The stability of inhibiting layers on AA2024-T3 intermetallic particles (IMPs) during re-immersion in saline following an initial immersion in a Ce(III)-containing electrolyte was investigated using in situ reflected light microscopy. Re-immersion behaviour varied due to differences in IMP composition, spatial distribution, and Ce(III) precipitation. IMPs were grouped into four categories based on whether their activity was high or low during both the immersion and re-immersion stages. Majority of the high activity particles during re-immersion had low activity during immersion. Longer immersion times (up to 72 h) and a brief delay in inhibitor supply (30 s) reduced re-immersion activity by increasing Ce(III) coverage. These findings suggest that corrosion protection systems promoting greater Ce(III) precipitation may enhance re-immersion stability.

There is no denying that the world is heading towards an era powered by green energy resources. The need for highly efficient devices for sustainable energy storage and utilization is vital in transitioning towards the full-time realization of renewable energy for our society. In the last four decades, there have been groundbreaking developments in the large-scale commercialization of Li-ion batteries, electric vehicles, and solar power, all made possible by an in-depth understanding of the science of materials. Theoretically, there exists no problem in the production of green hydrogen, as oxides of Ir, Rh, and Pt, and the elements themselves, are excellent catalysts for the electrochemical hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with fast kinetics. Thus, more work remains to be done in the area of green energy material technology. The problem lies with the critical availability and cost of these materials, which is the underlying motivation for finding alternative energy materials and technologies. This energy transition era presents us with an opportunity to expand our horizons and knowledge in chemical engineering, materials science, and allied fields through two-dimensional (2D) nanomaterials. These materials exhibit intriguing characteristics in contrast to their bulk counterparts, coupled with interchangeable electronic properties depending on the synthesis methodologies employed. The chapter begins by introducing the family of graphene nanosheets and expands into a discussion of advanced 2D families, such as transition metal dichalcogenides (TMDs), MXenes, transition metal oxides (TMOs), and hexagonal boron nitride (h-BN).

Chromium coatings, famed for their superior wear and corrosion resistance, are a critical component in countless industrial processes. However, the longevity of these coatings in aggressive corrosive environments continues to be a significant hurdle, even with recent advances in deposition technology and microstructural improvements. An advanced thin dense chromium (TDC) coating, with a near-nanocrystalline structure and unique morphology, naturally forms a non-conductive nano-bilayer oxide. This passive and protective layer effectively moderates electrical charge transfer, offering superior corrosion resistance. X-ray photoelectron spectroscopy (XPS) shows significant Cr³⁺ oxide layer formation, distinguished by multiplet splitting, after 7 days in a 0.6 M NaCl solution. The unique characteristics of this non-conductive bilayer oxide structure promote its growth and densification, leading to vertical differential charging in the O1s electron energy region. This effect arises from the enhanced resistivity of the oxide layer. Electrochemical impedance spectroscopy (EIS) confirmed these findings, showing a substantial increase in charge transfer resistance at the chromium metal/bilayer oxide interface, reaching 1.01 MΩ. Scanning Kelvin probe force microscopy (SKPFM) analysis shows that both TDC nodules and their boundaries exhibit high surface potential and work function. However, after exposure to NaCl media, these values are moderately reduced, likely due to diminished electrical surface charge distribution.

The search for non-toxic alternatives to hexavalent chromium based corrosion inhibitors requires a comprehensive understanding of the factors critical to effective corrosion protection. Key considerations include the evolution of corrosion inhibition with inhibitor concentrations and exposure times, the inhibition efficacy in the presence and following absence of inhibitors, and the stability of inhibition upon polarisation. In our electrochemical comparison of promising organic molecules with sodium dichromate, we found that even top-performing candidates can lead to premature conclusions if such critical factors are overlooked. While organic molecules can match the inhibition performance of chromates under specific conditions, this can be misleading when considering concentration, time, and polarisation dependent behaviour. Initial high performance can also be deceptive in dynamic environments, as we observed that the inhibition provided by most organic molecules drastically decreases when the inhibitor is absent in the electrolyte. These observations call for broader comprehensive inhibitor robustness studies that take into account factors including time, concentration, stability, and polarisation effects in inhibitor efficacy analysis.

