Low Ohmic Losses Research Articles

Low Dielectric Medium for Hyperbolic Phonon Polariton Waveguide in van der Waals Heterostructures.

Polar van der Waals (vdW) crystals, composed of atomic layers held together by vdW forces, can host phonon polaritons-quasiparticles arising from the interaction between photons in free-space light and lattice vibrations in polar materials. These crystals offer advantages such as easy fabrication, low Ohmic loss, and optical confinement. Recently, hexagonal boron nitride (hBN), known for having hyperbolicity in the mid-infrared range, has been used to explore multiple modes with high optical confinement. This opens possibilities for practical polaritonic nanodevices with subdiffractional resolution. However, polariton waves still face exposure to the surrounding environment, leading to significant energy losses. In this work, we propose a simple approach to inducing a hyperbolic phonon polariton (HPhP) waveguide in hBN by incorporating a low dielectric medium, ZrS2. The low dielectric medium serves a dual purpose-it acts as a pathway for polariton propagation, while inducing high optical confinement. We establish the criteria for the HPhP waveguide in vdW heterostructures with various thicknesses of ZrS2 through scattering-type scanning near-field optical microscopy (s-SNOM) and by conducting numerical electromagnetic simulations. Our work presents a feasible and straightforward method for developing practical nanophotonic devices with low optical loss and high confinement, with potential applications such as energy transfer, nano-optical integrated circuits, light trapping, etc.

Transitioning Low-Temperature GDC Socs: Lab to Commercialization Scale

Solid oxide fuel cells (SOFCs) electrochemically convert hydrogen and oxygen into electricity, heat, and water with high efficiency (~55%) [1], while in reverse operation, water and electricity are converted to hydrogen and oxygen in solid oxide electrolysis cells (SOECs). Appropriately designed solid oxide cells (SOCs) can operate in both SOFC and SOEC mode.Conventional SOCs typically demand elevated operating temperatures (800-1000°C), resulting in higher cost and accelerated degradation issues. Lowering operating temperatures below 600°C reduces thermal stresses, shortens start-up times, and broadens applications [2].Ce1-xGdxO2-δ (GDC), due to its superior oxygen ion conductivity at reduced temperatures, has lower ohmic losses than competing electrolyte materials. Thus, our 1.2 cm diameter circular anode supported GDC cell with 0.31 cm2 active area exhibits exceptional power densities, reaching approximately 3 watt per square centimeter at 650°C. Through optimal design, these cells exhibit exceptional performances in fuel cell mode, significantly enhancing efficiency and effectiveness when operating as an electrolyzer for fuel generation. This advance in performance is a result of mitigating the leakage current issues typical of ceria-based electrolytes through precise engineering of the cathodic microstructure and surface chemistry modification [3].The transition from lab-scale to large-scale commercialization (with active areas of 16 cm² &; 81 cm²) presents significant challenges such as tailoring material properties for large-cell versus button-cell synthesis while maintaining high performance levels.In this work we explore the challenges encountered during the scaling-up process. We report on fabrication strategies employed to achieve cell flatness, maintain high efficiency, ensure cost-effectiveness, and achieve long-term stability. Specifically, we have fabricated graded anode-supported cells [4] by developing an innovative lamination strategy involving tapes oriented perpendicular to each other. This approach notably contributed to achieving superior electrolyte densification and resulted in significantly flatter (low curvature values) with respect to both horizontal and vertical axes in cartesian coordinate space. When compared to the flatness values of 10x10 cm2 commercially available cells, our cells demonstrated remarkably flatter curvatures as shown in figure 1. This characteristic has proven highly beneficial for stack assembly, minimizing issues such as cell cracking and reducing sealing-related problems. By optimizing the cathode scaffold and infiltration process on larger area cells through a spray-coating machine, scaling up challenges are effectively mitigated compared to the button cell approach, where scaffold preparation and infiltration were performed using blade coating and a hand pipette, respectively. This approach effectively tackles electronic conduction issues in ceria-based electrolytes, leading to higher Open Circuit Voltages (OCVs) in fuel cell mode and increased efficiencies in reversible mode.

