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13 pages, 10201 KiB

Open AccessArticle

Highly Conducting Li(Fe_1−xMn_x)_0.88V_0.08PO₄ Cathode Materials Nanocrystallized from the Glassy State (x = 0.25, 0.5, 0.75)

by Justyna E. Frąckiewicz and Tomasz K. Pietrzak

Materials 2021, 14(21), 6434; https://doi.org/10.3390/ma14216434 - 27 Oct 2021

Cited by 2 | Viewed by 1723

Abstract

This study showed that thermal nanocrystallization of glassy analogs of LiFe

_{1 - x}

Mn

_{x}

PO

_{4}

(with the addition of vanadium for improvement of glass forming properties) resulted in highly conducting materials that may be used as cathodes for Li-ion batteries. [...] Read more.

This study showed that thermal nanocrystallization of glassy analogs of LiFe

_{1 - x}

Mn

_{x}

PO

_{4}

(with the addition of vanadium for improvement of glass forming properties) resulted in highly conducting materials that may be used as cathodes for Li-ion batteries. The glasses and nanomaterials were studied with differential thermal analysis, X-ray diffractometry, and impedance spectroscopy. The electrical conductivity of the nanocrystalline samples varied, depending on the composition. For

x = 0.5

, it exceeded

10^{- 3}

S/cm at room temperature with an activation energy as low as 0.15 eV. The giant and irreversible increase in the conductivity was explained on the basis of Mott’s theory of electron hopping and a core-shell concept. Electrochemical performance of the active material with

x = 0.5

was also reported. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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14 pages, 5300 KiB

Open AccessArticle

Mg²⁺ Doping Effects on the Structural and Dielectric Properties of CaCu₃Ti₄O₁₂ Ceramics Obtained by Mechanochemical Synthesis

by Piotr Dulian, Wojciech Bąk, Mateusz Piz, Barbara Garbarz-Glos, Olena V. Sachuk, Krystyna Wieczorek-Ciurowa, Agata Lisińska-Czekaj and Dionizy Czekaj

Materials 2021, 14(5), 1187; https://doi.org/10.3390/ma14051187 - 3 Mar 2021

Cited by 3 | Viewed by 1973

Abstract

In this study, ceramic CaCu₃Ti₄O₁₂ (CCTO) and CaCu_3−xMg_xTi₄O₁₂ solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The [...] Read more.

In this study, ceramic CaCu₃Ti₄O₁₂ (CCTO) and CaCu_3−xMg_xTi₄O₁₂ solid solutions in which 0.1 ≤ x ≤ 0.5 were prepared by the mechanochemical method, realized by a high-energy ball milling technique. The effects of the Mg²⁺ ion concentration and sintering time on the dielectric response in the prepared ceramics were investigated and discussed. It was demonstrated that, by the use of a sufficiently high energy of mechanochemical treatment, it is possible to produce a crystalline product after only 2 h of milling the mixture of the oxide substrates. Both the addition of magnesium ions and the longer sintering time of the mechanochemically-produced ceramics cause excessive grain growth and significantly affect the dielectric properties of the materials. The X-ray diffraction (XRD) analysis showed that all of the as-prepared solid solutions, CaCu_3−xMg_xTi₄O₁₂ (0.0 ≤ x ≤ 0.5), regardless of the sintering time, exhibit a cubic perovskite single phase. The dielectric study showed two major contributions associated with the grains and the grain boundaries. The analysis of the electric modules of these ceramics confirmed the occurrence of Maxwell–Wagner type relaxation, which is dependent on the temperature. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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9 pages, 3182 KiB

Open AccessArticle

Electrodeposition of CdTe Thin Films for Solar Energy Water Splitting

by Jun Ling, Xulei Zhang, Ting Mao, Lei Li, Shilin Wang, Meng Cao, Jijun Zhang, Haozhi Shi, Jian Huang, Yue Shen and Linjun Wang

Materials 2020, 13(7), 1536; https://doi.org/10.3390/ma13071536 - 27 Mar 2020

Cited by 15 | Viewed by 3266

Abstract

CdTe thin films have been prepared by electrochemical deposition. The morphological, structural, and optical properties of CdTe thin films deposited with different deposition time were investigated, and the influence of film thickness on the photoelectric characteristics of CdTe thin films was studied. At [...] Read more.