Eliminating hexavalent chromium-based corrosion inhibitors from structural aircraft coatings remains a significant challenge, primarily due to the lack of reliable accelerated test methods. This study evaluates the performance of various structural aircraft coatings under different exposure conditions, i.e. outdoor exposure, cyclic salt spray testing and in-service conditions, supplemented by environmental sensors. Quarterly inspections and scanning electron microscopy were used to evaluate corrosion damage. The findings highlight a lack of correlation between accelerated testing and outdoor exposure testing, likely driven by disparities in salt deposition, UV-radiation, time of wetness and temperature cycling. Additionally, galvanic couples between skin and fasteners remain difficult to protect, with chromate-based systems offering limited inhibition and alternative systems struggling to protect such complex assemblies. However, in lap-joints, alternative coatings outperformed chromate-based counterparts, likely due to their polymer matrices providing improved barrier properties, hence limiting access of electrolyte to the coating-aluminium alloy interface.

Chromium-based functional coatings (CFCs) are widely recognized for their outstanding wear and corrosion resistance across diverse industrial sectors. However, despite advancements in deposition techniques and microstructural enhancements, many contemporary CFCs remain vulnerable to degradation in highly corrosive environments. For the first time, this research delivers a thorough characterization of the corrosion resistance of advanced CFCs, focusing on the performance of a 5 μm thin dense chromium (TDC) coating. These TDCs exhibit a distinctive, uniform nodular microstructure, characterized by approximately 3.6 μm nodules composed of defect-free near-nanocrystalline grains (227 ± 75 nm) plus enhanced electrochemical nobility. This structure promotes the rapid formation of a stable, dense bilayer oxide, resulting in a remarkably low corrosion susceptibility, effectively impeding both charge transfer and mass transport, particularly the diffusion of Cl^- ions. Furthermore, the coating sustains an exceptionally high polarization resistance over extended exposure times in aqueous NaCl electrolyte. These findings offer critical insights into the design of CFCs optimized for extreme environmental durability.

The dream corrosion inhibitor would work for every substrate–environment combination, and the protection would be sustained indefinitely with an irreversible barrier layer when exposed to aggressive and changing environmental conditions. However our prior electrochemical experiments on AA2024-T3 have shown that despite the initial inhibition, all of the tested molecules had reversible bonds that limit their inhibition performance and applicability in dynamic environments, with the exception of 3-amino-1,2,4-triazole-5-thiol, which still showed 42% inhibition efficiency after being exposed to 0.1M NaCl only for three days. To our knowledge, this is the first mechanistic study that explains the origin of such quasi-sustained inhibition by an organic molecule under dynamic and aggressive conditions relevant to aerospace alloys. Potentiodynamic polarization, atomic force microscopy and scanning Kelvin probe force microscopy (AFM/SKPFM), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) complemented by density functional theory (DFT) calculations were used to identify the molecular mechanism responsible for the quasi-stable adsorption provided by 3-amino-1,2,4-triazole-5-thiol. Our findings suggest that a sulphatization of the Al-(hydr)oxide is the key contributor to the quasi-sustained corrosion inhibition. Sustained molecule adsorption over intermetallics in trace amounts was also observed, but their presence was insufficient to inhibit corrosion.

In the search for effective high-tech materials for energy conversion and storage devices, spinel-structured nickel ferrite (NiFe₂O₄) has been identified as a promising anode material for lithium-ion batteries (LIBs). However, the influence of different morphologies and surface properties of NiFe₂O₄ nanoparticles on battery performance is hardly addressed. To understand the effect of different morphologies and surface properties on the lithium-ion storage performance, NiFe₂O₄ nanoparticles were synthesized through four different synthesis conditions: NFO-S, NFO-U, NFO-G, and NFO-C. The formation of polycrystalline inverse spinel NiFe₂O₄ was confirmed through XRD, FTIR, and Raman spectroscopy. The morphologies of the obtained samples were studied using FESEM, and it was found that the four different synthesis conditions employed here enabled us to obtain NiFe₂O₄ with four different morphologies. The surface chemistry, surface area and porosity of the NiFe₂O₄ samples were respectively characterized using XPS and BET. The electrochemical performance of the four NiFe₂O₄ samples as anode material was studied by fabricating lithium-ion half-cells. NiFe₂O₄ sample obtained from surfactant-free synthesis condition (NFO-S) displayed a high initial discharge and charge capacity of 2258 mAh/g and 1815 mAh/g, respectively at the current density of 100 mA/g. Even after 100 cycles, NFO-S showed a better discharge capacity of 116 mAh/g at the current density of 100 mA/g, compared to the other samples studied here. The observed higher capacity of the NFO-S sample is attributed to the higher surface area (40.8 m²/g) and pore volume (0.190 cm³/g). The NiFe₂O₄ sample prepared with cationic CTAB surfactant (NFO-C) showed better cyclic stability with a stable coulombic efficiency of 98.5% at the 100th cycle, mainly attributed to its nanocube morphology with lower surface area (16.1 m²/g) and pore volume (0.087 cm³/g).

