High-resolution Secondary Mass Research Articles

Impact of Residual Compositional Inhomogeneities on the MCT Material Properties for IR Detectors.

HgCdTe is a well-known material for state-of-the-art infrared photodetectors. The interd-iffused multilayer process (IMP) is used for Metal-Organic Chemical Vapor Deposition (MOCVD) of HgCdTe heterostructures, enabling precise control of composition. In this method, alternating HgTe and CdTe layers are deposited, and they homogenize during growth due to interdiffusion, resulting in a near-uniform material. However, the relatively low (350 °C) IMP MOCVD growth temperature may result in significant residual compositional inhomogeneities. In this work, we have investigated the residual inhomogeneities in the IMP-grown HgCdTe layers and their influence on material properties. Significant IMP growth-related oscillations of composition have been revealed in as-grown epilayers with the use of a high-resolution Secondary Ion Mass Spectroscopy (SIMS). The oscillations can be minimized with post-growth annealing of the layers at a temperature exceeding that of growth. The electric and photoelectric characterizations showed a significant reduction in the background doping and an increase in the recombination time, which resulted in dramatic improvement of the spectral responsivity of photoconductors.

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

Cubic-stabilized zirconia doped with 8 mol% Y2O3 (8YSZ) is a highly popular electrolyte material for solid oxide fuel cells (SOFCs) due to its exceptional oxide ionic conductivity, which remains consistent across a broad range of oxygen partial pressures. However, previous studies [1,2] have shown that the addition of nickel oxide (NiO) to 8YSZ can expedite the phase transformation process (from cubic to tetragonal) when exposed to a reducing atmosphere at relatively high temperature as 900℃. This phase transformation is closely related to the degradation of 8YSZ's conductivity. Therefore, it is crucial to investigate whether NiO, which should dissolve into the YSZ electrolyte during the co-sintering process with the NiO-YSZ anode at high temperatures, can lead to a similar phenomenon in anode-supported cells (ASCs). Hence, investigating the NiO solid solution phenomenon and its effect on the phase transformation in the YSZ electrolyte of ASCs can offer insights into its degradation behavior.In this study, NiO-YSZ anode support and YSZ electrolyte were co-sintered at 1370℃, 1450℃, and 1550℃, respectively, for 2 hours to fabricate the half-cell samples. Subsequently, these samples were reduced at 900℃ and 700℃, respectively, with a flow of 50ccm dry H2. High-resolution secondary ion mass spectrometry (SIMS) was used to detect the presence of NiO in YSZ, and Raman spectroscopy was used to detect the phase transformation (cubic to tetragonal) occurring in the YSZ.The SIMS results showed that the amount of NiO in the YSZ electrolyte increased with higher sintering temperatures. Moreover, after reducing the cells at 900℃, phase transformation was detected in all samples. However, there was no significant difference among those cells in terms of the degree of phase transformation, which indicated that phase transformation was not accelerated by the increase of dissolved NiO in YSZ. On the other hand, no phase transformation was observed for the cells reduced at 700℃. The mechanism of phase transformation of YSZ in anode-supported SOFCs and its related conductivity degradation will be discussed in the presentation.

Understanding Degradation Behavior of Direct-Ammonia Solid Oxide Fuel Cells Using Nanoscale Analyses

