Protective Layer Research Articles

High-temperature corrosion mechanisms of a Ni-based alloy in simulated multi-source organic waste co-incineration environments

Due to the new trend of co-incinerating municipal solid waste (MSW) with sewage sludge, medical waste, or industrial organic waste to attain a “waste-free” status, mixing of multi-source organic wastes (MSOW) increases the complexity of solid waste, which fluctuates the composition of corrosive species in the boiler. The fluctuation of corrosive species alters the alkali metals/S/Cl ratios and increases the uncertainties of high-temperature corrosion of boiler key components. The corrosion behaviors and mechanisms in varying compositions of corrosive species are complex and remain elusive. To investigate the corrosion characteristics during the co-incineration of MSOW, this study examined the corrosion mechanisms of a nickel-based Ni59.08Cr24.31Al10.74W5.3B0.57 alloy in simulated co-incineration environments of MSOW. The environment contained either HCl, NaCl, or SO2 in wet oxygen at 600 °C. For each case experiment, the maximum possible value of each corrosive species expected in the actual incinerator and/or its absence was considered. HCl of either 0 or 1500 ppm, SO2 of 0 or 300 ppm, and NaCl of 0 or 50 mg/cm2 were systematically used in each experiment. The influence of each corrosive condition on the corrosion of the alloy was evaluated by mass gain measurements, and the corrosion mechanisms were elucidated through SEM, EDS mapping, XRD, XPS analyses, and thermodynamic equilibrium calculations. The results revealed that NaCl salt and HCl gas in wet oxygen have complementary effects, which accelerated the corrosion of alloy, reaching ∼ 65.6 mg/cm2 over one week. HCl enhanced the corrosion by affecting the chemical reactions that regenerated NaCl, which participated in prolonged corrosion processes. SO2 reduced the mass gain of the alloy to 38.4 mg/cm2. SO2 participated in the sulfation of NaCl, forming a mixed layer of Na2SO4 and (Al/Cr)2O3, reducing the mass gain by 1.71 times. In the environment without NaCl, SO2 helped in the formation of a protective oxide layer, which prevented HCl from reaching the alloy, reducing the corrosion impact by 23.5 times.

Mixed conductive layer formed by ZnO–graphite conversion–reaction enables dendrite–free all–solid–state lithium metal batteries

Largescale application of sulfide solid electrolytes (SSEs) in nextgeneration allsolidstate Limetal batteries is currently limited by an unstable Li/SSEs interface and fast Lidendrite formation/growth during charging. This work has addressed these challenges by introducing ZnO and graphite composite to the surface of lithium metal, creating a multifunctional conductive composite layer with Ligraphite and LiZn alloy. This interfacial layer enhances Liion transport and minimizes side reactions at the Li/SSEs interface. As a result, the interfacial resistance of Li/SSEs decreased from 14.2 to 11.7 Ω cm², and the critical current density (CCD) significantly improved from 0.8 to 2.7 mA cm2. Moreover, the protective layer enables stable cycling of both Li/Li symmetric and LiNi0.8Mn0.1Co0.1O2/Li cells even at high current densities.

Significantly lowering friction and wear of CoCrNi medium-entropy alloy film via massive interstitial carbon-induced amorphization

CoCrNi medium-entropy alloy (MEA) exhibits exceptional damage-tolerance, particularly at cryogenic temperatures, but demonstrates poor wear resistance. In this study, we propose a strategy to significantly reduce friction and wear of CoCrNi MEA film through the introduction of massive interstitial carbon-induced amorphization. The microstructure of as-sputtered CoCrNi film reveals an anisotropic columnar nanograin structure, featuring a primary face-centered-cubic (fcc) phase and a minor hexagonal-close-packed (hcp) phase. Upon the introduction of 16 at.% interstitial carbon (CoCrNi-C), a remarkable phase transformation occurs, resulting in an isotropic amorphous structure. Under low-load and low-sliding-velocity conditions, the CoCrNi-C film exhibits a 21% reduction in coefficient of friction (CoF) and 17% reduction in wear rate. More notably, when subjected to higher loads and sliding velocities, the CoCrNi film experiences rapid failure within the initial 100 cycles, manifesting as microcracks, breakage, and peeling. In contrast, the amorphous CoCrNi-C film demonstrates remarkable durability, sustaining over 5000 cycles without failure. The wear rate exhibits a negative correlation with load but a positive correlation with sliding velocity. This enhanced wear resistance can be attributed to the amorphous nature of the CoCrNi-C film, which inhibits local strain accumulation, preventing strain localization that typically leads to crack initiation and propagation in the CoCrNi film. Additionally, the formation of a protective oxide layer contributes to the improved wear resistance of CoCrNi-C film under higher loads and lower sliding velocities. This study provides valuable insights into the design of wear-resistant CoCrNi-based MEA coatings through massive interstitial carbon-induced amorphization.

