Severe Mechanical Stress Research Articles

Achieving High Performance with High Oxygen Permeability Ionomer (HOPI) in Heavy Duty Fuel Cell MEAs

Heavy-duty PEM fuel cells are expected to last 25,000-30,000 hours in the field. Therefore, materials, components, and interfaces used in these systems must be highly resistant to severe mechanical and chemical stress. Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. Integrating these catalysts integrated with high O2 permeability ionomer (HOPI) in membrane electrode assemblies (MEAs) improved their fuel cell performance and durability, allowing the MEAs to achieve >1.2 A/cm2 at 0.7 V after 150k square wave accelerated stress test (AST) cycles, with a performance loss < 40 mV after 150K AST cycles.In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we compare the performance and durability of electrodes made from ball milled inks for Mayer rod coating before and after the catalyst scale up. Ink rheology and catalyst particle size are used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We evaluate and discuss the challenges that arise when coating the more viscous inks on decals, where the HOPI creates many bubbles in the ink. We also present the challenges of hot-pressing inks that contain HOPI, and how employing a Nafion overspray made with different solvents (isopropanol vs. ethanol) can improve hot-pressing. We investigate the how ionomer to carbon ratio affects hot pressing with HOPI and crack formation in the electrode via scanning electron microscopy (SEM).This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-FOA-0002360 (Phase I) and DE-SC0021671 (Phase II). Figure 1

A Multifunctional Nanocomposite Hydrogel Delivery System Based on Dual-Loaded Liposomes for Scarless Wound Healing.

Increased inflammatory responses and oxidative stress at the wound site following skin trauma impair healing. Furthermore, skin scarring places fibroblasts under severe mechanical stress and aggravates pathological fibrosis. A novel liposomal composite hydrogel is engineered for wound microenvironment remodeling, incorporating dual-loaded liposomes into gelatin methacrylate to create a nanocomposite hydrogel. Notably, tetrahydrocurcumin (THC) and hepatocyte growth factor (HGF) are encapsulated in the hydrophobic and hydrophilic layers of liposomes, respectively. The composite hydrogel maintains porous nanoarchitecture, demonstrating sustainable THC and HGF release and enhanced mechanical properties and biocompatibility. This system effectively promotes cell proliferation and angiogenesis and attenuates apoptosis. It decreases the expression of the inflammatory factors by inhibiting the high-mobility group box /receptor for advanced glycation end product/NF-κB (HMGB1/RAGE/NF-κB)pathway and increases macrophage polarization from M1 to M2 in vitro, effectively controlling inflammatory responses. It exhibits remarkable antioxidant properties by scavenging excess reactive oxygen species and free radicals. Most importantly, it effectively prevents scar formation by restraining the transforming growth factor beta (TGF-β)/Smads pathway that downregulates associated fibrotic factors. It demonstrates strong therapeutic effects against inflammation and fibrosis in a rat skin wound model with biosafety, advancing the development of innovative hydrogel-based therapeutic delivery strategies for clinical scarless wound therapy.

Electric Cable Insulator Damage Monitoring by Lasso Regression

Since the discovery of electricity, electric cables have become ubiquitous in human constructions, from machines to buildings. Insulators play a crucial role in ensuring the proper functioning of these cables, so it is important to monitor their possible damage, which can be caused by environmental contamination, severe temperature variations, and electrical and mechanical stress. While shunt conductance is a direct health indicator of cable insulation, measuring the cable average shunt conductance is not sufficient for the detection of localized insulator damage, since localized conductance variations are diluted over a long cable length in such measurements. The objective of this paper is to assess the feasibility of reflectometry techniques for the monitoring of insulator damage in electric cables. To this end, the estimation of localized conductance variations is investigated based on electrical measurements made at one end of a cable. To avoid estimating a large number of discretized conductance values along a long cable, the proposed method relies on sparse regression, which automatically focuses on localized conductance variations at unknown positions caused by accidental insulator damage. In order to efficiently apply sparse regression techniques, the telegrapher’s equations describing electric wave propagation in cables are transformed through several steps into a simple linear regression form. Then, Lasso (Least Absolute Shrinkage and Selection Operator) regression is applied to process the voltage and current data collected at a single end of the monitored cable. Numerical simulations show the potential of this method for fast estimation of localized shunt conductance variations.

