Dissolution Reaction Research Articles

Design principles for transition metal nitride stability and ammonia generation in acid

<h2>Summary</h2> Transition metal nitrides have shown promise as electrocatalysts in proton exchange membrane fuel cells and electrolyzers, but the instability of these nitrides in acid has limited their function for such technologies. On the other hand, having fast, complete nitride dissolution and ammonia formation in acid can offer new opportunities for distributed, on-demand ammonia generation. Optimizing nitride chemistries for these clean energy applications requires design principles for nitride dissolution and ammonia formation in acid. Here, we report that lowering the nitrogen 2p band center of transition metal nitrides relative to the Fermi level weakens metal–nitrogen bonds and increases labile metallic character, reducing dissolution reaction barriers and boosting ammonia formation kinetics in acid. Increasing the solubility of dissolved metal cations further facilitates the decomposition of nitrides in acid by prohibiting surface oxide passivation. These findings highlight essential future directions for preventing nitride dissolution or facilitating ammonia production for diverse acidic applications.

Research on the corrosion behavior of low carbon mold flux on submerged nozzle refractory

AbstractIn this paper, the wetting and corrosion behavior between medium and low carbon mold flux and Al2O3‐ZrO2‐C nozzle refractory were studied through a high‐temperature wetting experiment. Combined with microstructure analysis, the corrosion mechanism of low carbon mold flux on nozzle slag line material was clarified. The results show that the wettability of low‐carbon mold flux and Al2O3‐ZrO2‐C nozzle refractory is better, compared with the traditional medium carbon mold flux, the contact angle between low‐carbon mold flux and Al2O3‐ZrO2‐C material is smaller and the mold flux spreads faster on the nozzle surface at the same temperature range. According to the microstructure analysis, the corrosion degree of low‐carbon protective slag on the ZrO2‐C material of the nozzle slag line is serious, and the corrosion depth is large. Due to the influence of carbon content, the wettability between low‐carbon mold flux and ZrO2‐C material of the nozzle slag line is better, which provides favorable kinetic conditions for the dissolution and penetration of low‐carbon mold flux into the nozzle. In addition, compared with medium carbon slag, the carbon concentration difference between low‐carbon mold flux and nozzle material is larger, resulting in greater diffusion driving force of carbon atoms, which affects the wetting, dissolution, and chemical reaction of the interface between the two phases.

Corrosion of pipeline steel weld metals containing alloying elements in CO2/H2S environment

The corrosion of weld metals with Cr, Ni, Cu or Mo in gas field produced water with saturated CO2 and H2S was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical profiler, and electrochemical tests. The addition of alloying elements led to a decrease in polygonal ferrite and pearlite, whereas an increase in acicular ferrite in weld metal. Morphological and compositional analysis manifested that corrosion scale on weld metals primarily consisted of FeCO3 and iron sulfides, and Cr(OH)3 also existed on Cr-containing weld metals. With increased alloying elements, especially chromium, localized corrosion resistance was improved. This improvement was ascribed to the presence of alloying elements in substrate and Cr-rich products in scale, which can inhibit the oxidation of iron sulfides, thereby improving the structure of corrosion scale. Electrochemical tests showed that the anodic dissolution reaction of weld metal with higher Cr, Ni, Cu or Mo was inhibited in more extent, and the increase in total reaction impedance depended on weld metal surface active state. The preliminary corrosion mechanism of weld metal in CO2/H2S environment was proposed.

Numerical Simulation of CO2 Migration and Geochemical Reactions in Shihezi Formation Caprock, China

CO2 geological storage, which is an effective way to reduce CO2 emissions, is of great significance to mitigate the current greenhouse effect. In long-term CO2 storage, although the chemical reaction rate of CO2–brine–rock is slow, it can significantly change the mineral composition of rock and the structure and properties of pores and joints, and then change the transport process and distribution state of CO2 in porous media. Therefore, a simplified 2D geological model is established based on the geological data of the Shihezi Formation in the Ordos Basin, China. The mechanism of the CO2–brine–rock reaction and its effect on mineral transformation and pore permeability are studied. In the early stage of CO2 geological sequestration, the rate of CO2 intrusion into the caprock is fast, the CO2–brine–rock reaction in the early stage is mainly a dissolution reaction, and the porosity and permeability of the caprock show an increasing trend. During the period from 100 to 1000 years of CO2 sequestration, the vertical distance of CO2 intrusion into the caprock does not change much. During this period, the type of CO2–brine–rock reaction is mainly a precipitation reaction, which reduces the porosity and permeability of the caprock and increases the sealing ability of the caprock to a certain extent. Our results can not only provide theoretical support for the site selection and risk assessment of CO2 geological sequestration, but also provide a theoretical basis and practical guidance for large-scale commercial storage in the future.