Bottle test technique for separating water-in-sunflower oil emulsion under an application of electric field stabilised by surfactant and hydrolysed polyacrylamide

The efficacy of separating water-in-oil emulsions depends on the stability of the emulsion, which is influenced by the interaction of the polymer and surfactant at the oil–water interface. We examined the role of hydrolysed polyacrylamide and surfactants on the stability of water-in-oil emulsions. The effects were investigated by implementing bottle tests (BT) and electrocoalescence bottle tests (EBT) using various types of surfactants over a wide range of concentrations. For a high volume fraction (10% v/v) of emulsion, the BT study showed 80% of separation in a short duration. At a small volume fraction (2% v/v), efficient separation was achieved by applying an electric field. These studies were further extended to a hybrid mode of operation, combining 1 kV/cm, non-uniform DC electrical fields at a temperature of 60 °C, to achieve maximum separation efficiency of up to 91% within 10 min for deionised water when the volume fraction of water in the emulsion was 2%. Under the same conditions, we observed an impressive 88% separation for surfactant and polymer-stabilised emulsions. HPAM does not affect interfacial tension due to its lack of amphiphilic character. However, it significantly increases the viscosity of the dispersed phase by forming a network that restricts coalescence, thereby affecting the separation rate. Surfactants enhance stability by reducing interfacial tension (IFT) and forming a protective layer around the droplet. The findings provide valuable insights for optimising separation processes using the synergy of the heating and electric fields. The study successfully and efficiently separates oil and water, even when dealing with challenging emulsions containing polymers and surfactants, by combining heating and electrical methods.

A manual operated and eco-friendly plasma-assisted polymerization method for enhancing surface weather resistance of insulation

With the increasing demand for high-voltage long-distance power transmission, insulation as the first protection of power system, faces serious challenges from material degradation caused by moisture invading, surface contamination and pollution flashover. Addressing the issue requires significant effort and may cause harmful by-product emission from large-scale wet type material processing. In this work, a novel eco-friendly dry treatment method based on manual operated Air/Alkoxysilane(PMDMS)/plasma is developed to enhance weather resistance and electrical performances of contaminated insulation. Tiny amounts of harmless reaction medium are transmitted to plasma through controllable air bubbling, and it implements precise dry type processing on material surface. Plasma pulverizes pre-existing contamination and synchronously activates hydrolysis-polymerization of PMDMS to deposit Si-containing protection layer (Si-O2, Si-CH3) on surface. It is demonstrated that the plasma treatment inhibits dirt pollution and electrical erosion of on-site 110 kV silicone rubber (SIR), and the electrical and hydrophobicity properties are both promoted. Flashover voltage increases from 4.65 to 8.71 kV, and water contact angle increases from 138.27° to 146.41°. Overall, this newly-developed dry portable plasma treatment strategy for insulation enhancement avoids environment pollution and economic losses, and provides a scalable avenue for on-site insulation recovery and service life prolonging.

Preparation and characterization of structural and antifouling properties of chitosan/polyethylene oxide membranes

It aims to prepare the chitosan (CS) and polyethylene oxide (PEO) hydrogel membranes with different CS/PEO blend ratios (100:0, 95:5, 90:10, 80:20 and 70:30) via solvent casting. The physicochemical properties of these membranes were investigated using various characterization techniques: Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX), contact angle, and tensile testing. The interaction of PEO and chitosan was investigated by DSC in terms of freezing bound, freezing free, and non-freezing PEO fraction. The cross-sectional surface morphology of membranes displayed a smoother surface with increasing PEO content up to 20 %, beyond which nonhomogeneity on the surface was visible. The antifouling behavior of membranes was investigated by bacterial adherence study, which showed an enhanced antifouling nature of membranes with the increase in the PEO content. The peeling strength of the membranes was measured using a 90° angle peeling test, and it was found that 20 % and more PEO content promotes easy removal from the gelatin slab. In addition to this, live/ dead assay of the CS was performed to visualize the presence of live and dead bacteria on the surface. The CS/PEO blend with 20 % PEO content has properties makes it suitable for use as a protective layer on wound dressings to prevent bacterial growth. It's use in wound dressings has the potential to reduce the pain during the time of dressing removal and improve patient outcomes. The present investigation leads to the development of a CS hydrogel matrix which exhibits very interesting interaction with the PEO moiety along with its innovative feature of antifouling and antimicrobial nature.

