Dominant Degradation Mechanism Research Articles

Electrochemical Analysis of an Electrolyte-Supported Solid Oxide Cell-Based MK35x Stack during Long-Term Electrolysis Operation

The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type “MK35x” with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816 °C and a current density of −0.6 A cm−2 and showed an average voltage evolution rate of −0.3%/kh demonstrating high stability. Initial and final characterization at the part load operating point at −0.39 A cm−2 and 800 °C led to the determination of a positive overall degradation rate of 0.4%/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.

Bio‐blends of virgin and post‐industrial poly(methyl methacrylate) waste/pristine chitosan: Structure, thermal, and physical properties

AbstractPolymer blends based on plastic waste and natural biodegradable polymers is an interesting strategy in view of environmental and technical concerns. This article investigates the structure, thermal and physical properties of virgin and post‐industrial polymethyl methacrylate (PMMA) waste/pristine chitosan (Cs) bio‐blends. Waste PMMA was generated by an extrusion process for the manufacturing of sheets. The results of gel permeation chromatography analysis (GPC) show a slight decrease (about 8%) in the average molecular weight of PMMA after extrusion. Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR‐ATR) spectra do not reveal changes in the chemical structure of post‐industrial PMMA/Cs blends compared to virgin PMMA/Cs samples, indicating that chain scission reactions are the dominant degradation mechanism of PMMA during processing. Dynamic mechanical analysis (DMA) results reveal a single glass transition temperature () for the blends, implying miscibility of the components. Post‐industrial PMMA/Cs samples exhibit slightly lower values of compared to virgin PMMA/Cs blends. The post‐industrial PMMA waste slightly reduces nano‐mechanical properties and thermal stability of the blends relative to those from virgin PMMA. In contrast, it increases the water uptake of the bio‐blends compared with virgin PMMA.Highlights Chain scission is the dominant degradation mechanism of PMMA during extrusion. Miscibility between the homopolymers within the blends. PMMA waste slightly reduced the nano‐mechanical properties of the bio‐blends. Post‐industrial PMMA waste increased the water uptake of the bio‐blends. Possibility of using post‐industrial PMMA waste by blending with chitosan.

Evaluation of the abilities of atomic oxygen/ultraviolet resistance for the filled silicone rubber coating: Structures, properties, and aging mechanism

A series of experimental techniques were used to study the erosion-damage effect of a silica-filled silicone rubber coating exposed to simulated space environment (atomic oxygen and ultraviolet irradiation). The elastomer is known to be chemically and thermally stable, but there are insufficient data on its durability in the space environment. In the present work, atomic oxygen doses up to 3.8 × 1021 atoms·cm−2 and ultraviolet irradiation doses up to 360 equivalent sun-hours (ESH) were applied from Space Environment Simulation Measurement System, respectively. Since the aging and failure processes of the filled silicone rubber relate to different aspects of chemical structure and physics form, therefore, this study explored the use of chemical-mechanics methods to comprehensively evaluate the erosion-damage effect of materials. Morphology and chemical changes due to radiation were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and nanoindentation test probed surface mechanical properties changed with exposure dose. Results demonstrated that, with increased exposure time and irradiation-induced free radicals，the aggregation state and molecular chain structure of the silica-filled silicone rubber have changed, which caused an increase in surface hardness and modulus. Taken together, the results indicated that oxidative cross-linking was the dominant degradation mechanism under the irradiation dose in this paper.

Impact of degradation mechanisms at the cathode/electrolyte interface of garnet-based all-solid-state batteries

All-solid-state batteries have the potential to improve the safety, energy-, and power density of lithium-ion batteries. However, the limited stability of rigid solid-solid interfaces remains a key challenge. The cathode/electrolyte interface is particularly prone to degradation during high-temperature sintering and electrochemical cycling, forming secondary phases that impede charge transport and limit cell performance. Experimental analysis of these phases is challenging since they result in thin resistive films that are sensitive to typical characterization techniques. In this study, we use structure-resolved electrochemical simulations to investigate the impact of resistive phases at the cathode/electrolyte interface on cell performance and identify dominant degradation mechanisms. We extend our simulation framework with a novel resistive film model that accounts for the additional charge transfer resistance at the interface based on interphase properties. Our approach combines continuum simulations with insights from density functional theory and experimental data, including secondary ion mass spectrometry measurements. This allows us, for the first time, to assess the impact of resistive films on the degradation of full-cell performance.