Direct-ammonia solid oxide fuel cells (SOFCs) offer a cost-effective and efficient avenue for accelerating the use of hydrogen as a major energy vector. The effect of directly feeding ammonia as a fuel into SOFCs and their associated degradation behavior, however, needs to be fully understood in order to design robust cells capable of operating with good performance and durability at the required high temperatures for extended periods of time. In this study, we performed detailed analyses using advanced techniques such as high-resolution secondary ion mass spectrometry (SIMS) imaging and microscopy methods to examine the microstructural evolution and factors affecting nickel nitriding behavior of model Ni metal surfaces as well as Ni/yttria-stabilized zirconia (YSZ) cermet anodes directly exposed to ammonia as a function of temperature. The results show preferential formation of nickel nitride and presence of OH- species on Ni metal surfaces directly exposed to ammonia, as well as grain boundaries in the bulk which were not directly exposed to ammonia, suggesting enhanced ionic diffusion along these regions. Nickel nitriding is also accompanied by volume expansion which is considered to result in additional mechanical stress. Ni/YSZ cermet anodes, on the other hand, exhibit a significantly higher amount of nickel nitride formed preferentially in pore regions at lower temperatures, suggesting the possibility of nickel nitride decomposition occurring at higher temperatures. The results further suggest a correlation between nickel nitride formation and microstructural features of Ni/YSZ cermet anodes which influence gas diffusion properties. Lastly, a model for the degradation behavior of Ni/YSZ cermet anodes on the basis these results will be proposed and discussed.

Towards Operando Secondary Ion Mass Spectrometry Imaging of Lithium Redistribution in Solid-State Lithium-Ion Batteries: Correlation of Structural, Chemical and Electrochemical Characteristics

Innovations in lithium-ion batteries rely crucially on the availability of advanced characterization techniques. High-resolution chemical imaging of low-Z elements e.g., lithium (Li) is often difficult in many conventional chemical analysis techniques such as Energy-Dispersive X-ray Spectroscopy. High-resolution Secondary Ion Mass Spectrometry (SIMS) imaging is a well-known technique for the analysis of all elements including isotopes. For this reason, SIMS imaging is used in numerous studies related to Li-ion battery research. While direct imaging of Li in post-mortem battery components is helpful to understand parts of the degradation mechanisms, a complete dynamic view of the evolution of the Li distribution at high resolution during operation (‘operando’) of batteries is required to fully understand the local interfacial processes, charge transport characteristics and the degradation mechanisms. A few reports presenting operando Time-of-Flight SIMS imaging of batteries have recently been published [1], but the lateral resolution demonstrated in these reports is not adequate to study local processes that occur at nanoscale.In order to demonstrate operando SIMS chemical imaging with sub-20 nm lateral resolution, we developed a novel operando methodology suitable for Focused Ion Beam (FIB)-SIMS imaging and analysis (see Fig. 1). An in-house designed magnetic-sector mass spectrometer [2] attached to a ThermoFisher SCIOS Ga+ FIB is used for SIMS chemical imaging. A special operando sample holder was designed to enable electrochemical cycling of batteries within the FIB-SIMS instrument. The micromanipulator inside the FIB (typically used for preparing thin lamellae for Transmission Electron Microscopy) is used to contact one of the battery electrodes through the operando sample holder and complete the electrical circuit. An external potentiostat is then connected to the instrument to drive the charging/discharging of batteries. The proof-of-concept experiments were performed using Li|Li7La3Zr2O12|Li symmetric half-cells. Galvanostatic cycling was performed in-situ inside the FIB-SIMS instrument until the sample failed. SIMS chemical mapping revealed a redistribution of Li during cycling. Lithium rich phases appeared during cycling which likely percolated through grain-boundaries and pores of the solid electrolyte causing a short-circuit failure. These results validate our methodology for operando analysis of Li-ion batteries with the possibility to obtain SIMS chemical images with sub-20 nm lateral resolution [3].This work was funded by the Luxembourg National Research Fund (FNR) through the grant INTER/MERA/20/13992061 (INTERBATT).[1] Y. Yamagishi, et al., J. Phys. Chem. Lett. 2021, 12, 19, 4623–4627[2] O. De Castro, et al., Analytical Chemistry, 2022, 94, 30, 10754–10763.[3] L. Cressa, et al., Analytical Chemistry, 2023, under review. Figure 1

Sulfur Impurities in COx Feed Gases of Solid Oxide Cells: Effect on Degradation and Removal Strategies

