Rich Layer Research Articles

A Lithiophilic–Lithiophobic Gradient Solid Electrolyte Interface Toward a Highly Stable Solid‐State Polymer Lithium Metal Batteries

AbstractThe functional lithiophilic−lithiophobic gradient solid electrolyte interphase (SEI) between Li‐metal anode and solid‐state polymer electrolytes may be effective in addressing the long‐standing issue of side reactions and Li‐dendrite growth during repeated deposition or dissolution in solid‐state polymer‐based high‐energy‐density batteries. Herein, a reliable lithiophilic–lithiophobic gradient SEI (G‐SEI) of LiAg‐LiF/Li3N is in situ formed by AgTFSI, used as an additive for polyethylene oxide‐based electrolyte (PEO‐Ag). The upper layer consists of a lithiophobic LiF/Li3N‐rich layer, wherein LiF possesses a high interfacial energy, while Li3N enables fast Li+ diffusion, which synergistically facilitates the uniform deposition of Li+. Lithiophilic Li–Ag alloy can effectively reduce the nucleation overpotential and promote more planar growth of lithium. Furthermore, such G‐SEI possesses a high mechanical modulus, mitigating the penetration of dendrites through the SEI and thereby preventing the continuous degradation of the PEO‐based electrolyte. As a result, an over three times improvement in the lifespan of Li | PEO‐Ag | LFP cell is achieved, demonstrating an 81.4% capacity retention rate after 500 cycles at 1C, as compared to Li | PEO | LFP cell with common SEI. Thus, the developments of the lithiophilic‐lithiophobic gradient SEI provide a substantial path toward high‐performance solid‐state lithium batteries.

Fabrication of large-scale steel-aluminum components with homogenously distributed amorphous interfacial layer and enhanced bonding strength using modified friction stir additive manufacturing

Large-scale components of steel and aluminum alloys (Fe-Al) with high bonding strength are highly needed from space exploration to the fabrication of transportation systems. The formation of detrimental intermetallic compounds at the Al-Fe interface has limited the application range of the Fe-Al components. The modified friction stir additive manufacturing was developed for fabricating large-scale Fe-Al components with homogenously distributed interfacial amorphous layers rather than detrimental intermetallic compounds. The interfacial amorphous layers comprised an Mg-O rich amorphous layer < 20 nm in thickness and an Al-Fe-Si amorphous layer < 120 nm in thickness. The interfacial amorphous layers exhibited high thermal stability and did not change even after the post-processing heat treatment of heating at 500 °C for 20 min and aging at 170 °C for 7 h. The tensile strengths of the Fe-Al tensile specimens were increased from 160 to 250 MPa after the application of the post-processing heat treatment. The fracture occurred in the aluminum alloys instead of at the dissimilar metal interface, demonstrating that high bonding strength at the Al-Fe interface was enabled by the formation of homogenously distributed interfacial amorphous layers.

High temperature oxidation behavior and microstructure evolution of medium Mn steel

The phase transition, microstructure evolution and oxidation behavior of Fe-0.2C-12Mn-3Al-2Cu-xNi steel during the oxidation process for 120 min at 1050 °C-1200 °C were systematically studied. The twin boundaries will provide rapid channels for the oxygen atoms diffusion, while the (110) and (111) grain orientations show a low oxidation resistance property, which also then promote the oxygen atoms diffuse along grain boundaries. Cu and Ni enrichment areas were formed on the subsurface in the 1100 °C-1200 °C oxidation stage, which limited the ion diffusion rate on the subsurface and prevented the further growth of the oxide layer. The oxidation temperature, Mn concentration gradient and [CuNi] rich region on the subsurface contribute to multi-oxide layer structure: Mn deficient region, Mn rich region, transition layer and inner oxide layer. The Mn deficient region with rough surface is mainly composed of Fe2O3, Fe3O4 and Mn3O4, while the Mn rich region is mainly composed of FeO and MnO. The honeycomb transition layer and inner oxide layer is composed of FeO, MnO, MnAl2O4, and Al2O3.

