Narrow Voltage Research Articles

Voltage bridge mapping in atrioventricular nodal reentry tachycardia ablation in adult population: results from a multicenter registry

Abstract Funding Acknowledgements Type of funding sources: None. Background The presence of Low Voltage Bridge (LVB) in Atrioventricular Nodal Reentry Tachycardia (AVNRT) ablation has been described in children populations. Slow pathway ablations visualizing and targeting the LVB has been described to be safe and effective. However, the incidence of LVB in AVNRT ablation has not been widely explored in adult population. Purpose We aim to investigate the presence of LVB in adult patients (pts) undergoing AVNRT ablation, and the relationship between the LVB and the successful ablation site. We have also investigated the correlations between the Koch’s triangle (KT) anatomy and biophysical pts data. Methods The observational registry prospectively collected data of 165 pts. undergoing AVNRT ablation guided by 3D electroanatomical mapping system (EnSite - Abott, St Paul, MN) in 6 EP centers. Gender: 90F – 75M (55% - 45%) - Age: 57 ± 17 ys (min 15 – max 87) - Weight: 73 ± 15 kgs (min 42 - max 150) Prior of ablation a voltage map of KT was created using diagnostic and ablation catheters. We define as Type I LVB a clear, long area of low voltage within the KT between the CS ostium and the AV node with the base on the edge of the tricuspid annulus and Type II LVB a narrow low voltage channel between normal-voltage regions with the base on the edge of the tricuspid annulus. The relationship between LVB and successful site was evaluated at the end of the procedure. KT anatomical data were correlated to gender, age and weight. Results The LVB was identified in 134 pts (81%) with a prevalence of type I (91 - 68%) over type II (33 - 25%). In 10 pts (7%) the LVB did not match type I nor type II. When an LVB was identified, the correspondence between the LVB and the successful ablation site was verified in 117 pts (87%). In addition, a shorter RF time was applied when an LVB was found (396s vs 298s; p = 0.03). Strong correlations between KT anatomy and biophysical pts data were not identified. The distance between His electrograms and the successful ablation site weakly correlated (ρ = -0.24, p < 0.01) with pts age suggesting a shortening in the distance with age progression. Conclusion The visualization of the Low Voltage Bridge may be a helpful tool to guide AVNRT ablation in a large cohort of pts; furthermore it is associated with reduced RF applications time. The KT characteristics are difficult to be predicted a priori according to patient gender, age or weight.

Self-supported metal sulfide electrode for flexible quasi-solid-state zinc-air batteries

Adopting self-supported electrodes with oxygen catalysts directly growing on the electrode support affords an available solution to improve the performance of zinc-air batteries (ZABs). Herein, we firstly fabricate a self-supported air electrode with manganese (Mn) doping nickel sulfide growing on the nickel foam (Mn–Ni3S2/NF) for ZABs via a facile approach. The optimized Mn–Ni3S2/NF electrode (S6M8) demonstrates an overpotential of 347 mV at 100 mA cm−2 toward oxygen evolution reaction (OER), being lowest among those of the most of reported metal sulfides. Also, S6M8 shows an improved catalytic activity toward oxygen reduction reaction (ORR) with the half-wave potential (E1/2) of 0.63 V, compared with the pristine sample (0.61 V). The self-supported electrode of S6M8 can directly serve as the air cathode of the flexible quasi-solid-state ZAB after a facile hydrophobic treatment, which exhibits the high maximum power density (Pmax = 75.8 mW cm−2), excellent charge-discharge property with a narrow charge-discharge voltage gap (0.86 V at 60 mA cm−2) and superior stability after 100 cycles. Moreover, the flexible ZAB with the self-supported electrode of S6M8 shows a superior charge-discharge reversibility among most of ZABs with the self-supported electrode. Our work sheds a light on the development of the low-cost self-supported air electrode for ZABs.