Mechanical regulation to interfacial thermal transport in GaN/diamond heterostructures for thermal switch.

Gallium nitride offers an ideal material platform for next-generation high-power electronics devices, which enable a spectrum of applications. The thermal management of the ever-growing power density has become a major bottleneck in the performance, reliability, and lifetime of the devices. GaN/diamond heterostructures are usually adopted to facilitate heat dissipation, given the extraordinary thermal conduction properties of diamonds. However, thermal transport is limited by the interfacial conductance at the material interface between GaN and diamond, which is associated with significant mechanical stress at the atomic level. In this work, we investigate the effect of mechanical strain perpendicular to the GaN/diamond interface on the interfacial thermal conductance of heterostructures using full-atom non-equilibrium molecular dynamics simulations. We found that the heterostructure exhibits severe mechanical stress at the interface in the absence of loading, which is due to lattice mismatch. Upon tensile/compressive loading, the interfacial stress is more pronounced, and the strain is not identical across the interface owing to the contrasting elastic moduli of GaN and diamond. In addition, the interfacial thermal conductance can be notably enhanced and suppressed by tensile and compressive strains, respectively, leading to a 400% variation in thermal conductance. More detailed analyses reveal that the change in interfacial thermal conductance is related to the surface roughness and interfacial bonding strength, as described by a generalized relationship. Moreover, phonon analyses suggest that the unequal mechanical deformation under compressive strain in GaN and diamond induces different frequency shifts in the phonon spectra, leading to an enhancement in phonon overlapping energy, which promotes phonon transport at the interface and elevates the thermal conductance and vice versa for tensile strain. The effect of strain on interface thermal conductance was investigated at various temperatures. Based on the mechanical tunability of thermal conductance, we propose a conceptual design for a mechanical thermal switch that regulates thermal conductance with excellent sensitivity and high responsiveness. This study offers a fundamental understanding of how mechanical strain can adjust interface thermal conductance in GaN/diamond heterostructures with respect to mechanical stress, deformation, and phonon properties. These results and findings lay the theoretical foundation for designing thermal management devices in a strain environment and shed light on developing intelligent thermal devices by leveraging the interplay between mechanics and thermal transport.

4-Hydroxybenzenesulfonic acid triggers rapid preparation of phenolic aerogel composites by ambient pressure drying

Phenolic aerogel composites, as an excellent thermal insulation material, have been used in aerospace to resist extreme working conditions of severe heating and intense mechanical stress. However, the high cost and lengthy preparation process seriously restricts their more extensive application. Herein, a novel strategy for rapid preparation of aerogel composites by ambient pressure drying is enabled by copolymerization with 4-hydroxybenzenesulfonic acid. That is, the reactive 4-hydroxybenzenesulfonic acid can serve as the acid catalyst to accelerate both the protonation step and the gelation step during the preparation process of phenolic aerogel. After copolymerization with 4-hydroxybenzenesulfonic acid, these sulfonic acid groups significantly accelerate the protonation of benzoxazine intermediates, leading to more carbocation formation. The activation energy of curing reaction is significant decreased from 300 kJ∙mol−1 to 90 kJ∙mol−1. Thus, 4-hydroxybenzenesulfonic acid containing phenol formaldehyde resin (PFS) aerogel precursors exhibit much faster gelation reaction (within 4 h) than phenol formaldehyde resin (PF) aerogel precursor (12 h), which further facilitates the preparation of phenolic aerogel composites with needled quartz fiber felt by ambient pressure drying. Importantly, the PFS aerogel composites exhibit excellent thermal insulation performance under low heat flux and good fire safety under high heat flux. Rapid gelation of PFS triggered by 4-hydroxybenzenesulfonic acid provides a new approach to develop phenolic aerogel composites with low energy consumption, low cost and short preparation cycle.