An experimental study on microanalytical characterizations and service performances of landfill modified municipal sludge liner materials in contact with leachate

This study aimed to evaluate the long-term service performance of modified municipal dewatered sludge as a landfill liner barrier. Industrial calcium-containing solid waste was used as a modified material for sludge. The shear strength parameters (cohesion c, friction angle φ), compressive strength, and hydraulic conductivity of the modified sludge were studied using direct shear, uniaxial compression, and penetration tests. The leaching toxicity, hydration products, and microscopic morphology of the modified sludge were determined using atomic emission spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The corrosion mechanisms of the landfill leachate and acid-base chemical solution on the modified sludge liner barrier were revealed. Under the long-term corrosive environment of the landfill leachate and acid-base chemical solution, the shear strength parameters, i.e., cohesion (c) and friction angle (φ) had values in the ranges of 0.51 − 3.79 MPa and 6.52 − 37.58° of the modified sludge, respectively. The uniaxial compressive strength reached 2.70 − 22.92 MPa, and the permeability coefficient ranged from 0.12 × 10−8 to 3.97 × 10−8 cm/s. After long-term corrosion by landfill leachate and an acid-base chemical solution, the modified sludge liner barrier still had significant bearing capacity and water-blocking properties. Under leachate corrosion, sulfate corrosion (such as ettringite and thaumasite formation) occurred, the modified sludge and some structures were damaged. Under an acidic chemical corrosion solution, alkaline substances, such as calcium hydroxide with hydrogen ions, underwent solvent-out crystallization and chemical dissolution reactions, which caused the decomposition of hydrated gel products such as C–S–H inside the specimen. Under alkaline chemical solution corrosion, the active components in the modified sludge underwent a hydration reaction to form ettringite, C–S–H, etc.

Highly improved structural stability and electrochemical properties of Ni-rich NCM cathode materials

We report a simple, easy way using WO3 to build a conductive protective coating layer on the surface of LiNi0.8Co0.1Mn0.1O2 cathode. The WO3 coating layer can block direct contact between the LiNi0.8Co0.1Mn0.1O2 and electrolyte, resulting in suppress the transition metal dissolution and interfacial unwanted reaction on the particle surface. Moreover, WO3 coating layer allows for the smooth and rapid lithium and electron kinetics. The WO3 coating improves the electrochemical performance, especially, this way significantly enhances the rate capability of 166.2 mAh g−1 at 6.0C and cyclability of 85.8% after 100 cycles. Therefore, WO3 coating provides a new breakthrough to improve the structural stability and suppress the resistance for superior electrochemical performances of lithium ion batteries.

Value of core for reservoir and top-seal analysis for carbon capture and storage projects

Abstract Carbon capture and storage (CCS) initiatives to mitigate greenhouse gas emissions are being planned in many countries, including offshore settings in the UK. To start with, almost all of these initiatives have utilized core that was originally collected to help with oil and gas exploration, appraisal and development projects. The objectives of core-based studies for CCS are subtly different to those for oil and gas studies. There are several significant reasons why core should be valued in CCS projects. Data from core provide a chance to calibrate lithology and porosity interpretations made from wireline logs that are used to characterize the subsurface and populate geocellular models. Permeability-related attributes, especially directional permeability ( k v and k h ) and relative permeability in CO 2 –water mixed fluid systems, are essential to predict CO 2 injection rates and CO 2 movement patterns in the reservoir and can only be acquired from core. Although many geomechanical data, necessary to undertake safe injection of CO 2 and avoid induced fracturing, can be acquired from wireline logs, borehole imaging and downhole tests, core samples from the reservoir and top-seal are required to reveal tensile strength and to calibrate elastic and other geomechanical properties acquired from logs. Top-seal performance is critical for carbon capture and storage; core samples from top-seals are the best way to determine capillary entry pressure and so define the maximum CO 2 column height and possible CO 2 leakage rates. The possibility of dissolution reactions between formation water, acidified by high pressure CO 2 , and minerals in both the reservoir and top-seal is best assessed by detailed petrographic and mineralogical study of core samples and a combination of modelling and core flow-through experiments. In summary, core is essential to CCS projects to determine CO 2 storage efficiency, CO 2 injection rates and the optimum way to safely store CO 2 .