Performance evolution analysis of solid oxide electrolysis cells operating at high current densities

Hydrogen generation by water electrolysis using solid oxide electrolysis cells (SOECs) is highly promising because of the favorable thermodynamics and kinetics. Commercial applications require SOEC operating at high current densities (ǀiǀ≥1 A·cm−2) to achieve substantial hydrogen production rates. This study demonstrates the operation of a full-size Ni–yttria-stabilized zirconia (Ni–YSZ) cell with an effective area of 16 cm2 at −2 A·cm−2 for 336 h, illustrating the feasibility of operating SOECs at a high current density. The electrochemical characteristics of the SOEC evolved during constant current electrolysis, exhibiting an activation stage with a degradation rate (DR) of 54.6 mV/100 h, followed by a rapid decline process(DR: 180.9 mV/100 h), a gentle decline period (DR: 105.5 mV/100 h), and a stable stage (DR: 11.0 mV/100 h). The contributions of individual processes to cell degradation during each process are identified using the distribution of relaxation times (DRT) and subsequent equivalent circuit model (ECM) fitting. The results suggest that the Ohmic resistance, ionic transport and charge-transfer reaction in the Ni-YSZ fuel electrode contribute the most to performance loss. Ni redistribution is regarded as the dominant degradation mechanism, as verified by detailed post-test characterization.

A sustainable nano-hybrid system of laccase@M-MWCNTs for multifunctional PAHs and PhACs removal from water, wastewater, and lake water

This study examined the use of modified multiwall carbon nanotubes (M-MWCNTs) with immobilized laccase (L@M-MWCNTs) for removing ciprofloxacin (Cip), carbamazepine (Cbz), diclofenac (Dcf), benzo[a]pyrene (Bap), and anthracene (Ant) from different water samples. The synthesized materials were characterized using an array of advanced analytical techniques. The physical immobilization of laccase onto M-MWCNTs was confirmed through Scanning electron microscope (SEM)-dispersive X-ray spectroscopy (EDS) analysis and Brunner-Emmet-Teller (BET) surface area measurements. The specific surface area of M-MWCNTs decreased by 65% upon laccase immobilization. There was also an increase in nitrogen content seen by EDS analysis asserting successful immobilization. The results of Boehm titration and Fourier transform infrared (FTIR) exhibited an increase in acidic functional groups after laccase immobilization. L@M-MWCNTs storage for two months maintained 77.8%, 61.6%, and 57.6% of its initial activity for 4 °C, 25 °C, and 35 °C, respectively. In contrast, the free laccase exhibited 55.3%, 37.5%, and 23.5% of its initial activity at 4 °C, 25 °C, and 35 °C, respectively. MWCNTs improved storability and widened the working temperature range of laccase. The optimum removal conditions of studied pollutants were pH 5, 25 °C, and 1.6 g/L of M-MWCNTs. These parameters led to >90% removal of the targeted pollutants for four treatment cycles of both synthetic water and spiked lake water. L@M-MWCNTs demonstrated consistent removal of >90% for up to five cycles even with spiked wastewater. The adsorption was endothermic and followed Langmuir isotherm. Oxidation, dehydrogenation, hydroxylation, and ring cleavage seem to be the dominant degradation mechanisms.

Consistently Tuned Battery Lifetime Predictive Model of Capacity Loss, Resistance Increase, and Irreversible Thickness Growth

Predicting changes in cell resistance and thickness as the battery ages can be as important as capacity fade in informing vehicle resale value, pack replacement schedules, and viability for repurposing before eventual recycling. Three well-known degradation mechanisms, namely SEI growth, lithium plating, and electrode particle fracture due to reversible expansion and contraction, are revisited and tuned using capacity fade data from cells experiencing plating and having significant loss of anode active material as the dominant degradation mechanism. Therefore, lifetime prediction achieved in this work cannot rely on SEI degradation that can be tuned mostly with calendar aging data. More importantly, our model uses capacity-predictive irreversible SEI growth, net growth in plating, and accumulation of particle fracture as the cells cycle to predict the irreversible increases in cell thickness through a single set of tuned parameters. Last but not least, the capacity-predictive degradation can also predict the increased resistance through another single set of parameters. These two sets of scaling parameters achieve for the first time a consistently tuned model of degradation mechanisms for lifetime prediction of changes in battery capacity, resistance, and thickness as the battery ages. The model prediction has been validated in conditions not used for parameter tuning.

