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12 pages, 2661 KiB

Open AccessFeature PaperArticle

Electrocatalytic Assisted Performance Enhancement for the Na-S Battery in Nitrogen-Doped Carbon Nanospheres Loaded with Fe

by Jianhui Zhu, Amr Abdelkader, Denisa Demko, Libo Deng, Peixin Zhang, Tingshu He, Yanyi Wang and Licong Huang

Molecules 2020, 25(7), 1585; https://doi.org/10.3390/molecules25071585 - 30 Mar 2020

Cited by 18 | Viewed by 3640

Abstract

Room temperature sodium-sulfur batteries have been considered to be potential candidates for future energy storage devices because of their low cost, abundance, and high performance. The sluggish sulfur reaction and the “shuttle effect” are among the main problems that hinder the commercial utilization [...] Read more.

Room temperature sodium-sulfur batteries have been considered to be potential candidates for future energy storage devices because of their low cost, abundance, and high performance. The sluggish sulfur reaction and the “shuttle effect” are among the main problems that hinder the commercial utilization of room temperature sodium-sulfur batteries. In this study, the performance of a hybrid that was based on nitrogen (N)-doped carbon nanospheres loaded with a meagre amount of Fe ions (0.14 at.%) was investigated in the sodium-sulfur battery. The Fe ions accelerated the conversion of polysulfides and provided a stronger interaction with soluble polysulfides. The Fe-carbon nanospheres hybrid delivered a reversible capacity of 359 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹ and retained a capacity of 180 mAh·g⁻¹ at 1 A·g⁻¹, after 200 cycles. These results, combined with the excellent rate performance, suggest that Fe ions, even at low loading, are able to improve the electrocatalytic effect of carbon nanostructures significantly. In addition to Na-S batteries, the new hybrid is anticipated to be a strong candidate for other energy storage and conversion applications such as other metal-sulfur batteries and metal-air batteries. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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10 pages, 2374 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhanced Reactant Distribution in Redox Flow Cells

by Nicholas Gurieff, Declan Finn Keogh, Victoria Timchenko and Chris Menictas

Molecules 2019, 24(21), 3877; https://doi.org/10.3390/molecules24213877 - 28 Oct 2019

Cited by 8 | Viewed by 4086

Abstract

Redox flow batteries (RFBs), provide a safe and cost-effective means of storing energy at grid-scale, and will play an important role in the decarbonization of global electricity networks. Several approaches have been explored to improve their efficiency and power density, and recently, cell [...] Read more.

Redox flow batteries (RFBs), provide a safe and cost-effective means of storing energy at grid-scale, and will play an important role in the decarbonization of global electricity networks. Several approaches have been explored to improve their efficiency and power density, and recently, cell geometry modification has shown promise in efforts to address mass transport limitations which affect electrochemical and overall system performance. Flow-by electrode configurations have demonstrated significant power density improvements in laboratory testing, however, flow-through designs with conductive felt remain the standard at commercial scale. Concentration gradients exist within these cells, limiting their performance. A new concept of redistributing reactants within the flow frame is introduced in this paper. This research shows a 60% improvement in minimum V³⁺ concentration within simulated vanadium redox flow battery (VRB/VRFB) cells through the application of static mixers. The enhanced reactant distribution showed a cell voltage improvement by reducing concentration overpotential, suggesting a pathway forward to increase limiting current density and cycle efficiencies in RFBs. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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15 pages, 1936 KiB

Open AccessArticle

Structural, Impedance, and EDLC Characteristics of Proton Conducting Chitosan-Based Polymer Blend Electrolytes with High Electrochemical Stability

by Shujahadeen B. Aziz, Rebar T. Abdulwahid, Muhamad H. Hamsan, Mohamad A. Brza, Ranjdar M. Abdullah, Mohd F. Z. Kadir and Saifful K. Muzakir

Molecules 2019, 24(19), 3508; https://doi.org/10.3390/molecules24193508 - 27 Sep 2019

Cited by 56 | Viewed by 4049

Abstract

In this report, a facile solution casting technique was used to fabricate polymer blend electrolytes of chitosan (CS):poly (ethylene oxide) (PEO):NH4SCN with high electrochemical stability (2.43V). Fourier transform infrared (FTIR) spectroscopy was used to investigate the polymer electrolyte formation. For the electrochemical property [...] Read more.