Assessment of CO2 storage potential in high water-cut fractured volcanic gas reservoirs—Case study of China’s SN gas field

CO2 storage is an important technique for achieving both carbon peak and carbon neutralization, and depleted gas reservoirs are primary potential candidates for geological CO2 storage. After 15 years of development, the recovery rate of the SN gas field in China has reached 70 % and entered the middle and late stages. Most importantly, it has entered the stage of high water cut, rendering the stabilization of production challenging. As the gas produced in this gas reservoir contains a considerable amount of CO2, high water-bearing wells can be selected for CO2 storage in volcanic depleted gas reservoirs on site. Therefore, in this study, combined with the salinity characteristics of the formation water of the target block, a buried-potential evaluation study on typical wells in volcanic gas reservoirs is conducted, the gas–water distribution characteristics of the gas reservoir after CO2 injection are evaluated, and the CO2 injection timing and volume are optimized. The results show that the different ion content in the formation water leads to two reaction processes: dissolution and precipitation of reservoir minerals. When the CO2 in the formation water is low, the reservoir is dominated by dissolution reaction and the CO2 mineralization buried amount is negative; gradually decreasing with the age of the reservoir. As more CO2 is injected into the formation, a considerable amount of HCO3– is produced. In this context, the formation water is dominated by a precipitation reaction, and the CO2 mineralization buried amount is positive. In 2026, compared with the dissolved buried capacity of 1.0 × 105 m3/d, the injection rate of 2.5 × 105 m3/d will increase by 6.38 × 108 mol. When the injection rate is 1.5 × 105 m3/d, the mineralization buried capacity is the highest (2.02 × 105 mol.). Combining the total amount of CO2 dissolution and mineralization storage, the total amount of storage is the highest (1.38 × 108mol.) when the injection rate is 2.5 × 105 m3/d, indicating that the SN volcanic gas reservoir has significant CO2-storage potential. Guided by the research results of this study, typical wells have been selected to inject CO2 for storage purposes.

Genesis of Significance of Carbonated Thermal Water Springs in Xining Basin, China

There are 30 carbonate hot springs in Yaoshuitan geothermal field, Xining Basin, China, with a temperature of 18~41.5 °C; and there are 10 carbonate hot springs in Qijiachuan geothermal field, with a temperature of 10~19.5 °C. Both geothermal fields are carbonate hot springs containing large amounts of CO2 gas. In order to reveal the origin of the carbonated hot springs in Yaoshuitan and Qijiachuan of Xining Basin, this paper offers a comprehensive study of the regional deep geology, tectonic setting, total analysis of carbonated hot springs, δ2H, δ18O, δ13C isotopes, main gas composition, and geochemical characteristics of travertine dating, travertine δ13C, and rare earth elements. The geological process of carbonated hot spring formation and the evolution of H+ content from deep to shallow is revealed, and the genetic mechanism of the carbonated hot spring in Xining Basin is systematically summarized. The results show that: (1) The characteristics of δ2H and δ18O isotopes indicate that the recharge source of carbonated thermal water springs in Xining Basin is mainly atmospheric precipitation. The age of carbonated thermal water springs at 14C is more than 20 ka, indicating that some of them may come from deep fluid (gas) sources. The R/Ra in carbonated thermal water springs is mostly less than 1, indicating that the helium in geothermal water is mainly crustal source helium, and there is no deep mantle source material. (2) The Piper three-plot indicates that the direction of groundwater evolution from the recharge area at the edge of Xining Basin to Yaoshuitan and Qijiachuan carbonated thermal water spring area near the edge of the basin is opposite to the normal path of groundwater evolution in the basin, which is due to the large amount of CO2 gas mixed in the deep fault along the northern margin of Laji Mountain. The ratio of (Ca2+ + Mg2+) and (HCO3− + SO42−) in the Potan and Qijiachuan carbonated thermal water springs is close to 1, and the ratio of (Na+ + K+)/HCO3− is less than 1. It indicates that the chemical composition of the Yaoshuitan carbonated thermal water spring and the Qijiachuan carbonated thermal water spring in Xining Basin is dominated by the dissolution of calcite, dolomite, and gypsum in deep carbonate reservoirs, supplemented by the dissolution of silicate minerals. The relationship between the volume fraction of CO2 and the δ13C value of carbon isotope of CO2 indicates that the source of CO2 is inorganic, which is mainly formed by metamorphism and decomposition of deep carbonate and marble. The δEu &lt; 1 and δCe &gt; 1 of the rare earth elements in the calcium center of the carbonated thermal water springs indicate that the groundwater supplying the travertine material has been in the acidic environment receiving CO2 from the deep crust for a long time. (3) A series of tectonic activities, such as late collision and post-collision between the Indian and Eurasian plates, has led to the uplift, asthenosphere upwelling, and thermal invasion of the northern Tibetan Plateau and other deep dynamic processes. The deep faults in the northern margin of the Laji Mountain and other deep faults with obvious neotectonic activity have provided channels for the up-invasion of deep thermal materials, and local geothermal anomalies were formed near the deep faults. The hidden carbonate rocks and silicate rocks with large thickness undergo thermal metamorphism under high temperature and high pressure in the deep geothermal anomaly area and form a large amount of CO2, which is dissolved in water and enhances the acidity of water. At the same time, the dissolution reaction of acidic water to carbonate rocks consumes H+, which keeps the carbonated thermal water spring weakly acidic. (4) The composition of travertine in carbonated thermal water springs is dominated by calcite, indicating that travertine may be formed in a deep geological environment with a temperature of 150~200 °C, indicating that there are abnormal heat sources in shallow carbonate strata with a burial depth of 3000~4000 m. The abnormal heat source may be caused by the deep fault in the northern margin of Laji Mountain, as well as other deep and large faults channeled in the deep crust and mantle heat source, indicating that the deep fault in the northern margin of Laji Mountain has an obvious heat-controlling effect, and there is a good prospect of geothermal resources exploration near the fault.