UV irradiation induced simultaneous reduction of Cu(II) and degradation of EDTA in Cu(II)-EDTA in wastewater containing Cu(II)-EDTA

Decomplexation of Cu(II)-EDTA followed by chemical precipitation of free Cu(II) ions can effectively degrade EDTA in Cu(II)-EDTA and remove Cu(II), but requires large precipitant dosage and inevitably produces a large amount of copper-containing sludge that is difficult to deal with. Herein, we demonstrated that simultaneous reduction of Cu(II) and degradation of EDTA in Cu(II)-EDTA can be achieved by UV irradiation of wastewater containing Cu(II)-EDTA without adding reagent. 93.65% of Cu(II) was reduced to Cu(0) with a high purity of 99.93 wt%, which can be recycled, thus avoiding the generation of copper-containing sludge. 96.67% of EDTA in Cu(II)-EDTA was degraded, and the final products were HCHO, NH4+, NO3- and low-molecular acids. In depth, the dominant degradation mechanism of EDTA in Cu(II)-EDTA was photo-induced successive decarboxylation through homolysis of C-O and C-C bond of -CH2-COOH group, followed by ligand to metal charge transfer (LMCT) and hydrolysis reactions. The minor degradation mechanism of EDTA in Cu(II)-EDTA was successive decarboxylation by •OH radicals. Simultaneously, Cu(II) was reduced to Cu(0) by H• and eaq- produced by UV irradiation of Cu(II)-EDTA. This study provided an approach of simultaneous removal of heavy metals and degradation of EDTA in Cu(II)-EDTA in wastewater containing heavy metal-EDTA complex.

DC to AC analysis of HC vs. BTI damage in N-EDMOS used in single photon avalanche diode cell