Stiff gel-protected fiber-shaped supercapacitors based on CNFA/silk composite fiber with superhigh interference-resistant ability as self-powered temperature sensor

The development of self-powered sensors with interference-resistant detection is a priority area of research for the next generation of wearable electronic devices. Nevertheless, the presence of multiple stimuli in the actual environment will result in crosstalk with the sensor, thereby hindering the ability to obtain an accurate response to a singular stimulus. Here, we present a self-powered sensor composed of silk-based conductive composite fibers (CNFA@ESF), which is capable of energy storage and sensing. The fabricated CNFA@ESF exhibits excellent mechanical performance, as well as flexibility that can withstand various deformations. The CNFA@ESF provides a good areal capacitance (44.44 mF cm−2), high-rate capability, and excellent cycle stability (91 % for 5000 cycles). In addition, CNFA@ESF also shows good sensing performance for multiple signals including strain, temperature, and humidity. It was observed that the assembly of the symmetrical device with a stiff hydrogel surface layer for protection enabled the real-time, interference-free monitoring of temperature signals. Also, the CNFA@ESF can be woven into fabrics and integrated with a solar cell to form a self-powered sensor system, which has been proven to convert and store solar energy to power electronic watches, indicating its huge potential for future wearable electronics.

Mechanical properties and biocompatibility of multilayer systems based on amorphous SiN:H/SiCN:H layers on Ti6Al7Nb titanium alloy

Surfaces of metallic implants that replace diseased joints are bound to degrade over time under constant mechanical wear and corrosion, caused by the presence of biological fluids. Production of wear particles and toxic metal ions that follows can undermine both implant stability and patient’s health. To counteract this process multiple surface modifications have been proposed in scientific literature, ranging from simple nitriding to protective layers (e.g.: DLC, CN:H) and multilayer systems. This work presents a combined approach to outlined issue, using multi-staged plasma deposition with SiCN:H layer as a key component, realized using the MW CVD (Microwave Chemical Vapour Deposition) system. The study covers chemical characterization by EDS and FTIR analysis and measurements of relevant functional parameters, such as hardness, Young’s modulus, coefficient of friction, specific wear rate and wettability. Additionally, biocompatibility of modified surfaces are tested on MG-63 cells using Alamar Blue assay, flow cytometry and alkaline phosphatase (ALP) assay. Chemical and microscopic studies revealed amorphous cauliflower-like microstructures that have proven to be hydrogenated SiCN/SiN structures. The obtained layers are turned out to be biocompatible (>70 % of cell survival rate), additionally layers based on amorphous SiCN:H boost ALP activity due to combination of their chemistry and mechanical properties.

A Ceramic/Lithiophilic Metal Dual Protective Layer for Stable Lithium Metal Anodes Fabricated via Transfer-Printing Methods

Lithium metal has attracted researcher’s attention because of its superior theoretical capacity (3860mAh g-1 or 2061 mAh cm-3), which is nearly 10 times higher than commercialized anode materials, for example, graphite (372 mAh g-1). However, lithium metal is not currently used in commercial lithium metal batteries due to safety and efficiency issues that arise during long-term battery operation. The high reactivity of lithium metal causes almost all available electrolytes to be spontaneously reduced on the Li surface to form a solid-electrolyte interface (SEI) layer. Unfortunately, this passivating SEI layer is typically too fragile to withstand significant mechanical deformation of the electrode during cycling, resulting in crack formation. These cracks expose fresh Li underneath, which locally enhances Li-ion flux and promotes morphological deformation of the lithium metal surface. This often leads to dendritic Li deposition that can cause internal short circuits and compromise battery safety. Additionally, repeated failures and repairs of SEIs result in the continued loss of both Li and electrolyte, leading to low coulombic efficiency (CE) and rapid capacity decrease.To mitigate these problems, researchers have attempted to suppress lithium dendrite growth by slurry coating on the lithium metal surface such as ceramic layer and lithiophilic metal. These materials and conventional lithium metal protection coating methods partially inhibit the growth of lithium dendrites; however, they come with several significant drawbacks. The ceramic layer possesses high mechanical properties that physically inhibit the growth of lithium dendrites. However, it exhibits poor interfacial characteristics with lithium metal, leading to increased resistance. This heightened resistance results in the formation of uneven lithium deposition layers at high current densities, causing cracks in the ceramic layer. Lithiophilic metals exhibit an advantage in reducing nucleation resistance through alloying reactions with lithium prior to nucleation, thereby facilitating uniform lithium ion deposition. However, their low mechanical properties limit their potential for enhancing electrochemical performance. Furthermore, the conventional coating method used for lithium metal protection involves the direct application of solvent-containing slurries onto the lithium metal surface using slurry coating techniques. Given the inherent reactivity of lithium metal, the presence of residual moisture and impurities within the solvent may induce sub-reactions, ultimately compromising the stability of lithium metal.In this study, we propose an approach to improve the cycling stability of lithium metal through Ceramic/lithiophilic metal dual protective layer fabricated via transfer-printing methods. The dual lithium metal protection layer, consisting of Ceramic/lithiophilic, involves coating a lithiophilic metal layer between the ceramic layer and the lithium metal. This method aims to maximize electrochemical performance improvement through a synergistic effect that utilizes the high mechanical properties of ceramics and solves the problem of interfacial resistance between the ceramic layer and lithium metal through the lithiophilic metal. Furthermore, we propose a coating process for lithium metal protection layers using a method based on transfer printing. This method involves applying pressure to the lithium metal surface through transfer printing of pre-finished composite protective layers on a film, rather than directly applying slurry onto the lithium metal surface. Transfer printing offers the advantage of maintaining the stability of lithium metal by avoiding direct application of slurry onto the lithium metal surface, thereby ensuring the integrity of the protection layer.