In-situ regulated competitive proton intercalation and deposition/dissolution reaction of MnO2 for high-performance flexible zinc-manganese batteries

Due to the limitation of energy density caused by the one-electron reaction and capacity loss caused by the Mn(Ⅲ) disproportionation reaction, it is difficult to realize the synchronous improvement of energy density and cycle performance of Zn//MnO2 secondary batteries. Here, a competition mechanism is designed for the zinc-manganese battery to achieve both improved energy density and cycling stability by coupling a high crosslinking density hydrogel electrolyte (HCH) with MnO2 deposition and dissolution reaction. Compared to conventional aqueous electrolytes (2 M ZnSO4, 0.2 M MnSO4), the ultrathin HCH (101 μm) widens the battery's voltage window to 2.4 V without significantly increasing the weight of the electrolyte. HCH not only broadens the voltage window but also effectively delays the proton shuttle from cathode to anode, providing a favorable environment for MnO2/Mn2+ reversible cyclic reaction. The Zn//MnO2 battery achieved an energy density of 858 Wh/kgα-MnO2 and a stable cycle of 7000 cycles due to the limitation of disproportionated reactants by the in situ deposition and dissolution of MnO2 at the cathode.

Waxberry‐Shaped Ordered Mesoporous P‐TiO2−x Microspheres as High‐Performance Cathodes for Lithium–Sulfur Batteries

As a candidate for a new generation of inexpensive and high‐performance energy storage systems, lithium–sulfur (Li–S) batteries have attracted widespread research. However, the development and application of Li–S batteries are limited by severe polysulfide dissolution and slow reaction kinetics. Herein, a type of ordered mesoporous P‐TiO2−x microsphere with a waxberry‐like shape as the sulfur host material for Li–S batteries is put forward, which combines the radially arranged mesoporous structure with oxygen defects in the mesoporous framework. In addition, the introduction of phosphorus impurities greatly improves the conductivity of the sulfur electrode, enhances electron mobility, and promotes the interaction between the sulfur species and P‐TiO2−x microspheres. Finally, S/P‐TiO2−x cathodes have achieved a high capacity of 1174.9 mAh g−1 at 0.2C and stable cycling (the average capacity attenuation is only 0.086% per cycle at 1C after 600 cycles).