N-channel Extended Drain Metal Oxide Semiconductor (EDMOS) device is analysed through its sensitivity to Hot-Carrier (HC), hot hole (HH) injections and Positive Bias Temperature (PBT) instability degradation using accelerated DC to AC lifetime technique. EDMOS device is optimized for an effective gate-length Leff = 0.25 μm, with a gate-oxide thickness Tox = 5 nm operating at a frequency of 3 MHz at nominal supply voltage VDD = 5 V. The device is used in a mixed structure dedicated to 3D integration of Single Photon Avalanche Diode (SPAD). We show that HC reliability of EDMOS transistor can be obtained using worst-case DC accelerating degradation at high temperature transferred to the real AC waveforms applied to N-channel device placed into the SPAD cell. This allows to deduce the AC device lifetime obtained from DC stressing using a quasi-static approach considering the dominant degradation mechanism at condition of maximum gate-voltage VGSmax. This is explained by the optimized structure in Tox, VDD and lateral isolation where PBT, Off mode and recovery effects have limited impacts during switching operation of the N-EDMOS device used in SPAD circuit environment.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) provides the combined benefit of reducing anthropogenic CO2 emissions while supplying a wide variety of valuable chemical feedstock chemicals.[1] While many transition metals are CO2RR active catalysts, only copper can form products requiring more than two electrons in the electrochemical conversion of CO2. This includes a multitude of high-value-added products such as ethylene, ethanol, or propanol.[1-3] The selectivity of the CO2RR is strongly influenced by the structure and morphology of the copper catalysts. Consequently, structural properties such as copper nanoparticle size, display an influence on CO2RR product selectivity.[4] This creates a substantial problem as copper is highly susceptible to reorganization during the electrochemical CO2RR, which inhibits the retention of apparently favorable surface structures during the CO2RR.[5] As a consequence, structure-selectivity relations can neither be reliably described nor completely understood. This problem is exacerbated by a lack of understanding of the underlying reasons that drive reorganization and therefore degradation of the catalyst. At reductive potentials, as used in the electrochemical CO2RR, coalescence and subsequent agglomeration are assumed to be the dominant degradation mechanism, while oxidative potentials generally trigger support corrosion and dissolution. Strategies for stabilization to retain activity and selectivity are therefore essential. Nevertheless their importance in the electrochemical CO2RR, stabilization methods are largely missing. For other reactions, such as the oxygen reduction reaction, various studies showed an increase in overall stability by containing the catalysts in a confined space.[6-8] This work presents the stabilizing effect of three different carbon support materials with unique morphologies on copper nanoparticles (CuNPs). Through the use of a non-porous Vulcan, a Ketjenblack with a diverse pore size distribution and highly defined mesoporous graphitic spheres (MGS) with a unimodal pore size distribution, the influence on structural characteristics of the carbon material on the stabilization of the CuNPs can be presented. The representative copper catalysts were prepared by colloidal synthesis or incipient wetness impregnation and evaluated through micro-flow cell measurements with online gas chromatography (GC) analytics and pre-/post catalytic high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), visualizing changes in the catalyst structure and morphology after the reaction. We demonstrate the successful stabilization of CuNPs by pore confinement against particle coalescence and subsequent agglomeration for up to 20 h of electrochemical CO2RR conditions, with GC analysis providing great insight into the influence of particle size, morphology, and location of the CuNPs on CO2RR product selectivity. Intriguingly, a high share of CO2RR products was observed for stabilized < 4 nm CuNPs putting the established particle size effect for the CO2RR, where the hydrogen evolution reaction was predominantly observed on nanoparticles below 15 nm, into question.[4] These results present new ways of stabilizing CuNPs and highlight the need for post-catalytic evaluation of the catalysts' morphological state to precisely derive performance-structure indicators.Work accepted and soon to be published in ChemElectroChemdoi.org/10.1002/celc.202200924Literature:[1] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramollo, I. Chorkendorff, Chem Rev. 2019, 119, 7610–7672.[2] Y. Hori, Modern Aspects of Electrochemistry No. 42, Springer, 2008.[3] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ. Sci. 2012, 5, 7050–7059.[4] R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. 2014, 136, 6978–6986.[5] W. T. Osowiecki, J. J. Nussbaum, G. A. Kamat, G. Katsoukis, M. Ledendecker, H. Frei, A. T. Bell, A. P. Alivisatos, ACS Appl. Energy Mater. 2019, 2, 7744–7749.[6] Y. Li, F. Cui, M. B. Ross, D. Kim, Y. Sun, P. Yang, Nano Lett. 2017, 1312–1317.[7] Y. T. Guntern, J. R. Pankhurst, J. Vavra, M. Mensi, V. Mantella, P. Schouwink, R. Buonsanti, Angew. Chem. 2019, 131, 12762–12769.[8] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc. 2012, 134, 20457 – 20465. Figure 1

Degradation Behavior of MK35x Stacks with Chromium-Based Interconnects in Steam Electrolysis Operation

The currently ongoing commercialization of high-temperature solid oxide electrolysis (SOEL) requires the understanding of the underlying dominant degradation mechanisms to enable continuous progress in reducing stack degradation rates.In the present study, the degradation behavior of stacks with chromium-based interconnects (MK35x) and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS is investigated. For this purpose, the initial electrochemical performance of 10-layer stacks was extensively characterized in various operating conditions in both fuel cell and electrolysis mode by electrochemical impedance spectroscopy (EIS). Degradation was evaluated during galvanostatic steady-state steam electrolysis operation over >3000 h in the temperature range of 800-825°C at a current density of -0.6 A cm-2, corresponding to a steam conversion rate of 75%. EIS analysis was used to separate the different loss contributions in the stack and showed that the ohmic resistance increase was the dominating performance degradation phenomenon. Moreover, electrochemical degradation rates in steady-state SOEL mode are compared to the ones in reversible mode with a daily cycling between electrolysis and fuel cell operation.Post-mortem analysis was carried out with scanning electron microscopy (SEM) to correlate the observed degradation phenomena with microstructural and morphological changes. The observed low degradation rates demonstrate that MK35x are ready for scale-up, and the present work gives guidance for operation strategies and stack design to extend their lifetime even further.