Reversible Mn/Cr dual redox in cation-disordered Li-excess cathode materials for stable lithium ion batteries

Cation-disordered Li-excess oxides/oxyfluorides have opened the door for designing alternative, high energy cathodes. However, achieving long cycle life and high rate capability represents a major challenge for disordered rocksalt cathodes (DRX). Herein, we develop Li2Mn3/4Cr1/4O2F (LMCOF) DRX materials through a distinct redox mechanochemical method. The LMCOF contains trivalent Cr3+ and Mn3+, which allows for simultaneously accessing stable Mn/Cr dual redox at a narrow voltage window acceptable for conventional carbonate electrolytes. Coupled with the mitigated and reversible oxygen chemical changes, the LMCOF delivers high capacity, rate capability, as well as long cycle life upon extensive 1,000 cycles at various current densities. The multiscale synchrotron and neutron scattering, spectroscopic, and imaging analyses demonstrate that the capacity originates from the Mn/Cr dual redox with minimal contribution from oxygen redox, and that the good cycle life is attributed to the stable global crystal structure and local oxygen chemical environment.

Weak Ionization Induced Interfacial Deposition and Transformation towards Fast‐Charging NaTi2(PO4)3 Nanowire Bundles for Advanced Aqueous Sodium‐Ion Capacitors

AbstractAqueous sodium‐ion capacitors (ASICs) offer great promise for inexpensive and safe energy storage. However, their development is plagued by a kinetics imbalance at high rates between battery and capacitive electrodes and a narrow voltage window due to water electrolysis. Here a unique nanowire bundles anode is designed that simultaneously affords ultrahigh rate capability and manifests robust Na+ insertion to suppress hydrogen evolution, enabling an advanced ASIC. The NaTi2(PO4)3 (NTP) is grown on thin titanium foil by elaborately utilizing the weak ionization chemistry of NaH2PO4 (NHP), where single‐agent NHP not only partially etches titanium to release TiO2+, but also induces the interfacial phase‐transformation of pre‐deposited orthomorphic Na4Ti(PO4)2(OH)2 cubes to hexagonal NTP nanowires. This anode has hierarchical architectures to facilitate charge and mass transport, thus working stably at considerably high rates of 15–150 C with high capacities. The first 2.4 V flexible solid‐state NTP‐based ASIC is designed with high energy densities (5.8–12.8 mWh cm−3; 57.9–62.1 Wh kg−1; total mass loading up to 8.1 mg cm−2) comparable to NASICON‐based devices using organic electrolytes, demonstrating outstanding stability of 10 000 cycles and no performance decay even after continuous bending at 180o. This work presents a versatile strategy to construct NASICON phosphate electrodes for advanced energy storage.

High-rate supercapacitor based on 3D hierarchical N-doped porous carbon derived from sustainable spongy cornstalk pith

Carbon-based supercapacitors have been widely applicated in the energy storage fields due to superior physicochemical stability and large specific power. However, there is still an urgent need for improvement of specific energy which can be attributed to low mesoporosity, poor conductivity and narrow working voltage. This paper has introduced spongy and porous cornstalk pith aerogel as carbon precursor and one-step facile carbonation treat to prepare the 3D hierarchical N-doped porous carbon as supercapacitor electrode materials. The obtained cornstalk porous carbon exhibits high mesoporous volume ratio (90.7%) and large specific surface area of 2155 m2 g-1 to the benefit of fast electrolyte ions diffusion and forming large double layer interface. And the N doping of 3.96 at% from cornstalk pith biological component and NH3 enhance the electron conductivity, a certain amount of capacitive performance and surface wettability of carbon materials with electrolyte ions. The electrochemical measurements have demonstrated that the sample shows a high specific capacitance of 381 F g-1 at 0.2 A g-1 with prominent rate performance (82% retention at 80 A g-1) and 97.6% capacitance retention after 50,000 cycles. Furthermore, to extend working voltage using an organic electrolyte (MeEt3NBF4/acetonitrile solutions), the cornstalk porous carbon electrode presents high specific energy of 47.5 W h kg-1 (1.50 kW kg-1) and an ultra-large specific power of 113 kW kg-1 (36 W h kg-1).

