Pristine Cell Research Articles

Multifunctional polymeric coating on stainless steel current collectors in aqueous energy storage devices

Herein, low cost stainless steel foils are employed as current collectors in aqueous Na-ion supercapacitors, while the foils are coated with following conducting polymers, namely, polyimide (PI), Schiff base polymer (SBP), polyanthraquinone sulfide (PAQS) and polyaniline (PANI). The foremost purpose of these polymeric coatings is the prevention of corrosion, and the resultant improvements in device performances. Notwithstanding, these polymeric coatings provide few additional benefits in device characteristics, and these are following: (i) enhancement of electrolyte stability window, (ii) contributing charge storage capacitance, (iii) conversion of 2D pristine substrate to 3D porous current collector. The four coating polymers are electrochemically characterized, and PI is selected for fabricating Na-ion supercapacitor cells. The PI-coating reduces the stainless steel’s corrosion rate ∼ 68 times, expands the electrolyte stability window ∼ 1.2 times, and delivers ∼ 2 times higher capacitance with respect to pristine current collector, whereas no appreciable interfacial resistances are observed. The supercapacitor cell with PI-functionality demonstrates ∼ 6.6 times improved capacitance than that of pristine cell at 25 mA/g current density, while > 95 and ∼ 90 % Faradaic efficiencies are noted for former and latter, respectively. The distinct enhancement of cell performances clearly demonstrates the effectiveness of multifunctional polymeric coating on corrosion-prone metallic current collectors.

Reactivation of dissolved polysulfides with nitrogen doped graphene decorated carbon cloth as an effective interlayer for magnesium-sulfur battery

The theoretically high energy densities and wide availability of active materials have led to great interest in the development of magnesium‑sulfur (MgS) batteries. However, poor electronic conductivity of sulfur, active material dissolution, polysulfide shuttling, and poor cycling stability are major challenges that need to be tackled. Herein we observed the pristine MgS cell faces significant overcharging issues and cell failure is common within 30 cycles with significant capacity decay. With the help of XRD and elemental mapping realized that the dissolved liquid polysulfides are metastable in nature. Due to the high sulfophilic nature of the separator, polysulfide absorption leads to slow crystal growth inside the separator. This active material trapping might be the reason for quick capacity decay. We attempted to revive the dissolved polysulfides by introducing conductive nitrogen-doped graphene (N-gpn)@Carbon cloth(CC) interlayer between the electrodes and separator. This interlayer has a high polysulfide absorption nature, which allows the battery to demonstrate an initial capacity of 1075 mAh g−1 and increased cycling stability to 100 cycles. However, this stability was further enhanced to 300 cycles by protecting the anode. Theoretical considerations suggest that among all polysulfides, MgS8, has the strongest interaction with N-gpn and can be trapped most favorably in a defective N-gpn. This leads to enhanced utilization of the active material and improved cycling stability.

Ru Decoration By PEALD for Bifunctional Oxygen Electrocatalysis in Solid Oxide Cells

Solid oxide cells (SOCs) are electrochemical devices that have garnered significant attention due to their high efficiency, fuel flexibility, and reversibility for operation in both fuel cell and the electrolysis modes. However, the relatively high operating temperature (typically > 800 °C) required presents various challenges such as fast degradation, high operating costs, and slow start-up. To overcome these issues, significant efforts have been made to decrease the operating temperature, but this causes a dramatic decrease in performance due to the low catalytic activity of typical electrode materials. One strategy to increase the catalytic activity is to introduce highly active nanoparticles onto a conventional electrode backbone, but while noble metals such as Ru and Ir have been utilized as oxygen evolution reaction (OER) catalysts, their widespread application in SOECs is hindered by their high cost and limited availability.In this presentation, we demonstrate a highly effective approach to enhance air electrode performance through the deposition of an ultrathin layer of metallic Ru, as thin as ∼7.5 Å, onto (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) using plasma-enhanced atomic layer deposition (PEALD). The Ru-decorated cell exhibited a current density of 656 mA cm–2 at 1.3 V, significantly outperforming a bare cell (440 mA cm–2 at 1.3 V). The decorated cell also showed a largely enhanced cell durability, which is ascribed to the beneficial role of SrRuO3 that emerges from the reaction between PEALD-based Ru and surface-segregated Sr species, in suppressing Sr segregation and maintaining favorable oxygen desorption kinetics. Further, the PEALD Ru coating on LSCF also reduces the resistance to the oxygen reduction reaction (ORR), highlighting the bifunctional electrocatalytic activities for reversible fuel cells. When the LSCF electrode of a test cell is decorated with ∼7.5 Å of the Ru overcoat and tested in fuel cell mode at 700 °C, this results in a current density of 656 mA cm-2 at 1.3 V in electrolysis mode and a peak power density of 803 mW cm-2, corresponding to an enhancement of 49.1% and 31.9%, respectively, compared to the pristine cell.