Determination of Cutting Tool Performance Characteristics in Machining Nickel Based Super Alloys

Cutting tool materials often undergo severe mechanical stresses and thermal changes when machining nickel-based superalloys. The stresses and temperatures that arise when machining nickel-based superalloys greatly increase the blunting and wear rate of the cutting tool. As a result, tool life is adversely affected. It is seen from important studies that adhesion and abrasion wear mechanisms are more dominant in the processing of Inconel 718. The work material adheres to the cutting edge, forming a BUE. Depending on the cutting conditions, stable BUE is not always formed and this layer is sometimes repeatedly removed with the chips. Notching in the depth of cut, wear on the tool nose and coating layer is caused by the presence of hard particles in Inconel 718 and causes severe flank wear. Flank wear and notch are the main factors limiting tool life, and oxidation and diffusion occur as a result of high temperatures.

Structural integrity and skeletal trace elements in intertidal coralline algae across the Northeast Atlantic reveal a distinct separation of the leading and the trailing edge populations

Intertidal macroalgae, such as coralline algae, represent an essential structural element and substrate in rocky coastal zones. They have a high degree of flexibility allowing their survival in environments with severe mechanical stress during tidal cycles. This study characterised the genicula and intergenicula of the calcifying red algae Corallina officinalis across its geographic distribution in the Northeast Atlantic. Poleward populations have constructed more sturdy cell walls compared to equatorward populations, potentially due to greater local adaptations to higher frequency and intensity of environmental factors like storms and wave action. Southern populations showed a lack of local adaptation culminating in survival rather than thriving within their current environment, hence, they are located at the margin of this species' favourable conditions. Results clarify significant differences between latitudes and indicate a north-to-south gradient in this species’ skeletal elemental composition. Northern populations were dominated by cadmium, whereas chromium was the major trace element found in southern populations. In the future, these characteristics could lead to a permanent decline and a decrease in the ecosystem functions of C. officinalis in the southern locations in the Northeast Atlantic, which may be accelerated by predicted future climatic changes.

Analysis of the circadian distribution of metal ions in blood samples after knee replacement surgery – Consideration for athletes

SiO2 exhibits impressive theoretical specific capacity (1965 mAh g−1) as the anode of lithium-ion batteries. However, its commercial development is seriously hindered by security risks due to capacity fading and sharp fluctuations. Herein, we apply defect engineering to SiO2/C composites and report a stable preparation method of D‐[email protected]@SiO2 @N-C sandwich nanorods. The sandwich structure effectively alleviates the severe mechanical stress caused by volume expansion. The carbon materials with the structural defects provides abundant lithium storage sites for the electrode. It alleviates the influence of the low capacitance of C in the SiO2/C composite on the overall capacity. Furthermore, the flexibility and sulfur carrying capacity of copper foil are not outstanding, which limits the rate capacity of the battery. Therefore, aramid conductive fibers(AF) with excellent electrical conductivity were prepared to load D[email protected]2 @N-C (D-AF) in this work. The unique flexible skeleton in D-AF could realize the internal encapsulation of the active substances and adapt to the deformation of the electrode sheet under stress. Moreover, the dense CNTs network promotes the improvement of the electrode conductivity. D-AF exhibits more stable service life and stronger rate ability, compared with the copper foil. The reversible capacity of the cell with the D-AF electrode remains 789.55 mAh g−1, after 500 cycles at 1.0 C. It improves the cycle life and actual specific capacity of the battery, effectively. This work provides a new path for the development of flexible self-supported electrodes and the application of Multifunctional Silica in electrode.

Flexible aramid current collector loaded with D-CNTs@SiO2 @N-doped carbon composite for enhanced electrochemical performance

SiO2 exhibits impressive theoretical specific capacity (1965 mAh g−1) as the anode of lithium-ion batteries. However, its commercial development is seriously hindered by security risks due to capacity fading and sharp fluctuations. Herein, we apply defect engineering to SiO2/C composites and report a stable preparation method of D‐CNTs@SiO-CNTs@SiO2 @N-C sandwich nanorods. The sandwich structure effectively alleviates the severe mechanical stress caused by volume expansion. The carbon materials with the structural defects provides abundant lithium storage sites for the electrode. It alleviates the influence of the low capacitance of C in the SiO2/C composite on the overall capacity. Furthermore, the flexibility and sulfur carrying capacity of copper foil are not outstanding, which limits the rate capacity of the battery. Therefore, aramid conductive fibers(AF) with excellent electrical conductivity were prepared to load D-CNTs@SiO2 @N-C (D-AF) in this work. The unique flexible skeleton in D-AF could realize the internal encapsulation of the active substances and adapt to the deformation of the electrode sheet under stress. Moreover, the dense CNTs network promotes the improvement of the electrode conductivity. D-AF exhibits more stable service life and stronger rate ability, compared with the copper foil. The reversible capacity of the cell with the D-AF electrode remains 789.55 mAh g−1, after 500 cycles at 1.0 C. It improves the cycle life and actual specific capacity of the battery, effectively. This work provides a new path for the development of flexible self-supported electrodes and the application of Multifunctional Silica in electrode.