Towards Reversible High-Voltage Multi-Electron Reactions in Alkali-Ion Batteries Using Vanadium Phosphate Positive Electrode Materials.

Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V2+ to V5+) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V3+/V4+ in Na3V2(PO4)2F3) could allow the achievement the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V3+/V4+ and V4+/V5+ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V3+/V4+ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. Here, through the review of redox mechanisms and structural evolutions upon electrochemical operation of selected widely studied materials, we identify the crystallographic origin of this trend: the distribution of PO4 groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O…V4+=O or O…V5+=O). While the vanadyl entity massively lowers the voltage of the V3+/V4+ and V4+/V5+ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O2− by F−, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments.

High-performance 2.5 V aqueous asymmetric supercapacitor based on MnO2 nanowire/hierarchical porous carbon composite

ABSTRACT Aqueous supercapacitor shows a narrow operating voltage range because of the limitation of the water electrolysis, resulting in low energy density. In this work, a nanoporous MnO2 entangled hierarchical porous carbon skeleton (simplified to MHPC) has been successfully prepared. Aqueous asymmetric supercapacitor has been assembled by employing the MHPC as a positive electrode, a hierarchical porous carbon skeleton (HPC) as a negative electrode, and a neutral Na2SO4 aqueous solution as electrolyte. The assembled asymmetric supercapacitor can be stably charged in an aqueous medium in a wide voltage range of 0–2.5 V and delivers a maximum energy density of 20.8Wh/kg at a power density of 0.25 kW/kg and 25 kW/kg at an energy density of 11.1 Wh/kg in a 1 M Na2SO4 aqueous solution. This strategy provides a new idea for developing high-energy supercapacitor.

A New Approach for Power Losses Evaluation of IGBT/Diode Module

Electric power systems are facing tremendous changes and power electronic devices are playing an increasingly crucial role in this transformation. In this contest, the study of power electronic devices behavior becomes of the utmost importance, and in particular, evaluation of their losses to understand their performance. Several methods can be found in literature to evaluate power or energy losses, but each of them is associated with shortcomings (such as missing an important factor or having narrow current or voltage range) that in practice become a strong limit to implement them or in a simulation process. To overcome this problem, this paper evaluates existing methods and proposes new loss calculation methods for power electronics losses that can be used within simulation tools at any converter configuration and application range, splitting power electronic losses into switching and conduction losses. The proposed new approach formulates each loss calculation procedure in a systematic way. The presented methods are implemented in Matlab Simulink and simulation results are compared with data obtained from the Semikron SemiSel v4 online tool, which is used as a benchmark. The outcomes reveal that, with this new approach, the proposed methods can cover wider working operation range compared to the existing methods having better accuracy.

Graphene Integrated in a Ring Type Fabry-Perot Cavity: Polarization Insensitive, Low Voltage and Tunable Modulation of Light at Near-IR Telecommunications Band

In this article, a novel graphene based resonant free space modulator for modulating optical signals in the wavelength range of 1-2 μm is designed and numerically investigated. The presented modulator is highly versatile. It can function in both transmission and reflection regimes and is polarization insensitive and can be easily tuned to any particular wavelength. In this device, an ingenious Fabry-Perot (FP) cavity composed of concentric Au disks and rings and a single layer graphene is proposed. Incoming light is totally transmitted provided that the wavelength coincides the resonant wavelengths of the cavity, otherwise it is reflected. Hence, unlike common graphene modulators based on electro-absorption, here, the main role of graphene is to shift the resonant wavelengths of the FP cavity and its absorption is indeed negligible. Several highly efficient modulators are designed which can be summarized as follows: A transmission (reflection) type modulator with central wavelength of 1.55 μm, modulation depth of 95% (92%) at this wavelength, modulation depth of 48% (46%) in the wavelength range of 1.42- 1.63 μm (1.46-1.6 μm) covering entire C+S bands, insertion loss of 1.5 dB (1.3 dB) and gate voltage of 4.5 V (4.2 V). Other narrow band low voltage modulators requiring voltages of less than 1.5 V are designed either.