CdTe thin films have been prepared by electrochemical deposition. The morphological, structural, and optical properties of CdTe thin films deposited with different deposition time were investigated, and the influence of film thickness on the photoelectric characteristics of CdTe thin films was studied. At the deposition time of 1.5 h, CdTe thin films had good optical properties and the photocurrent reached 20 μAcm⁻². Furthermore, the Pt/CdS/CdTe/FTO structure was prepared to improve its PEC stability and the photocurrent of 240 μAcm⁻² had been achieved. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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15 pages, 7249 KiB

Open AccessArticle

Development by Mechanochemistry of La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 Electrolyte for SOFCs

by Francisco J. Garcia-Garcia, Yunqing Tang, Francisco J. Gotor and María J. Sayagués

Materials 2020, 13(6), 1366; https://doi.org/10.3390/ma13061366 - 18 Mar 2020

Cited by 20 | Viewed by 3274

Abstract

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) powders from the corresponding stoichiometric amounts of La₂O₃, SrO, Ga₂O₃, [...] Read more.

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) powders from the corresponding stoichiometric amounts of La₂O₃, SrO, Ga₂O₃, and MgO in a short time. After 60 min of milling, the desired final product was obtained without the need for any subsequent annealing treatment. A half solid oxide fuel cell (SOFC) was then developed using LSGM as an electrolyte and La_0.8Sr_0.2MnO₃ (LSM) as an electrode, both obtained by mechanochemistry. The characterization by X-ray diffraction of as-prepared powders showed that LSGM and LSM present a perovskite structure and pseudo-cubic symmetry. The thermal and chemical stability between the electrolyte (LSGM) and the electrode (LSM) were analyzed by dynamic X-ray diffraction as a function of temperature. The electrolyte (LSGM) is thermally stable up to 800 and from 900 °C, where the secondary phases of LaSrGa₃O₇ and LaSrGaO₄ appear. The best sintering temperature for the electrolyte is 1400 °C, since at this temperature, LaSrGaO₄ disappears and the percentage of LaSrGa₃O₇ is minimized_. The electrolyte is chemically compatible with the electrode up to 800 °C. The powder sample of the electrolyte (LSGM) at 1400 °C observed by HRTEM indicates that the cubic symmetry Pm-3m is preserved. The SOFC was constructed using the brush-painting technique; the electrode–electrolyte interface characterized by SEM presented good adhesion at 800 °C. The electrical properties of the electrolyte and the half-cell were analyzed by complex impedance spectroscopy. It was found that LSGM is a good candidate to be used as an electrolyte in SOFC, with an Ea value of 0.9 eV, and the LSM sample is a good candidate to be used as cathode. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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13 pages, 2863 KiB

Open AccessArticle

Application of PVDF Organic Particles Coating on Polyethylene Separator for Lithium Ion Batteries

by Yuan Wang, Chuanqiang Yin, Zhenglin Song, Qiulin Wang, Yu Lan, Jinpeng Luo, Liwen Bo, Zhihao Yue, Fugen Sun and Xiaomin Li

Materials 2019, 12(19), 3125; https://doi.org/10.3390/ma12193125 - 25 Sep 2019

Cited by 23 | Viewed by 4969

Abstract

Surface coating modification on a polyethylene separator serves as a promising way to meet the high requirements of thermal dimensional stability and excellent electrolyte wettability for lithium ion batteries (LIBs). In this paper, we report a new type of surface modified separator by [...] Read more.