Modeling Mechanical Behavior of Membranes in Proton Exchange Membrane Water Electrolyzers

Membranes in proton exchange membrane water electrolysis (PEMWE) stacks are exposed to severe mechanical stress due to mechanical compression. Particularly critical is the gap between cell frame and porous transport layers (PTL). In this work mechanical stresses and strains on the membrane occurring during assembly and operation are quantified using a finite-element analysis applied to a simplified single cell sandwich. Within the simulation a Nafion® 117 membrane and the elastic-viscoplastic Silberstein material model is used. The material model parameters are based on and validated by experimental data from tensile tests to ensure matching with real PEMWE systems. The validated material model is used in cell simulations to identify resulting stresses and strains acting on the membrane. In accordance with experimental data, no critical states were identified. Furthermore, differential pressure up to 10 bar could not cause any significant change compared to deformations resulting during balanced pressure operation. Varying the gap size between cell frame and PTL resulted in a buckling in the simulated membrane for sizes of 0.3 mm and more during the membrane swelling. Such simulations can improve future cell designs while using an appropriate gap size with a given membrane thickness to avoid buckling and therefore possible failures.

Disulfide bond reduction and exchange in C4 domain of von Willebrand factor undermines platelet binding

BackgroundThe von Willebrand factor (VWF) is a key player in regulating hemostasis through adhesion of platelets to sites of vascular injury. It is a large, multi-domain, mechano-sensitive protein that is stabilized by a net of disulfide bridges. Binding to platelet integrin is achieved by the VWF-C4 domain, which exhibits a fixed fold, even under conditions of severe mechanical stress, but only if critical internal disulfide bonds are closed. ObjectiveTo determine the oxidation state of disulfide bridges in the C4 domain of VWF and implications for VWF’s platelet binding function. MethodsWe combined classical molecular dynamics and quantum mechanical simulations, mass spectrometry, site-directed mutagenesis, and platelet binding assays. ResultsWe show that 2 disulfide bonds in the VWF-C4 domain, namely the 2 major force-bearing ones, are partially reduced in human blood. Reduction leads to pronounced conformational changes within C4 that considerably affect the accessibility of the integrin-binding motif, and thereby impair integrin-mediated platelet binding. We also reveal that reduced species in the C4 domain undergo specific thiol/disulfide exchanges with the remaining disulfide bridges, in a process in which mechanical force may increase the proximity of specific reactant cysteines, further trapping C4 in a state of low integrin-binding propensity. We identify a multitude of redox states in all 6 VWF-C domains, suggesting disulfide bond reduction and swapping to be a general theme. ConclusionsOur data suggests a mechanism in which disulfide bonds dynamically swap cysteine partners and control the interaction of VWF with integrin and potentially other partners, thereby critically influencing its hemostatic function.

Nano-Silica Bubbled Structure Based Durable and Flexible Superhydrophobic Electrospun Nanofibrous Membrane for Extensive Functional Applications.