Damage Characteristics Analysis of Laser Ablation Triple-Junction Solar Cells Based on Electroluminescence Characteristics.

To study the physical property effects of the laser on GaInP/GaAs/Ge solar cells and their sub-cell layers, a pulsed laser with a wavelength of 532 nm was used to irradiate the solar cells under various energy conditions. The working performance of the cell was measured with a source meter. The electroluminescence (EL) characteristics were assessed using an ordinary and an infrared camera. Based on the detailed balance theory, in the voltage characteristics of an ideal pristine cell, the GaInP layer made the most significant voltage contribution, followed by the GaAs layer, with the Ge layer contributing the least. When a bias voltage was applied to the pristine cell, the top GaInP cell emitted red light at 670 nm, the middle GaAs cell emitted near-infrared light at 926 nm, and the bottom Ge cell emitted infrared light at 1852 nm. In the experiment, the 532 nm laser wavelength within the response spectrum bands of the GaInP layer and the laser passed through the glass cover slip and directly interacted with the GaInP layer. The experimental results indicated that the GaInP layer first exhibited different degrees of damage under laser irradiation, and the cell voltage was substantially attenuated. The GaInP/GaAs/Ge solar cell showed a decrease in electrical and light emission characteristics. As the laser energy increased, the cell's damage intensified, gradually leading to a loss of photoelectric conversion capability, the near-complete disappearance of red light emission, and a gradual degradation of near-infrared emission properties. The EL imaging revealed varying damage states across the triple-junction gallium arsenide solar cell's sub-cells.

Investigating the Performance and Safety of Li-Ion Cylindrical Cells Using Acoustic Emission and Machine Learning Analysis

Acoustic emission (AE) is a low-cost, non-invasive, and accessible diagnostic technique that uses a piezoelectric sensor to detect ultrasonic elastic waves generated by the rapid release of energy from a localised source. Despite the ubiquity of the cylindrical cell format, AE techniques applied to this cell type are rare in literature due to the complexity of acoustic wave propagation in cylindrical architectures alongside the challenges associated with sensor coupling. Here, we correlate the electrochemical performance of cells with their AE response, examining the differences during pristine and aged cell cycling. AE data was obtained and used to train various supervised binary classifiers in a supervised setting, differentiating pristine from aged cells. The highest accuracy was achieved by a deep neural network model. Unsupervised machine learning (ML) models, combining dimensionality reduction techniques with clustering, were also developed to group AE signals according to their form. The groups were then related to battery degradation phenomena such as electrode cracking, gas formation, and electrode expansion. There is the potential to integrate this novel ML-driven approach for widespread cylindrical cell testing in both academic and commercial settings to help improve the safety and performance of lithium-ion batteries.

Superwetting Nanofluids of NiOx-Nanocrystals/CsBr Solution for Fabricating Quality NiOx-CsPbBr3 Gradient Hybrid Film in Carbon-Based Perovskite Solar Cells.

The wettability of precursor solution on substrates is the critical factor for fabricating quality film. In this work, superwetting nanofluids (NFs) of non-stoichiometric nickel oxide (NiOx) nanocrystals (NCs)-CsBr solution are first utilized to fabricate quality NiOx-CsPbBr3 hybrid film with gradient-distributed NiOx NCs in the upper part for constructing hole transport ladder in carbon-based perovskite solar cells (C-PSCs). As anticipated, the crystalline properties (improved crystalline grain diameters and reduced impurity phase) and hole extraction/transport of the NiOx-CsPbBr3 hybrid film are improved after incorporating NiOx NCs into CsPbBr3. This originates from the superb wettability of NiOx-CsBr NFs on substrates and the excellent hole-transport properties of NiOx. Consequently, the C-PSCs with the structure of FTO/SnO2/NiOx-CsPbBr3/C displays a power conversion efficiency of 10.07%, resulting in a 23.6% improvement as compared with the pristine CsPbBr3 cell. This work opens up a promising strategy to improve the absorber layer in PSCs by incorporating NCs into perovskite layers through the use of the superwettability of NFs and by composition gradient engineering.