Weathering as a control on the triple oxygen isotopes of groundwater-associated ferromanganese deposits: lessons from the Grimlock Ni–Co–Mn prospect, Northern Territory, Australia

At the Grimlock laterite deposit (Northern Territory, Australia), Co and Ni mineralization occurs mainly in the Mn-oxide rich layers of the ferromanganese (Fe-Mn) crust overlying ultramafic bedrock. Groundwater-associated Fe-Mn crusts consist of mineral (e.g. Mn-oxide, Fe-oxyhydroxide and silicate) groups suitable for studying triple oxygen isotopes and present unique interpretative challenges (e.g. small Mn-oxide fractions relative to Fe-Mn precipitates from other formation environments and extensive weathering). We evaluate triple oxygen isotopes within the context of changes to properties (i.e. mineralogy, major and trace element geochemistry, and degree of weathering) of a lateritic profile. We use pre-existing mineral-water fractionation factors, meteoric water δ 18 O and temperature data to calculate δ 18 O values of fully altered mineralogical endmembers, then, using mass balance, discuss scenarios to elucidate measured whole-rock δ 18 O values. The δ ′ 18 O (′ denotes linearized notation) and Δ ′ 17 O of near-surface samples (0–8 m) are generally lower (mean of 8.892‰) and higher (mean of −0.141‰), respectively, than the δ ′ 18 O (mean of 12.767‰) and Δ ′ 17 O (mean of −0.176‰) of samples from greater depths (19–22 m). At 16–17 m depth, δ ′ 18 O and Δ ′ 17 O are relatively high (means of 17.509 and −0.118‰, respectively). The measured whole-rock δ 18 O values are explainable by substituting lower δ ′ 18 O values for the Mn-oxide and Fe-oxyhydroxide fractions, and higher δ ′ 18 O values for the aluminosilicate fraction, changes coinciding with greater alteration. These results suggest that mineral weathering is primarily responsible for observed variations in the triple oxygen isotopes of groundwater-associated Fe-Mn crusts, rather than variation in the initial source of oxygen incorporated into Mn-oxide. Supplementary material: Grimlock sample photographs, XRD patterns and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7071907

Stabilized Li‐Rich Layered Oxide Cathode by a Spontaneously Formed Yb and Oxygen‐Vacancy Rich Layer on the Surface (Small 8/2024)

Stabilized Li‐Rich Layered Oxide Cathode by a Spontaneously Formed Yb and Oxygen‐Vacancy Rich Layer on the Surface (Small 8/2024)

Monitoring Erosion of a Submerged Stone Age Site and Its Implications for Managing Underwater Cultural Heritage. A Case Study at Tybrind Vig, Denmark

Abstract Known locations with submerged and well-preserved Stone Age sites in Denmark are, in most cases, under constant threat of erosion. The results presented here have been gathered at Tybrind Vig by surveying a 165 m-long transect at 5-metre intervals from the shore, by measurements taken with a total station. To supplement this, the surrounding area was surveyed with an echo sounder/sonar unit that yielded 3D coordinates post-processed in GIS to investigate volumetric changes in the seabed over time. The transect data was used to calibrate the elevation data from the echo sounder, following the correction of sea level change with data gathered from the Danish Coastal Authority. It was established that sediment transport – both erosion and accumulation – has occurred, but from the methods used, it cannot be determined how much of the archaeologically rich gyttja layers have been eroded at Tybrind Vig.

High-Rate SiO Lithium-Ion Battery Anode Enabled by Rationally Interfacial Hybrid Encapsulation Engineering.