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies for carbon dioxide electrolysis. However, it is yet unclear which contaminant level in carbon monoxide and carbon dioxide feed gases are tolerable to achieve low degradation rates in commercial applications. In the present work, electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) fuel electrodes were exposed to CO/CO2 gas mixtures at open circuit voltage and in electrolysis operation. The resistance evolution over time was monitored by means of electrochemical impedance spectroscopy. With this approach it is shown that a severe reversible degradation over time periods of up to 72 h occurs. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that this degradation effect is related to sulfur impurities on the Ni surface. Inlet gas composition variations were carried out to show that sulfur impurities most likely in the low ppb level are present in both industrial CO and CO2 feed gases. The efficacy of different gas cleaning units at room temperature was investigated to identify a suitable desulfurization solution. The results demonstrate the importance of feed gas purity for the commercialization of high-temperature CO2 electrolysis.

Advanced Nanoscale Characterizations of Solid Oxide Cell Electrodes

The growing interest in the transition towards a fossil-free energy system has accelerated research and development on hydrogen-based energy conversion technologies. In this context, solid oxide cells (SOCs) have attracted attention as they can be operated in both electrolysis (SOEC) and fuel cell (SOFC) modes providing a clean and sustainable way of producing both green hydrogen and electricity at high efficiency. Despite their great potential, the current SOC technology faces some challenges due to the significant cell degradation upon operation. The performance loss has been attributed to several factors, such as microstructural evolution in the electrodes [1], and inter-diffusion of elements between the cell layers associated to material decomposition and reactivity [2–4]. Despite several efforts, all these degradation phenomena are still not precisely understood as they involve complex and intricate processes arising at different length scales. To address this issue, durability tests have been performed in representative operating conditions at high current density and humidity at the air side for both SOFC and SOEC modes. In addition, the tested cells were analyzed with advanced characterization techniques to study the material degradation down to the nanometer and the atomic scales.In this work, standard fuel electrode supported cells have been studied. They are composed of a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) current collecting layer (CCL) and a LSCF/Ce0.8Gd0.2O2-δ (LSCF/GDC) composite functional layer (FL) for the air electrode, GDC for the barrier layer, (Y2O3)0.08(ZrO2)0.92 (YSZ) for the electrolyte and Ni-YSZ for the fuel electrode. The samples were aged for 2000 h in various operating conditions: temperature (750, 800, 850 °C), humidity in the air flow (0%, 3% and 8%) and operating mode (SOEC and SOFC at ±1 A cm-2). The electrochemical behaviour of the cells has been characterized using electrochemical impedance spectroscopy (EIS) and polarization curves. The advanced post-mortem characterizations include techniques such as synchrotron X-ray nano-diffraction and nano-fluorescence (nano-XRD and nano-XRF) spectroscopy performed at the European Synchrotron Radiation Facility (ESRF, ID16B), scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDX), and atom probe tomography (APT). A larger range of information was acquired by using complementary techniques, including focused ion beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), and high-resolution secondary ion mass spectroscopy (SIMS) imaging.The electrochemical characterizations (Fig. 1a) have shown that the degradation was aggravated by increasing the operating temperature, the presence of humidity at the air side and the operation in electrolysis mode. The impedance spectra have been interpreted using a physically-based multiscale model [5]. The analysis has revealed that the performance loss was mainly due to the fuel electrode degradation, while the air electrode degradation remained limited, except when operated under humid conditions in the SOEC mode. The post-mortem characterizations have shown that such degradation in the SOEC mode was mainly related to a strong Ni depletion, which became more pronounced with increasing operating temperature. For the cell operated under humid air in the SOEC mode, a significant amount of SrCO3 phase was observed on top of the air electrode. On the contrary, the cell operated under humid air in the SOFC mode did not show such phase formation. Advanced characterization techniques (nano-XRD, nano-XRF, STEM-EDX, and APT) put in evidence an intermixing of elements in the air electrode (LSCF/GDC) at the atomic scale (Fig. 1b). Moreover, the presence of an inter-diffusion layer (IDL) between GDC and YSZ phases was observed (Fig. 1c) for all samples, including the freshly prepared sample. Nevertheless, neither the mixing of elements in the air electrode nor the presence of the IDL seem to have a major influence on the cell degradation. It can be speculated that these phenomena make the air electrode more stable against phase decomposition by inhibiting the formation of commonly observed insulating phases such as SrZrO3 and SrO.