Effect of the operating temperature on the degradation of solid oxide electrolysis cells

The present work aims to better understand the effect of operating temperature on the degradation of Solid Oxide Electrolysis Cells (SOECs). The studied SOECs consist of La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Gd0.2O2-δ (LSCF-GDC) oxygen electrode, GDC diffusion barrier layer, Y0.16Zr0.84O1.92 (YSZ) electrolyte and Ni-YSZ hydrogen electrode. Durability tests are carried out at 750, 800 and 850 °C for 2000 h at −1 A cm−2, using 10/90 vol% H2/H2O and dry air at the hydrogen and oxygen electrodes, respectively. The electrochemical impedance spectra measured before and after ageing reveal a strong evolution related to the hydrogen electrode, while the change in the oxygen electrode contribution remains negligible. A set of advanced characterization techniques are employed to study the cell degradation. For the hydrogen electrode, a large Ni depletion is observed after ageing, which increases with the operating temperature. The analysis of the oxygen electrode shows an elemental inter-diffusion between the LSCF-GDC/GDC/YSZ layers on the manufactured cells that seems to not evolve significantly upon operation. Moreover, the presence of SrZrO3 is not detected in the pristine cell and in the operated ones. Besides, only a limited LSCF decomposition is found in good agreement with the electrochemical characterizations. Hypotheses that could explain the good oxygen electrode stability are discussed.

Chemical prelithiation of SiOx/Gr anode for improved cycling performance in lithium-ion batteries

Owing to its high specific capacity and excellent cycling performance, SiOx is an appealing alternative to traditional graphite anodes. In order to increase the anode's cycling stability, this work demonstrates the chemical prelithiation of SiOx/Gr anode for real-world applications. The highest ICE obtained is 98.8 % using the chemical prelithiation method for half cell. The prelithiated anode was characterized using various techniques, and the viability of the process was tested using a pouch cell assembly, demonstrating enhanced capacity compared to the pristine pouch cell. This research has implications for portable electronics, electric vehicles, renewable energy storage, and other applications requiring high-capacity and long-lasting batteries.

Multiple‐dimensioned defect engineering for graphite felt electrode of vanadium redox flow battery

AbstractThe scarcity of wettability, insufficient active sites, and low surface area of graphite felt (GF) have long been suppressing the performance of vanadium redox flow batteries (VRFBs). Herein, an ultra‐homogeneous multiple‐dimensioned defect, including nano‐scale etching and atomic‐scale N, O co‐doping, was used to modify GF by the molten salt system. NH4Cl and KClO3 were added simultaneously to the system to obtain porous N/O co‐doped electrode (GF/ON), where KClO3 was used to ultra‐homogeneously etch, and O‐functionalize electrode, and NH4Cl was used as N dopant, respectively. GF/ON presents better electrochemical catalysis for VO2+/VO2+ and V3+/V2+ reactions than only O‐functionalized electrodes (GF/O) and GF. The enhanced electrochemical properties are attributed to an increase in active sites, surface area, and wettability, as well as the synergistic effect of N and O, which is also supported by the density functional theory calculations. Further, the cell using GF/ON shows higher discharge capacity, energy efficiency, and stability for cycling performance than the pristine cell at 140 mA cm−2 for 200 cycles. Moreover, the energy efficiency of the modified cell is increased by 9.7% from 55.2% for the pristine cell at 260 mA cm−2. Such an ultra‐homogeneous etching with N and O co‐doping through “boiling” molten salt medium provides an effective and practical application potential way to prepare superior electrodes for VRFB.

Maneuverable B-site cation in perovskite tuning anode reaction kinetics in vanadium redox flow batteries

The actual performance of vanadium redox flow batteries (VRFBs) is still significantly constrained by the slow kinetics and major parasitic reactivity of anode issues. Herein, a B-site management strategy of SrBO3 (B = Ti, Zr, Hf) perovskites was proposed to promote the anode reaction jointly explored by experiments and first–principle calculations. As the atomic number of B increases, the enhanced polarity of the B–O bond and the increased oxygen defect can boost the adsorption of vanadium ions, while the weakened orbital hybridization of the B–O bond facilitates the charge transfer of anode reaction. Compared with SrTiO3 and SrZrO3, oversized particles and deformed crystals of SrHfO3 reduce its catalysis. Of SrBO3 perovskites, SrZrO3 stands out in catalysis, owing to its outstanding combination of high hydrophilicity, large surface area, and desired crystal structure. Further, the VRFB using SrZrO3 presents a superior energy efficiency (EE) of 63.2% at 300 mA cm–2 and an increase of 15% in EE compared with the pristine cell at 200 mA cm–2. This work lays the foundation for building the connections between the structural and compositional flexibility and the tunable perovskite properties desirable for vanadium redox reactions.