In this report, a facile solution casting technique was used to fabricate polymer blend electrolytes of chitosan (CS):poly (ethylene oxide) (PEO):NH4SCN with high electrochemical stability (2.43V). Fourier transform infrared (FTIR) spectroscopy was used to investigate the polymer electrolyte formation. For the electrochemical property analysis, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) techniques were carried out. Referring to the FTIR spectra, a complex formation between the added salt and CS:PEO was deduced by considering the decreasing and shifting of FTIR bands intensity in terms of functional groups. The CS:PEO:NH₄SCN electrolyte was found to be electrochemically stable as the applied voltage linearly swept up to 2.43V. The cyclic voltammogram has presented a wide potential window without showing any sign of redox peaks on the electrode surface. The proved mechanisms of charge storage in these fabricated systems were found to be double layer charging. The EIS analysis showed the existence of bulk resistance, wherein the semicircle diameter decreased with increasing salt concentration. The calculated maximum DC conductivity value was observed to be 2.11 × 10⁻⁴ S/cm for CS:PEO incorporated with 40 wt% of NH₄SCN salt. The charged species in CS:PEO:NH₄SCN electrolytes were considered to be predominantly ionic in nature. This was verified from transference number analysis (TNM), in which ion and electron transference numbers were found to be t_ion = 0.954 and t_el = 0.045, respectively. The results obtained for both ion transference number and DC conductivity implied the possibility of fabricating electrolytes for electrochemical double layer capacitor (EDLC) device application. The specific capacitance of the fabricated EDLC was obtained from the area under the curve of the CV plot. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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24 pages, 8347 KiB

Open AccessEditor’s ChoiceArticle

A Promising Polymer Blend Electrolytes Based on Chitosan: Methyl Cellulose for EDLC Application with High Specific Capacitance and Energy Density

by Shujahadeen B. Aziz, M. H. Hamsan, Ranjdar M. Abdullah and M. F. Z. Kadir

Molecules 2019, 24(13), 2503; https://doi.org/10.3390/molecules24132503 - 9 Jul 2019

Cited by 111 | Viewed by 5531

Abstract

In the present work, promising proton conducting solid polymer blend electrolytes (SPBEs) composed of chitosan (CS) and methylcellulose (MC) were prepared for electrochemical double-layer capacitor (EDLC) application with a high specific capacitance and energy density. The change in intensity and the broad nature [...] Read more.

In the present work, promising proton conducting solid polymer blend electrolytes (SPBEs) composed of chitosan (CS) and methylcellulose (MC) were prepared for electrochemical double-layer capacitor (EDLC) application with a high specific capacitance and energy density. The change in intensity and the broad nature of the XRD pattern of doped samples compared to pure CS:MC system evidencedthe amorphous character of the electrolyte samples. The morphology of the samples in FESEM images supported the amorphous behavior of the solid electrolyte films. The results of impedance and Bode plotindicate that the bulk resistance decreasedwith increasing salt concentration. The highest DC conductivity was found to be 2.81 × 10⁻³ S/cm. The electrical equivalent circuit (EEC) model was conducted for selected samples to explain the complete picture of the electrical properties.The performance of EDLC cells was examined at room temperature by electrochemical techniques, such as impedance spectroscopy, cyclic voltammetry (CV) and constant current charge–discharge techniques. It was found that the studied samples exhibit a very good performance as electrolyte for EDLC applications. Ions were found to be the dominant charge carriers in the polymer electrolyte. The ion transference number (t_ion) was found to be 0.84 while 0.16 for electron transference number (t_el). Through investigation of linear sweep voltammetry (LSV), the CS:MC:NH₄SCN system was found to be electrochemically stable up to 1.8 V. The CV plot revealed no redox peak, indicating the occurrence of charge double-layer at the surface of activated carbon electrodes. Specific capacitance (C_spe) for the fabricated EDLC was calculated using CV plot and charge–discharge analyses. It was found to be 66.3 F g⁻¹ and 69.9 F g⁻¹ (at thefirst cycle), respectively. Equivalent series resistance (R_esr) of the EDLC was also identified, ranging from 50.0 to 150.0 Ω. Finally, energy density (E_d) was stabilized to anaverage of 8.63 Wh kg⁻¹ from the 10th cycle to the 100th cycle. The first cycle obtained power density (P_d) of 1666.6 W kg⁻¹ and then itdropped to 747.0 W kg⁻¹ at the 50th cycle and continued to drop to 555.5 W kg⁻¹ as the EDLC completed 100 cycles. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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16 pages, 15631 KiB