Polymerized Acrylonitrile Artificial SEI for Long-Life Li-Metal Battery and Enhanced Stability for Li/Li10GeP2S12 Interface

Lithium metal anode batteries have attracted significant attention as a promising energy storage technology, offering a high theoretical specific capacity and low electrochemical potential. Utilizing lithium metal as the anode material can substantially increase energy density compared to conventional lithium-ion batteries. However, the practical application of lithium metal anodes has encountered notable challenges, primarily due to the formation of dendritic structures during cycling. These dendrites pose safety risks and degrade battery performance. Addressing these challenges necessitates the development of a reliable and effective protection layer for lithium metal. This study presents a cost-effective and convenient method to produce lithium metal protective layers by creating ex-situ polymer layers using acrylonitrile (AN). This method extends the lifetime of lithium metal anodes by a remarkable factor of six under high current (1 mA/cm²) cycling conditions. While the cycle life of bare lithium metal is approximately 150 hours under high current conditions, AN-treated lithium metal anodes exhibit an impressive longevity of over 900 hours.Furthermore, with the increasing attentions on solid-state electrolytes – which address the safety concerns and energy density limitations associated with conventional liquid electrolytes in lithium-ion batteries, the interface between Li metal and solid-state electrolytes has been the major challenges. For example, Li10GeP2S12 (LGPS) stands out among these solid electrolyte materials, boasting high ionic conductivity (1 x 10⁻² S cm⁻¹). Nonetheless, the severe instability of the interface between lithium metal anodes and solid electrolytes, including dendrite formation and electrolyte degradation, hindering their practical implementation. This work also goes deeply to explore the stability and performance of Li | LGPS systems by utilizing a polymerized acrylonitrile interfacial. By elucidating the mechanisms governing the interfacial layers, this low-cost fabrication of AN-treated lithium metal holds significant potential for advancing the commercialization of future lithium-metal batteries, surpassing the capabilities of traditional lithium-ion batteries.

Effect of Bacterial Infection By-Products on the Corrosion of Titanium Osteo-Implants