Monitoring the Particle Size Distribution, Phase Quantification and Chemical Composition of Acid-Leached PtCo Electrocatalyst Under Start-up/Shut-Down Conditions Probed By in-Situ SAXS and WAXS Techniques

Large progress has been made towards commercialization of polymer electrolyte membrane fuel cells (PEMFCs) through the development of highly active and robust Pt-Co alloy catalysts for oxygen reduction reaction (ORR).[1,2] However, most ORR catalyst materials suffer from the extremely corrosive conditions occurring during start-up/shut-down (SUSD).[3] Consequently, understanding the degradation mechanisms during SUSD is highly crucial for designing new catalyst materials with enhanced ORR activity and long-term durability.In this work, we show a comprehensive and complementary combination of different advanced techniques such as in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) as well as ex-situ scanning transmission electron microscopy in combination with electron energy loss spectroscopy (STEM-EELS) to provide deeper insights into the degradation processes of acid-leached Pt-Co catalyst under SUSD conditions.Firstly, Pt-Co nanoparticles supported on high surface area carbon (HSAC) were synthesized using wet impregnation – freeze-drying – thermal annealing method.[4] Compared to our previous works [4-6], an acid-leaching (1 M H2SO4, 15 °C, 2 h) was applied to dissolve the less noble metal from the surface of alloy nanoparticles forming a Pt-enriched skin. STEM-EELS data has also confirmed the formation of the Pt-enriched skin. In addition, ex-situ WAXS data signifies that the acid-leached PtCo catalyst consists of two face-centered cubic (fcc) disordered crystal phases: Pt90Co10 phase with a crystallite size of 3.6 ± 0.4 nm and Pt70Co30 phase with 4.2 ± 0.4 nm size.In terms of ORR performance, the acid-leached PtCo catalyst exhibits a 2.5- & 2-times higher mass activity (0.61 ± 0.12 A mgPt -1) and a 3.5- and 1.3-times higher specific activity (665 ± 84 µA cmPt -2) at 0.9 VRHE compared to commercial ~2 nm Pt/C (0.24 ± 0.05 A mgPt -1, 187 ± 29 µA cmPt -2) and heat-treated 4-5 nm Pt/HSAC (0.30 ± 0.04 A mgPt -1, 297 ± 42 µA cmPt -2), respectively. After SUSD experiments (800 cycles, 0.5 - 1.5 VRHE, 50 mV s-1, 0.1 M HClO4), the mass activity decreases to 0.21 ± 0.06 A mgPt -1 (-65 %) and 0.15 ± 0.03 A mgPt -1 (-38 %) for the acid-leached PtCo catalyst and commercial Pt/C, respectively.To monitor the potential-dependent changes in particle/crystallite size, phase quantification and chemical composition of the acid-leached PtCo catalyst under the SUSD conditions, in-situ SAXS and WAXS experiments were simultaneously performed at the beamline ID31 at European Synchrotron Radiation Facility (ESRF).In-situ WAXS analysis reveals that the lattice parameter of both Pt90Co10 and Pt70Co30 phases increases as a function of the SUSD cycle number, signifying the successive depletion of cobalt mainly from the Pt70Co30 phase. More precisely, the lattice parameter changed from 3.819 ± 0.004 Å (Pt70Co30) to 3.829 ± 0.004 Å (Pt76Co24) during the first 150 SUSD cycles. Only a slight change in lattice parameter for Pt90Co10 phase is observed during the SUSD protocol. Based on the Rietveld quantification, the amount of the Pt70Co30 phase decreases from 61 ± 2 wt.% to 47 ± 2 wt.% during the first 150 SUSD cycles. Afterwards, the Co depletion from this phase is less pronounced with additional cycle number. Furthermore, STEM-EELS investigations on acid-leached PtCo catalyst after first 150 SUSD cycles has confirmed the drastic Co depletion within the nanoparticles. After the SUSD protocol, the chemical composition of the acid-leached PtCo catalyst alters from Pt67±3Co33±3 to Pt81±3Co19±3 (-42 at.%) obtained from the bulk techniques like EDX and µ-XRF.In addition, the Rietveld refinement reveals an increase in crystallite sizes for both Pt-Co crystal phases over the course of the SUSD protocol which is in excellent agreement to the in-situ SAXS and ex-situ TEM results (from 4.1 ± 1.0 nm to 5.2 ± 0.8 nm, +27 %). In detail, the initial larger Pt70Co30 phase shows only a small increase in crystallite size (from 4.3 ± 0.4 nm to 4.8 ± 0.4 nm, +12 %), whereas for the initial smaller Pt90Co10 phase a gradual increase from 3.2 ± 0.3 nm to 4.5 ± 0.4 nm (+41 %) is observed during the SUSD experiment.Based on the in-situ SAXS/WAXS and the ex-situ STEM-EELS data, the Co depletion is the dominant degradation mechanism for the disordered fcc Pt70Co30 phase during the first 150 SUSD cycles. With increasing SUSD cycle number, the particle growth via Ostwald ripening and particle coalescence predominates. Our degradation model can be used to further improve the ORR performance and durability of acid-leached Pt-Co catalysts under the SUSD conditions.Literature:[1] L.R.Borup et al.,Curr.Opin.Electrochem.,2020,21,192-200.[2] C.Wang et al.,Energies,2016,9,603-642.[3] Y.Yu, et al.,J.Power Sources,2012,205,10-23.[4] M.Oezaslan et al.,J.Electrochem.Soc.,2012,159,B394-B405.[5] D.J.Weber et al.,J.Mater.Chem.A,2021,9,15415-15431.[6] P.Weber et al.,ACS Catal.,2022,12,6394-6408.