Unraveling the Effects of Carbon Corrosion on Oxygen Transport Resistance in Low Pt Loading Proton Exchange Membrane Fuel Cells.

Cost and durability have become crucial hurdles for the commercialization of proton exchange membrane fuel cells (PEMFCs). Although a continuous reduction of Pt loading within the cathode catalyst layers (CCLs) can lead to cost savings, it also increases the oxygen transport resistance, which is further compounded by key material degradation. Hence, a further understanding of the mechanism of significant performance loss due to oxygen transport limitations at the triple phase boundaries (TPBs) during the degradation process is critical to the development of low Pt loading PEMFCs. The present study systematically investigates the impact of carbon corrosion in CCLs on the performance and oxygen transport process of low Pt loading PEMFCs through accelerated stress tests (ASTs) that simulate start-up/shutdown cycling. A decline in peak power density from 484.3 to 251.6 mW cm-2 after 1500 AST cycles demonstrates an apparent performance loss, especially at high current densities. The bulk and local oxygen transport resistances (rbulk and Rlocal) of the pristine cell and after 200, 600, 1000, and 1500 AST cycles are quantified by combining the limiting current method with a dual-layer CCL design. The results show that rbulk increased from 1527 to 1679 s cm-2, Rlocal increased from 0.38 to 0.99 s cm-1, and the local oxygen transport resistance with the normalized Pt surface area (rlocal) exhibited an increase from 18.5 to 32.0 s cm-1, indicating a crucial impact on the structure collapse and changes in the chemical properties of the carbon supports in the CCLs. Further, the interaction between the ionomer and carbon supports during the carbon corrosion process is deeply studied via electrochemical quartz crystal microbalance and molecular dynamics simulations. It is concluded that the oxygen-containing functional groups on the carbon surface could impede the adsorption of ionomers on carbon supports by creating an excessively water-rich layer, which in turn aggravates the formation of ionomer agglomerations within the CCLs. This process ultimately leads to the destruction of the TPBs and hinders the transport of oxygen through the ionomer.

Multimodal Characterization of Nucleation and Progression of Interfacial Degradation in All Solid-State Batteries

We face an immediate need for more energy-dense batteries that are stable over long-term cycling, to address the increased electrification of the transportation sector. All-solid state batteries (ASSBs) that combine a solid-state electrolyte with a Li metal anode offer the potential to achieve this objective by replacing intercalation anodes such as graphite with Li metal. However, interfacial degradation at the Li | solid electrolyte interface currently compromises the safety and cycling stability of ASSBs [1]. This interfacial degradation is usually a combination of instabilities of mechanical, chemical or electrochemical origin. This in turn compromises the structural and morphological stability of ASSBs over cycling, causing them to fail in fewer cycles than required for implementation as next-generation batteries in automobiles [2]. Thus, in order to improve their cycling stability, the understanding of the origin and nature of these interfacial instabilities needs to be multimodal, to understand the interplay between the different degradation mechanisms. Argyrodite (Li6PS5Cl) is a particularly attractive solid-state electrolyte (SSE) due to a high ionic conductivity (comparable to liquid electrolytes), as well as potential for batch processing [3]. However, its brittle nature and chemical composition makes it susceptible to cracking and deleterious side reactions, which hamper its stability. This work will focus on elucidating the effect of (1) current density and (2) processing conditions on the cycling stability of Li | LPSCl | Li ASSBs.We use 4-D XRD-CT (X-ray diffraction computed tomography) combined with phase contrast micro-computed tomography (μCT) to conduct the multimodal investigation of interfacial degradation, under pseudo operando conditions. The methodology is to obtain a 3-D XRDCT scan around the interface in a particular cycled condition, followed by a higher-resolution 3D μCT scan on the same region. This sequence is repeated after every stripping/plating cycle, starting from the pristine cell up to cell failure. These experiments are conducted at a synchrotron source, to enable the acquisition at high spatial resolution (~5 μm) over large volumes (~mm3), in a reasonable amount of time. A standard swagelok-style cell is used for repeatability of results and optimal geometry for conducting tomography. XRD-CT can furnish quantitative phase maps of all phases (argyrodite and reaction by-products), as well as the elastic strain in the sample. The μCT on the other hand gives information on the evolution of morphology around the interface with cycling (cracks/voids). Thus, by correlating the two datasets together over cycling, we are able to connect mechanical instabilities to the chemical/electrochemical instabilities.Here, we focus on varying two specific processing parameters for argyrodite: the sintering temperature and pressure, and studying their effect on nucleation and propagation of interfacial instabilities over repeated cycling. Through cycling, we track the evolution of cracks/voids, chemical by-products such as LiCl, Li3P and Li2S using XRD-CT and μCT. Finally, we track the filling of metallic Li into certain cracks in dendritic form, which leads to shorting and failure of the cell. We find that both of these parameters heavily influence the behavior of the interface, with cells failing between 4-20 cycles, and a marked difference in how the degradation initiates and propagates. Finally, for the processing condition that shows the best cycling behavior, we do a C-rate study, by increasing the current density for plating/stripping with each cycle up to failure. This discusses the utility of a parameter such as critical current density for a cell, where the local current densities are very heterogeneous and different from the global current reading while cycling.We envisage these results being used as inputs into modeling studies to optimize strategies for interfacial stabilization in ASSBs going forward.[1] Paul, P. P. et al. Interfaces in all solid state Li-metal batteries: a review on instabilities, stabilization strategies, and scalability. Energy Storage Materials 2022, 45, 969-1001.[2] Hao, S. et al. Tracking lithium penetration in solid electrolytes in 3D by in-situ synchrotron X-ray computed tomography. Nano Energy 2021, 82, 105744.[3] Chen, Y-T. et al., Investigating dry room compatibility of sulfide solid-state electrolytes for scalable manufacturing, Journal of Materials Chemistry A 2022, 10, 7155-7164.