Investigating the impact of long-term agricultural practices on selected peri-urban aquifers in tropical Southwest India

Hydrogeochemical evaluation of groundwater resources is of paramount significance in the tropics as it aids identification of safe and sustainable water resources. Evaluation of heavy metals in water is necessary as they integrate into the food chain and pose deleterious effects on human and aquatic life. To identify the extent of heavy metal occurrence in groundwater, 40 samples were collected seasonally from dug wells located in agriculture-intensive areas and analysed for physicochemical parameters and heavy metals. Water quality and pollution indices were used to evaluate overall groundwater quality and threat to humankind. The heavy metal concentrations in groundwater were observed in the increasing sequence of Zn > Cu > Pb > Ni > Co (post-monsoon) and Zn > Pb > Cu > Ni > Co (pre-monsoon). Heavy metal pollution index (HPI) revealed that the dissolved heavy metal content was found below critical value. Correlation analysis (CA) and principal component analysis (PCA) revealed that the groundwater hydrochemistry is influenced by geogenic (rock-water interaction, precipitation, simple dissolution, and base-exchange reactions) and anthropogenic sources. The results of this study will help in developing a long-term groundwater monitoring system for metal pollution, sustainable management, and conservation of peri-urban groundwater resources to achieve water security.

Description of Si and Al Release from Aluminosilicate in the Acidic Condition Using Density Functional Theory: Protonated Terminal Oxygen

The molecular clusters ((HO)3Si-O-Si(OH)3 and (HO)3Al-O-Si(OH)3) representative of aluminosilicate mineral surface were employed to study the dissolution of aluminosilicate in acidic condition via density functional theory (DFT) with the M06-2X+G(d,p) methodology. The surface termination sites (Si and Al) were both tetra-coordinated and the terminal oxygen was protonated in an acidic condition. In the dissolution reaction, the calculated barrier height of the six-membered ring transition state complex containing two water molecules was predicted to be 76.13 kJ/mol, lower than that of the four-membered ring transition state complex containing one water molecule. The barrier height of the reaction decreased to 6.17 kJ/mol and was 91.90% lower than that for the Siter-O-Si without protonation. In addition, the calculated barrier heights for Al-terminated sites were predicted to be 22.23 kJ/mol, lower than those for the Si-terminated sites, suggesting that breaking the Al-O bond is easier than the Si-O bond in the aluminosilicate mineral surface. With the fracture of Si-O and Al-O bonds, the Si and Al release from the aluminosilicate. The results indicate that the acidic condition facilitates the release of Si and Al from the aluminosilicate, and the concentration of Al leaching from the aluminosilicate is higher than the Si.

Variance-Based Sensitivity Analysis of Fitting Parameters to Impact on Cycling Durability of Polymer Electrolyte Fuel Cells

Degradation of a catalyst layer in polymer electrolyte membrane fuel cells is considered, which is caused by electrochemical reactions of the platinum ion dissolution and oxide coverage. An accelerated stress test is applied, where the electric potential cycling is given by a non-symmetric square profile. Computer simulations of the underlying one-dimensional Holby–Morgan model predict durability of the fuel cell operating. A sensitivity analysis based on the variance quantifies how loss of the platinum mass subjected to the degradation is impacted by the variation of fitting parameters in the model.

Vanadium selective separation enhancement from iron in black shale using oxalic acid due to FeS2 (1 0 0) surface passivation: A theoretical and experimental study

Iron impurity tends to precipitate and reduces vanadium product purity during vanadium extraction from black shale. Oxalic acid is an eco-friendly leachant which can enhance vanadium selective separation from iron impurity. In this paper, the separation mechanism was systematically investigated. The mineral phases transformations and thermodynamics analysis indicate that the FeS2 in black shale can react with H2C2O4, HC2O4-, C2O42- and O2, as a result, the pyrite surface was coated by ferrous oxalate passivation layer, which can depress pyrite dissolution reaction. Meanwhile, the density functional theory (DFT) calculations show that the H2C2O4, HC2O4- and C2O42- can reconstruct FeS2 (100) surface by adsorption, and the adsorption energy can be as low as −3.73 eV for C2O42- adsorption configuration. The electrons in Fe atoms were transferred to O atoms and the stable Fe-O bands together with closed seven/eight-membered rings structures were formed as passivation layer, which can weaken and reduce Fe atoms reactive activation for the FeS2 during oxalic acid leaching. This study reveals vanadium separation from iron due to pyrite passivation in presence of oxalic acid at an atomic level.

Catalytic Effect of Alkali Metals on the Gasification Dissolution Reaction and Deep Reaction Behavior of Metallurgical Cokes.