Long-term stability of graphene/c-Si Schottky-junction solar cells

A long operational lifetime is required for the use of solar cells in real-life photovoltaic applications. The optimization of operational lifetimes is achieved through understanding the inherent degradation phenomena in solar cells. In this study, graphene/Si Schottky-junction solar cells were produced, utilizing liquid-phase-exfoliated graphene as an active surface. The operational and interface stability of these solar cells over a period of 5 years in ambient conditions (following ISOS-D protocols: dark storage/shelf life) was examined, and the origin of their degradation was reported. It was found that the dominant degradation mechanism could be attributed to the degradation of silver contacts. This was indicated by a decrease in shunt resistance, an increase in the ideality factor (due to a higher carrier recombination), and a constant defect density in graphene films for up to 4 years. Measurements across the solar cell's active area during the 5-year period revealed neither significant spatial inhomogeneity, nor shunt channel defects.

Multidimensional Mission-Profile-Based Lifetime Estimation Approach for IGBT Modules in MMC–HVdc Application Considering Bidirectional Power Transfer

MMC applied in high voltage direct current (HVdc) field consists of numerous submodules (SMs) and supports bidirectional power transfer, leading to the diverse mission and temperature profiles among SMs and IGBT modules. In this paper, an IGBT lifetime estimation approach in terms of the bidirectional power transfer of MMC is proposed. The temperature profile of each module is translated based on the multi-dimensional mission profile, including arm current, heatsink temperature, active power, and reactive power. In this way, the average junction temperature and junction temperature fluctuation of each SM can be readily estimated according to the power transfer direction. Furthermore, both the line-frequency and low-frequency fatigue are considered in the estimation process by using corresponding lifetime models. The proposed lifetime estimation method is compared with the traditional power loss average method and one-direction power transfer method by the application of the multi-dimensional mission profile of the practical Nanao project. The results show the bidirectional power transfer has a big influence on the damage distribution inside SM. The lower IGBT, upper FWD, and lower FWD all suffer considerable degradation under bidirectional power transfer conditions. Moreover, bond wire fatigue is the dominant degradation mechanism in MMC-HVdc application.