The development of a high-rate SiO lithium-ion battery anode is seriously limited by its low intrinsic conductivity, sluggish interfacial charge transfer (ICT), and unstable dynamic interface. To tackle the above issues, interfacial encapsulation engineering for effectively regulating the interfacial reaction and thus realizing a stable solid electrolyte interphase is significantly important. Hybrid coating, which aims to enhance the coupled e-/Li+ transport via the employment of dual layers, has emerged as a promising strategy. Herein, we construct a hybrid MXene-graphene oxide (GO) coating layer on the SiO microparticles. In the design, Ti3C2Tx MXene acts as a "bridge", which forms a close covalent connection with SiO and GO through Ti-O-Si and Ti-O-C bonds, respectively, thus greatly reducing the ICT resistance. Moreover, the Ti3C2Tx with rich surface groups (e.g., -OH, -F) and GO outer layers with an intertwined porous framework synergistically enable the pseudocapacitance dominated behavior, which is beneficial for fast lithium-ion storage. Accordingly, the as-made Si@MXene@GO anode exhibits considerably reinforced lithium-ion storage performance in terms of superior rate performance (1175.9 mA h g-1 at 5 A g-1) and long cycling stability (1087.6 mA h g-1 capacity retained after 1000 cycles at 2.0 A g-1). In-depth interfacial chemical composition analysis further reveals that an inorganically rich interphase with a gradient distribution of LiF and Li2O formed at the electrolyte/anode interface ensures mechanical stability during repeated cycles. This work paves a feasible way for maximizing the potential of SiO anodes toward fast-charging lithium-ion batteries.

High-Temperature Corrosion of High- and Medium-Entropy Alloys CrMnFeCoNi and CrCoNi Exposed to a Multi-Oxidant Atmosphere H2O–O2–SO2

The high-temperature corrosion behaviors of the equimolar CrCoNi medium-entropy alloy and CrMnFeCoNi high-entropy alloy were studied in a gas atmosphere consisting of a volumetric mixture of 10% H2O, 2% O2, 0.5% SO2, and 87.5% Ar at 800 °C for up to 96 h. Both alloys were initially single-phase fcc with a mean grain size of ~ 50 μm and a homogeneous chemical composition. The oxide layer thickness of CrMnFeCoNi increased linearly with exposure time while it remained constant at ~ 1 μm for CrCoNi. A Cr2O3 layer and minor amounts of (Co,Ni)Cr2O4 developed on the latter while three oxide layers were detected on the former, i.e., a thin and continuous chromium rich oxide layer at the oxide/alloy interface, a dense (Mn,Cr)3O4 layer in the center and a thick and porous layer of Mn3O4 and MnSO4 at the gas/oxide interface. Additionally, a few metal sulfides were observed in the CrMnFeCoNi matrix. These results were found to be in reasonable agreement with thermodynamic calculations.

Rational construction Ag/LiF/sulfide rich protective layer for remarkably enhancing the stability of Li metal anodes

Li metal is a promising anode material for high-energy–density batteries due to its high theoretical capacity and low redox potential. However, both the uncontrolled Li dendrite growth and unstable solid electrolyte interphase (SEI) layer restricts its large-scale practical applications. Herein, an artificial protective layer consisting of Ag nanoparticles, lithium fluoride (LiF) and sulfide are innovatively designed and fabricated via the in-situ chemical reaction between Ag(I) trifluoromethylthiolate (AgSCF3) and Li metal. Density functional theory (DFT) results indicate that Ag nanoparticles have a high binding energy with Li atom and LiF/sulfide have wide band gap, which would provide plenty of nucleation sites for Li+ and reduce the direct contact between inner Li metal and the electrolyte. The co-existence of Ag and LiF/sulfide results in a strong synergistic effect, and this is confirmed by the systematical comparison with single modified Ag-Li and double modified F/S-Li anodes. Benefitting from this synergistic effect, the Ag/F/S-Li symmetrical cells can stably work for 2000 h with low-voltage hysteresis at current density of 1 mA cm−2. Full cells assembled with LiCoO2 (LCO) and LiFePO4 (LFP) cathodes displays much better long‐term cycle performance when the Ag/F/S-Li anode is applied. Furthermore, this Ag/F/S-Li modification can significantly enhance discharge capacity, rate performance, as well as energy density of Li(or LiB alloy)||MnO2 primary cells. This promising work promotes the practical application of Li metal and provides new insight into the protective layer design in stable Li metal batteries.