The use of titanium (Ti) in dental and orthopedic implant applications is extensive, owing to its remarkable resistance to corrosion, biocompatibility, low density, mechanical strength, and elastic modulus, which closely aligns with bone properties compared to alternative metals 1. There are numerous titanium grades (40-50), only a select few are officially recognized and specified by the American Society for Testing and Materials (ASTM) for use in biological applications. Biomedically compatible grades 1–4, classified as commercially pure (cp-Ti), contain <1% alloying elements, while others are considered Ti alloys with a higher percentage of alloying elements. Among titanium alloys, grade 5 Ti (Ti6Al4V) is predominantly utilized in orthopedic implants 2.Approximately 800,000 knee replacement surgeries are performed annually in the United States alone 3. Projections indicate an anticipated four million joint replacements (hip, knee, and shoulder) annually in the US by 2030 4. Infection rates for orthopedic implants are reported to be below 2%, with the majority occurring within the initial 2 years post-operation 4. The ten-year survival rate for orthopedic implants stands at 85-90% 5 and only 58% of patients can expect their hip replacements to endure for 25 years 6. Implant failure often necessitates revision surgery, incurring high costs, a relatively low success rate, and considerable patient discomfort. Corrosion, arising from the dissolution of titanium and/or alloying elements from the implant, is a prevalent cause of orthopedic failure 7.Surgical procedures, compromising the skin barrier and introducing foreign materials during joint replacement, predispose the body to infection, including bacteria that form biofilms. Gram-negative bacteria are a source of lipopolysaccharide (LPS) 8. Joint movements have the potential to rupture biofilms, releasing LPS into the synovial fluid surrounding the joint. This study aims to explore the impact of LPS in synovial fluid on implant corrosion.The study utilized simulated synovial fluid (SSF) and LPS from Escherichia coli, employing electrochemical techniques to investigate corrosion behavior. Titanium grade 2, 4, and 5 were evaluated for corrosion under unpolished and polished conditions, with and without the presence of LPS in SSF at 37℃ (Figure 1). The unpolished Ti surface consist of titanium with an oxide protective layer on top, as a fresh titanium surface naturally develops a protective oxide layer of titanium oxides when exposed to air or aqueous environments 9. The corrosion resistance of this natural TiO2 layer was examined in the presence of LPS. Furthermore, the disruption of the native oxidation film on the implant surface due to joint movement was examined as a potential factor that may accelerate corrosion. Consequently, the self-healing process of titanium oxide layers emerges as crucial in mitigating failures in orthopedic implants. The influence of LPS on this self-healing process was explored by immersing polished titanium in SSF both with and without LPS for a duration of 80 days. The corrosion current density was measured for all cases using linear sweep voltammetry (LSV) and fitting the data to the Butler-Volmer equation. The native oxide layer was indeed found to be protective compared to the naked metal and the “self-healing” of this film overtime was found to significantly reduce corrosion rates over the 80-day test. Interestingly, LPS was found to both reduce the protective effect of the native layer and disrupt the self-healing process. Electrochemical oxidation of the Ti surface was found strengthen the corrosion resistance of the native film and found to offer a simple pathway towards enhanced corrosion resistance even in the presence of LPS. We propose a mechanism for the LPS effect and conclude that post-operative bacterial infections can significantly exacerbate the corrosion of Ti osteo-implants and increase the likelihood of implant failure. Reference: G. Szczęsny, M. Kopec, D. J. Politis, Z. L. Kowalewski, A. Łazarski, and T. Szolc, Materials (Basel), 15 (10), (2022).J. Quinn, R. McFadden, C.-W. Chan, and L. Carson, iScience, 23 (11), 101745 (2020).G. Castillano, Total Orthopaedic Care, (2022).A. Connaughton, A. Childs, S. Dylewski, and V. J. Sabesan, Frontiers in medicine, 1 22 (2014).R. M. Grzeskowiak, J. Schumacher, M. S. Dhar, D. P. Harper, P. Y. Mulon, and D. E. Anderson, Frontiers in surgery, 7 601244 (2020).J. T. Evans, R. W. Walker, J. P. Evans, A. W. Blom, A. Sayers, and M. R. Whitehouse, The Lancet, 393 (10172), 655-663 (2019).Y. Bao, A. I. Muñoz, C.-O. A. Olsson, B. M. Jolles, and S. Mischler, Materials (Basel), 15 (5), 1726 (2022).C. R. Raetz and C. Whitfield, Annual review of biochemistry, 71 (1), 635-700 (2002).I. Milošev, T. Kosec, and H. H. Strehblow, Electrochimica Acta, 53 (9), 3547-3558 (2008). Figure 1

Characterization of Degradation Mechanisms of Alternative Electrolytes Solutions in Fast Charging Li-Ion Batteries

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

(Invited) Enhancing Stability for Elevated Temperature CO2 Electrolysis: Insights from Catalyst Development and Impact of Carbon Protection

While most lab-scale CO2 reduction experiments are conducted at ambient temperatures (20-25°C), maintaining such low temperatures at an industrial scale will become challenging due to joule heating. In our study, we pushed the boundaries further than the already existing systems, opting for a higher temperature of 85°C for CO2 reduction. This deliberate choice was made to accentuate the deviations from ambient conditions and explore their effects on CO2 electrolyzers.Our current emphasis at elevated temperatures focuses on catalyst development, specifically addressing stability issues induced by the increased temperature. Nevertheless, it was soon discovered that several modifications were required to the system, both in terms of cell materials and operational conditions (e.g. gaskets, pressure arrangements, GDE type, etc.) to allow stable operation at 85°C for extended duration and especially to avoid flooding. Prior research provided valuable insights into the multifaceted impacts of elevated temperatures on the electrochemical reduction of CO2, and proof they go beyond catalyst kinetics. With this in mind, we have synthesized a series of bismuth-related nano catalysts, including oxidized, metallic and carbon containing nanoparticles, and have quantitatively evaluated their activity, selectivity towards formate, and stability at 85°C. Preliminary observations suggest that catalysts without carbon exhibit high initial selectivity, but demonstrate diminished stability over a 24-hour timeframe compared to catalysts with a protective carbon layer. Specifically, we observed an initially high faradaic efficiency toward formate of 85% for commercial bismuth oxide nanoparticles, in contrast to 75% for bismuth nanoparticles with carbon. However, over a 24-hour timeframe, the carbon-free catalyst showed a 20% decrease in FE, while for the carbon-containing catalyst this drop was halved in the same timeframe.By evaluating the role of carbon additives (e.g. their oxidation state, pore size, surface area, hydrophobicity, etc.) our results yield valuable insights into the impact of carbon additives on stability and overall performance, especially at elevated temperature. These findings uncovered critical aspects for catalyst design, providing essential knowledge for future larger-scale applications. Moreover, we shed light on the required advancements and remaining challenges for elevated temperature CO2 reduction electrolysis, which we believe will become the predominant mode of operation for CO2 electrolysis in the future. Figure 1