Degradation of I c due to residual stress in high-performance Nb3Sn wires submitted to compressive transverse force

Future particle colliders in search for new physics at the energy frontier require the development of accelerator magnets capable of producing fields well beyond those attainable with Nb-Ti. As the next generation of high-field accelerator magnets is presently planned to be based on Nb3Sn, it becomes crucial to establish precisely the mechanical limits at which this brittle and strain sensitive superconductor can operate safely. This paper reports on the stress dependence and the permanent reduction of the critical current under transverse compressive loads up to 240 MPa in state-of-the-art restacked-rod-process (RRP®) and powder-in-tube Nb3Sn wires. Single-wire experiments were performed at 4.2 K in magnetic fields ranging between 16 T and 19 T on resin-impregnated samples to imitate the operating conditions of a wire in the Rutherford cable of an accelerator magnet. Depending on the wire technology, we measured irreversible stress limit values—defined as the transverse stress value, leading to a permanent reduction in the critical current of 5%, assessed by convention at 19 T—ranging between 110 MPa and 175 MPa. This permanent reduction of the critical current after mechanical unload can occur for two reasons, which can be concomitant: the plastic deformation of the Cu matrix that produces residual stresses on the Nb3Sn lattice and the formation of cracks. We developed a method to identify the dominant degradation mechanism in our experiments that allowed us to predict the fraction of critical current lost due to residual stresses. Interestingly, we found that in the RRP® wires the measured reduction of Ic after unload from stresses as high as 240 MPa can be fully ascribed to residual stresses. An independent confirmation of this conclusion coming from a study combining x-ray tomography and deep learning Convolutional Neural Networks is also reported.

Quantification and evolution on degradation mechanisms of proton exchange membrane fuel cell catalyst layer under dynamic testing conditions

The catalyst layer is one of the core components of the Proton Exchange Membrane Fuel Cell (PEMFC). Studying its degradation mechanism is very important to improve the durability of PEMFC. Therefore, the degradation of the catalyst layer after the 100 h, 225 h, and 650 h durability tests are studied quantitatively in this paper. The results show that the agglomeration of Pt particles is the main reason for the degradation of the catalyst layer in the first 100 h, accounting for 80%. Catalyst dissolution and the loss of proton connectivity caused by the ionomer are the main factors for the degradation of the catalyst layer between 225 and 650 h, which increases from 23% in the initial stage to 46%. In addition, the corrosion degree of the carbon support inside the catalyst layer gradually intensified with the test time. This study reveals the dominant degradation mechanism of the catalyst layer in different degradation stages and the evolution of the whole degradation process, which has important guiding significance for the structural design of the catalyst layer for long-life fuel cells.

Effects of Aging in an Aqueous Solution of NaCl on Impact Strength and Structure of Bisphenol A Polycarbonate

The responses of the impact strength and structure of bisphenol A polycarbonate (PC) to aging in a 5 wt% aqueous solution of NaCl were studied in detail. The results of the Izod notched impact test showed that the impact strength decreased from 71.1 kJ/m2 to 17.5 kJ/m2 after an aging time of only 1 day in the aqueous solution of NaCl. The surface appearance of the aged PC observed by polarizing optical microscopy indicated that a large number of microvoids formed, and the size and number of these microvoids increased substantially with an increase in the aging time. The glass transition temperature, measured by differential scanning calorimetry, underwent a slight decrease after aging in the NaCl solution. In addition, no crystallization could be inferred from the heating curves. Thermal gravimetric analysis showed that the thermal decomposition temperature moved to a lower temperature, and the changes of the NaCl solution pH values indicated that hydrolysis was the dominant mechanism of degradation during aging in the aqueous solution of NaCl. Furthermore, the presence of NaCl accelerated the hydrolysis during the early stages of aging. A ductile-brittle transition caused by aging was inferred from observations of fracture surfaces using scanning electron microscopy.