Mycorrhizae enhance reactive minerals but reduce mineral-associated carbon.

Soil organic carbon (C) is the largest active C pool of Earth's surface and is thus vital in sustaining terrestrial productivity and climate stability. Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil C dynamics. Yet, it remains unclear whether and how AMF-root associations (i.e., mycorrhizae) interact with soil minerals to affect soil C cycling. Here we showed that the presence of both roots and AMF increased soil dissolved organic C and reactive Fe minerals, as well as litter decomposition and soil CO2 emissions. However, it reduced mineral-associated C. Also, high-resolution nanoscale secondary ion mass spectrometry images showed the existence of a thin coating (0.5-1.0 μm thick) of 56 Fe16 O- (Fe minerals) on the surface of 12 C14 N- (fungal biomass), illustrating the close physical association between fungal hyphae and soil Fe minerals. In addition, AMF genera were divergently related to reactive Fe minerals, with Glomus being positively but Paraglomus and Acaulospora negatively correlated with reactive Fe minerals. Moreover, the presence of roots and AMF, particularly when combined with litter addition, enhanced the abundances of several critical soil bacterial genera that are associated with the formation of reactive minerals in soils. A conceptual framework was further proposed to illustrate how AMF-root associations impact soil C cycling in the rhizosphere. Briefly, root exudates and the inoculated AMF not only stimulated the decomposition of litter and SOC and promoted the production of CO2 emission, but also drove soil C persistence by unlocking mineral elements and promoting the formation of reactive minerals. Together, these findings provide new insights into the mechanisms that underlie the formation of reactive minerals and have significant implications for understanding and managing soil C persistence.

SHRIMP U–Pb ages of the detrital zircons from the Cretaceous Ullyeonsan Formation, SE Korea: A small piece for stratigraphic correlation in eastern Asia

To constrain the maximum depositional age of the Ullyeonsan Formation in the Yeongyang Subbasin, southeast Korea, detrital zircon U–Pb age determination was conducted using high-resolution secondary ion mass spectrometry (HR-SIMS). The U–Pb populations of detrital zircons from the Ullyeonsan Formation show a broad range of ages from the Archean to early Cretaceous and diverse patterns depending on the temporal and spatial distribution of sedimentation. The difference in location-dependent age distribution indicates that sediments originated from adjacent areas and source rocks were exposed during the sedimentation period of the Ullyeonsan Formation. The youngest detrital zircon cluster of the Ullyeonsan Formation yields concordia age of 110.4 ± 2.5 Ma (n = 5, MSWD = 1.2), indicating the maximum depositional age. Therefore, the Ullyeonsan Formation began to be deposited from the Albian period, and the Yeongyang Subbasin started to form around the same time as the deposition of the Hayang Group in other subbasins of the Gyeongsang Basin (e.g., Miryang and Uiseong).