This research provides detailed insights into the correlation of microstructural and morphological characteristics of a Cr/CrN multilayer coating deposited onto steel and its corrosion behavior, by examining its local surface electronic properties, nanomechanical behavior, and electrochemical activity in a 3.5 % NaCl solution. A key focus of the study is the influence of physicochemical surface evolution on nano-mechanical properties of Cr/CrN coating. This is investigated by correlating electrochemical data from electrochemical impedance spectroscopy (EIS) with findings from X-ray photoelectron spectroscopy (XPS) and nanoindentation analysis. The integrated approach shed light on physicochemical evolution of the coating, and its resistance to corrosion in demanding environments.

The development of advanced catalysts with innovative nanoarchitectures is critical for addressing energy and environmental challenges such as the electrochemical CO₂ reduction reaction (CO₂ RR). Herein, the synthesis of an innovative copper–sulfur planar structure, Cu–S–BDC, within a metal–organic framework (MOF) catalyst is presented, which demonstrates 100% selectivity toward formate as the sole carbon product. Structural analysis and surface characterizations reveal that Cu–S–BDC exhibits quasi-2D inorganic building units, with Cu bonded to two S-CH (Formula presented.) groups and one BDC linker, while carboxylate groups adopt a bridging coordination mode. This unique arrangement not only imparts remarkable structural stability but also enhances the electronic properties of the MOF, as evidenced by a narrow bandgap of 1.203 eV that facilitates efficient charge transfer and increased electrochemical current density in CO (Formula presented.) RR. Notably, it offers a Faradaic efficiency of 92% for formate at an overpotential as low as −0.4 V versus the reversible hydrogen electrode (RHE) in an aqueous electrolyte of 1 m KOH, as well as a current density of −25.8 mA cm² at −0.9 V versus RHE, averaged over 24 h of electrolysis. This study highlights a fresh perspective in the field of MOF electrocatalysts by demonstrating that engineering the metal coordination environment can significantly enhance the electronic properties and consequently improve the electrocatalytic performance of these materials.

NiTi alloys, widely used for their shape memory and superelastic properties, face corrosion challenges when fabricated via laser powder bed fusion (LPBF). This study investigates the dual-phase formation in LPBF NiTi and its impact on corrosion resistance. Thermal simulations and microstructural analysis reveal that thermal stress drives martensite formation near melt pool boundaries. Martensitic regions act as anodic sites, leading to localized corrosion. Optimizing LPBF parameters produced single-phase [001]-textured NiTi, eliminating martensite and significantly reducing the corrosion current by almost two orders of magnitude and enhancing superelastic performance simultaneously. These findings highlight texture control as a key strategy to improve corrosion resistance and functionality for advanced applications.

A 2D finite element model is developed to simulate the protection of active protective coatings in a defect. The leaching kinetics, inhibitor-electrolyte reactions and electrochemical surface reactions on homogenized AA2024-T3, are considered. Changes in local oxygen distribution, pH, and current density over time are validated using surface scanning micro-probe techniques. The limitations posed by the prediction of surface current density at the metal interface using a FEM model with a homogenized microstructure are identified and addressed. The validated FEM is then used to predict inhibitor concentration and pH dependent on the initial inhibitor pigment concentration in an organic coating.