Digital twin-driven intelligent assessment of gear surface degradation

Gearbox has a compact structure, a stable transmission capability, and a high transmission efficiency. Thus, it is widely applied as a power transmission system in various applications, such as wind turbines, industrial machinery, aircraft, space vehicles, and land vehicles. The gearbox usually operates in harsh and non-stationary working environments, expediting the degradation process of the gear surface. The degradation process may lead to severe gear failures, such as tooth breakage and root crack, which could damage the gear transmission system. Therefore, it is essential to assess the progression of gear surface degradation in order to ensure a reliable operation. The digital twin is an emerging technology for machine health management. A high-fidelity digital twin model can help reflect the operation status of the gearbox and reveal the corresponding degradation mechanism, which could benefit the remaining useful life (RUL) prediction and the predictive maintenance-based decision-making framework. This paper develops a digital twin-driven intelligent health management method to monitor and assess the gear surface degradation progression. The developed method can effectively reveal the gear wear propagation characteristics and predict the RUL accurately. Furthermore, the knowledge learned from digital twin models can be well transferred to the surface wear assessment of the physical gearbox in wide industrial applications, which is of great practical significance. Two endurance tests with different dominant degradation mechanisms were conducted to validate the effectiveness of the proposed methodology for gear wear assessment.

Accelerated radiation tolerance testing of Ti-based MAX phases

MAX phases have recently attracted significant attention for potential nuclear applications due to their novel properties such as unique hexagonal-compact nanolayered crystal structure, high-machinability due to lower hardness levels than conventional ceramics, and high-chemical inertness. In order for MAX phases to be used in nuclear reactors, two aspects deserve detailed investigations: (i) their phase stability at high-temperatures and (ii) microstructural defect formation and recovery induced by energetic particle irradiation. To date, degradation mechanisms of MAX phases at high-temperatures and following irradiation are largely unexplored fields of research. This work focuses on the evaluation of two Ti-based MAX phases—Ti2AlC and Ti3SiC2—within the context of extreme environments. To accomplish this, a one-of-a-kind comparison between neutron irradiations, performed over a decade of research at the high flux isotope reactor, and heavy-ion irradiations, carried out in situ in a transmission electron microscope, has been conducted. The results show Ti-based MAX phases are prone to accelerated decomposition under the conditions investigated. This questions the hypothesis that MAX phases exhibit high phase stability, especially when used in future nuclear energy systems where energetic particle irradiation is a dominating degradation mechanism.

(Invited) Development of a Simple and Rapid Diagnostic for Redox-Flow-Battery Cells

Prof. Robert Savinell has made many important contributions to fuel-cell and flow-battery systems. Both of these systems utilize electrochemical flow cells to either generate or store electricity. Because of this commonality, one can leverage concepts used in one for adoption in the other. An important topic for any electrochemical system is durability. A considerable amount of work has been on this topic with polymer-electrolyte fuel cells (PEFCs); in fact, a textbook devoted to this topic was published over a decade ago [1]. However, despite a recent renaissance in redox-flow-battery (RFB) technologies, assessing the durability of RFB cells is a topic that has not received much attention in the open literature, to date, and further research is needed to better understand dominant degradation mechanisms [2, 3].A simple and fast diagnostic tool has been developed for analyzing polymer-electrolyte fuel-cell degradation [4, 5]. The tool is based on analyzing changes in polarization curves of a cell over its lifetime. Using the polarization-change curve methodology, the primary mechanism for degradation (kinetic, ohmic, and/or transport related) can be identified. This technique can also be applied to RFB cells, which will be the focus of this presentation. This diagnostic tool provides a simple method for rapid determination of primary degradation mechanisms. Areas for more detailed future investigations shall also be summarized. References Modern Topics in Polymer Electrolyte Fuel Cell Degradation, Mench, M.; Kumbur, E.; and Veziroglu, T.; Editors; Elsevier, Denmark (2011).Yuan, X.-Z.; Song, C.; Platt, A.; Zhao, N.; Wang, H.; Li, H.; Fatih, K.; Jang, D.; “A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies,” J. Energy Res., 43 (2019) 6599−6638.Yao, Y.; Lei, J.; Shi, Y.; Ai, F.; Lu, Y. C.; “Assessment methods and performance metrics for redox flow batteries,” Energy, 6 (2021) 582−588.L. Perry, R. Balliet, and R. Darling, “Experimental Diagnostics and Durability Testing Protocols,” a chapter in [1].M. Pant, Z. Yang, M. L. Perry, and A. Z. Weber, “Development of a Simple and Rapid Diagnostic Method for Polymer-Electrolyte Fuel Cells,” J. Electrochem. Soc., 165 (2018) F3007.