G-band traveling wave tube based on the elliptical pillar defected photonic crystal

In order to reduce the ohmic losses in the slow wave structure (SWS), an elliptical pillar defected photonic crystal waveguide (EPDPCW) is proposed as a SWS for the terahertz traveling wave tube (TWT). Compared with rectangular pillar defected photonic crystal waveguides (RPDPCW), the EPDPCW shows better high-frequency characteristics and lower ohmic losses. According to the particle-in-cell (PIC) results, in the frequency range of 188 GHz to 218 GHz, the saturated output power of EPDPCW is greater than 13.4 W, and the maximum saturated output power is 26.8 W at 196 GHz at a voltage of 9.78 kV and a beam current of 150 mA. Compared to the RPDPCW-TWT, the performance of the EPDPCW-TWT has been significantly improved.

Selective Flocculation and H2O2-Free Oxidative Etching-Based Synthesis of Highly Monodisperse Ag Nanospheres for Uniform Quantum Dot Photoluminescence-Enhancing Plasmonic Cavity Applications.

Ag nanoparticles have garnered significant attention for their excellent plasmonic properties and potential use as plasmonic cavities, primarily because of their intrinsically low ohmic losses and optical properties in the visible range. These are particularly crucial in systems involving quantum dots that absorb light at low wavelengths, where the need for a high threshold energy of interband transitions necessitates the incorporation of Ag nanostructures. However, the synthesis of Ag nanoparticles still encounters challenges in achieving structural uniformity and monodispersity, along with chemical stability, consequentially inducing inconsistent and poorly reliable optical responses. Here, we present a two-step approach for synthesizing highly uniform spherical Ag nanoparticles involving depletion-induced flocculation and Cu(II)-mediated oxidative etching. We found that the selective flocculation of multitwinned Ag nanocrystals significantly enhances the uniformity of the resulting Ag nanostructures, leaving behind only single-crystalline and single-twinned nanostructures. Subsequent oxidative etching, in which cupric ions are directly involved in the reaction, was designed based on Pourbaix diagrams to proceed following thermodynamically favorable states and circumvent the generation of reactive chemical species such as H2O2. This leads to perfectly spherical shapes of final Ag nanoparticles with a synthetic yield of 99.5% and additionally reduces the overall reaction time. Furthermore, we explore the potential applications of these monodisperse Ag nanospheres as uniform plasmonic cavities. The fabricated Ag nanosphere films uniformly enhanced the photoluminescence of InP/ZnSe/ZnS quantum dots, showcasing their capabilities in exhibiting consistent plasmonic responses across a large area.

Exploiting graded triangular gratings for optimal nano-focusing: A novel approach to enhance SERS efficiency

Plasmonic graded nano-gratings enable rainbow trapping of multiple resonant modes over a wide wavelength spectrum, useful for multi-channel Surface Enhanced Raman Spectroscopy (SERS) of molecular species. However, rectangular nano-gratings have limitations in achieving efficient rainbow trapping and localizing a wide spectrum of plasmonic modes due to their stepwise geometry, which induces high dissipation of surface plasmon polaritons into the substrate. An alternative platform of graded triangular nano-gratings enables increased localization and more efficient adiabatic transformation between neighboring grooves. Varying groove angles, depths, and periods in the tapered geometry allow for smooth adjustment of the surface plasmon polariton propagation constant, reducing losses and maximizing nano-focusing inside the groove tips. To overcome the limitation of low aspect ratio in wet-etching silicon, we employed a multi-step process of reactive ion etching of a SiO2 barrier layer to generate aperture width, followed by anisotropic wet-etching. The resulting graded triangular nano-gratings showed excellent SERS enhancement along three laser wavelength excitations. The enhancement factors of 638 and 785 nm wavelengths are 8.5 × 109 and 9 × 108, respectively, for the detection of 1 µM Rhodamine 6G. In addition, graded triangular nano-gratings show similar enhancement factors for other species, specifically the lipid DPEE-PEG, at the 532 nm laser excitation wavelength with an excellent SERS enhancement factor of 1.5 × 109. Owing to the ability of the graded triangular gratings to elicit pronounced SERS responses across three distinct laser excitations, they unequivocally qualify as “rainbow trapping” structures. Wider apertures, lower ohmic losses, and the ability to tune the groove angle beyond conventional etching methods bode well for graded triangular gratings as a superior platform for miniature sensors.