Nanoscale surface roughness has conventionally been induced by using complicated approaches; however, the homogeneity of superhydrophobic surface and hazardous pollutants continue to have existing challenges that require a solution. As a prospective solution, a novel bubbled-structured silica nanoparticle (SiO2) decorated electrospun polyurethane (PU) nanofibrous membrane (SiO2@PU-NFs) was prepared through a synchronized electrospinning and electrospraying process. The SiO2@PU-NFs nanofibrous membrane exhibited a nanoscale hierarchical surface roughness, attributed to excellent superhydrophobicity. The SiO2@PU-NFs membrane had an optimized fiber diameter of 394 ± 105 nm and was fabricated with a 25 kV applied voltage, 18% PU concentration, 20 cm spinning distance, and 6% SiO2 nanoparticles. The resulting membrane exhibited a water contact angle of 155.23°. Moreover, the developed membrane attributed excellent mechanical properties (14.22 MPa tensile modulus, 134.5% elongation, and 57.12 kPa hydrostatic pressure). The composite nanofibrous membrane also offered good breathability characteristics (with an air permeability of 70.63 mm/s and a water vapor permeability of 4167 g/m2/day). In addition, the proposed composite nanofibrous membrane showed a significant water/oil separation efficiency of 99.98, 99.97, and 99.98% against the water/xylene, water/n-hexane, and water/toluene mixers. When exposed to severe mechanical stresses and chemicals, the composite nanofibrous membrane sustained its superhydrophobic quality (WCA greater than 155.23°) up to 50 abrasion, bending, and stretching cycles. Consequently, this composite structure could be a good alternative for various functional applications.

Work-function-tunable metal-oxide mesh electrode and novel soluble bipolar host for high-performance solution-processed flexible TADF-OLED

Substantial effort has been dedicated to the development of solution-processed flexible organic light-emitting diodes (sf-OLEDs). However, to simultaneously enhance device performance and ensure stable operation under severe mechanical deformation, highly flexible transparent electrodes and efficient soluble organic emitting materials must be optimized together. Here, highly efficient green-emitting thermally activated delayed fluorescence (TADF) sf-OLEDs were developed using a mesh-structured Ni-doped indium zinc oxide (mNIZO) flexible electrode and a novel soluble bipolar host. The mNIZO electrode had excellent optical, electrical, and mechanical properties. The work function of the mNIZO electrode was engineered through surface doping with Ni without optical and electrical losses. 5-(9 H-Carbazol-9-yl)− 3′-(3,6-di-tert-butyl-9 H-carbazol-9-yl)-[1,1′-biphenyl]− 3-carbonitrile (CzCN-tCz) was synthesized as a soluble host material by incorporating a tert-butyl group into 3,3′-di(carbazol-9-yl)− 5-cyano-1,1′-biphenyl (mCBP-CN). Consequently, the mNIZO-based TADF sf-OLED with CzCN-tCz had a maximum external quantum efficiency of 21.0 % on a poly(ethylene 2,6-naphthalate) substrate, and 82 % of the initial luminance was maintained under severe mechanical stress, which is attributable to the high deformability of the mNIZO electrode. The proposed framework is expected to facilitate the design of high-performance cost-effective flexible displays with various forms through a simple process.

Modeling Mechanical Behavior of Membranes in Proton Exchange Membrane Water Electrolysis

The reliability of a proton exchange membrane water electrolysis (PEMWE) depends significantly on the long-term mechanical stability of the membrane due to its relatively low mechanical robustness. Membrane defects can be caused, for example, by severe mechanical stress in the critical gap between the cell frame and the porous transport layer (PTL). In this work the mechanical stresses and strains are quantified for such scenarios by using a finite element (FE) analysis which is applied to a simplified model setup.Nafion® is used as a standard material for the membrane and an appropriate material model is implemented into a FE software. The used parameters are based on and validated by experimental data from tensile tests to ensure matching with real PEMWE systems. The validated material model is used in the cell simulation to identify resulting stresses and strains during assembly and operation. In accordance with experimental experience, no critical states were identified. Furthermore, differential pressure up to 10 bar in the model could not cause any significant change compared to deformations resulting from boundary conditions for balanced pressure operation. Varying the gap size between the cell frame and PTL resulted in a buckling in the simulated membrane for sizes of 0.3 mm and more during membrane swelling.