Influences of counterparts on the high-temperature tribological properties and glaze layer formation of pre-oxidized cobalt-based alloys

The tribological behaviors, wear mechanism and formation of the glaze layer of a cobalt-base alloy dry sliding against different counterparts (Si3N4 and GCr15 steel) were investigated. Cobalt-base alloys tend to suffer from adhesive wear when GCr15 steel is used as a counter material compared to Si3N4. At 800 °C, the counter material strongly influences the formation of glaze layers on the surface of cobalt-base alloys.When Si3N4 sliding against the cobalt-base alloy, a (Cr, O)-rich glaze layer is formed by the “compaction-sintering” of wear debris on wear surface of cobalt-based alloys.When GCr15 steel was used as the counterpart material, a (Fe, O)-rich glaze layer was formed on the wear surface due to thermal softening and material transfer.

MTUW-GAN: A Multi-Teacher Knowledge Distillation Generative Adversarial Network for Underwater Image Enhancement

Underwater imagery is plagued by issues such as image blurring and color distortion, which significantly impede the detection and operational capabilities of underwater robots, specifically Autonomous Underwater Vehicles (AUVs). Previous approaches to image fusion or multi-scale feature fusion based on deep learning necessitated multi-branch image preprocessing prior to merging through fusion modules. However, these methods have intricate network structures and a high demand for computational resources, rendering them unsuitable for deployment on AUVs, which have limited resources at their disposal. To tackle these challenges, we propose a multi-teacher knowledge distillation GAN for underwater image enhancement (MTUW-GAN). Our approach entails multiple teacher networks instructing student networks simultaneously, enabling them to enhance color and detail in degraded images from various perspectives, thus achieving an image-fusion-level performance. Additionally, we employ middle layer channel distillation in conjunction with the attention mechanism to extract and transfer rich middle layer feature information from the teacher model to the student model. By eliminating multiplexed branching and fusion modules, our lightweight student model can directly generate enhanced underwater images through model compression. Furthermore, we introduce a multimodal objective enhancement function to refine the overall framework training, striking a balance between a low computational effort and high-quality image enhancement. Experimental results, obtained by comparing our method with existing approaches, demonstrate the clear advantages of our proposed method in terms of visual quality, model parameters, and real-time performance. Consequently, our method serves as an effective solution for real-time underwater image enhancement, specifically tailored for deployment on AUVs.

Application of Small- and Ultra-Small-Angle Neutron Scattering for the Characterization of Mechanically Plated Coatings

Post-mechanical plating heat treatment induces the formation of an iron–zinc (Fe-Zn) rich intermetallic layer between Zn and ZnSn coatings and the substrate. Despite increased outer coating porosity, the corrosion resistance of Zn- and ZnSn-coated steels significantly improves after heat treatment, attributed to the formation of intermetallic phases. This study employs small- and ultra-small-angle neutron scattering (SANS and USANS) to investigate the behavior of mechanically plated Zn and ZnSn coatings pre- and post-heat treatment. In the presence of a relatively thick steel substrate, strong multiple scattering occurs. However, by identifying a specific high Q-range region where multiple scattering is negligible, we reveal small but significant differences. Porod’s slopes, denoted as ‘n’, are calculated for uncoated steel, and Zn- and ZnSn-coated steels (both with and without heat treatment). These slope values reflect contributions from different interfaces on the particles’ surface roughness. Despite the challenges of multiple scattering, our findings offer valuable insights into coatings’ behavior. The study lays a foundation for future investigations into coating behavior using SANS/USANS techniques.

A Spectral Analytical Study of Melodic Innovations in the Opera “Aleko” and Rachmaninoff

Abstract The opera “Aleko” is a graduation work composed by Rachmaninoff, for which the opera was born in Russia in the nineteenth century and has a strong literary and artistic value. This study tries to extract the time-frequency melodic characteristics of the opera “Aleko” by using the spectral analysis technique as a research tool combined with the Fourier transform and constant Q transform. From the perspective of quantitative analysis, the innovative laws of Rachmaninoff’s melodic features are summarized with the intention of revealing the great artistic charm of this opera work. The results of the spectral analysis show that the amplitude of the first part of “Aleko” is 27.5dB, which forms its unique “Rach’s style” through its innovative “stepped” meandering tones. At the same time, the rich melodic layers of “Aleko” emphasize the drama of the opera and make the internal structure of the phrases stronger.