All-dielectric asymmetric planar metasurface based dual-parametric sensor

All-dielectric metasurfaces are a rapidly growing area of research because they have lower ohmic losses and sharper resonances than their metallic equivalents. In this work, we have reported a novel all-dielectric metasurface design for dual parameter (refractive index and temperature) sensing applications. The design consists of a square GaAs block on the top of a quartz substrate with a square hole etched on it. An outer cut to the GaAs block is introduced to break the symmetry. The asymmetry enables a sharp Fano resonance mode with 90% spectral contrast and extremely high quality (Q) factor of value 2.8×104 in the near-infrared (NIR) window. The multipolar nature of the high-Q resonance is studied using the cartesian multipolar decomposition technique, which reveals the electric dipolar nature of the resonance. To examine the refractive index capability of the proposed device, we varied the refractive index of the background medium and found that the device is highly sensitive and results in a very high Figure of Merit (FoM) 5384 RIU−1, owing to the very narrow linewidth of the resonance. The same design is also used for temperature sensing, which shows a notable improvement in sensitivity (72.4 pm/∘C) compared to various existing methods available. The in-depth analysis of the resonance in an optimized all-dielectric metasurface and its potential for sensing presented through this paper can be significant in designing high-performance optical sensors.

Low Ohmic Losses and Mode Selectivity Provided by a Distributed Bragg Reflector for Cavities of Terahertz Gyrotrons

Low Ohmic Losses and Mode Selectivity Provided by a Distributed Bragg Reflector for Cavities of Terahertz Gyrotrons

Label-Free Detection of Ultra-Low Weight Molecules Based on Fiber Optic Sensors With Low Loss Dielectric Nanostructures

Fiber optic (FO) sensors have great potential for low-cost, microsample testing and compact medical diagnostics. In this work, a FO sensor based on dielectric nanostructure is proposed and demonstrated based on the unique characteristics of dielectric materials, such as low ohmic loss and good biocompatibility. Specifically, we fabricate a SPR-FO sensor by inserting a sleeve with a large-scale, highly ordered dielectric nanodisk array at the end of the fiber probe. And we systematically investigate the sensing performance of the FO sensor including bulk and surface sensitivities. It is found that due to very low absorption losses, the FO sensor based on dielectric nanodisk exhibits a narrow resonance, thus leading to a sensing figure-of-merit almost twice larger than that of based on the metal plasmonic nanodisk. Also, the FO sensor shows a linear response to adsorbate layer thickness changes, which is clearly advantageous for quantitative analysis. Due to the highly localized electromagnetic fields, it can detect small molecules with a concentration of 1 μM, in which a molecular layer with thickness less than 1 nm can produce resonance changes as large as 6 nm. Our work could open a new opportunity for future bio-compatible, robust and low-loss medical diagnostic devices.

Coupled magnetic Mie resonances induced extraordinary optical transmission and its non-linear tunability

Dielectric metamaterials with low ohmic losses and resonating in the local magnetic mode are preferable for enhancing material non-linearity. Here, we propose and experimentally demonstrate broadband extraordinary electromagnetic transmission (EET) behavior, which is induced by the coupling of magnetic modes of two ceramic cuboids. It is shown that extraordinary electromagnetic transmission behavior through a perforated metal sheet with a subwavelength aperture can be achieved by exciting the first-order magnetic mode Mie resonant coupling of these cuboids. Our findings indicate that the transmission bandwidth and amplitude are dependent on the strength of coupling between the two ceramic cuboids. Additionally, we utilized non-linear effects within the dielectric cuboids to achieve tunable extraordinary electromagnetic transmission behavior. Our results are promising for developing non-linearly tunable microwave devices such as filters and modulators of their strong light-matter interactions.

A Novel Folded Rectangular-Grating Slow Wave Structure for Dual-Beam Traveling Wave Tube