Is Transition Metal Dissolution a Major Degradation Process in Commercial Li-Ion Cells? Application of Impedance with Extended Sub-mHz Low-Frequency Range

Transition metal dissolution is a well-known degradation process in Li-ion batteries correlated with capacity fade1. Transition metals from a lithium transition metal oxide cathode can dissolve which causes structural changes in the crystal structure leading to deterioration of the material. Additionally, dissolved transition metals can migrate to the anode and reduce on the surface, impacting the surface activity of the anode composite and increasing its impedance.It is generally known that electrochemical performance of a Li-ion insertion battery electrode is primarily defined by the active material chemistry, further it is strongly impacted by the material and electrode-level engineering (particle size and aggregation, electrode porosity and tortuosity, electrolyte amount and properties, conductive additive and binder choice and their distribution in electrode composite). Furthermore, impedance response of an insertion electrode exhibits a strong dependence upon lithiation level (x). The specific dependence of impedance of an electrode upon x should allow to help in separating the two individual contributions of the two electrodes in a full cathode-anode battery cell. Thus, not surprisingly, Electrochemical Impedance Spectroscopy (EIS) is a common electrochemical technique of choice for degradation studies of Li-ion batteries2. Typically, EIS spectra of batteries are measured in frequency spans from MHz (laboratory cells) or kHz (commercial cells) down to mHz ranges. However, impedance measurements down to lower minimal frequencies (below 1 mHz) are often avoided from the practical reasons due to the inevitably longer measurement times being required.In the present work cylindrical commercial 18650-size high-energy NMC-Graphite(+Si) cells were electrochemically (galvanostatically) cycled at various conditions. In the constant temperature regime (10°C, 23°C, 35°C or 45°C) the tested cells were systematically cycled within various depth of discharge (DoD) ranges to observe the effect of the voltage range on the evolution (decline) of cell capacity. EIS responses were measured at different selected states of charge (SoC), with the aim to help to resolve the individual contributions of cathode and anode. State of health (SoH) of a battery was determined by current integrated capacity measurement and was periodically monitored after specific number of cycles and correlated with the impedance growth. EIS measurements down to conventional 10 mHz as well as to very low frequencies (0.1 mHz) were performed and compared to determine what additional information and insights for developing of a physics-based battery cell model and degradation modes can be obtained by including the extended low-frequency range (down to 0.1 mHz). We systematically investigated evolution (increase) of impedance of commercial Li-ion cells including the extended low-frequency range.After completion of the cycling test, post-mortem analysis of the cell components was performed on selected cells. Cells were disassembled, electrodes carefully removed, properly washed and SEM-EDX and ICP-MS analysis was performed on the cathode and anode samples. The amount of transition metals in both cathode and anode was determined.We thoroughly confirmed that the impedance of the commercial (full cells) in general increases during the decrease of capacity at all the tested conditions. Importantly, EIS spectra measured down to very low frequencies show that in addition to the (expected) increase of the real component (Re(Z)) simultaneously also the imaginary component (Im(Z)) significantly increases. We provide novel physics-based explanation of the underlying phenomena. Electrochemical characterization of the half cells prepared from the harvested electrodes in general showed a decrease in capacity and increase in voltage hysteresis for both cathode and anode – the actual changes showing strong dependence upon conditions during cycling. EDX and ICP-MS analysis revealed that the composition of the cathode active material remained practically unchanged and that the amount of the transition metals (TMs) deposited on the anode did not increase greatly with the cycling – the total amount of detected TMs remaining well below 300 ppm (relative to the amount of TMs in pristine cathode). Gilbert, J. A., Shkrob, I. A. & Abraham, D. P. Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells. J. Electrochem. Soc. 164, A389–A399 (2017).Meddings, N. et al. Application of electrochemical impedance spectroscopy to commercial Li-ion cells: A review. J. Power Sources 480, 228742 (2020). Figure 1. a) Typical examples of EIS response of 811-NMC-Graphite(+Si) full cells measured at SoC = 0.5 (3.705 V) down to 1 mHz (dark colors) and down to 0.1 mHz (lighter dolors) for pristine cell (black/grey), cell cycled at 23°C (blue), and cell cycled at 45°C (red). The corresponding SoH values were: 1, 0.39, and 0.39, respectively. b) Comparison of capacity of the half-cells prepared with the cathodes and anodes harvested from the initial commercial cells (panel a). Figure 1