High-temperature oxidation behaviors and mechanical properties of TiAlCrMnHEAs during heat treatment

A series of TiAlCrMn high entropy alloys (HEAs) with variable atomic ratios of Al, Cr, and Mn were prepared using vacuum melting. High-temperature oxidation behaviors and mechanical properties were investigated before and after heat treatment. The oxidation mass gain rate is declined dramatically with increasing Al, Cr, and Mn element contents. Enhanced oxidation resistance is attributed to a continuously dense (Al,Cr)-rich oxidation layer, which can hinder the inter-diffusion of O and alloying elements. Furthermore, microhardness increases monotonously with increasing Al, Cr, and Mn element contents of the alloys before and after heat treatment. Grain coarsening can result in lower microhardness, but precipitation strengthening contributes to higher hardness of the alloys with high alloying element contents. Meanwhile, deformation-induced strengthening also contributes to higher compressive strength. The value after heat treatment at 500 °C is lower than that of as-cast samples while an increased value occurs after heat treatment at 900 °C accompanied by sacrificing the malleability.

The Early PPNB of Amqa (Upper Galilee, Israel) from a Regional Perspective

Abstract. Salvage excavations at the site of Amqa (upper Galilee, Israel) revealed a rich PPN occupation layer confined to a natural bedrock depression covering ca. 25 m2. The finds present an intriguing combination of EPPNB traditions and PPNA elements, including a dominant component of imported bi-directional blade blanks and the prominent use of non-local pink/purple and beige flint types, as well as a significant microlithic component. Among the projectile points, Helwan points are the most common, with a notable presence of Khiam points and single examples of northern types, such as “Foliate”/“Nemrik” points and Hollow-based points. Reaping knives are abundant alongside finely denticulated sickle blades. Bifacial tools are thin and unpolished, some of them bearing tranchet removal scars. Long-distance contacts are indicated by a rich obsidian assemblage and by the presence of bifacial tools made of the green mineral nephrite. Although absolute dating could not be achieved due to the poor preservation of organic material, the site of Amqa presents a notable addition to the discussion of early Neolithic dynamics and settlement patterns in the southern Levant. This paper presents the site of Amqa and the analyses of the material culture reflected through the finds and discusses its contribution to the regional debate regarding the onset of “Neolithic lifeways” in our region.

АРХЕОЛОГІЧНІ ДОСЛІДЖЕННЯ ДАВНЬОРУСЬКИХ ПОСЕЛЕНЬ 10–13 СТОЛІТЬ НА ТЕРИТОРІЇ СЛОВЕЧАНСЬКО-ОВРУЦЬКОГО КРЯЖУ

The article highlights the history of research on the peculiarities of the settlement structure of theAncient Rus period on the territory of a unique natural formation – the Slovechansko-Ovruchskyi ridge, located in the north of the Zhytomyr region. The purpose of the article: to analyze the stages of research of ancient Rus objects that had special conditions of development during the 10–13 centuries. The methodological basis of the research is the principle of scientificity, methods of empirical and theoretical research. Scientific novelty: for the first time, information on the study of ancient Russian settlements, which arose and developed in specific economic conditions during the 10-13 centuries, was analyzed and systematized. Conclusions. In addition to good fertile soils and a favorable climate for agriculture, the territory of the Ovrutsky ridge also attracted people with deposits of pink pyrophyllite slates. Mining, processing and manufacturing of things from it become the main occupation of the local the Ancient Rus population. A unique settlement structure is formed on the territory of the ridge, which traditionally consists of a settlement, a post, open settlements and burial grounds. But the peculiarity is that open settlements have a large area, they can conditionally be combined into agglomerations. Also, the settlements are specialized, their population is closely related to the development of pyrophyllite deposits, its extraction, processing, and transportation are the main occupations of the ancient Rus population of the Ovrutsky Ridge. Ancient Rus on the specified territory were destroyed for a long time, but from the end of the 9th century. they began to be discovered and recorded by scientists. During the entire 20th century the sights of the region were examined by archaeologists, but no research was carried out. only from the end of the 20th century. The Ovrutsk archaeological expedition started working in the region, which discovered unique sights - specialized settlements with a rich cultural layer. But the archaeological sites of the region also require protection. The activities of the employees of the Ovrutsk archaeological expedition within the framework of the "Ovrutsk project" created for the study and protection of the monuments of the former Ovrutsk volost are aimed at this.