In this paper, the deep reaction behaviors of tamping and top-charging cokes with different K2CO3 and Na2CO3 contents were investigated and the evolution of the functional group structure and the carbon structure of coke with the extension of the deep reaction was clarified. The results showed that the deep reaction gasification of coke steadily increased with the K2CO3 and Na2CO3 content. However, the catalytic effect of different contents of K2CO3 seemed to be stronger than that of different contents of Na2CO3. Meanwhile, the catalytic effect of alkali metals on the gasification reaction of tamping coke was more significant. The gasification dissolution of coke gradually decreased from the outside to the inside of the particle with the extension of the deep reaction, while the catalytic effect of K2CO3 and Na2CO3 seemed to be more dramatic on surface of the coke particle. In contrast, the gasification dissolution reaction on the surface of tamping coke was more severe; consequently, the surface pore area of tamping coke was much higher than that of top-charging coke. According to the variations in the functional group structure of cokes, aromatic hydrocarbon gradually became the dominant functional group in the coke structure with the extension of the deep reaction. The above variation led to a gradual decrease in the reactivity of coke, though the decomposition reactions of oxygen-containing functional groups in coke were promoted to some extent by the addition of K2CO3. With the extension of the deep reaction of coke, amorphous carbon was gradually transformed into sequential carbon.

A novel Sb-Zn electrode with ingenious discharge mechanism towards high-energy-density and kinetically accelerated liquid metal battery

Liquid metal battery (LMB) has recently captured intensive attention for large-scale energy storage, originating from its attractive cost-efficiency, robust cyclability, and ultralong service lifetime. Nevertheless, realizing high energy density remains a great challenge. Herein, a novel dual-active Sb-Zn electrode is elaborately designed. A unique lithiation mechanism is demonstrated for the first time in LMB field. A ternary intermetallic compound LiZnSb is preferentially formed with a high discharge plateau at ca. 1.1 V, which is followed by a conversion reaction to Li3Sb and Zn at around 0.8 V and then a consecutive dissolution reaction of lithium in molten Zn, significantly ameliorating the voltage and capacity properties. Meanwhile, part Zn melts regenerate and disperse among discharge product layer, constructing rapid electron/lithium percolating networks in-situ, which accelerates the electrode reaction kinetics. As a result, the Li||Sb-Zn battery exhibits high average discharge voltage of 0.763 V at 100 mA cm−2 and superior rate performance (0.596 V at 1000 mA cm−2). Outstanding energy and power densities (290.6 Wh kg−1 and 239.66 W kg−1) are achieved, remarkably surpassing most reported LMBs and even comparable to Na-S battery. This work showcases an innovative electrochemistry system, opening a new avenue for high-performance LMBs.

