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Pitting corrosion is one of the most dangerous forms of corrosion, leading to sudden catastrophic failures in engineering systems. Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film. Here the ORR kinetics on conventional and high Cr content FeCr alloys made by arc-melter were investigated by experimental and computational methods. Density functional theory calculations suggested that the overpotentials for the ORR on FeCr oxides are in the order Cr2O3 > Fe3O4 > Fe2O3 > FeCr2O4, which was experimentally confirmed on the FeCr alloys by rotating disc electrode experiments in both O2 saturated 0.1 M NaOH and 3.5 wt% NaCl. Koutecky-Levich analysis demonstrated that ORR follows a 4-electron pathway on all surfaces investigated. Moreover, the investigation of the Pourbaix diagrams of FeCr revealed that at potentials where pitting corrosion initiates the main constituents of the passive films should be a mixture of Fe2O3 and Cr2O3, rather than FeCr2O4, which is proved to be a good ORR catalyst. The results support the postulation that one role Cr additions play in the prevention of pitting corrosion is to suppress the ORR reaction.

Thin film corrosion is a serious issue in almost every sector. Thus, simulation of corrosion under thin electrolyte films has always been of high interest as experimental studies are often challenging. Thus far, progress has been made to model the effect of several important factors on thin film corrosion rates. Some of these parameters are electrolyte thickness, electrolyte composition, chemical reactions in the electrolyte, electrode size and change in electrode size, environmental parameters, and corrosion products deposition. However, these parameters are mainly drawn from different studies and have not been modelled concurrently in a single simulation study, making the thin film corrosion model far from being complete yet. Therefore, despite the many efforts so far, thin film corrosion modelers still strive to push the modelling edges further. This paper takes into account some of the highlighted recent advances in thin film corrosion modelling based on the mentioned parameters to provide a perspective on not only how far the field has come, but also how far it still is from a complete thin film corrosion model. Discussions have also been made on future needs and prospects to advance the thin film corrosion models further.

Developing inexpensive, noble metal-free, efficient, stable, and bifunctional electrocatalysts has attracted significant research interest in electrocatalysis and air battery-based energy storage d...

In ferrous alloys, chromia (Cr2O3) and hematite (Fe2O3) could serve as impervious passive layers to protect metals from corrosion. However, their passivating effect becomes questionable when locali...

Rechargeable batteries and supercapacitors are currently considered as promising electrochemical energy storage (EES) systems to address the energy and environment issues. Self-supported transition metal (Ni, Co, Mn, Mo, Cu, V)-based materials are promising electrodes for EES devices, which offer highly efficient charge transfer kinetics. This review summarizes the latest development of transition metal-based materials with self-supported structures for EES systems. Special focus has been taken on the synthetic methods, the selection of substrates, architectures and chemical compositions of different self-supported nanoarrays in energy storage systems. Finally, the challenges and opportunities of these materials for future development in this field are briefly discussed. We believe that the advancement in self-supported electrode materials would pave the way towards next-generation EES.

Volta potential measurements from Scanning Kelvin Probe Force Microscopy (SKPFM) have been used over the years to discuss the nobility of an alloy’s surface and its tendency to localised corrosion. This has led to classical interpretations that may (unfortunately) over-generalise the actual Volta potential behaviour of the surface during ongoing localised corrosion. Consequently, issues on correlating Volta potential measurements to corrosion potentials and mechanisms arise. With the advent of in-situ SKPFM, which allows for the Volta potential measurements during ongoing dynamic surface electrochemical and/or physicochemical reactions, novel observations regarding Volta potential evolution are available. This calls for an updated and re-evaluated interpretation of the Volta potential measurements from SKPFM relating to localised corrosion analysis. The novel interpretation includes an additional layer of information, as compared to classical interpretations; there is greater information on the role of interfacial parameters and time (kinetics). Optimistically, this will bridge the gap of Volta potential measurements and its correlation to corrosion potentials.

In this work, three dimensional self-supported Co3O4@Ni3S2 nanowire arrays on nickel foam substrates are prepared by a multi-step method. The as-synthesized product harvests the advantages of the high electrical conductivity of the Co3O4 nanowire arrays, large surface area provided by the Ni3S2 nanosheets, and the efficient ion diffusion pathway offered by the self-supported structure. The sample is subsequently used as the electrode material for supercapacitors, at a current density of 2 mA cm−2 a charge storage capability of 2.41C cm−2 (5.5 F cm−2) was achieved. When the sample is charged and discharged at 50 mA cm−2 for 10000 cycles, a stable capacity of 0.86C cm−2 (1.5 F cm−2) can still be maintained at the end of the test. Such a performance is better than those values reported in the literature obtained with similar systems even at a lower current density. We also assemble an asymmetric supercapacitor by pairing the Co3O4@Ni3S2 nanoarrays with activated carbon, and it shows good cyclability over 10000 cycles. The device yields energy densities of 65 and 32.3 Wh kg−1 at power densities of 361 and 9090 W kg−1, respectively. Furthermore, it is able to light up 12 red light-emitting diodes, showing promising potential for practical applications.