Optimization of composite-modified asphalt ratio and performance evaluation of rich bottom layer mixes

This study focused on developing a high-toughness composite-modified asphalt (CMA), to enhance the performance of rich bottom layer mixes and its crack resistance. The content of crumb rubber (CR), epoxy resin (ER), and polyaryl polymethylene isocyanate (PMDI) were chosen as design parameters. Response surface methodology (RSM) was employed to develop models for creep strength (S), fatigue performance parameter (Nf), yield energy (YE), and Brookfield viscosity (BV) of CMA. Then, these models were used to optimize the content of modifiers. Additionally, rich bottom layer mixes were designed using SBS-modified asphalt (SMA) and the newly developed CMA as binders, and their performances were evaluated. The results demonstrated the accuracy and predictive ability of the RSM models. The composite-modified asphalt mixes (CMAM) showed superior road performance and crack resistance compared to SBS-modified asphalt mixes (SMAM). Importantly, CMAM aligned effectively with the functional requirements of the rich bottom layer. This research contributes novel materials and methods for enhancing pavement crack resistance, providing valuable insights for improving the durability and longevity of pavements.

Realization High-Voltage Stabilization of O3-Type Layered Oxide Cathodes for Sodium-Ion Batteries by Sn Simultaneously Dual Modification

The total global production of lithium-ion batteries (LIBs) used in electric vehicles and stationary energy storage devices has increased sharply to reach the targeted Net Zero by 2050. This leads to concerns about the future and long-term availability and cost of critical raw materials (cobalt, nickel, lithium and copper) employed in LIBs. Therefore, alternative new-generation batteries with comparable performance but using less critical raw materials are needed.Sodium-ion Batteries (NIBs) offer a wealth of possibilities for inexpensive and sustainable energy storage devices. To maximize their potential, new cathode materials with high energy densities and stable structures are required. Cobalt-free sodium transition metal oxides of O3 type are a predominant cathode for NIBs due to their appreciable specific capacity, reduction in the use of critical elements, and the potential to rival LiFePO4 in terms of energy density. However, rapid capacity fading caused by serious structural and interfacial degradation hamper this process.Herein, we provide a novel Sn-modified O3-type NaNi1/3Fe1/3Mn1/3O2 cathode with improved high-voltage stability by bulk Sn doping and surface coating simultaneously. The bulk substitution of Sn4+ stabilizes the crystal structure by alleviating the irreversible high voltage phase transition and lattice structure degradation. In the meantime, the spontaneously formed tin rich surface layer effectively inhibits surface parasitic reactions and improves interfacial stability during cycling. As a result, the Sn-modified NaNi1/3Fe1/3Mn1/3O2 cathode exhibited excellent cycling performance by an almost doubled capacity retention increase after 200 cycles within 2.0-4.1V. The influence of Sn modification on the crystal structure and electrochemical properties has been investigated for the first time, and the mechanism was studied through an extensive analysis by in situ XRD, HRTEM, FIB-SEM, XPS and Mössbauer spectroscopy.This work offers an industrially feasible strategy to simultaneously stabilize the bulk structure and interface for O3-type layered cathodes for SIBs and raises the possibility of similar effective strategies to be employed for other energy storage materials Figure 1

Effect of Secondary Oxidants (CO2 and/or H2O) on Oxidation of Fe-20Cr-(Mn, Si)