Increasing the input current is an important method to achieve the high-power output for the traveling wave tubes (TWTs) operating in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{W}$</tex-math> </inline-formula> -band and higher terahertz (THz) band. For the folded waveguide (FW) TWT, increasing the height of the straight waveguide section of slow wave structure (SWS) can realize a double tunnel to increase the input current, but its electromagnetic characteristics, such as the operating passband, interaction impedance, and ohmic loss, become worse. Thus, a novel SWS, called folded rectangular-grating (FRG), with two tunnels for more input current, was proposed. Its two beam tunnels, where the electromagnetic wave in the operating band is cutoff, are located on the upper and lower edges of the grating, respectively, which makes the FRG-SWS have a wider operating passband, higher interaction impedance, and lower ohmic loss by freely adjusting its grating height. More importantly, its structural complexity is the same as that of FW-SWS. First, the electromagnetic characteristics, including dispersion, interaction impedance, and ohmic loss, are analyzed. Then, the particle-in-cell (PIC) simulation was carried out to verify that the saturated power, gain, and electron efficiency of TWT using FRG-SWS have been significantly improved compared with the TWT using FW-SWS. In the end, the cold test of transmission characteristics for FRG-SWS was done, and the experimental results are basically in good agreement with the simulation ones when the conductivity is set as 2.25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{7}}$</tex-math> </inline-formula> S/m.

A Novel Staggered Double-Segmented Grating Slow-Wave Structure for 340 GHz Traveling-Wave Tube

In this paper, a novel staggered double-segmented grating slow-wave structure (SDSG-SWS) is developed for wide-band high-power submillimeter wave traveling-wave tubes (TWTs). The SDSG-SWS can be considered as a combination of the sine waveguide (SW) SWS and the staggered double-grating (SDG) SWS; that is, it is obtained by introducing the rectangular geometric ridges of the SDG-SWS into the SW-SWS. Thus, the SDSG-SWS has the advantages of the wide operating band, high interaction impedance, low ohmic loss, low reflection, and ease of fabrication. The analysis for high-frequency characteristics shows that, compared with the SW-SWS, the SDSG-SWS has higher interaction impedance when their dispersions are at the same level, while the ohmic loss for the two SWSs remains basically unchanged. Furthermore, the calculation results of beam–wave interaction show that the output power is above 16.4 W for the TWT using the SDSG-SWS in the range of 316 GHz–405 GHz with a maximum power of 32.8 W occurring at 340 GHz, whose corresponding maximum electron efficiency is 2.84%, when the operating voltage is 19.2 kV and the current is 60 mA.

Nanoparticles enrichment to carbon felt electrodes for non-aqueous redox flow battery

Non-aqueous electrolytes enable redox flow batteries to achieve higher energy density. However, commercially available, pristine carbon felt electrodes display high overpotentials for electrochemical reactions in a non-aqueous medium. It is then crucial to develop stable high-performance electrodes which display low activation overpotentials, low ohmic losses, and high porosity to ensure uniform flow-through distribution of the electrolyte. This study acknowledges the influence of using attached carbon-based nanoparticles to the fibers of the supporting carbon-felt electrodes. The use of reduced graphene oxide, graphene, multi-walled carbon nanotubes (CNT), carbon black Vulcan XC72, and Ketjen carbon nanoparticles bounded to the support carbon felt electrode using a Nafion ionomer was assessed. Post-mortem analysis revealed that the nanoparticles remained attached to the fibers even after intense charge-discharge cycling. The carbon felt containing CNT added to the fibers displayed the best performance on running the charge/discharge electrochemical reactions while achieving a 23 % higher energy efficiency compared to commonly used electrodes. The addition of noble metal-based nanoparticles Pt-rGO displayed only a slightly better performance of rGO. Good binding of the carbon nanoparticles was obtained by the addition of the ionomer in a ratio of 15 wt%.

Pyrochlore-type cobalt and manganese antimonate electrocatalysts with excellent activity and stability for OER in acidic solution.

Developing robust electrocatalysts for the oxygen evolution reaction (OER) in acidic solutions that exhibit both good activity and stability remains a significant challenge. This study focuses on the pyrochlore-type Co2Sb2O7 (CSO) material, which exhibits high electrocatalytic activity in harsh acidic solutions by exposing more Co2+ atoms on the surface. In 0.5 M H2SO4, CSO requires a low overpotential of 288 mV to achieve a current density of 10 mA cm-2, and its high activity can remain for 40 h at a current density of 1 mA cm-2 in acidic solutions. BET measurement and TOF calculation verify that the high activity results from the large number of exposed active sites on the surface, as well as the high activity of each active site. The high stability in acidic solutions is due to the in situ formation of the acid-stable oxide CoSb2O6 on the surface during the OER test. Based on first-principles calculations, the high OER activity arises from the special CoO8 dodecahedra and the intrinsic formation of oxygen and cobalt vacancy complexes, which decrease the charge-transfer energy and improve interfacial electron transfer from the electrolyte to the CSO surface. Our findings provide a promising direction for developing efficient and stable OER electrocatalysts in acidic solutions.