Developing high voltage Zn(TFSI)2/Pyr14TFSI/AN hybrid electrolyte for a carbon-based Zn-ion hybrid capacitor.

Aqueous Zn-ion hybrid capacitors (ZIHCs), integrating the typical characteristics of Zinc ion batteries and supercapacitors, have become a promising candidate to replace or supplement lithium-ion energy storage technology. However, the narrow operating voltage window and the instability of the Zn/electrolyte interface caused by aqueous solvents have become a great challenge for practical applications. Here, we developed a new type of hybrid electrolyte (Zn(TFSI)2/[[Pyr14TFSI]3]16/[AN]4) based on the organic solvent (AN) combined with ionic liquid (Pyr14TFSI) and Zn salt (Zn(TFSI)2). This non-flammable electrolyte benefited from the synergistic advantages of Pyr14TFSI and AN, and could output a wide electrochemical window (3.32 V vs. Zn/Zn2+) and good compatibility with metallic Zn, while possessing excellent wettability. Theoretical and experimental results further reveal that such superb performance originates from the change of Zn coordination environment. Consequently, the constructed ZIHC displays a stable cycling performance (10 000 cycles at 5 A g-1 without significant capacity fade) and a high operating voltage of 2.1 V. This newly developed electrolyte, which solves the conventional interface problem and improves the voltage window, will promote the development of ZIHCs.

Hybrid Improved Carrier-Based PWM Strategy for Three-Level Neutral-Point-Clamped Inverter With Wide Frequency Range

The three-level neutral-point-clamped inverter used in the variable frequency system has the characteristics of a wide frequency range, and the pulsewidth modulation (PWM) strategy needs to be designed for the low-frequency region with low modulation index and the high-frequency region with low carrier ratio, respectively. The traditional carrier-based PWM (CBPWM) is simple to implement, but in the low-frequency region, CBPWM will cause narrow pulse and output voltage distortion; while in the high-frequency region, CBPWM can only achieve the synchronized modulation with half-wave symmetrical (HWS) and three-phase symmetrical (TPS) waveforms when the carrier ratio is an odd integer multiple of three, and it cannot realize the square-wave modulation. To solve the defects of CBPWM, this article proposes improved CBPWM (ICBPWM) I, which can avoid narrow pulse and generate line voltage accurately at any low modulation index, ICBPWM II, which can ensure the voltage to meet TPS and HWS when the carrier ratio is an arbitrary integer multiple of three, and ICBPWM III, which can achieve square-wave modulation, separately. On this basis, by using ICBPWM I, ICBPWM II, and ICBPWM III in combination, a hybrid ICBPWM strategy with wide frequency range is further proposed. Finally, the proposed strategy is verified by simulation and experiment.

High-Efficiency LLC Resonant Converter With Reconfigurable Voltage Multiplying Rectifier for Wide Output Voltage Applications

This article presents a reconfigurable voltage multiplying rectifier (RVMR) to improve the performance of an LLC resonant converter for wide output voltage applications. The RVMR can operate as voltage-doubler mode or voltage-quadrupler mode according to the primary switching strategy. Two operation modes split a wide output voltage range into two narrow ranges. Therefore, the RVMR enables the LLC resonant tank to be designed in a narrow output voltage range, which results in a narrow switching frequency range, high efficiency, and high power density. A smooth mode transition can be achieved by adopting a phase-shift control to general pulse frequency modulation control without any additional switch. The proposed RVMR LLC converter can improve its efficiency by 2.9% and reduce component volume by 26% compared to the conventional full-bridge LLC resonant converter. A 750-W prototype with 400 V input, 100-300 V output voltage, and 2.5 A max output current has been built and tested to verify the effectiveness of the proposed converter.