Medical devices contribute to the carbon footprint generated by the healthcare sector. The development of implants and biomaterials using recycled waste materials promotes sustainable advances in tissue engineering. Additively manufactured (AM) bone-substituting biomaterials with multifunctional properties, e.g., biodegradability, antibacterial and osteogenic potential, can contribute to sustainable healthcare. Biodegradable biomaterials eliminate secondary surgeries to remove implants, reduce post-surgical complications, and enhance patient recovery, thus decreasing the energy usage and waste associated with medical treatments. Herein, we present porous iron (Fe) scaffolds incorporating 20 vol% waste-derived eggshell particles for bone substitution. The Fe-eggshell scaffolds were fabricated using direct ink writing (DIW) technique and underwent post-AM heat treatment. During sintering, the eggshell's main component – CaCO₃, transformed into CaO. Atomic diffusion between α-Fe and CaO phases resulted in the formation of Ca₂Fe₂O₅ phase at the interface. The scaffolds were 70 % porous and displayed a biodegradation rate of 0.11 mm/year. The mechanical properties were comparable to trabecular bone and the scaffolds endured 3 million loading cycles at 0.7σ_y in r-SBF. The scaffolds showed apatite-forming ability, evidenced by the formation of (carbonaceous) hydroxyapatite, which are conducive to preosteoblast adhesion, proliferation, and differentiation. RT-qPCR analysis confirmed the osteogenic potential of the specimens as evidenced by the upregulated expression of osteopontin and osteocalcin as compared to Ti6Al4V controls. Furthermore, the scaffolds exhibited bactericidal activity (>3.9-log CFU reduction) against methicillin-sensitive and multidrug-resistant strains of Staphylococcus aureus and delayed their biofilm formation. Our research showcases the exceptional multifunctionality of DIW Fe-eggshell composite scaffolds for the sustainable development of orthopedic biomaterials. Statement of significance: We aim to improve the biofunctionalities and sustainability of biodegradable bone substitutes, by developing the extrusion-based 3D printed porous Fe composite scaffolds containing eggshell-derived CaO bioceramics. Our results demonstrated that Fe-eggshell scaffolds exhibited hydroxyapatite-forming ability in simulated body fluid, having mechanical properties in the range of trabecular bone even after 4 weeks biodegradation, supported the proliferation of preosteoblasts and upregulated the expression of osteogenic genes. Moreover, the scaffolds were bactericidal against methicillin-sensitive and multi-drug resistant strains Staphylococcus aureus and delayed their biofilm formation.

The targeted removal of efficient but toxic corrosion inhibitors based on hexavalent chromium has provided an impetus for discovery of new, more benign organic compounds to fill that role. Developments in high-throughput synthesis of organic compounds, the establishment of large libraries of available chemicals, accelerated corrosion inhibition testing technologies, the increased capabilities of machine learning (ML) methods, and a better understanding of mechanisms of inhibition provide the potential to make discovery of new corrosion inhibitors faster and cheaper than ever before. These technical developments in the corrosion inhibition field are summarized herein. We describe how data-driven machine learning methods can generate models linking molecular properties to corrosion inhibition that can be used to predict the performance of materials not yet synthesized or tested. The literature on inhibition mechanisms is briefly summarized along with quantitative structure–property relationships models of small organic molecule corrosion inhibitors. The success of these methods provides a paradigm for the rapid discovery of novel, effective corrosion inhibitors for a range of metals and alloys, in diverse environments. A comprehensive list of corrosion inhibitors tested for various substrates that was curated as part of this review is accessible online https://excorr.web.app/database and available in a machine-readable format.

The pursuit of scalable and efficient electrode materials is essential for advancing lithium-ion battery (LIB) technologies. Among the anode candidates, spinel-structured ZnMn2O4 (ZMO) is attractive due to its high theoretical capacity (∼1008 mAhg−1), environmental friendliness, and cost-effectiveness. However, large volume expansion during lithium insertion/extraction and poor electrical conductivity limit its long-term performance. Conventional ZMO nanostructure synthesis involves complex, multi-step processes requiring high-temperature calcination, making them time-consuming and unsuitable for large-scale production. To overcome these challenges, we developed a rapid, one-pot microwave-assisted hydrothermal synthesis technique to fabricate a ZnMn2O4/α-MnO2 (ZMO/α-MO) nanocomposite. This method reduces processing time and enables in-situ formation of a mixed morphology. The composite consists of nano-polyhedral ZnMn2O4 integrated with 1D α-MnO2 nanowires, which buffer volume changes and enhance structural stability during cycling. The synergistic architecture improves electron transport, reduces lithium-ion diffusion paths, and provides superior mechanical resilience. Electrochemical results showed that the ZMO/α-MO nanocomposite as an anode material in the Li half-cell delivered a high discharge capacity of 891.6 mAhg−1 at 100 mAg−1 after 100 cycles. The electrode exhibited stable cycling across varying current densities and self-adaptive capacity recovery at different rates. These performance enhancements are attributed to improved reaction kinetics enabled by its porous structure, high surface area, and controlled volume expansion of ZMO nanoparticles composited with α-MnO2 nanowires. This green, scalable, and time-saving synthesis strategy offers promising potential for next-generation high-performance LIBs.