Cyclability Improvement of Recycled Graphite Materials in Lithium-Ion Batteries Via Conductive Polymer Coating

In recent years, lithium-ion batteries have been widely adopted in electric vehicles and electronics. However, the growing number of retired lithium-ion batteries poses a significant environmental challenge, generating substantial material waste and potential pollution. In most commercial batteries, graphite is the prevalent choice for anode material, owing to its high electrical conductivity and mechanical stability. Therefore, recycling graphite from spent lithium-ion batteries is a potential solution to eliminate the waste and meet the increasing demand.While considerable attention has been directed toward recovering metallic components of the spent lithium-ion batteries, limited effort has been dedicated to recycling graphite. Some previously developed methods include the pyrometallurgy process and hydrometallurgy process. However, due to high energy consumption and environmental pollutions, these methods have not been applied in large scales. Additionally, graphite particles have experienced various aging mechanisms during charge and discharge cycles, such as the formation of a solid electrolyte interface (SEI) and the intercalation of solvent molecules, potentially leading to structural alterations and degradation. Hence, it is advisable to implement surface treatment to enhance capacity stability if the recycled graphite does not perform optimally following the recovery treatment.In this study, we developed a simple process to recycle spent graphite utilizing aqueous and organic wash with N-Methylpyrrolidone (NMP) and toluene, followed by surface coating with the conductive polymer poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic ester) (PFM). The surface coating served as a protective layer of graphite particles and a charge transport agent to enhance conductivity. The morphologies and structures of the pristine, recycled, and PFM-coated recycled graphite samples were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis.To investigate the impact of employing PFM as a binder, electrochemical tests were done using anodes with both recycled graphite and PFM-coated recycled graphite. In recycled-graphite||NMC532 full cell testing, cells with PFM-coated recycled graphite exhibits higher coulombic efficiency (>99.90%) than cells without PFM coating at a rate of 0.33 C. A capacity retention of 77.49% was achieved for PFM-coated cells after 300 cycles, whereas the ones without coating have a capacity retention of 70.21% in average. Rate tests were also conducted on both the cells with and without PFM-coating. It shows that both types of cells support high-rate cycling. About 85% of charge capacity was delivered for cycling at 1 C for both cells with and without PFM-coating.Overall, the recycling method can be easily operated with minimal waste production, low energy consumption, and low economical costs. The PFM coating on the recycled graphite particles leads to enhancement of mechanical strength and efficiency in battery cycling.Fig. A, The process scheme of recycling graphite; B, Pictures of an electrode from spent lithium-ion batteries (left) and an electrode fabricated with recycled graphite (right); C, Capacity retention of recycled graphite without PFM coating (blue) and with PFM coating (green); D, Coulombic Efficiency of recycled graphite without PFM coating (blue) and with PFM coating (green). Figure 1