Selenide/sulfide heterostructured NiCo2Se4/NiCoS4 for oxygen evolution reaction, hydrogen evolution reaction, water splitting and Zn-air batteries

Rational design and constructing multifunctional electrocatalysts featuring with low cost and high efficiency is critical for promoting the implement of sustainable energy devices such as water splitting and zinc air batteries. Herein, we report a facile means to prepare a selenide/sulfide hetero-structured NiCo2Se4/NiCoS4 catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), overall water splitting (OWS), and Zn-air batteries (ZABs). The NiCo2Se4/NiCoS4 heterostructure showed excellent OER and HER performance, evidenced by the small overpotential of 248 mV and 180 mV @ 10 mA cm−2 for OER and HER, and superior long-term stability to the benchmark IrO2 and Pt/C catalyst for OER and HER, respectively. It also exhibited a potential of 1.660 V @ 10 mA cm−2 in the practical OWS test, close to the Pt/C + IrO2 catalyst. Furthermore, when employed as air-cathode catalyst for ZABs, the NiCo2Se4/NiCoS4 modified battery exhibited the narrow charge-discharge voltage gap of 0.98 V @ 50 mA cm−2 and a maximal specific capacity of 693.17 mA h g−1, outperforming the IrO2 counterpart. Such excellent performance can be attributed to the advantageous structural merit of the NiCo2Se4 nanoflowers, and especially the heterostructure interfaces created in NiCo2Se4/NiCoS4, which significantly boosted the catalytic synergistic effects. This study can offer a new avenue to design and prepare abundant-element-based cost effective, efficient and durable electrocatalysts with multifunctionalities that hold great promises to be applied in electrochemical devices.

Systems-Level Investigation of Aqueous Batteries for Understanding the Benefit of Water-in-Salt Electrolyte By Synchrotron Nano-Imaging

The concept of “Water-in-salt” (WIS) electrolyte enabled the application of higher voltage aqueous battery, overcoming the limitation of the narrow voltage window of water (~1.23V) for better safety and environmental sustainability. Recent work in the field has been exploring the electrochemical performance of batteries using WIS electrolytes with different electrode couples as well as the intrinsic electrochemistry and physical chemistry properties of WIS electrolytes. In this work, LiV3O8 anode and LiMn2O4 cathode for aqueous Li-ion batteries are coupled to investigate the mechanism by which WIS electrolyte improves the cycling stability at an extended voltage window. The study probed the morphological evolution of the active electrode particles as a function of the electrochemistry. While delaying the water decomposition process, the WIS electrolyte improves the cycling stability of the battery by suppressing the mechanical damage to the electrode network and dissolution of the electrode particles through the operando observation under synchrotron transmission X-ray microscopy on the LiMn2O4 cathode. As the viscosity of WIS is significantly higher, the reaction heterogeneity of the electrodes cycled with WIS electrolyte is quantified with X-ray absorption spectroscopic imaging, visualizing for the first time the kinetic limitations of the WIS electrolyte. This work furthers the mechanistic understanding of electrode – WIS aqueous electrolyte interactions and paves the way to explore the strategy to mitigate their possible kinetic limitations in 3D architectures. Figure 1

Hybrid LLC Converter with Wide Range of Zero-Voltage Switching and Wide Input Voltage Operation

A new hybrid inductor-inductor-capacitor (LLC) converter is investigated to have wide voltage input operation capability and zero-voltage turn-on characteristics. The presented circuit topology can be applied for consumer power units without power factor correction or with long hold-up time requirement, photovoltaic energy conversion and renewable energy power transfer. To overcome the weakness of narrow voltage gain of resonant converter, the hybrid LLC converter with different turns ratio of transformer is presented and the experimental investigation is provided to achieve wide voltage input capability (400 V–50 V). On the input-side, the converter can operate as full bridge resonant circuit or half bridge resonant circuit with input split capacitors for high or low voltage input region. On the output-side, the less or more winding turns is selected to overcome wide voltage input operation. According to the circuit structures and transformer turns ratio, the single stage LLC converter with wide voltage input operation capability (400 V–50 V) is accomplished. The laboratory prototype has been developed and the experimental waveforms are measured and demonstrated to investigate the effectiveness of the presented hybrid LLC converter.