The evolution of corrosion products that develop within the scratched region of a 96 wt% zinc-rich paint exposed to continuous salt spray for 1,000 h has been investigated by both electrochemical a...

Many previous simulations of the plastic deformation in metallic glasses showed that shear banding is the dominant mode accompanied by Voronoi volume continuous generation and softening. In the present work, we report a contrary phenomenon where Voronoi volume recovery is dominant during plastic deformation in CuZr metallic glasses under tension. By creating a notched geometry, the deformation mode of notched samples transits from shear banding to necking due to the introduction of triaxial stress state. With the suppressing of shear banding, a notch strengthening and structure ordering phenomenon together with the recovery of Cu-centered full-icosahedra fraction are also observed. The present work enriches our understanding on the mechanical behavior and deformation mechanism of metallic glasses.

Economical electro-catalysts for the oxygen reduction reaction (ORR) are highly desirable for a range of advance energy storage technologies. Chromium compounds have been suggested as one possible source of non-precious metal based catalysts for oxygen reduction reaction (ORR), especially chromia (Cr2 O3 ) which is the most stable form of Cr oxide at room temperature. Using density functional theory+U calculations, we investigate the 4-electron ORR on the hydroxylated Cr2 O3 surfaces alloyed with 17 different transition metals. On the one hand, we find that the ORR overpotential is lower when the Cr2 O3 surface alloyed with elements towards the end of both the first and second rows of transition metals. Among these elements, Cd alloyed Cr2 O3 surface is found to promote the ORR the most, but due to its high toxicity and price it loses out to Zn as the recommended alloyant. On the other hand, we find that the ORR overpotential is generally higher and less varied on the Cr2 O3 surface alloyed with the early-to-mid row transition metal elements (e. g. Zr, Ti). As Cr2 O3 is also a major component in the passive film on stainless steels, where a low ORR rate is desirable to reduce the impact of localized corrosion. This implies that alloying with early-to-mid row transition elements could be beneficial to stainless steels. The difference in oxygen reduction activity is attributed to the tendency of forming stable ORR intermediates during the oxygen reduction process.

Nanocrystalline and amorphous nickel-tungsten alloy with relatively high tungsten contents of up to 34 at.% were produced by electrodeposition. The Hall-Petch relationship and breakdown was studied in this alloy, with grain sizes ranging from 25 nm to fully amorphous. In this higher tungsten content alloy, evidence of solid-solution strengthening was found, which was previously absent in alloys with

Positively charged nanodiamond (ND) is used to decorate negatively charged graphene oxide (GO) to form a GO-ND hybrid nanomaterial by electrostatic force. Structural studies results showed that after the decoration, the aggregation of GO sheets is extensively hindered in both at the powder and dispersion states, with a clear reduction in the layer numbers in the latter. The mechanical properties of epoxy/GO, epoxy/ND and epoxy/GO-ND were investigated and compared. The results showed that the GO increased the ductility of epoxy, while the ND increased the rigidity. The best mechanical performance was found for the epoxy/GO-ND nanocomposites, at a GO:ND ratio of 1:5. The reinforcement mechanism of the nanophases was further illustrated by the fracture surface of SEM/optical images and TGA analysis. In addition, the anti-corrosion property of the thus developed epoxy nanocomposite coatings was revealed by electrochemical impedance spectroscopy (EIS), and the results demonstrated that the epoxy/GO-ND coatings exhibited better anti-corrosion property.

Microbiologically influenced corrosion (MIC) is a major concern in a wide range of industries, with claims that it contributes 20% of the total annual corrosion cost. The focus of this present work is to review critically the most recent proposals for MIC mechanisms, with particular emphasis on whether or not these make sense in terms of their electrochemistry. It is determined that, despite the long history of investigating MIC, we are still a long way from really understanding its fundamental mechanisms, especially in relation to non-sulphate reducing bacterial (SRB) anaerobes. Nevertheless, we do know that both the cathodic polarization theory and direct electron transfer from the metal into the cell are incorrect. Electrically conducting pili also do not appear to play a role in direct electron transfer, although these could still play a role in aiding the mass transport of redox mediators. However, it is not clear if the microorganisms are just altering the local chemistry or if they are participating directly in the electrochemical corrosion process, albeit via the generation of redox mediators. The review finishes with suggestions on what needs to be done to further our understanding of MIC.