Boron segregation at austenite grain boundaries: An equilibrium phenomenon

High-resolution secondary ion mass spectrometry imaging, atom probe tomography and transmission electron microscopy have been employed to investigate boron segregation at austenite grain boundaries (γGB) in a high-strength steel. Boron content in solid solution, interfacial excess at γGB and precipitate number density were quantified after heat treatments specifically designed to promote non-equilibrium segregation of boron. The samples were first soaked at 1100°C, followed by rapid cooling to different isothermal holding temperatures, and then quenched to room temperature. We found that boron distribution does not evolve after holding at 460°C, even after bainitic transformation, suggesting a low mobility of boron at this temperature. In contrast, after holding at high temperatures (780°C and 820°C), boron distribution evolves remarkably: boron content in solid solution close to the interface and boron interfacial excess decrease similarly with the increase of holding time, while their ratio remains almost constant; at the same time, transient precipitation of M23(B,C)6 particles occurs at the grain boundaries. The experimental results on interfacial excesses at γGB and the solute profiles in the vicinity of the grain boundary agree with the results of a numerical model of coupled diffusion and equilibrium segregation phenomena. These results unambiguously exclude the hypothesis that non-equilibrium segregation controls the kinetics of boron segregation and confirm that boron segregation is only controlled by the equilibrium segregation mechanism.

Sulfur Impurities in COx Feed Gases of Solid Oxide Cells: Effect on Degradation and Removal Strategies

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies for carbon dioxide electrolysis. However, it is yet unclear which contaminant level in carbon monoxide and carbon dioxide feed gases are tolerable to achieve low degradation rates. In this work, electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) fuel electrodes were exposed to CO/CO2 gas mixtures at open circuit voltage. The resistance evolution over time was monitored by means of electrochemical impedance spectroscopy. With this approach it is shown that a degradation over times of up to 96 h occurs. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that the degradation is related to sulfur impurities on the electrode surface. The results demonstrate the importance of feed gas purity for the commercialization of high-temperature CO2 electrolysis.

Nanoscale Surface Analysis Reveals Origins of Enhanced Interface Passivation in RbF Post Deposition Treated CIGSe Solar Cells

AbstractAlkali post deposition treatments (PDTs) of Cu(In,Ga)Se2 absorbers have boosted the power conversion efficiency (PCE) of the solar cell devices in the last years. A detailed model explaining how the PDTs impact the optoelectronic properties at the nanoscale is still lacking. Here, via various scanning probe techniques, X‐Ray photo‐electron spectroscopy and high resolution secondary ion mass spectroscopy it is shown that the RbF PDT treatments lead to a one to one exchange of Rb with Cu at the surface. This exchange takes place in the naturally occurring Cu‐depleted CIGSe surface, known as the ordered vacancy compound. A detailed comparison between samples with different PDTs after various cleaning procedures furthermore highlights the necessity to perform all the measurements on NH4OH cleaning surfaces only. After NH4OH, no RbInSe2 phase could be detected at the surface anymore and the surface bandgap, as measured with scanning tunneling spectroscopy is only 1.7 eV. The findings demonstrate that the existence of a RbInSe2 phase is most likely not responsible for the recent improvements in power conversion efficiency for state of the art solar cells. The primary effect of the PDT treatment is a modification of the ordered vacancy compound, where Cu is exchanged with Rb.

Foliar cadmium uptake, transfer, and redistribution in Chili: A comparison of foliar and root uptake, metabolomic, and contribution

Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdSN), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

Austenite grain boundary segregation and precipitation of boron in low-C steels and their role on the heterogeneous nucleation of ferrite

The addition of boron (B) to steels suppresses the austenite to ferrite phase transformation dramatically, thus increasing their hardenability. It achieves this through grain boundary (GB) segregation at the austenitic GBs that delays the ferrite nucleation. Though the effects of B segregation on hardenability have long been known, the mechanisms of B segregation and how exactly B suppresses the ferrite nucleation remain elusive. We designed a B-containing low-C steel to study the B segregation and precipitation behavior. We conducted heat treatments with different austenitization temperatures and cooling rates. Site-specific atom probe tomography, complemented by high-resolution secondary ion mass spectrometry reveals B segregation at prior austenite grain boundaries (PAGBs) along with carbo-boride precipitation. The B segregation mechanisms are discussed in detail based on these observations considering their dependence on austenitization temperature and cooling rate. Furthermore, we analyzed the impact of GB energy reduction through nucleation kinetics calculations. From our analysis, we conclude that the reduction in GB energy affects the grain corner and grain edge nucleation substantially. However, the retarding effects of carbo-boride precipitation on ferrite nucleation cannot be completely excluded. We provide a detailed account of the possibilities of how B-containing precipitates may be suppressing ferrite nucleation.