Open AccessArticle

Structure, Shift in Redox Potential and Li-Ion Diffusion Behavior in Tavorite LiFe_1−xV_xPO₄F Solid-Solution Cathodes

by Jia-Li Yan, Gang-Qin Shao, Shu-Hao Fan, Can Zhu, Yong Zhang, Jun Wang and Qi Liu

Molecules 2019, 24(10), 1893; https://doi.org/10.3390/molecules24101893 - 16 May 2019

Cited by 5 | Viewed by 2780

Abstract

Solid-solution Li-ion cathode materials transform through a single-phase reaction thus leading to a long-term structural stability and improved cyclability. In this work, a two- to single-phase Li⁺-extraction/insertion mechanism is studied through tuning the stoichiometry of transition-metal Fe/V cations to trigger a [...] Read more.

Solid-solution Li-ion cathode materials transform through a single-phase reaction thus leading to a long-term structural stability and improved cyclability. In this work, a two- to single-phase Li⁺-extraction/insertion mechanism is studied through tuning the stoichiometry of transition-metal Fe/V cations to trigger a transition in the chemical reactivity path. Tavorite triclinic-structured LiFe_1−xV_xPO₄F (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) solid-solution powders were prepared by a facile one-step solid-state method from hydrothermal-synthesized and commercial raw materials. The broad shape of cyclic voltammetry (CV) peaks, sloping charge/discharge profiles and sloping open-circuit voltage (OCV) profiles were observed in LiFe_1−xV_xPO₄F solid-solution cathodes while 0 < x < 1. These confirm strongly a single-phase behavior which is different from the two-phase behavior in the end-members (x = 0 or 1). The electronegativity of M (M = Fe_1−xV_x) for the redox potential of Fe^2+/3+ couple or the M–O₄F₂ bond length for the V^3+/4+ couple plays respectively a dominant role in LiFe_1−xV_xPO₄F solid-solution cathodes. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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10 pages, 10021 KiB

Open AccessArticle

Well-Wrapped Li-Rich Layered Cathodes by Reduced Graphene Oxide towards High-Performance Li-Ion Batteries

by Di Liu, Fengying Wang, Gang Wang, Congjie Lv, Zeyu Wang, Xiaochuan Duan and Xin Li

Molecules 2019, 24(9), 1680; https://doi.org/10.3390/molecules24091680 - 30 Apr 2019

Cited by 8 | Viewed by 4094

Abstract

Layered lithium-rich manganese oxide (LLO) cathode materials have attracted much attention for the development of high-performance lithium-ion batteries. However, they have suffered seriously from disadvantages, such as large irreversible capacity loss during the first cycle, discharge capacity decaying, and poor rate performance. Here, [...] Read more.

Layered lithium-rich manganese oxide (LLO) cathode materials have attracted much attention for the development of high-performance lithium-ion batteries. However, they have suffered seriously from disadvantages, such as large irreversible capacity loss during the first cycle, discharge capacity decaying, and poor rate performance. Here, a novel method was developed to coat the surface of 0.4Li₂MnO₃∙0.6LiNi_1/3Co_1/3Mn_1/3O₂ cathode material with reduced graphene-oxide (rGO) in order to address these drawbacks, where a surfactant was used to facilitate the well-wrapping of rGO. As a result, the modified LLO (LLO@rGO) cathode exhibits superior electrochemical performance including cycling stability and rate capability compared to the pristine LLO cathode. In particular, the LLO@rGO with a 0.5% rGO content can deliver a high discharge capacity of 166.3 mAh g⁻¹ at a 5C rate. The novel strategy developed here can provide a vital approach to inhibit the undesired side reactions and structural deterioration of Li-rich cathode materials, and should be greatly useful for other cathode materials to improve their electrochemical performance. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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9 pages, 1795 KiB