Eco-Friendly Boost for Perovskite Photovoltaics: Harnessing Cellulose-Modified SnO2 as a High-Performance Electron Transporting Material.

In this study, a passivated tin oxide (SnO2) film is successfully obtained through the implementation of sodium carboxymethyl cellulose (Na-CMC) modifier agent and used as the electron transporting layer (ETL) within the assembly of perovskite solar cells (PSCs). The strategic incorporation of the Na-CMC modifier agent yields discernible enhancements in the optoelectronic properties of the ETL. Among the fabricated cells, the champion cell based on Na-CMC-complexed SnO2 ETL achieves a conversion efficiency of 22.2% with an open-circuit voltage (VOC) of 1.12 V, short-circuit current density (JSC) of 24.57 mA/cm2, and fill factor (FF) of 80.6%. On the other hand, these values are measured for the pristine SnO2 ETL-based control cell as VOC = 1.11 V, JSC = 23.59 mA/cm2, and FF = 76.7% with an efficiency of 20.1%. This improvement can be ascribed to the high charge extraction ability, higher optical transmittance, better conductivity, and decrease in the trap state density associated with the passivated ETL structure. In addition, the cells employing Na-CMC-complexed SnO2 ETL exhibit prolonged stability under ambient conditions during 2000 h. Based on the preliminary results, this study also presents a set of findings that could have substantial implications for the potential use of the Na-CMC molecule in both large-scale perovskite cells and perovskite/Si tandem configuration.

Reactivity of Stone-Wales defect in graphene lattice – DFT study

Understanding the reactivity of carbon surfaces is crucial for the development of advanced functional materials. The SW defect is commonly present in carbon materials, but a comprehensive understanding of its effects on the reactivity of carbons is missing. In this study, we systematically investigate the reactivity of graphene surfaces with the Stone-Wales (SW) defect using Density Functional Theory calculations. We explore the atomic adsorption of various elements, including rows 1–3 of the Periodic Table, potassium, calcium, and selected transition metals. Our results demonstrate that the SW defect enhances binding with the studied adsorbates when compared to pristine graphene, with carbon and silicon showing the most significant differences. Additionally, we examine the effects of mechanical deformation on the lattice by constraining the system with the SW defect to the pristine graphene cell. Interestingly, these constraints lead to even stronger binding interactions. Furthermore, for carbon, nitrogen, and oxygen adsorbates, we observe that mechanical deformation triggers the incorporation of adatoms into the carbon bond network, leading to the reorganization of the SW defect structure. This work establishes a foundation for future studies in the defect and strain engineering of graphene, opening avenues for developing advanced materials and catalysts with enhanced reactivity and performance.

Analysis of geometric defects in square locally resonant phononic crystals: A comparative study of modeling approachesa).