Cathode materials are important in determining the performance of a capacitive deionization cell. In this work activated carbon cloth (ACC) grafted with tungsten oxide was employed as cathode, which was first grown on ACC with a flaky morphology by a self-anodization method. The oxide was uniformly distributed over the surface of the ACC. The desalination capacity of the obtained material is deduced from electrochemical characterization, based on the preliminary stage, in the static 1 M NaCl aqueous solution over a potential range from −1 V to 0.2 V. The modified ACC attained an enhanced ion removal ability, which gives promising potential in the further application on removing heavy ions from the wastewater of industries.

Toxic metal ions, such as Ni2+ and Mn2+, in industrial waste streams are nonbiodegradable and can cause damage to the human body. Electrochemical cleaning techniques are attractive as they offer more control and produce less sludge than do chemical/biological approaches without the high pressures needed for membranes. Here, nanoneedle-structured α-MnO2/carbon fiber paper (CFP) composites were synthesized by a hydrothermal approach and used as electrodes for combined electroadsorption and capacitive deionization removal of nickel and manganese ions from pseudoindustrial waste streams. The specific performance of α-MnO2/CFP (16.4 mg Ni2+ per g of active material) not only shows a great improvement in comparison with its original CFP substrate (0.034 Ni2+ mg per g), but also is over 6 times that of activated carbon (2.5 mg Ni2+ per g). The high performance of α-MnO2/CFP composites is attributed to their high surface area, desirable mesoporosity, pore-size distribution that permits the further access of ions, and their property as a pseudocapacitor, which contributes to a more efficient electron/charge transfer in the faradic process. Unfortunately, it was also found that some Mn2+ ions are released due to the partial reduction of MnO2 when operated as a negative electrode. For the removal of Mn2+ ions, an asymmetric arrangement, consisting of a MnO2/CFP positive electrode and an activated carbon negative electrode, was employed. This arrangement reduced the Mn2+ concentration from 100 ppm to less than 2 ppm, a vast improvement over the systematical two-activated carbon electrode system that could only reach 42 ppm under the same conditions. It was also observed that as long as the MnO2/CFP composite was maintained as a positive electrode, it was completely stable. The technique was able to reduce both Ni2+ and Mn2+ ions to well below the 10 ppm requirement for discharge into public sewers in Singapore.

The role of biogenic H 2 S in the microbiologically influenced corrosion (MIC) of carbon steel was investigated. Desulfovibrio vulgaris (ATCC 7757), a sulfate reducing bacterium, was tested against C1018 carbon steel in anaerobic vials with three different sizes, each filled with 40 mL of ATCC 1249 culture medium, providing headspace volumes of 10 mL, 85 mL and 160 mL, respectively for H 2 S to escape. Results showed that a larger headspace led to a lower H 2 S concentration in the culture medium, and this increased the sessile cell count and made the iron sulfide film thinner, resulting in increased MIC.

Recently, nickel sulfides have been widely investigated as an electrode material for pseudocapacitors. Among them, self-supported nickel sulfides have been intensively studied; yet, their structures are rather limited to nanosheet or nanorod arrays. Herein, a facile one-step hydrothermal method was developed to synthesize self-supported Ni3S2 on a Ni foam substrate with an urchin-like hierarchical structure consisting of nanowire subunits with a diameter of about 20–30 nm, thus combining the advantages of both hierarchical and self-supported structures. Because of this unique structure, when the sample was applied as an electrode for supercapacitors, it demonstrated an ultrahigh areal capacitance of 21.54 F cm−2 at a current rate of 2 mA cm−2, and even at a very high current rate of 50 mA cm−2, a reversible capacitance of 5.40 F cm−2 can still be retained after 1000 charge–discharge cycles. When the sample was employed as the cathode to build an asymmetric supercapacitor (ASC) with activated carbon as the anode, the device exhibited an areal capacitance of 1.26 F cm−2 at a current rate of 2 mA cm−2 and a coulombic efficiency of 97.7%. Furthermore, this device showed great potential for practical application by lighting up 8 red light-emitting diodes.