Evaluation of guaiacyl lignin aromatic structures using 13CO2 administered Ginkgo biloba L. xylem by quantitative solid- and liquid-state 13C NMR

Abstract Ginkgo biloba L. saplings were cultivated in an airtight growth chamber with 13CO2 for two months. The 13C ratio of the newly developed xylem region was ca. 85%, evaluated by high lateral resolution secondary ion mass spectrometry and thioacidolysis/GC-MS. Quantitative solid-state 13C direct polarisation/magic angle spinning (DP/MAS) NMR measurements with high-speed MAS of 70.0 kHz were conducted for cutting-milled wood (CMW), ball-milled wood (BMW), and enzymatically saccharified lignin (EL) samples. In addition, quantitative liquid-state 13C NMR measurements were carried out for EL in DMSO-d 6. Major lignin aromatic signals were classified into three groups of aromatic carbons of C–H, C–C, and C–O, and their area ratio was compared within these measurements. EL samples in solid- and liquid-state showed nearly the same results. However, the results for CMW and BMW in solid-state NMR suggest the structural alteration of lignin within the sample preparation procedure, including ball milling.

On the significance of oxygen-isotope variations in chondrules from carbonaceous chondrites

Oxygen-isotope studies of carbonaceous chondrite chondrules are of pivotal importance for understanding of the evolution of the solar protoplanetary disk. It has been previously concluded that the observed variations in Δ17O (=δ17O – 80.52 × δ18O) of chondrule olivines and pyroxenes are intimately tied to their Mg# (=MgO/(MgO + FeO) × 100, mol%) and the inferred oxygen fugacity (fO2) of gaseous reservoirs produced by evaporation of disk regions with different (silicate dust ± water ice)/gas ratios. Using high resolution cathodoluminescence and secondary ion mass spectrometry, we show, in contrast to host chondrule data, that Δ17O of chondrule olivines from the Yamato 81020 CO3.05 carbonaceous chondrite is independent of their Mg# and of the imposed fO2. Instead, there is a Δ17O bimodal distribution of Mg-rich olivines that gradually turns into a unimodal distribution as Mg# decreases. We suggest that chondrules recorded an evolution of an isotopically heterogeneous vapor plume resulting from a high temperature mixing of the 16O-enriched (Δ17O ≈ −6 ± 2‰) and 16O-depleted (Δ17O ≈ −2.5 ± 1‰) reservoirs. Drop in the vapor plume temperature under unbuffered redox conditions favors the dissolution of Fe,Ni-metal of chondrules and the subsequent crystallization of FeO-rich olivines at saturation; the 16O-depleted signature being the most resilient at lower temperature. Chondrules are thus inferred to have formed in a same turbulent heterogeneous environment in which locally high temperatures and reducing conditions prevailed (Type I), adjacent in space and/or in time to areas submitted to lower temperatures and more oxidizing conditions (Type II). Subtracting of chondrules at different stages of the gaseous plume evolution by fast cooling rates give rise to the chemical and isotopic diversity of chondrules. No extrinsic oxidizing agents (e.g., water ice) are needed in this scenario.