Photopolymerized Gel Electrolyte with Unprecedented Room‐Temperature Ionic Conductivity for High‐Energy‐Density Solid‐State Sodium Metal Batteries

AbstractSolid‐state sodium metal batteries (SMBs) are highly promising rechargeable batteries owing to the abundance and cost effectiveness of sodium. However, the low room‐temperature ionic conductivity and narrow voltage window of solid‐state electrolytes seriously inhibit the development of SMBs. Herein, an ethoxylated trimethylolpropane triacrylate based quasisolid‐state electrolyte (ETPTA–NaClO4–QSSE) is developed by photopolymerization for high‐energy‐density solid‐state SMBs. The ETPTA–NaClO4–QSSE exhibits remarkable room‐temperature ionic conductivity of 1.2 mS cm−1, a wide electrochemical window of >4.7 V versus Na+/Na, and excellent flexibility. Owing to outstanding interfacial compatibility between this electrolyte and the electrode, Na metal symmetrical batteries show ultralong cyclability with 1000 h at 0.1 mA cm−2, and ultralow overpotential of 355 mV at 1 mA cm−2, indicative of significant suppression of the Na dendrite growth. Notably, Na3V2(PO4)3 (NVP) full batteries (NVP||ETPTA–NaClO4–QSSE||Na) display unprecedented rate capability, with a recorded capacity of 55 mAh g−1 at 15 C, higher than any achieved so far in solid‐state SMBs, and long‐term cycling stability at 5 C, offering a capacity retention of 97% after 1000 cycles. Furthermore, NVP||ETPTA–NaClO4–QSSE||Na pouch cells represent excellent flexibility and exceptional safety, demonstrative of wide applicability. Therefore, this work will open new opportunities to develop room‐temperature high‐energy‐density solid‐state SMBs.

Initial Experience with High-density Mapping of Ischemic Ventricular Tachycardia Using a Narrow 0.1-mV to 0.25-mV Border-zone Window.

This study sought to determine (1) whether the use of a narrow border-zone voltage of 0.1 to 0.25 mV predicts the ventricular tachycardia (VT) exit site better than when using the conventional 0.5 to 1.5 mV window and (2) the feasibility of utilizing the Rhythmia mapping system (Boston Scientific, Natick, MA, USA) to map hemodynamically unstable VT without hemodynamic support. The Ablation of ischemic VT is challenging especially in the setting of hemodynamic instability, yet efficient and accurate mapping of VT and VT substrate is critical for procedural success. In this study, a total of 24 patients with ischemic cardiomyopathy and recurrent monomorphic VT underwent mapping and ablation using the Rhythmia system. Contact-force sensing ablation catheters were use in two cases. In patients with mappable VTs, the distance between the exit site and border zone was calculated for border zone-voltage windows of 0.5 to 1.5 mV and 0.1 to 0.25 mV. The percentage of LV scar for each patient was visually estimated into quartiles of scar burden in both windows. Twenty patients were inducible into VT, while 15 patients had mappable VTs for a total of 16 VTs (11 stable VTs and five unstable VTs). There were no adverse complications in patients who underwent mapping in unstable VT. The mean distance from the VT exit site to the border zone was 13.3 mm in the conventional window and 3.4 mm in the narrow window (95% confidence interval: 4.0–15.8; p = 0.003). Separately, 94% (15/16) of the VTs were mapped to the narrow border-zone voltage versus 31% (5/16) using the conventional border zone (p = 0.0006). The use of a narrow 0.1- to 0.25-mV border-zone window highlights relevant scar and constitutes a border zone where VT exit sites are frequently located. We also found that exit sites of hemodynamically unstable VTs can be identified without an increase in procedural complications using the Orion catheter (Boston Scientific, Natick, MA, USA).