Reviewing Alumina-Zirconia Composite as a Ceramic Biomaterial

In orthopedics, increasing the implant lifetime minimizes the need for repair surgery, which benefits the patient’s health and the practice bottom line. The quality of the materials and designs is always being enhanced to reach the ultimate objective of a single implant that would last a person their whole life. The purpose of orthopedic treatments is to enhance the patient’s ability to participate in normal activities and socialize, and the implant carrier should not be subjected to unnecessary limitations. As a result, implants are exposed to severe mechanical stress and the inherently hostile in vivo biochemical environment, which is particularly prevalent in younger and more active people. The development of hip prosthesis design and materials has taken this path in recent years. This development is one of the most challenging problems in the field of implant technology in this century. In this study, various materials, including ceramics, glass, metal alloys, polymers, metal alloys, composites, and others, were used in an effort to combine biocompatibility with fatigue resistance, stiffness, hardness, the capacity to withstand dynamic and static stresses, and excellent chemical and mechanical wear resistance. The fracture toughness of zirconia-toughened alumina composites is increased by a factor of four compared to alumina by itself. Zirconia was first included in alumina as a densifier; however, it was not until much later that zirconia was used as a reinforcement particle to increase the level of toughness in the material. The use of ZTA to improve the mechanical properties of orthopedic implants has lately been the subject of several studies, which have all just been concluded. This research includes a literature review primarily concerned with the Biolox Delta composite, its microstructural properties, manufacturing and prosthesis materials for it to identify as a bioceramic material for medical applications.

Unveiling the Stress‐Buffering Mechanism of Deep Lithiated Ag Nanowires: A Polymer Segmental Motion Strategy toward Ultra‐Robust Li Metal Anodes

AbstractThe severe volume expansion and uncontrolled mechanical stress restrict the high‐areal‐capacity Li storage in the alloy‐type or metallic anodes. Hitherto, most of the mitigation coating strategies are still based on the “trial‐and‐error” attempts, without the quantitative elucidation of the stress‐relaxation mechanism. This article herein constructs a prototypical coating model based on the Si‐O bonding, with the virtual and experimental screening of various structural parameters (for instance, the thickness, elasticity and cross‐linking density), for the deep lithiation of the Ag nanowires (AgNWs) framework. The operando X‐ray diffraction analysis and density functional theory calculations show that γ2(Li10Ag3) exhibits the highest Li affinity to induce the piled‐up deposits till 10 mA h cm–2; while the molecular dynamics simulations depict the optimal stress‐buffering pattern of the segmental motion in polydimethylsiloxane (PDMS) coating layer. As pairing the integrated anode of the AgNWs@PDMS slurries that casted on the AlOx modified polyethylene separator with the NMC‐811 cathode (12.5 mg cm–2), the constructed single‐layer pouch cell can balance the robust cyclability even at the mechanical deformations. This study demonstrates a tentative inverse design strategy to realize the stress‐buffering purpose upon the priori defining of the structural properties.

Pre-lithiated TiSb2 alloy-based lithium-ion capacitor exceeding 20000 cycles and standing for more than 1000 hours of float time

The dream of using beyond-carbon metalloids or transition metals as anode materials in electrochemical energy storage systems has been long pursued for the sake of greater capacity. However, two major challenges remain unresolved: the high volumetric expansion suffered by those materials, causing severe mechanical stress ending up in device failure, and the large first cycle irreversibility. In this work, we tackle both in a single approach, by using titanium to buffer mechanical stress of antimony (TiSb 2 ) and by adopting the recently proven dilithium squarate sacrificial salt (Li 2 C 4 O 4 ) strategy to pre-lithiate the system. Overall, herein developed alloy-based lithium-ion capacitor (LIC) demonstrates between double and triple volumetric performance respect to a dual carbon LIC. Moreover, the system is shown to be stable over 20000 cycles and 1000 h of floating at 3.8 V and room temperature. Post-mortem analysis correlates the origin of failure to the electrolyte oxidation and not to the degradation of the alloying material itself. Re-assembled TiSb 2 , AC, and full device with fresh electrolyte show to almost perform as good as the originals. • Lithium-ion capacitor based on alloying TiSb 2 and activated carbon. • TiSb 2 is pre-lithiated by using a sacrificial salt, namely, Li 2 C 4 O 4 . • LIC is stable over 20000 cycles. • LIC is stable over 1000 h floating at 3.8V. • Post-mortem analysis reveals electrolyte degradation to be the source of failure.