The micro-galvanic interactions between Cu-Fe-Mn-Li-containing aluminides and the alloy matrix of aluminium alloy AA2099 during chloride-induced corrosion were investigated in-situ with real-time monitoring of the local contact potential difference (VCPD) using the scanning Kelvin probe force microscopy (SKPFM) at controlled relative humidities. The aluminides showed noble potentials and were able to ennoble their neighbouring matrix sites when a cluster of aluminides surrounded the matrix. The matrix, hence, adopted a more positive VCPD, towards that of the aluminides. The anode-to-cathode ratio changed throughout the corrosion exposure and was seen to show a dynamic character. Much higher local VCPD activities were recorded during the earliest stages of corrosion, when the Al-Li AA2099 surface was first exposed to high humidities, than in later RH cycles; a phenomenon not seen in other aluminium alloys.

The Scanning Vibrating Electrode Technique is a valuable method for investigating localized corrosion, which has the potential to provide further insights if used in conjunction with simulation. This paper demonstrates, by combining experimental data with finite element simulations, that variation in the height of the probe to the electrode surface will cause an imbalance in the measured anodic and cathodic currents, with IR drop being a main determining factor. In addition, the simulations obtain the actual current density at/across the electrode’s surface, whereas the electrolyte current density is obtained by SVET. The galvanic corrosion at scratched and cut-edge zinc-based coated steel in a saline solution are used as examples.

Biofouling induced corrosion of stainless steels grades UNS S31603 and UNS S31254 was investigated at three sites off Singapore for 30 months. No corrosion was observed on grade UNS S31254, while the propensity for corrosion by shellfish of UNS S31603 is ranked as oyster >> barnacles >> green mussels. Oysters caused extensive localised corrosion, penetrating 2 mm thick plates with 12 months with tracks of corrosion several centimetres long. Shallow crevice corrosion was observed under dead barnacles, with an explanation presented for why corrosion is more severe under dead barnacles than live ones. Green mussels did not cause any corrosion.

Investigations in microbiological-influenced corrosion in recent years have suggested a positive correlation in steel corrosion with methanogens. However, many cases reported in the literature were performed in medium containing Na2S·9H2O or l -cysteine, from which the methanogens can produce H2S that in itself is corrosive. Here it is demonstrated that if all sources of H2S are removed, the methanogenic strain Methanosarcina barkeri only cause accelerated corrosion when deprived of traditional energy sources for methanogenesis, such as methanol and H2. Possible mechanisms for this phenomenon of starvation conditions triggering accelerated corrosion are discussed.

In this work, we have developed a system to prepare self-supported nickel-based nanobelts of similar morphology but varying chemical compositions. After a simple hydrothermal treatment, phase-pure self-supported nickel sulfate hydroxide (Ni(SO4)0.3(OH)1.4) nanobelts can be directly prepared on a nickel foam substrate, which can be converted into NiO nanobelts by calcination without any change in the morphology. Alternatively, the pristine Ni(SO4)0.3(OH)1.4 nanobelts can be transformed into Ni3S2 nanobelts via a facile hydrothermal sulfidization. When these nanobelts were applied in supercapacitors they demonstrated contrasting performances, with the Ni3S2 nanobelts showing a high reversible capacitance of about 3.5 F cm–2 at 10 mA cm–2 over 1000 cycles, while the Ni(SO4)0.3(OH)1.4 sample delivered insignificant capacitance. This huge difference in electrochemical activity relates to dramatically different amounts of charge being stored within their bulks, with charge and discharge rates limited by the bul...

Motivated by the primary benefit of reduced material cost, the thickness of crystalline silicon solar cells has been continuously reduced. Laboratory and industrial studies have explored ultrathin crystalline silicon solar cells below 50 μ m with ambitious endeavors toward thicknesses of only a few micrometers. Ultrathin crystalline silicon solar cells require compatible small-scale surface textures to enhance the optical absorption. For this purpose, a novel submicron periodic nanostructure—periodic upright nanopyramids (PuNPs)—is fabricated by an integrated process of laser interference lithography and anisotropic etching of silicon in an alkaline solution. By simulation and measurements, we demonstrate that PuNPs are able to reduce front surface reflectance more effectively than conventional micron-scale pyramid textures and previously investigated periodic inverted nanopyramids (PiNPs). With a silicon nitride antireflection coating, we predict that PuNPs reduce the front surface reflectance to below 1% at an angle of incidence of 8°, which is comparable to black silicon. The superior antireflective property of PuNPs contributes to an absorbed photocurrent density of 40.8 mA/cm2 for a 40 μ m silicon absorber layer, which is 0.7 mA/cm2 higher than PiNPs, 0.8 mA/cm2 higher than inverted pyramids and 1 mA/cm2 higher than upright pyramids.