Electroforming 4.0 – Significance, Challenges & Optimisation

Since the concept of “Industry 4.0” was introduced the most competitive industrial manufacturers around the world have been trying to secure sustainable, high quality, low-cost technological developments. Alongside the total computerisation of manufacturing and fabrication, new manufacturing technologies will need to arise to replace traditional production lines with more flexible ones able to support the evolved industrial needs of the next transition.Among these technologies, additive manufacturing processes have significantly contributed to the rapid transformation of the industrial landscape during the last decade. In particular, “low-volume/high-value" industrial sectors, such as the aerospace, marine and energy industries, are expected to benefit from this kind of approaches. This is mainly because manufacturing of larger volumes of customised products could be achieved in that manner, followed by a reduction of industrial and economic waste, decrease in the cost of operation and reduction of environmental impact.Electroforming is increasingly gaining recognition as a promising and sustainable additive manufacturing process of the “Industry 4.0” era. Numerous important laboratory-scale studies try to shed light onto the pressing question as to which are the best industry approaches to be followed towards the process’s optimisation. However, for electroforming to be successfully optimised and efficiently applied in industry, systematic scale up studies need to be conducted. Well-informed simulations can provide a much-desired insight into the novelties and limits of the process, and therefore, scaling up modelling studies are of essence.Additive-free nickel electroforming, in particular, could also play an important role in the much-desired “green” transition of lightweight manufacturing. Even within the currently available infrastructure, the same electroforming reactors can remain in use for years if properly maintained, the stainless-steel cathodes (mandrels) and titanium anode baskets are re-usable and recyclable, while process efficiency (especially for sulphamate baths) is usually close to 100%. Hazards arising from the use of nickel can easily be mitigated, while developments on nickel recovery and recycling are increasingly promising.Modelling studies can help further, towards process optimisation at all three (system, process and product) sustainability levels. Since electroforming’s final products can be of various scales and requirements, well-informed modelling studies could assist with efficient tooling and process design for different cases. That way, key process parameters, such as the deposition duration, applied currents, heating and agitation requirements, or even quantitative material requirements, could be fine-tuned on a case-by-case basis.Therefore, to better understand the process and its potential, a systematic nickel electroforming modelling approach was followed; starting from primary current distribution (PCD) simulations which depend solely on the system’s geometry, moving forward to introducing kinetic contributions through secondary current distribution (SCD) studies and, finally, developing tertiary current distribution (TCD) models completed by the introduction of mass transfer effects.In practice, time-dependent nickel electroforming models of different scales were developed and studied using COMSOL Multiphysics®, a finite element method commercial software. The models were experimentally validated. Electrochemical experimental data, collected via polarisation studies, were used as input for the models. The boundary conditions at the cathode and anode were based on the overall nickel reduction and dissolution reactions, respectively. Current-potential data was used to fit the exchange current density, equilibrium potential, limiting current, as well as anodic and cathodic charge transfer coefficients.Modelling and experimental results were interpreted in terms of the deposit thickness distribution and uniformity. PCD modelling offered a preliminary insight into the system’s electrochemical behaviour, confirmed the direct relation between current and thickness distribution, and highlighted the dependence of the simulated results on the setup’s geometrical configuration. SCD simulations were subsequently used for mesh, geometry, and kinetic sensitivity studies, to be followed by TCD simulations involving multiple species and reactions.These studies confirmed that commercial simulation software can reliably model precision electrodeposition processes, such as electroforming. At the same time, the models’ credibility is dependent on good quality input parameters, derived through practical experiments. Among other observations, simplified SCD models were proven to be efficient in modelling processes not affected by tertiary phenomena. Targeted investigations on how the size, geometry and configuration of an electroforming reactor can affect the final product suggested time- and cost-effective modifications of the setup itself which can lead to process optimisation. Overall, computational studies allowed for the development of a study approach aiming to optimise both electroforming simulations and application in production lines. Figure 1

Simulation of Cathode Catalyst Durability Under Fuel Cell Vehicle Operation - the Effect of Temperature

Fuel cell vehicles (FCVs) emerge to be promising candidates to produce clean power for the transportation sector in order to tackle climate change issues. Although the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) has progressed in the past few decades, there are still obstacles to address, including high cost and limited hydrogen infrastructure. For heavy duty transportation applications, the PEMFC durability is also not yet proven, and extrapolating from lab data to real-world field operating conditions remains a significant challenge [1].In this work, the cathode catalyst degradation in PEMFCs is studied to make an estimation of fuel cell durability in the FCV application. The well-known Butler-Volmer approach is utilized to model platinum dissolution and redeposition, platinum oxidation and platinum ion formation during the fuel cell operation [2]. First, the model is calibrated with the results presented by Ferreira et al. [3] at 80℃; the calibrated model is then validated with Kocha’s results [4] to demonstrate the model’s capability of generating reliable results at different temperatures. In order to realistically predict the cathode degradation pattern and lifetime, the real-life fuel cell operating conditions should be obtained. Therefore, a drive cycle recorded based on a real-life transit bus operation in the city of Victoria is utilized to calculate the input fuel cell voltage profile. The procedure to calculate fuel cell operating voltage profile using the drive cycle has been thoroughly explained by Ahmadi and Kjeang [5]. This procedure employs Newton’s second law to calculate the required cell power density considering the air flow drag force counteracting the vehicle thrust. Finally, polarization curves representing the fuel cell performance are used to calculate the fuel cell voltage profile with the determined required cell power density. Polarization curves measured under a range of temperatures are employed to adequately reflect the effect of temperature on the fuel cell performance. The cell active area is considered to be 500 cm2 and the stack is assumed to contain 225 cells, representing a nominal stack power of 74 kW at 80℃. The fuel cell operation and degradation are simulated at three different temperatures: 60, 70, and 80℃. The change of remaining electrochemically active surface area (ECSA) with time is calculated as the output of the model.Temperature highly affects the electrochemical reactions of platinum dissolution in several ways. First, it affects the Tafel slope in the platinum dissolution reaction. Second, it substantially impacts on platinum degradation reaction rate constant [6]. The Arrhenius approach is taken in this study to apply the effect of temperature on the reaction rate constants. Fuel cell voltage loss over time is determined by assuming simple Tafel kinetics. The cathode lifetime is calculated at 0.6 A/cm2 and is estimated by considering 10% voltage drop as the failure criterion. Fig. 1 shows the simulated change of remaining ECSA over time and the resulting fuel cell lifetime for the three different cell temperatures. The results indicate that the cathode lifetime increases 168% when the cell temperature drops from 80℃ to 60℃ due to a significantly lower platinum degradation rate at 60℃. The results show relatively low cathode catalyst lifetimes for a transit bus. The reason is attributed to the bus drive cycle used as the model input. The drive cycle contains a great portion of deceleration and idling time which leads to a fuel cell operation close to open circuit voltage (OCV), thus experiencing a high degradation rate.In this regard, the present modeling framework could become a useful tool for fuel cell and FCV developers to predict lifetime for new products and systems prior to commercial release. Scientifically, the present model can also be used to further explore key influencing factors on fuel cell durability and develop more durable cell, stack, and system designs for a targeted FCV application. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