Electroforming free enhanced resistive switching in reduced graphene oxide films embedded with silver nanoparticles for nonvolatile memory applications

In this paper, the reduced graphene oxide (rGO)-based resistive random access memory (RRAM), embedded with Ag NPs, for nonvolatile memory applications has been investigated. The device exhibited enhanced I on/I off current ratio at lower switching voltage. The rGO-Ag thin film was deposited by spin-coating technique on an indium tin oxide coated glass substrate. Top contacts of aluminum (Al) were deposited by thermal evaporation technique for electrical measurements. The morphology of thin film has been characterized by scanning electron microscopy, and elemental quantification has been done using energy-dispersive x-ray spectroscopy. The structural and chemical analysis of thin film has been performed using x-ray diffraction (XRD) characterization and x-ray photoelectron spectroscopy, respectively. During applied potential, the device switches between two resistance states; low resistance state (LRS) and high resistance state (HRS). Initially when potential is applied across the device, the deposited thin film (rGO-Ag) was found in LRS which did not require initial forming voltage to activate the device. The requirement of this forming voltage may induce severe mechanical and electrical stress in the device and degrades the device performance. The rGO-Ag-based RRAM devices required (<1 V) to switch from LRS to HRS or vice versa with a large (∼103) on/off current ratio. The electrical stability of the devices has been tested for 4 × 103 s and repeatability for >60 cycles, which did not exhibit too much degradation. In rGO-Ag thin film-based RRAM devices, Ag NPs act as charge trapping sites, which results in enhanced switching characteristics. The trapping and detrapping mechanism of charges by Ag NPs is responsible for the enhanced switching characteristics in these films.

Regulating Ag Wettability via Modulating Surface Stoichiometry of ZnO Substrates for Flexible Electronics

AbstractA novel and highly efficient methodology to regulate (enhance or suppress) the Volmer–Weber 3D growth mode of ultra‐thin (&lt;10 nm) Ag layers by modulating the surface stoichiometry of ZnO substrates prior to Ag deposition is presented. Relative to pristine ZnO layers, oxygen‐deficient surface states formed by preferential removal of surface oxygen atoms remarkably improve Ag layer wettability, whereas oxygen‐excessive surface states formed by oxygen atom incorporation strongly facilitate Ag agglomeration. The dissimilar nucleation and coalescence dynamics are elucidated via combined molecular dynamics and force‐bias Monte Carlo simulations. The improved wettability results in significantly lower sheet resistance in the ultra‐thin (6–10 nm) Ag layers, for example, 6.03 Ωsq−1 at 8 nm, than the previously reported values from numerous other approaches in the equal thickness range. When this unique methodology is applied to ZnO/Ag/ZnO transparent electrodes, simultaneous improvement in electrical conductivity and visible transparency is realized, with a resultant Haacke figure of merit value of 0.139 Ω−1 that is &gt;50% higher than the best reported value for an identically structured electrode. We select transparent heating devices as a model system to confirm that the superior optoelectronic properties are highly sustainable under simultaneous and severe electrical, mechanical, and thermal stresses.

(Invited) Foldable Perovskite Solar Cells Using Carbon Nanotube-Embedded Ultrathin Polyimide Conductor

Recently, foldable electronics technology has become the focus of both academic and industrial research. The foldable device technology is distinct from flexible technology, as foldable devices have to withstand severe mechanical stresses such as those caused by an extremely small bending radius of 0.5 mm. To realize foldable devices, transparent conductors must exhibit outstanding mechanical resilience, for which they must be micrometer-thin, and the conducting material must be embedded into a substrate. Here, a single-walled carbon nanotubes–polyimide composite film with a thickness of 7 μm is synthesized and used as a foldable transparent conductor in perovskite solar cells. During the high-temperature curing of the carbon nanotubes-embedded polyimide conductor, the carbon nanotubes are stably and strongly p-doped using MoOx, resulting in enhanced conductivity and hole transportability. The ultrathin foldable transparent conductor exhibits an sheet resistance of 82 Ω sq.-1 and transmittance of 80% at 700 nm, with a maximum-power-point-tracking-output of 15.2% when made into a foldable solar cell. The foldable solar cells can withstand more than 10,000 folding cycles with a folding radius of 0.5 mm. Such mechanically resilient perovskite solar cells are unprecedented; further they exhibit the best performance among the carbon-nanotube-transparent-electrode-based flexible solar cells. Figure 1