ZIF-67-derived Co nanoparticles anchored in N doped hollow carbon nanofibers as bifunctional oxygen electrocatalysts

Developing highly active and robust bifunctional non-precious oxygen electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of paramount importance for enhancing the efficiency of zinc-air battery. Herein, Co nanoparticles anchored in N doped hollow and porous carbon nanofibers (CoN-HPCNF) are obtained via an in-situ growth-pyrolysis approach with the hybrid of ZIF-67 and carbon nanofibers as the precursor. Originating from its high surface area, firm and hierarchical porous structure, effective doping of N as well as synergistic effect from Co nanoparticles and HPCNF, the optimized CoN-HPCNF shows prominent bifunctional catalytic activity and long-term stability toward OER and ORR. Importantly, the assembled aqueous zinc-air battery with the prepared catalyst as the air cathode delivers a peak power density of 126.6 mW cm−2 and narrow charge-discharge voltage gap together with excellent operation durability (more than 280 h at the current density of 5 mA cm−2), outdoing the commercial precious metal catalysts (Pt/C + IrO2).

Bacterial cellulose hydrogel: A promising electrolyte for flexible zinc-air batteries

Flexible zinc-air battery is a promising energy source for wearable electronic devices. However, few studies have focused on solid-state electrolyte which determines the servicing life and energy efficiency of zinc-air batteries. Herein, we propose a facile method to prepare a solid-state electrolyte based on bacterial cellulose (BC) hydrogel. Benefiting from the three-dimensional network structure, excellent hydrophilicity and stable chemical properties of BC, the prepared electrolyte bacterial cellulose-potassium hydroxide-potassium iodide (BC-KOH-KI) exhibits ultra-high mechanical strength of 2.1 MPa and excellent ionic conductivity of 54 mS cm−1. Moreover, the KI is introduced to drive a more energy-efficient path for charging reaction. The flexible zinc-air battery based on BC-KOH-KI displays a narrow charge-discharge voltage gap of 0.46 V at 5 mA cm−2 (energy efficiency: 73%), a high power density of 129 mW cm−2, a high capacity of 794 mAh g−1 and a large cycling number of over 100. The battery also keeps stable output at various bending angle, indicating a great potential for wearable applications.

Exploring the electrochemical properties of mixed ligand Fe(II) complexes as redox couples

Redox flow batteries are a promising technology for large scale energy storage systems. Although some types of the battery have been commercialized, the narrow working voltage ranges in the aqueous electrolytes limit their further applications. Organic solvents have shown to allow the use of a wider range of redox couples and the idea of non-aqueous redox flow batteries has been proposed. However, the low solubilities and poor electrochemical properties including stability and reversibility of the redox couples in the organic electrolytes remain a significant issue. In this work, a series of heteroleptic (mixed ligand) iron(II) complexes based on a combination of 2,2′-bipyridine, 1,10-phenanthroline and 4,4′-dimethyl-2,2′-bipyridine ligands were synthesized and their chemical and electrochemical properties investigated. For Fe (II) complexes, it was confirmed that ligand equilibration occurs in solution. The electrochemical properties of the complexes were studied by cyclic voltammogram and chronoamperometric methods. The mechanism of the redox processes of these complexes are proposed and how the mixed ligands will affect the redox potentials of the Fe (II) complexes is discussed. Furthermore, we show that the mixed ligand system can improve the total solubility of redox active species. The mixed ligand approach will also be beneficial for designing other new high solubility redox materials for non- aqueous flow batteries.