(Corrosion Division Morris Cohen Graduate Student Award) Microscopic Electrochemical Properties of Carbon Steels and Metallurgical Approach for High Corrosion Resistance

Carbon steels are widely used in the production of automobiles, bridges, plates, and so on because of their superior mechanical properties and low cost. Carbon steels contain various types of microstructures such as ferrite, pearlite, and martensite, and desired mechanical properties can be obtained by combining these microstructures. While carbon steels exhibit excellent mechanical properties, their pitting corrosion resistance is relatively low in chloride-containing environments. Although the steels are successfully protected from corrosion by coating and/or painting, localized corrosion is readily initiated at cut edges and in coating defect areas in atmospheric environments. To prolong their service life and improve their reliability, it is necessary to elucidate the initiation mechanism of pitting corrosion on carbon steels. While it is widely known that the microstructures of carbon steels affect their corrosion resistance, the detailed mechanism is still unclear. The objective of this research is to clarify the relationship between the microstructure and pitting corrosion resistance of carbon steels in chloride-containing near-neutral pH environments.The pitting corrosion resistance of the typical microstructures of carbon steels was investigated using a micro-electrochemical polarization technique. Various microstructures (ferrite, pearlite, tempered martensite, decarburized martensite, as-quenched martensite etc.) were obtained by conducting different heat-treatments, and micro-scale electrodes (ca. 100 μm × 100 μm) were prepared with only one microstructure included. Small areas without any non-metallic inclusions were chosen as the micro-scale electrodes to eliminate the effect of pit initiation at the inclusion and evaluate the intrinsic corrosion behavior of the microstructure itself. Then, potentiodynamic anodic polarization measurements were carried out in NaCl-containing boric-borate buffers at pH 8.0. It was determined that the pitting corrosion resistance depends on the type of microstructure, with the as-quenched martensite showing the highest pitting corrosion resistance. The as-quenched martensite includes a high amount of interstitial C in the Fe lattice, and it was also clarified that the anodic dissolution of steels was clearly suppressed with increasing interstitial C content. During pitting corrosion, the local breakdown of the passive film is induced by chloride ions, which results in the initiation of active dissolution. It was considered that the low dissolution rate provided by interstitial C results in the superior pitting corrosion resistance of as-quenched martensite.To clarify the reason for the superior active dissolution resistance obtained by interstitial C, first-principles calculations were conducted. At first, the electronic structure of martensite was analyzed using bulk-model supercells with bct Fe crystal structures which included interstitial C. According to first-principles calculations, the electronic density of states (DOS) at and around the Fermi level decreased due to the presence of interstitial C. In addition, a valence electron transfer occurred from Fe to C atoms, resulting in a decrease in the number of valence electrons of Fe. Because the presence of valence electrons at and around the Fermi level affects the kinetics of electron (charge) transfer in oxidation/reduction reactions, including the active dissolution reaction, it was considered possible that the presence of interstitial C suppressed the electronic reactivity of Fe. Furthermore, first-principles calculations were also carried out for slab-model supercells consisting of a metal/vacuum interface, and the effect of interstitial C on the work function of martensite was analyzed. The result of the calculations indicated the work function of martensite linearly increased with increasing interstitial C content. Since the work function and ionization energy of metals are the same, the electrochemical properties of metals, such as dissolution resistance, are considered to be principally associated with their work function. In other words, it is understood that metals with a high work function are associated with a higher dissolution resistance. According to the above calculation results, the change in the electronic structure of Fe and the increase in the work function provided by interstitial C are key factors contributing to the superior dissolution resistance of martensite.