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• Investigation of native and passive surface films formed on Ni-20 at.% Cr alloy surfaces. • Surface analysis by in situ electrochemical measurements combined with advanced ex situ surface analysis. • Mechanistic understanding of the effects of high-temperature hydrogen annealing pretreatment. • Enhanced corrosion resistance of electrochemically passivated surface by high-temperature hydrogen annealing pretreatment. • Increase in Cr enrichment of initially weakly protected sites of the inner barrier layer. The effect of high-temperature annealing under hydrogen gas (H 2) surface preparation on a binary polycrystalline Ni-20 at.% Cr alloy was investigated in comparison with conventional mechanical grinding surface preparation. Duplex surface films with inner Cr(III) oxide and outer Ni(II) and Cr(III) hydroxide layers natively formed before and after H 2 annealing were characterized by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thinner and less homogeneous inner barrier layer formed after H 2 annealing caused an oxidation peak at the active/passive transition in the linear sweep voltammetry measurement in a 0.5 M H 2 SO 4 solution. Despite this high oxidation peak, passivation of the H 2 annealed surface resulted in the formation of a more corrosion resistant inner layer than on the mechanically ground surface, as demonstrated by electrochemical impedance spectroscopy. The corrosion resistant passive film formation of the H 2 annealed surface is attributed to the increased Cr enrichment of the inner layer caused by the selective Ni dissolution providing corrosion resistance to the initially weakly protected sites of the natively formed surface film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal pre-oxidation effects on passive film properties studied on stainless steel. • Combined surface analytical and electrochemical approach applied with closed transfer. • Thermal pre-oxidation improves corrosion resistance at active/passive transition. • Thermal pre-oxidation promotes the enrichment of molybdenum and chromium. • Thermal pre-oxidation enhances growth of the inner layer after anodic passivation. A combined X-ray photoelectron spectroscopy, time-of-fight secondary ion mass spectrometry and electrochemical approach was used to investigate the mechanisms of molybdenum and chromium enrichment of a passive film formed on a model austenitic stainless steel single crystal in aqueous acid media and the effect that thermal pre-oxidation at 250 ° C plays in the composition, thickness and stratification of the film. A clean FeCrNiMo (1 0 0)-oriented surface, prepared under ultra-high vacuum (UHV), was exposed to ultra-low pressures of oxygen at 250 ° C, forming a thin oxide film, rich in iron and chromium, as well as containing molybdenum. An argon-filled glovebox, directly attached to the UHV system, allowed for electrochemical alterations to be carried out without exposure to ambient air. After being held at open circuit potential for 30 min, hydroxylation of chromium and molybdenum was promoted, with a marked enrichment of both elements in the oxide film. A distinct bilayer film was observed. Anodic polarisation resulted in a significant growth of the inner layer and further enrichment of chromium. Pre-oxidation at 250 ° C, using an ultra-low pressure of oxygen, was found to promote protection against transient active dissolution during anodic passivation, and to cause enrichment of molybdenum in the outer layer of the passive film. [ABSTRACT FROM AUTHOR]