Three-dimensional assemblies of graphene have been considered as promising starting materials for many engineering, energy, and environmental applications due to its desirable mechanical properties, high specific area, and superior thermal and electrical transfer ability. However, little has been done to introduce designed shapes into scalable graphene assemblies. In this work, we show here a combination of conventional graphene growing technique-chemical vapor deposition with additive manufacturing. Such synthesis collaboration enables a hierarchically constructed porous 3D graphene foam with large surface area (994.2 m2/g), excellent conductivity (2.39 S/cm), reliable mechanical properties (E = 239.7 kPa), and tunable surface chemistry that can be used as a strain sensor, catalyst support, and solar steam generator.

Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with associated damage costs ranging to many billions of US$ annually. In spite of extensive research and numerous publications, fundamental questions relating to MIC remain unanswered. The following review provides an overview of current MIC research and stresses the lack of information related to MIC recognition, prediction and mitigation. The review establishes a link between management decisions and root causes. A holistic, proactive approach to MIC is suggested in which an entire system is considered, monitored and improved.

Sensitized AA5083-H2 aluminum alloy was exposed to chloride-laden thin-film electrolyte at ambient temperature (20%–85% relative humidity) and the local Volta potential measured, in-situ and in real-time, using the Scanning Kelvin Probe Force Microscopy, with the intention to elucidate the earliest stage of localized corrosion. Positive Volta potentials vs alloy matrix were measured for magnesium silicides in ambient air, which, however, underwent a severe nobility loss during corrosion, causing their nobility to invert to active potentials (negative) relative to the alloy matrix. The reason for the nobility inversion was explained by the preferential dissolution of Mg2+, which resulted in an electropositive surface. Aluminides, both with and without silicon, were seen to form the main cathodes at all exposure conditions. The local alloy matrix next to closely-separated aluminides were seen to adopt the Volta potential of the neighbor aluminides, which, hence, resulted in local corrosion protection. The phenomenon of nobility adoption introduced in this work raises questions regarding the anode-to-cathode ratio, which was observed to change during corrosion, and the resulting impact to localized micro-galvanic corrosion. This work further demonstrates that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential.

A perspective is provided on mechanisms for microbially influenced corrosion by sulfate-reducing bacteria and metal-oxidizing bacteria. The authors discuss the confusion introduced by cross-disciplinary discussions of MIC mechanisms and the divergent terminologies used by microbiologists and electrochemists, e.g. “anaerobic” and “direct electron transfer.” Examination of the cathodic depolarization theory for corrosion of carbon steel by sulfate-reducing bacteria suggests that the theory cannot explain the observations. Stainless steels containing

To improve the corrosion resistance of the steel matrix, 1% and 3% Cr and 1% Al are added to ordinary carbon steel for the design of a corrosion-resistant alloying composition. And based on the principle of electrochemical tests, a method for determining the depassivation of Cr and Al alloy steel bars in coral aggregate concrete (CAC) is established. The equivalent circuit model was used based on the electrochemical impedance spectroscopy (EIS) results to characterise the corrosion behaviour of the Cr and Al alloy steel bars and determine their corrosion resistance and the protective effect of the steel bar passivation film. The corrosion resistance of the Cr1 reinforcement to chloride increases by 37.67%, that of the CrAl reinforcement increases by 64.08%, and that of the Cr3 reinforcement increases by 171.82% with respect to that of the HPB 400 bar. The polarisation curves of the alloy steel bars with different Cr and Al contents in CAC were recorded by linear polarisation resistance (LPR), and the time variations of the corrosion potential and corrosion current in the low-alloy steel bars containing Cr and Al were analysed. In addition, the free chloride ion concentration and pH value of the CAC were measured while the Cr and Al alloy steel bars were rusting. The chloride threshold values (% by weight of concrete) of the HPB 400, Cr1, CrAl, and Cr3 steel bars are 0.515%, 0.718%, 0.950%, and 1.084%, and the chloride thresholds (Cl−/OH− ratio) are 0.288, 0.382, 0.502, and 0.693, respectively. Initial-corrosion condition behavior of the Cr and Al alloy steel bars in CAC was obtained. There is considerable scientific value and application significance attainable from the examination of the corrosion mechanism and behavior of corrosion-resistant steel bars in a harsh marine environment.