Ferritic heat resisting alloys are widely used in industry owing to their combination of economy, reasonable strength, and high temperature corrosion resistance. Alloy design centres on forming and maintaining an external, slow growing protective oxide scale by selective oxidation of the desired metal, commonly chromium. Design methods based on diffusion theory succeed when the service environment is oxygen or clean, dry air. However, they can fail badly when secondary oxidants (like CO2 and water vapour) are present, which is commonly the case in energy production etc. This work investigates the effect of CO2 and H2O on corrosion behaviour of Fe-20Cr, in comparison with that in pure O2. The alloying effect of Si and Mn on oxidation behaviour of Fe-20Cr in different gases is also investigated.Model alloys Fe-20Cr, Fe-20Cr-1Si, Fe-20Cr-2Mn (all in wt%) were arc melted and annealed. Sample coupons were cut, ground, mechanically polished to 3mm finish, and further electro-polished to remove subsurface deformation zones. They were then exposed to Ar-2O2, Ar-20H2O-2O2, Ar-20CO2-2O2, Ar-CO2-H2O and Ar-CO2-H2O-O2 (all vol%) gas mixtures, at 650°C for 150h. Corrosion products and cross-sections were examined using optical microscopy, X-ray diffraction, Raman Spectroscopy and scanning electron microscopy equipped with energy dispersive X-ray spectrometry.The alloy behaved protectively in Ar-2O2, forming a very thin Cr2O3 layer on its surface. However, when CO2 or/and H2O was added to oxygen, breakaway oxidation resulted, forming thick multi-layered oxide scales. Detailed analysis revealed that this multi-layered structure contains four layers, where the outer layer was Fe2O3, overlying an Fe3O4 layer and FeCr2O4 spinel innermost layer, and an internal oxidation zone was formed beneath the scale. In the low environment of Ar-20CO2-20H2O, Fe3O4 layer, FeCr2O4 spinel layer and internal oxidation zone formed a three-layered structure. No Fe2O3 was found, which is attributed to the decrease in oxygen partial pressure.Carburisation of Fe-20Cr also resulted from exposure to the three CO2-bearing gases. The deepest and densest internal carburisation zone formed in Ar-20CO2-2O2. In Ar-20CO2-20H2O-2O2 and Ar-20CO2-20H2O, internally precipitated carbides were sparser, but still obvious.Silicon addition dramatically improved the oxidation resistance of Fe-20Cr. Weight gains in all gases were sharply decreased compared with those of Fe-20Cr. As with Fe-20Cr, a very thin Cr2O3 layer on the Si-bearing alloy reacted in Ar-2O2,together with a thin underlying silica layer, indicating that the alloy was fully protected. Unlike Fe-20Cr, the Fe-20Cr-1Si alloy was also protected in Ar-20CO2-2O2. However, when water vapour was present, the alloy started to go into breakaway, forming local Fe-rich oxide nodules. In Ar-20H2O-2O2, some small nodules, consisting of external Fe2O3 and inner spinel were distributed on an otherwise thin, protective chromia scale. In Ar-20H2O-20CO2-2O2 and Ar-20H2O-20CO2, an additional Fe3O4 layer was observed in nodules, between Fe2O3 and inner spinel. Thus, for Fe-20Cr-1Si samples, Fe3O4 can only be observed if 20%CO2 and 20%H2O were both present. Additionally, some small internal oxide particles were observed at breakaway nodule areas in all these three gasses. Internal carbides were found only under the big iron oxides nodules grown in Ar-20CO2-20H2O-2O2.Manganese addition did not much influence the corrosion resistance of Fe-20Cr. In general, oxide morphologies were similar to those of Fe-20Cr. In Ar-2%O2 gas, a thin Mn rich chromium oxide layer was formed over the entire alloy surface, indicating that sample was fully protected. Multi-layered thick oxides developed when CO2 or/and H2O were added. For high gases with the addition of H2O or CO2 (Ar-20H2O-2O2, Ar-20CO2-2O2, and Ar-CO2-H2O-O2), three-layered oxide structures were found to be made up of Fe2O3, Fe3O4, and spinel layers, in sequence from the outer surface to the inner alloy. It is worth noting that the oxide layers were not completely continuous in Ar-20CO2-2O2. About 15% of the cross-section area was protected which indicated that Mn can slightly improve the corrosion resistance in dry CO2 and O2 environments. In lower oxygen partial pressure gas (Ar-CO2-H2O), no Fe2O3 was found, and only Fe3O4 and spinel constituted the oxide scale. The main difference was that the internal oxidation zone became tiny on Fe-20Cr-2Mn samples. Internal carbides were still found under inner oxide in all CO2 bearing gases, most obviously in Ar-20CO2-2O2. However, in all cases the carbide quantities were far less than those in Fe-20Cr, indicating that Mn addition partially inhibited carburisation.After the thermodynamics of the reaction product phase assemblages are considered, this complex pattern of reaction products is discussed in terms of the permeability of different oxides to carbon- and hydrogen-bearing species, along with interactions between secondary oxidants on oxide surfaces and grain boundaries.