The discovery of synergistic strategies effectively improves the corrosion inhibition capability of amino acids. However, the wide variety of amino acid formulations and the time-consuming nature of corrosion tests make combinatorial discovery challenging to achieve. Herein, a library of 70 amino acids was created and tested in a high-throughput manner. Benefiting from a vast amount of labeled data of amino acid formulations, an interpretable machine learning approach was used to reveal the contribution of molecular features to inhibition performance of amino acids and the synergisms in the optimal formulation. The synergism was verified by electrochemical tests and quantum chemical calculations.

Mg and its alloys are promising biodegradable materials for orthopedic implants and cardiovascular stents. The first interactions of protein molecules with Mg alloy surfaces have a substantial impact on their biocompatibility and biodegradation. We investigate the early-stage electrochemical, chemical, morphological, and electrical surface potential changes of alloy WE43 in either 154 mM NaCl or Hanks’ simulated physiological solutions in the absence or presence of bovine serum albumin (BSA) protein. WE43 had the lowest electrochemical current noise (ECN) fluctuations, the highest noise resistance (Zn = 1774 Ω·cm2), and the highest total impedance (|Z| = 332 Ω·cm2) when immersed for 30 min in Hanks’ solution. The highest ECN, lowest Zn (1430 Ω·cm2), and |Z| (49 Ω·cm2) were observed in the NaCl solution. In the solutions containing BSA, a unique dual-mode biodegradation was observed. Adding BSA to a NaCl solution increased |Z| from 49 to 97 Ω·cm2 and decreased the ECN signal of the alloy, i.e., the BSA inhibited corrosion. On the other hand, the presence of BSA in Hanks’ solution increased the rate of biodegradation by decreasing both Zn and |Z| while increasing ECN. Finally, using scanning Kelvin probe force microscopy (SKPFM), we observed an adsorbed nanolayer of BSA with aggregated and fibrillar morphology only in Hanks’ solution, where the electrical surface potential was 52 mV lower than that of the Mg oxide layer.

The substitution of chromate-containing structural coating systems in aviation with alternatives complying with nowadays strict environmental, health and safety regulations remains a formidable challenge. This complexity is partly due to the absence of a standardized from-test-to-market methodology, including a performance comparison between chromate-containing and alternative coating systems. To address this gap, the present study delves into the identification of crucial degradation factors that merit inclusion in such a methodology. Concurrently, it investigates the protective mechanisms inherent in chromate-containing coating systems and proposes improvements that can be applied to alternative coating systems. This study entails a comprehensive post-service examination of the degradation of paint applied to an aircraft component with over 35 years of service, employing electrochemical, microscopic and spectroscopic techniques. The findings underscore the role of thermo-oxidation as a significant degradation factor in the aging process of such coatings. Furthermore, the investigation elucidates a notable phenomenon in which aluminium ions within the coating pores form an aluminium hydroxide gel onto which chromate adsorbs. This process contributes to an increase in pore resistance upon exposure to electrolyte, leading to a self-healing barrier effect within the coating. Remarkably, this self-healing mechanism continues to offer long-term protection even when the coating matrix is sub-optimally cured due to application errors. Furthermore, this study reveals that the significant changes in capacitance during immersion testing result primarily from inhibitor leaching, emphasizing the effectiveness of combining Electrochemical Impedance Spectroscopy (EIS) with Scanning Electron Microscopy (SEM) analysis for studying coating degradation.