes.

We examined the unusual passive character of Hybrid steel in de-aerated sulfuric acid and aqueous sodium chloride solutions by benchmark corrosion and surface analytical tests in combination with CalPhaD-based thermochemical modelling. The electrochemical potentiodynamic polarization measurements have shown that Hybrid steel possesses all characteristic features of what makes steel stainless, such as passivity, breakdown and pitting, similar to standard low-alloyed stainless steel. Synchrotron hard X-ray photoelectron spectroscopy (HAXPES) analysis revealed that the stainless nature of Hybrid steel is achieved by a dynamically protective nanometre-sized passive film consisting of Fe, Cr, Ni, and Al oxides. The thermodynamic calculations showed that the surface oxide composition is Fe2O3•FeCr2O4•NiO•Al2O3, which changes structure, fraction and existence over electrochemical polarization. It has become understood that the presence of Al and Ni supports Cr in forming a spontaneously passive and hence protective surface, yielding exceptional corrosion resistance in acidic and chloride-containing aqueous solutions. The surface oxide could withstand breakdown and remain passive/repassivated even after transpassing the Cr(III)-to-Cr(VI) redox potential. While Cr is the prime passivating agent, an adverse effect of Cr was seen on grade 304 and 420 stainless steel when Cr(VI) species were released, savaging the passive film due to extensive interfacial pH reduction. However, among all tested stainless steels, Hybrid steel could repassivate due to the remaining and enriching Al and Ni oxides providing superior anodic passivation. Our work demonstrates that delicate alloying and microstructure engineering can design sustainable stainless steel with optimum high-strength properties without needing the well-known Cr threshold concentration of 10.5 per cent.

The inherent defective morphology of the physical vapor deposition (PVD) hard coatings limits their corrosion protective ability. We examined the impact of nitride‐based PVD coatings, including TiN, TiAlN, and CrN deposited on inert substrates by cathodic arc PVD method (CA‐PVD), on the galvanic corrosion of carbon steel. Their contribution was evaluated by zero‐resistance ammeter (ZRA) and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl at pH 2 and 6, with and without aeration. The results indicated the prominent role of the coating type and the coupling environment on the generated galvanic currents. Immersion tests for the TiN‐, TiAlN‐, and CrN‐coated steel cross‐sections visually verified these results. The galvanic current contribution was distinct in environments where oxygen reduction is the dominant cathodic reaction. However, the layers' contribution to galvanic corrosion was minimal in deaerated acidic solutions, which is attributed to the high bonding strength of adsorbed intermediates to the coating surfaces.