Determining the Composition and Structure of a High-Performing SEI Layer for Lithium-Mediated Nitrogen Reduction to Ammonia

The industrial synthesis of ammonia (NH3) via the Haber-Bosch process has enabled mass production of fertilizer and the human population growth to 8 billion.1 NH3 also shows promise as a long-term, energy-dense fuel amenable to widespread distribution.2 However, the Haber-Bosch process operates at high temperatures and pressures in centralized facilities and accounts for 1.3% of global carbon emissions.1,2 To ensure a food-secure future and realize NH3 as a truly carbon-free fuel, we must develop an NH3 synthesis alternative that operates at ambient conditions and can be driven by renewables.One of the most promising NH3 synthesis method under mild conditions is the electrochemical, Li-mediated process (Li-NRR). In this process, Li is electrodeposited from solution and reacted with N2 to form Li3N. A proton shuttle, e.g., ethanol, protonates Li3N to form NH3.3 The electrodeposited Li forms a solid-electrolyte interphase (SEI) layer that controls N2, Li+, and H+ transport and is key to system performance. The use of fluorinated Li salts, e.g., LiBF4, have recently advanced Li-NRR system performance. Improved selectivity has been attributed to changes in the SEI layer, but evaluating SEI structure and composition remains a significant challenge.3 Neutron-based characterization methods, complementary to X-ray methods, offer unique benefits to study SEI layers containing light elements such as Li- and H; for example, an element’s neutron scattering cross section does not depend on its atomic number.4 In this work, we studied the formation of the SEI layer in-situ before and after applying -0.3 mA/cm2 in galvanostatic experiments (chronopotentiometry, CP) on a copper (Cu) working electrode. We utilized a combination of deuterated and non-deuterated solvents and proton donors to distinguish their contributions to the SEI. We found that the SEI forms two layers: a compact, lithium rich layer, and a diffuse layer with carbonaceous species (Figure 1).4 We also identified the presence of boron in the layers, indicated by neutron absorption. Finally, we observed more proton-rich species in experiments containing the non-deuterated H+ donor, corroborating previous studies that indicate that Li-ethoxide may be a major component of the diffuse SEI (Figure 1b-c).5 Compared to LiClO4-based electrolytes, the structure of these LiBF4-derived layers is consistent even after repeated current cycling, indicating a more stable SEI structure and suggesting a relationship between SEI stability and increased Li-NRR performance.References Nørskov, J. et al. DOE Roundtable Report (2016).Chang, F. et al. Advanced Materials 33, 2005721 (2021).Li, S. et al. Joule 6, 2083–2101 (2022).Blair, S.J., Doucet, M. et al. ACS Energy Lett., 7, 6, 1939-1946 (2022).Steinburg, K. et al. Nature Energy, 8, 138-148 (2023). Figure 1: (a) reflectivity curve before and after 4 mins constant applied current at -0.3 mA/cm2 (chronopoteniometry, CP) to plate Li using 1 M LiBF4 with 1 vol% ethanol, (b) resulting scattering length density (SLD) profile, and (c) schematic of layers indicated in SLD profile Figure 1