Process challenges of high-performance silicon heterojunction solar cells with copper electrodes

Substitution of expensive silver paste becomes essential for mass production of silicon heterojunction (SHJ) solar cell, which calls for high efficiency and low-cost metallization techniques. Copper metallization together with multi-busbar cell interconnection is considered as effective way to low shading loss and electrode ohmic loss. While, the electrode adhesion and parasitic plating are the key process challenges limiting the copper metallization of SHJ solar cells. In this research, the copper plated SHJ solar cells with high electrode aspect ratio and an efficiency of 23.35% have been achieved on M2 wafers. The SEM images show the holes in the plated layers will deteriorate the adhesion between plated copper and seed-layer. The glass/back sheet structure (GBS) modules have been laminated to evaluate the influence of parasitic plating on damp-heat (DH) performance. The degradation in output power ( P max ) is up to 4.90%, which is primarily due to a decreased open-circuit voltage ( V oc ) and fill factor ( FF ). It can be ascribed to the deteriorated surface recombination and interconnection. Although the parasitic plating on the wafer edge has ignorable influence on damp heat test after etch-back process, it is still necessary to protect the cell edge to avoid parasitic plating. The research evaluates the process challenges of copper metallization of SHJ solar cells, which offers a refer for achieving high reliability and low levelized cost of energy (LCOE) of photovoltaic power generation. • This work evaluates the challenge of ghost plating on high-performance SHJ solar cells and modules for the first time. • The surface morphology and element distribution at the interface is analyzed and an efficiency of 23.35% is obtained. • The glass/back sheet modules have been laminated to evaluate the influence of ghost plating on damp-heat (DH) performance.

Fabry–Perot interference enhanced transverse magneto-optical Kerr effect in Ce:YIG nanopore array on an anodic aluminum oxide template

The all-dielectric magneto-optical (MO) structure has garnered considerable interest due to its enhanced MO effect and low ohmic loss compared to the magnetoplasmonic structure. In this study, the effect of Fabry–Perot (F–P) interference on the enhancement of the transverse magneto-optical Kerr effect (T-MOKE) as well as sensing performance is theoretically investigated in a dielectric MO structure composed of cerium-substituted yttrium iron garnet (Ce:YIG) nanopore array coating a nanoporous anodic aluminum oxide (AAO) film standing on an aluminum sheet referred to as the AAO/Al template. The system is particularly interesting because the MO response is significantly enhanced in the position of the F–P interference, in which the T-MOKE signal is close to a 5-fold increase compared with the reference Ce:YIG film. Additionally, the sensing performance shows that the all-dielectric nanopore-based system proposed here provides an alternative to fabricating gas and solution detectors with low ohmic loss.

Sediment microbial fuel cells in oxidative sedimentary environments using iron substrate as voltage booster

The voltage variation of in situ sediment microbial fuel cells with the sedimentary environment hinders their practical applications. In this study, an iron substrate that provides equal cell voltage output regardless of the sedimentary environment, was used to elucidate the electron-transfer-mediating characteristics of soil organic matter. The cell exhibited voltages of 0.3 and 0.5 V in oxidative and reductive sediments, respectively. However, the addition of the iron substrate enabled the cell to output 0.8 V regardless of the sediment inoculum and alleviated its activation and concentration losses. The oxidative sediment with iron substrate showed relatively low ohmic loss, leading to a 1.3 × higher current than with the reductive sediment. Cyclic voltammetry revealed that the quinone-like moieties in the oxidation state influenced the redox reaction of the iron substrate by facilitating electron/proton transfer. In conclusion, the iron-substrate-based voltage-boosting strategy can help expand the utility of these cells as a power source, particularly in low-voltage aerobic sedimentary environments.