Phononic crystals can develop defects during manufacturing that alter the desired dynamic response and bandgap behavior. This frequency behavior change can enable successful defect inspection if the characteristic defect response is known. In this study, the behavior of a defective square unit cell comprising a freed and shortened leg is studied using a wave finite element method and an approximate continuous-lumped model to elucidate the defect induced qualitative dynamical features. These metrics are a computationally inexpensive alternative to modeling a defective unit cell within a large pristine array entirely in finite elements. The accuracy of these models is validated by comparing the result to a full finite element model. The impact of a shortened unit cell leg on the behaviors of an infinite array of defective cells and a finite array with a single defect are successfully predicted through dispersion curves and frequency response functions, respectively. These methods reveal defect-induced modes that split the local resonance bandgap of the pristine cell, as well as new anti-resonances resulting from the shortened leg. The study uses both approaches to evaluate the effect of defects in complex phononic crystal geometries and provides a comparative evaluation of the results of each model.

Thickness effect of thin-film barrier layers for enhanced long-term operation of solid oxide fuel cells

Highly efficient solid oxide cells are one of the most promising technologies for a sustainable future based on renewable hydrogen. The diffusion barrier layer employed between zirconia-based electrolytes and state-of-the-art oxygen electrodes aims to limit the formation of electrically insulating secondary phases that dramatically reduce the cells’ performance. Conventional barrier layers manufactured by screen-printing technology lead to porous microstructures that enable the formation of insulating SrZrO3, partially blocking the active area of the cells. Opposite, homogeneous and dense barrier layers have proven to be the ultimate solution to limit interdiffusion, substantially improving the cells’ performance. Despite the relevance of this solution, the impact of the barrier layer thickness on the final performance of the cells is still unknown. In this work, gadolinia-doped ceria barrier layers with thicknesses between 200 and 800 nm made by pulsed laser deposition were studied in button cells. Excellent electrochemical performance was obtained for all the cells, improving 45% of the power output of the reference counterparts. Moreover, durability tests performed on the cell with the thinnest layer (200 nm) did not show any measurable degradation for 3500 h of continuous operation under high current densities of 0.77 A cm−2 (∼0.87 V) at 750 °C. Post-mortem characterization by synchrotron nano-x-ray fluorescence of a pristine cell and the aged cell allowed us to observe that some spots of SrZrO3 were present at the cathode/electrolyte interface since the cell manufacturing step without increasing during long-term operation. Indeed, the discontinuity of this insulating phase seems not to be critical for cell operation.

Enhanced ZnO-based ETL and nanostructured interface modification for improved perovskite solar cells efficiency

Compared to standard silicon solar cells and other thin film cells, perovskite solar cells (PSCs) can achieve high power conversion efficiency and reduce the production costs. ZnO-based ETL in perovskite solar cells provides a lot of benefits, such as low processing temperature and high mobility. However, the reported instability of perovskite layers placed atop ZnO, resulting in poor device performance, has prevented it from being widely used in perovskite solar cells, though. In this work, an innovative way of insuring device performance and longer-term stability is proposed via the incorporation of a novel efficient process. Herein, a V-doped ZnO/Y-doped TiO2 electron transport bilayer was developed to combine the benefits of strong electron extraction and minimal interfacial recombination. This combined approach of engineering both the improved performance of VZnO as ETL and YTiO2 flower like structures at the interface ETL/Perovskite results in large improvements in the performance of the PSC. V-doped ZnO (VZnO) was introduced into the PSC structure as an ETL, due to its excellent electrical and optical properties, to improve electron extraction efficiency, with a doping amount of 4 at.% of vanadium. The latter has been optimized in our previous study. On the other hand, extrinsically doping TiO2 with an amount of 5 at.% of Yttrium (YTiO2) was utilized to enhance its physicochemical properties. The PSC based on VZnO/YTiO2 bilayer ETL possess the best PCE of 15.1%, compared to 9.4% in the pristine ZnO-based ETL solar cell, with the open-circuit voltage (Voc) of 923 mV, short-circuit photocurrent density (Jsc) of 22 mA cm−2, and fill factor (FF) of 74%. Obtained improvements are ascribed to the suppressed charge recombination via the incorporation of YTiO2 flower-like nanostructures at the interface VZnO/perovskite and the enhanced electron transporting in the resulting ETL bilayer structure.