The influence of sulfur impurities in industrial COx gases on solid oxide electrolysis cell (SOEC) degradation

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies during carbon dioxide electrolysis. However, it is still unclear which gas quality and impurity level is required for low degradation rates in their commercial application. Here, it is shown that the polarization resistance of electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) degrades strongly over time periods of up to 72 h when operated in CO/CO2 gas mixtures. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that this degradation effect is related to sulfur impurities in the feed gas and their poisoning of the Ni surface. Variation of the inlet gas composition showed that impurities are present in both CO and CO2. The degradation was significantly less pronounced for Ni/CGO fuel electrodes compared to Ni/Yttria-stabilized zirconia (YSZ) and also when hydrogen was introduced into the feed gas. Generic natural gas cleaning desulfurization units were not able to remove the impurities from the feed gases. After initial electrode deactivation, stable cell performance was obtained for >900 h. The results clearly underline the importance of feed gas purity and the necessity for advanced cleaning units for the commercialization of high-temperature CO2 electrolysis.

Elucidating the performance benefits enabled by YSZ/Ni-YSZ bilayer thin films in a porous anode-supported cell architecture.

Increasing the performance and improving the stability of solid oxide cells are critical requirements for advancing this technology toward commercial applications. In this study, a systematic comparison of anode-supported cells utilizing thin films with those utilizing conventional screen-printed yttria-stabilized zirconia (YSZ) is performed. High-resolution secondary ion mass spectrometry (SIMS) imaging is used to visualize, for the first time, the extent of Ni diffusion into screen-printed microcrystalline YSZ electrolytes of approximately 2-3 μm thickness, due to the high temperature (typically >1300 °C) used in the conventional sintering process. As an alternative approach, dense YSZ thin films and Ni(O)-YSZ nanocomposite layers are prepared using pulsed laser deposition (PLD) at a relatively low temperature of 750 °C. YSZ thin films exhibit densely packed nanocrystalline grains and a remarkable suppression of Ni diffusion, which are further associated with some reduction in the ohmic resistance of the cell, especially in the low temperature regime. Moreover, the use of a Ni-YSZ nanocomposite layer resulted in improved contact at the YSZ/anode interface as well as a higher density of triple phase boundaries due to the nanoscale Ni and YSZ grains being homogeneously distributed throughout the structure. The cells utilizing the YSZ/Ni-YSZ bilayer thin films show excellent performance in fuel cell operation and good durability in short-term operation up to 65 hours. These results provide insights into ways to improve the electrochemical performance of SOCs by utilizing innovative thin film structures in conjunction with commercially viable porous anode-supported cells.

Hydrogen Localisation in Metallurgical Samples With High Resolution Secondary Ion Mass Spectrometry (NanoSIMS)

Hydrogen Localisation in Metallurgical Samples With High Resolution Secondary Ion Mass Spectrometry (NanoSIMS)

Subcellular Mapping of Trace Elements in Plants Using High Resolution Secondary Ion Mass Spectrometry (NanoSIMS)

Subcellular Mapping of Trace Elements in Plants Using High Resolution Secondary Ion Mass Spectrometry (NanoSIMS)

Contamination-induced inhomogeneity of noise sources distribution in Al2O3-passivated quasi-free-standing graphene on 4H-SiC(0001)

In this report, we introduce a novel method based on low-frequency noise analysis for the assessment of quality and pattern of inhomogeneity in intentionally-aged Hall effect sensors featuring hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene mesa on semi-insulating high-purity on-axis 4H-SiC(0001), all passivated with a 100-nm-thick atomic-layer-deposited Al2O3 layer. Inferring from the comparison of the measured noise and one calculated for a homogeneous sensor, we hypothesize about possible unintentional contamination of the sensors’ active regions. Following in-depth structural characterization based on Nomarski interference contrast optical imaging, confocal micro-Raman spectroscopy, high-resolution Transmission Electron Microscopy and Secondary Ion Mass Spectrometry, we find out that the graphene’s quasi-free-standing character and p-type conductance make the Al2O3/graphene interface exceptionally vulnerable to uncontrolled contamination and its unrestrained lateral migration throughout the entire graphene mesa, eventually leading to the blistering of Al2O3. Thus, we prove the method’s suitability for the detection of these contaminants’ presence and location, and infer on its applicability to the investigation of any contamination-induced inhomogeneity in two-dimensional systems.