Fano resonance with high Q and figure of merit in terahertz band based on structural perturbation

Fano resonance with high quality (Q) factor and figure of merit (FoM) has significant application prospects in biosensors and lasers. However, most of the previous studies achieve Fano resonance with high Q and FoM by directly regulating the structural asymmetry, which needs high processing precision. To maximize the Q factor of a given resonator, the best constituent material could be a hypothetical perfect electrical conductor (PEC) without ohmic losses. Here, we can indirectly regulate the asymmetry of the structure by perturbation between structures. At low asymmetry, PEC double split rings can obtain high Q factor of 374 and FoM of 257 by adjusting structural asymmetry based on structural perturbation. These are significant for Fano resonances of extremely low-loss and low ohmic losses practical application in the THz band.

In-Plane Printed Batteries Based on Mxenes

In the era of miniaturization, micro energy storage devices become an essential part of the progress in many fields starting from simple sensors to medical devices. However upcoming developments in all these fields are restricted to finding safe, reliable and high-performance micro batteries with the shapes that is not limited only to rectangles, cylinders, and pouches. The research is confronted with challenges of fitting a battery into a microdevice. Lithium-ion batteries (LIBs), a mature energy storage technology, are a leading candidate for the development of micro batteries that can be easily integrated into microelectronic devices. However, despite significant achievements in the field of micro batteries, limitations in areal capacity and in power densities still motivate the search for alternative designs and novel concepts in the battery field. Insufficient areal energy density from planar micro batteries has inspired a search for three-dimensional micro batteries. The power output of a three-dimensional micro battery is expected to be higher than that of a two-dimensional battery of equal size, as a result of the higher ratio of electrode-surface-area to volume and lower Ohmic losses. Within a battery electrode, the 3D architecture provides large surface area, increasing power by reducing the diffusion path for Li ions. Additive manufacturing, also known as 3D printing, has appeared as a novel class of free form fabrication technologies that have a variety of possibilities for the rapid creation of complex architectures at lower cost than conventional methods. 3D printing enables the controlled creation of functional materials with three-dimensional architectures, representing a promising approach for the fabrication of next-generation electrochemical energy-storage devices and has many unique advantages over conventional manufacturing methods. In this work, printer is employed to print a 3D micro battery with MXene electrodes that can be printed easily and can be fitted into any small device.

(Digital Presentation) Large–Scale High-Performance Low Catalyst Loaded Membrane Electrode Assemblies for Advanced Proton Exchange Membrane Water Electrolyzers

Hydrogen is regarded as the next-generation energy carriers for the future hydrogen economy.1 Among the hydrogen production technologies, proton exchange membrane (PEM) water electrolyzers is considered the favored approach for the implementation of the global hydrogen energy transformation due to its several benefits including high power density operation, low ohmic losses and differential pressure operation. However, (i) high cost mainly from the high platinum group metals (PGM) loading in the catalysts layers; (ii) low durability due to instability of the catalysts layers and membrane; and (iii) poor safety because of hydrogen crossover of PEM water electrolyzers have jeopardized their widespread commercialization. Currently, a new Department of Energy Consortium (H2NEW) has targeted hydrogen production from electrolysis, especially PEM water electrolysis, for use as a clean, sustainable fuel, which can achieve $2/kg hydrogen production cost by 2025.2 This requires a balance between the performance, durability and scale-up cost of membrane electrode assemblies (MEAs) for PEM water electrolyzers.In this work, we demonstrate the capability to fabricate large scale MEAs by the unique Reactive Spray Deposition Technology (RSDT), that have one order of magnitude lower PGM loadings in the catalyst layer than the state-of-the-art (SOA) designs, and activity and durability performance comparable to the SOA commercial MEAs. RSDT is a flame-based method that combines the catalysts synthesis and electrodes deposition processes into one step and thus substantially reduces the time and cost for their fabrication.3–5 The RSDT fabricated MEA with 680 cm2 geometric area electrodes, and loadings of 0.2 mgPt/cm2 in the cathode and 0.3 mgIr/cm2 in the anode has been tested at current density of 1.8 A cm-2, 50 oC, and 400 psi differential hydrogen pressure. The initial steady-state test for over 250 hours, clearly shows excellent activity and stability. In addition, the RSDT fabricated MEA has integrated dual recombination layers that effectively reduce the hydrogen crossover to below 10 %LFL at all current densities from 0.58 to 1.8 A/cm2.Reference1. M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy, 38, 4901–4934 (2013).2. https://www.energy.gov/sites/default/files/2021-09/h2-shot-summit-panel1-lte-status.pdf3. H. Yu et al., Appl. Catal. B Environ., 239, 133–146 (2018) https://doi.org/10.1016/j.apcatb.2018.07.064.4. H. Yu et al., Electrochim. Acta, 247, 1155–1168 (2017) http://dx.doi.org/10.1016/j.electacta.2017.07.093.5. G. Mirshekari et al., Int. J. Hydrogen Energy, 46, 1526–1539 (2021) https://doi.org/10.1016/j.ijhydene.2020.10.112.