• PANI coating on mildsteel is reported in sodium-potassium tartrate (Na-K Tartrate) and benzoic acid in alcohol-water (BAW) system. • A new composition of the BAW system is optimized and used for aniline polymerization for the first time. • The PANI coating formed in Na-K Tartrate and BAW electrolyte is a pore-free, compact, and fine-grained nanostructured. • The new electrolyte systems do not show an anodic peak during the cathodic scan indicates superior cyclic stability. Polyaniline (PANI) is extensively researched as a corrosion protection coating for mild steel (MS) against acidic and neutral media. Corrosion inhibition performance of PANI coating on MS depends on the electrolytic solution employed for polymerization. In this study, the electropolymerization of aniline onto MS using sodium potassium tartrate (Na-K tartrate) and benzoic acid in the alcohol-water (BAW) medium is reported. The composition of BAW system was optimized and used for electropolymerization of aniline for the first time. The results showed the formation of a passive yet electro-conductive layer before the polymerization initiated. A compact layer with a fine structured PANI coating in both media was obtained. Cyclic voltammetry (CV) produced a stable PANI coating without showing anodic current in the cathodic scan. The concentration of aniline and electrolytes were optimized for better coating conditions. The prepared PANI coating was characterized by Fourier-transform infrared (FTIR) spectroscopy, Ultraviolet-visible (UV–vis) spectroscopy, Scanning electron microscope (SEM) in combination with energy dispersion spectrometer (EDX) and X-ray diffractometer (XRD). The results of PANI coating in Na-K tartrate and BAW medium are compared with a standard PANI coating prepared in oxalic acid medium. The inhibition efficiencies of PANI coating obtained in Na-K tartrate and BAW were estimated to be 82.5 % and 99.99 %, respectively in 0.1 M NaCl solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work explores MXene and cobalt oxide nanoparticle composites for supercapacitors. • The Co@MXene- composite exhibits a specific capacitance of 732.5 F g−1 at 1 A g−1. • The ASC device (Co@MXene-2//AC) demonstrates a maximum energy density of 26.6 Wh Kg−1 at 700 W Kg−1 power density. • Hierarchical MXene/transition metal oxide composite enhances electrochemical performance for energy storage. The 2D layered material, MXene has incited a lot of interest in energy storage research due to its high metallic conductivity, high hydrophilicity, high energy storage capability, biocompatibility, and excellent electrochemical activity due to rich surface chemistry. However, the restacking of MXene layers lowers the number of active sites in MXene, which in turn limits the use of MXene in supercapacitors. Furthermore, the narrow working potential window of MXene limits the energy density of the electrodes. To address these issues and improve the electrochemical performance of MXene, several hierarchical MXene/transition metal oxide composites have been synthesized and characterized. This work explores MXene and its composites with cobalt oxide nanoparticles for supercapacitor applications. The Co@MXene composite was synthesized by using a one-pot hydrothermal method. As prepared, the nanocomposite exhibited a specific capacitance of 732.5 F g−1 at 1 A g-1 current density and excellent cycling stability of 83% over 5000 cycles. The as-fabricated ASC device (Co@MXene-2//AC) demonstrates the maximum energy density of 26.6 Wh Kg−1 at 700 W Kg−1 power density. The above results illustrate that MXene/transition metal oxide nanocomposite can be an alternative to enhance electrochemical performance for energy storage applications. [ABSTRACT FROM AUTHOR]

The incorporation of conjugated polyelectrolytes as cathode interlayers in organic photovoltaics has been proven to be an effective way to boost the device efficiency. Nevertheless, more detailed investigations of the structure–property relationships of these interlayer materials, in particular related to the film deposition behavior, can provide further insights into their mode of action. With this aim, a series of ionic (co)polythiophenes is successfully synthesized via Kumada catalyst-transfer condensation polymerization and subsequent introduction of ionic moieties on the polymer side chains. Both the topology (i.e. homopolymers, random and block copolymers) and the amount of ionic groups are systematically varied. The polymers are fully characterized and then applied as cathode interlayers in polymer solar cells based on PCDTBT:PC 71 BM, affording an average efficiency increase of ∼15%. The structural screening on one hand indicates that the efficiency gain is a rather general phenomenon for this material class. On the other hand, the best photovoltaic responses are observed for the conjugated polyelectrolytes with a higher triethylene glycol side chain ratio and the block copolymer structure performs slightly better as compared to the random copolymer with the same (50/50) monomer ratio. Based on these findings, the field can move on to a more rational development of novel interfacial materials and thereby push the device efficiency even further. [ABSTRACT FROM AUTHOR]

• Simplistic correlations between molecular parameters and corrosion inhibition efficiencies critically evaluated. • 24 heterocyclic organic compounds tested as corrosion inhibitors for Cu in 3 wt.% NaCl aqueous solution. • None among usually considered molecular parameters correlates with inhibition efficiency. • Pros and cons of the inhibition efficiency (IE) metric discussed: IE suffers from nonlinearity. • Inhibition power proposed as a new metric for evaluating the performance of corrosion inhibitors. The often used simplistic correlations between molecular electronic parameters and experimentally determined corrosion inhibition efficiencies are critically evaluated for a set of 24 heterocyclic organic compounds, tested as corrosion inhibitors for copper in 3 wt.% NaCl aqueous solution. Twelve different molecular electronic descriptors—such as ionization potential, electron affinity, HOMO–LUMO gap, dipole moment—are tested and it is shown that none of them displays any noticeable correlation with the inhibition efficiency. Our results, therefore, cast serious doubt on reported correlations between such parameters and inhibition efficiency, obtained for only a few inhibitors, which are abundant in the literature. We also discuss some pros and cons of inhibition efficiency as a metric for evaluating the performance of corrosion inhibitors, and introduce a new metric termed inhibition power that uses the universal logarithmic scale and dimensionless decibel (dB) units. [ABSTRACT FROM AUTHOR]