Cation-Doped Nasicon-Type Electrolyte for Lithium-Ion Batteries

In response to the global challenge of climate change, scientists are actively engaged in developing diverse energy storage solutions. Among these, lithium-ion batteries (LIBs) remain the most prevalent due to their high energy density and reliable cycling performance. Nonetheless, the liquid electrolytes utilized in LIBs pose safety concerns, including the risk of combustion and explosion. To address these issues, extensive efforts have been directed towards the development of solid electrolytes, which offer enhanced thermal stability, thereby improving safety during usage. However, solid electrolytes face challenges such as low ionic conductivity and suboptimal contact with electrodes.Li1.3Al0.3Ti1.7(PO4)3 (LATP) stands out as a promising lithium-ion solid electrolyte, characterized by relatively high ionic conductivity and chemical stability in atmospheric conditions. This study first optimized the stoichiometric ratio and heat treatment during LATP synthesis. The resulting LATP exhibited an ionic conductivity of approximately 4 × 10-4 S/cm at room temperature. Additionally, efforts were made to substitute Ti4+ with another element in the lattice sites, inducing slight lattice distortion and promoting the segregation of a Li-ion-conductive second phase at grain boundaries. Consequently, the ionic conductivity of cation-doped LATP was successfully enhanced to 8 × 10-4 S/cm at room temperature.Nevertheless, an inherent challenge faced by LATP involves its reactivity with lithium metal, posing a significant threat to the cycle life of LIBs. To mitigate direct contact between LATP and lithium metal, a protective layer composed of Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane was introduced. This not only prevented direct contact but also substantially improved the contact resistance. The culmination of these advancements led to the assembly of an all-solid-state lithium-ion battery (ASSLIBs) comprising PVDF-HFP, cation-doped LATP ceramic pellet, LiFePO4 cathode, and Li anode.

Intergranular Shielding of Ultrafine-Grained Ni-Rich Layered Cathode for Advanced Lithium-Ion Batteries

To achieve carbon neutrality on a global scale, fuel-powered vehicles are being steadily phased out over environmentally recommended electrified vehicles (EVs) with low greenhouse gas emissions. In a battery, the cathode is among the foremost components, as it predominantly determines the LIB’s performance and price. However, since current fleet of layered oxide NCM and NCA cathodes have a relatively lower Ni content, they can extract only a limited amount of reversible capacity (210 mAh∙g-1), restricting the driving range of EVs. To achieve higher energy densities, many studies have focused on increasing the average fraction of Ni in NCM or NCA cathodes to more than 90%. However, the extraction of large amounts of lithium ions is seriously compromised by the rapid deterioration of both cycle life and thermal safety. Recent studies on X-doped cathodes (X = B, Nb, Ta, Sb, W, and Mo) have offered promising results by engineering their geometric microstructural configurations to suppress intergranular cracking.1,2 This approach has proven its potential to improve the electrochemical cycling performance of Ni-rich NCA, NCM(A), and NM cathodes. However, prolonged exposure of the Ni-enriched (Ni ≥ 95%) cathode to the electrolyte generally results in continuous oxidative decomposition of electrolytes and subsequent cathode structural transformation, rendering the cathode unsuitable for applications requiring long battery life.3 Herein, we propose a highly stabilized Ni-enriched (Ni ≥ 95%) layered cathode by adopting a multi-stage engineering strategy, i.e., the construction of an ultrafine-scaled microstructure and subsequent intergranular shielding of the refined grains. The formation of an F induced protective layer at the intergranular boundaries of the ultrafine grains in Li[Ni0.95Co0.04Mo0.01]O2 (denoted as Mo1-NC96) noticeably improved both the structural and chemical stability of the cathode, with a limited degree of structural degradation and gas evolution. Reference s : [1] U.-H. Kim, G.-T. Park, B.-K. Son, G.W. Nam, J. Liu, L.-Y. Kuo, P. Kaghazchi, C.S. Yoon, Y.-K. Sun, Nat. Energy, 5 (2020) 860-869.[2] G.-T. Park, B. Namkoong, S.-B. Kim, J. Liu, C.S. Yoon, Y.-K. Sun, Nat. Energy, 7 (2022) 946-954.[3] F. Kong, C. Liang, L. Wang, Y. Zheng, S. Perananthan, R.C. Longo, J.P. Ferraris, M. Kim, K. Cho, Adv. Energy Mater., 9 (2019) 1802586.

Enhancing Efficiency and Durability of PEM Water Electrolysis with Low Iridium Loading through Nanofiber-Modified Porous Transport Electrodes