Open AccessArticle

Synthesis and Luminescence Properties of a Novel Green-Yellow-Emitting Phosphor BiOCl:Pr³⁺ for Blue-Light-Based w-LEDs

by Qi Wang, Meiling Xie, Minghao Fang, Xiaowen Wu, Yan’gai Liu, Zhaohui Huang, Kai Xi and Xin Min

Molecules 2019, 24(7), 1296; https://doi.org/10.3390/molecules24071296 - 3 Apr 2019

Cited by 8 | Viewed by 3286

Abstract

The development of white-light-emitting diodes (w-LEDs) makes it meaningful to develop novel high-performance phosphors excited by blue light. Herein, BiOCl:Pr³⁺ green-yellow phosphors were prepared via a high-temperature solid-state reaction method. The crystal structure, luminescent properties, lifetime, thermal quenching behavior, and quantum yield [...] Read more.

The development of white-light-emitting diodes (w-LEDs) makes it meaningful to develop novel high-performance phosphors excited by blue light. Herein, BiOCl:Pr³⁺ green-yellow phosphors were prepared via a high-temperature solid-state reaction method. The crystal structure, luminescent properties, lifetime, thermal quenching behavior, and quantum yield were studied in detail. The BiOCl:Pr³⁺ phosphors presented several emission peaks located in green and red regions, under excitation at 453 nm. The CIE coordinates could be tuned along with the changed doping concentration with fair luminescence efficiency. The results also indicated that the optimized doping concentration of Pr³⁺ ions was at x = 0.0075 because of the concentration quenching behavior resulting from an intense exchange effect. When the temperature reached 150 °C, the intensity of the emission peak at 495 nm could remain at 78% of that at room temperature. The activation energy of 0.20 eV also confirmed that the BiOCl:Pr³⁺ phosphor exhibited good thermal stability. All these results indicate that the prepared products have potential to be used as a high-performance green-yellow-light-emitting phosphor for blue-light-based w-LEDs. Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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9 pages, 1763 KiB

Open AccessConcept Paper

How to Measure and Calculate Equivalent Series Resistance of Electric Double-Layer Capacitors

by Rafael Vicentini, Leonardo Morais Da Silva, Edson Pedro Cecilio Junior, Thayane Almeida Alves, Willian Gonçalves Nunes and Hudson Zanin

Molecules 2019, 24(8), 1452; https://doi.org/10.3390/molecules24081452 - 12 Apr 2019

Cited by 72 | Viewed by 7668

Abstract

Electric double-layer capacitors (EDLCs) are energy storage devices that have attracted attention from the scientific community due to their high specific power storage capabilities. The standard method for determining the maximum power (P_max) of these devices uses the relation P [...] Read more.

Electric double-layer capacitors (EDLCs) are energy storage devices that have attracted attention from the scientific community due to their high specific power storage capabilities. The standard method for determining the maximum power (P_max) of these devices uses the relation P_max = U²/4R_ESR, where U stands for the cell voltage and R_ESR for the equivalent series resistance. Despite the relevance of R_ESR, one can observe a lack of consensus in the literature regarding the determination of this parameter from the galvanostatic charge-discharge findings. In addition, a literature survey revealed that roughly half of the scientific papers have calculated the R_ESR values using the electrochemical impedance spectroscopy (EIS) technique, while the other half used the galvanostatic charge discharge (GCD) method. R_ESR values extracted from EIS at high frequencies (>10 kHz) do not depend on the particular equivalent circuit model. However, the conventional GCD method better resembles the real situation of the device operation, and thus its use is of paramount importance for practical purposes. In the latter case, the voltage drop (ΔU) verified at the charge-discharge transition for a given applied current (I) is used in conjunction with Ohm’s law to obtain the R_ESR (e.g., R_ESR = ΔU/ΔI). However, several papers have caused a great confusion in the literature considering only applied current (I). In order to shed light on this important subject, we report in this work a rational analysis regarding the GCD method in order to prove that to obtain reliable R_ESR values the voltage drop must be normalized by a factor of two (e.g., R_ESR = ΔU/2I). Full article

(This article belongs to the Special Issue Advances in Electrochemical Energy Storage Devices)

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