Advanced electrode decorated with peanut-shell-derived carbon for vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) have been regarded as one of the most promising energy storage systems at grid-scale owing to their advantages of safe operation, flexible design, and long cycle life. However, the low electrochemical activities and poor hydrophilicity of conventional carbon-based electrodes (e.g., carbon felt, CF) greatly restrict the further improvements of cell performance and commercial applications. Therefore, fabricating advanced electrodes is crucial to the progress and practical applications of VRFBs. In this work, the waste biomass of peanut shells (PS) is used as the raw material to produce carbon particles that coat on the surface of CF (PS/CF) via adsorption and carbonization procedures. The redox reactions of VO2+/VO2+ are remarkably promoted on the as-prepared PS/CF electrode. When PS/CF is employed as the positive electrode, the resulting VRFB cell shows energy efficiency of 87% over 500 cycles under 100 mA cm−2, which is significantly higher than the pristine CF-based VRFB cell (79%). Additionally, the cycling stability of PS/CF-based cell has been remarkably enhanced. This study demonstrates that the cost-effective and sustainable peanut-shell-derived carbon modified CF holds a broad application prospects in the practical applications of advanced VRFBs as energy storage systems.

Improving Gas Diffusion in Solid Oxide Cells Through Laser-Ablated Electrode Supports

Improving solid oxide cell power density will enable cheaper commercial-scale SOFCs and SOECs. In Ni-YSZ electrode-supported cells, gas diffusion through the electrode support layer can be a major limitation at high H2 or H2O utilization and high temperature. Conventional methods of improving diffusion through the electrode support include increasing the support porosity and reducing the support thickness, but these can reduce the cell’s structural integrity. Freeze casting1 and 3D printing2 have also been explored to enhance diffusion. Here we explore cells in which the Ni-YSZ supports have macroscopic channels, produced by laser ablation, that reduce the average gas diffusion length.To test the difference in mass transport through patterned and pristine electrode supports, symmetric electrode-supported Ni-YSZ cells are patterned on one side, which enables comparison of the electrochemical performance of two otherwise identical electrodes (Figure 1a). Cells with varying pattern geometry, pore geometries, Ni/YSZ ratios, and Ni-YSZ particle sizes were created to fully understand how the support layer microstructure and macrostructure affects the cell performance. Patterned and pristine cells were tested together at three temperatures (600C, 700C, and 800C) in a 97%H2:3%H2O environment, chosen to produce a clear gas diffusion limitation in H2O electrolysis. j-V sweeps and electrochemical impedance spectroscopy (EIS) were carried out on each cell at each test condition, and the microstructure of patterned and control supports was characterized through SEM imaging.Upon removing the ohmic portion and fitting the j-V data to Equation 1 (see Figure 1), patterned electrodes consistently demonstrated higher limiting current density and lower mass transport losses than the control (Figure 1c-d). Three-point-bend mechanical testing revealed that the mean flexural fracture strengths of pristine cells and patterned cells are 36.0 ± 11.4 MPa and 33.0 ± 8.9 MPa respectively.Combining the equations for limiting current density with diffusion in a system with prismatic channels, we determined the ratio of the limiting current density for a patterned and pristine electrode using Equation 2 (see Figure). For the cell data shown in Figures 1c-1d, we expect an average 33% increase (with a standard deviation of 3.5%) in limiting current density based on microscopy measurements of channel and support layer thicknesses. In 1c, we see that the limiting current density of the patterned electrode is 32% higher than the pristine electrode, which matches our expectation. Furthermore, the Nyquist plot in Figure 1d demonstrates that patterned symmetric cells have similar impedance to pristine cells in the high-frequency regime with less impedance in the low-frequency regime, which is consistent with our expectations that the patterned cells have reduced mass transport losses with similar ohmic and activation losses. These j-V and EIS results suggest that macroscopic support patterning is a promising method for improving performance without compromising structural integrity. Figure 1: a) Ni-YSZ symmetric cell cross-section, laser-patterned with 600 µ m by 600 µ m channels and 200 µ m channel spacing. b) Comparison of the flexural fracture strength for pristine and patterned cells, under 3-point-bend testing. c) IR-free current density-voltage profiles of a patterned Ni-YSZ symmetric cell with a predicted current density improvement of 33%, at 700C in a 97%H2:3%H2O environment. Two distinct j-V responses are observed, based on whether the pristine electrode or the patterned electrode is under a cathodic bias. d) Unbiased potentiostatic EIS (1 MHz - 100 mHz) of a pristine cell versus two patterned cells at 700 C in 97%H2:3%H2O. The cells all have similar Ohmic resistances, but the impedance of the patterned cells is significantly lower in the low-frequency regime, due to the reduction in mass-transport losses. Equation 1: a is a constant, α is the transfer coefficient, j is current density, and jlim,H2O is the limiting current density for H2O diffusion. Equation 2: jlim/jlim,0 is the limiting current density ratio, A is the fraction of the cell surface that is patterned, and tc is the ratio of the channel depth to the patterned electrode thickness.