(Invited) Detection of Bacterial Rhamnolipid Toxin By Redox Liposome Single Impact Electrochemistry

The single-entity impact method is a very sensitive and powerful electroanalytical tool for biological and environmental purposes such as electrochemical detection of pathogens.[1] The versatility of ultramicroelectrodes (UMEs) gives unique and essential properties for electroanalytical sensing owing to their small size, high sensitivity, fast steady-state response, low double-layer charging current and minimal ohmic loss. The observation of these stochastic events can provide information on various single nanoparticles contrary to ensemble (bulk) measurements. The main advantage of studying collisions of single entities is the low limit of detection (in principle, one single species) inherent to this electroanalytical method and the ability to study single entities (cells, viruses, nanoparticles...) in real time (dynamic measurement).[2–4]Electrochemistry of single redox liposome impacts at an UME consists in detecting the electrolysis of a redox probe encapsulated inside a liposome when it is released at the UME after impact (or collision). The UME is polarized at the oxidation or reduction potential of the encapsulated redox probe and a concentration of several pico-molar of redox liposomes added to the aqueous buffer electrolyte is enough to detect “current spikes” in the chronoamperometry (i-t) curve corresponding to discrete collision events.[3,4] The electron transfer does not readily occur across a lipid bilayer, thus the electrolysis of the liposome redox active content after collision and membrane rupture or opening at the UME surface led to many studies dealing with the membrane permeation mechanism.[3,4]Here, our work is based on the previous results where no current spike was observed in the chronoamperometry curve because the redox DMPC liposomes did not break during impact (or collision) onto the UME surface.[3,4] Hence, the electrochemical sensing principle is based on the weakening of the liposomes lipid membrane upon interaction with a destructive bacterial virulence factor which leads upon impact at an UME to the breakdown of the liposomes and the release/electrolysis of its encapsulated redox probe, as previously reported.[5] In the presence of RL toxin in solution (acting like a surfactant in the lipid membrane), current spikes corresponding to the electrolysis of the encapsulated redox probe released from weakened liposomes are detected (see Figure). Thanks to the redox liposome single impact electrochemistry, the highest detection limit of RL toxin (500 nM) has been reached in comparison to several micromoles per liter previously reported.[5][1] Lebègue, E.; Costa, N.L.; Louro, R.O.; Barrière, F. Communication—Electrochemical Single Nano-Impacts of Electroactive Shewanella Oneidensis Bacteria onto Carbon Ultramicroelectrode. J. Electrochem. Soc. 2020, 167, 105501, doi:10.1149/1945-7111/ab9e39.[2] Dick, J.E.; Lebègue, E.; Strawsine, L.M.; Bard, A.J. Millisecond Coulometry via Zeptoliter Droplet Collisions on an Ultramicroelectrode. Electroanalysis 2016, 28, 2320–2326, doi:10.1002/elan.201600182.[3] Lebègue, E.; Anderson, C.M.; Dick, J.E.; Webb, L.J.; Bard, A.J. Electrochemical Detection of Single Phospholipid Vesicle Collisions at a Pt Ultramicroelectrode. Langmuir 2015, 31, 11734–11739, doi:10.1021/acs.langmuir.5b03123.[4] Lebègue, E.; Barrière, F.; Bard, A.J. Lipid Membrane Permeability of Synthetic Redox DMPC Liposomes Investigated by Single Electrochemical Collisions. Anal. Chem. 2020, 92, 2401–2408, doi:10.1021/acs.analchem.9b02809.[5] Luy, J.; Ameline, D.; Thobie-Gautier, C.; Boujtita, M.; Lebègue, E. Detection of Bacterial Rhamnolipid Toxin by Redox Liposome Single Impact Electrochemistry. Angew. Chem. Int. Ed. 2021, accepted , doi: 10.1002/anie.202111416. Figure 1