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1

Protective Layers to Improve the Durability of Lithium Anode

Lithium metal anode possesses the advantages of high theoretic special capacity (3860 mAh g-1), low redox potential (-3.04 V vs. S.H.E.) and abundant lithium source. Therefore, tremendous efforts have been paid to explore the remedies of practical utilization. Its applications were seriously hindered by the severely side reactions between the electrolyte solvents and Li metal due to the mismatched energy-gap and large volumetric variation of lithium deposition layer. To address this challenge, various strategies were developed in whole world to prolong the operational life of lithium metal anode.Our group focused on the development of Li+ filtrated membrane to isolate the fresh Li metal from the solvents. Firstly, we established the transplantable LiF-rich membrane via NiF2 film during formation to significantly improve the durability of lithium metal anode.[1] Then, we prepared a Li-filtrated film via a homemade stacked grapheme (SG), which possesses the higher Li nucleation over-potential than that on rational nano-structured copper scaffold (NCS-SG).[2] Additionally, an advanced SEI-functional membrane derived from LiF decorated SG were proposed to protect lithium anode by retarding electron transfer via C-Fx to avoid lithium deposition on the film surface.[3] Finally, the approaches on compatible electrolytes would be proposed.[4-5] In summary, the durability of lithium metal anode could be significantly prolonged by the appropriate protective strategies. Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant No. 22179052) and the Excellent Discipline Cultivation Project by JHUN (2023XKZ013). Reference [1] Z. Peng, N. Zhao, Z. Zhang, et al., Nano Energy, 2017, 39: 662-672.[2] F. Ren, Z. Peng, M. Wang, et al., Energy Storage Materials, 2019, 16: 364-373.[3] M. Wang, Z. Peng, D. Wang, Advanced Energy Mater., 2019, 1802912.[4] Y. Qin, D. Wang, M. Liu, et al., ACS Appl. Mater. Interfaces, 2021, 13, 49445−49452.[5] Y. Qin, D. Wang, Submitted to Advanced Mater.

(Invited) In Situ spectroscopy of Electrocatalytic and Photocatalytic Interfaces

We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces in situ under electrochemical working conditions. These spectroscopies include sum frequency generation (SFG), transient reflectance/absorption spectroscopy (TAS/TRS), and surface enhanced Raman spectroscopy (SERS). Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields using Stark-shifts of nitrile-functionalized silicon photoelectrodes.6 We also report several spectroscopic methods for monitoring local electric fields (within the double layer), local pH,1 photo-induced surface potential and charge transfer2 at electrode surfaces using surface reporter molecules. The Figure below illustrates two surface reporter molecules for determining the local pH, local surface potential, and charge transfer at electrode and photoelectrode surfaces. We also measured the stacking dependence and Resonant interlayer excitation of monolayer WSe2/MoSe2 heterostructures for photocatalytic energy conversion.3 Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D2O molecules at a graphene electrode surface, which is related back to the “stiffness of the ensemble”.4 Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.5 Using transient reflectance spectroscopy (TRS), we measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interfaces in situ under various electrochemical potentials.6 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes.7 1 Wang, Y.Y., et al., Measuring Local pKa and pH Using Surface Enhanced Raman Spectroscopy of 4‐Mercaptobenzoic Acid. Langmuir, DOI:10.1021/acs.langmuir.3c02073 (2023).2 Li, R., et al., SERS Detection of Charge Transfer at Electrochemical Interfaces Using Surface-Bound Ferrocene. The Journal of Physical Chemistry C, 127, 14263 (2023).3 Chen, J., et al., Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).4 Montenegro, A., et al., Field-Dependent Orientation and Free Energy of D2O at an Electrode Surface Observed via SFG Spectroscopy. Journal of Physical Chemistry C, 126, 20831 (2022).5 Wang, Y., et al., In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society, 144, 3517 (2022).6 Xu, Z.H., et al., Direct In Situ Measurement of Quantum Efficiencies of Charge Separation and Proton Reduction at TiO2-Protected GaP Photocathodes. Journal of the American Chemical Society, 2860-2869 (2023).7 Wang, Y. and S.B. Cronin, Performance Enhancement of TiO2-encapsulated Photoelectrodes Based on III–V Compound Semiconductors, in Ultrathin Oxide Layers for Solar and Electrocatalytic Systems. 2022, Royal Society of Chemistry. p. 103-134. Figure 1

Peculiar photoelectrochemical activity of zinc oxide and tin dioxide

Zinc oxide thin films made by pulsed reactive magnetron sputtering combined with RF ECWR plasma on FTO or ITO substrates exhibit high photoelectrochemical activity for water splitting under UV light, but are unstable against photocorrosion. It can be suppressed by a protective layer of SnO2 made by atomic layer deposition. The SnO2 layer is quasi-amorphous in the as-received state, but the thermal treatment causes partial crystallization to cassiterite, without significant change of the optical band gap. Ferrocene in acetonitrile electrolyte solution is a useful redox probe for the blocking-quality tests of thin films of n-semiconductors. Both ZnO and SnO2 are sensitive to irreversible electrochemical doping at potentials negative to the flatband potential. The flipping of electrochemical work functions of the Zn-terminated (0001) and O-terminated (000–1) faces of ZnO (wurtzite) takes place in acetonitrile vs. aqueous electrolyte solutions. The potentials for photocurrent onset are near the flatband potentials in an aqueous electrolyte solution for both ZnO and SnO2.