Surface coating modification on a polyethylene separator serves as a promising way to meet the high requirements of thermal dimensional stability and excellent electrolyte wettability for lithium ion batteries (LIBs). In this paper, we report a new type of surface modified separator by coating polyvinylidene fluoride (PVDF) organic particles on traditional microporous polyethylene (PE) separators. The PE separator coated by PVDF particles (PE-PVDF separator) has higher porosity (61.4%), better electrolyte wettability (the contact angle to water was 3.28° ± 0.21°) and superior ionic conductivity (1.53 mS/cm) compared with the bare PE separator (51.2%, 111.3° ± 0.12°, 0.55 mS/cm). On one hand, the PVDF organic polymer has excellent organic electrolyte compatibility. On the other hand, the PVDF particles contain sub-micro spheres, of which the separator can possess a large specific surface area to absorb additional electrolyte. As a result, LIBs assembled using the PE-PVDF separator showed better electrochemical performances. For example, the button cell using a PE-PVDF as the separator had a higher capacity retention rate (70.01% capacity retention after 200 cycles at 0.5 C) than the bare PE separator (62.5% capacity retention after 200 cycles at 0.5 C). Moreover, the rate capability of LIBs was greatly improved as well—especially at larger current densities such as 2 C and 5 C. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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10 pages, 7777 KiB

Open AccessArticle

Tunable Magnetocaloric Properties of Gd-Based Alloys by Adding Tb and Doping Fe Elements

by Lingfeng Xu, Chengyuan Qian, Yongchang Ai, Tong Su and Xueling Hou

Materials 2019, 12(18), 2877; https://doi.org/10.3390/ma12182877 - 6 Sep 2019

Cited by 4 | Viewed by 2468

Abstract

In this paper, the magnetocaloric properties of Gd_1−xTb_x alloys were studied and the optimum composition was determined to be Gd_0.73Tb_0.27. On the basis of Gd_0.73Tb_0.27, the influence of different Fe-doping content [...] Read more.

In this paper, the magnetocaloric properties of Gd_1−xTb_x alloys were studied and the optimum composition was determined to be Gd_0.73Tb_0.27. On the basis of Gd_0.73Tb_0.27, the influence of different Fe-doping content was discussed and the effect of heat treatment was also investigated. The adiabatic temperature change (ΔT_ad) obtained by the direct measurement method (under a low magnetic field of 1.2 T) and specific heat capacity calculation method (indirect measurement) was used to characterize the magnetocaloric properties of Gd_1−xTb_x (x = 0~0.4) and (Gd_0.73Tb_0.27)_1−yFe_y (y = 0~0.15), and the isothermal magnetic entropy (ΔS_M) was also used as a reference parameter for evaluating the magnetocaloric properties of samples together with ΔT_ad. In Gd_1−xTb_x alloys, the Curie temperature (T_c) decreased from 293 K (x = 0) to 257 K (x = 0.4) with increasing Tb content, and the Gd_0.73Tb_0.27 alloy obtained the best adiabatic temperature change, which was ~3.5 K in a magnetic field up to 1.2 T (T_c = 276 K). When the doping content of Fe increased from y = 0 to y = 0.15, the T_c of (Gd_0.73Tb_0.27)_1−yFe_y (y = 0~0.15) alloys increased significantly from 276 K (y = 0) to 281 K (y = 0.15), and a good magnetocaloric effect was maintained. The annealing of alloys (Gd_0.73Tb_0.27)_1−yFe_y (y = 0~0.15) at 1073 K for 10 h resulted in an average increase of 0.3 K in the maximum adiabatic temperature change and a slight increase in T_c. This study is of great significance for the study of magnetic refrigeration materials with adjustable Curie temperature in a low magnetic field. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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Review

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26 pages, 18543 KiB

Open AccessFeature PaperReview

Recent Progress in Multiphase Thermoelectric Materials

by Raphael Fortulan and Sima Aminorroaya Yamini

Materials 2021, 14(20), 6059; https://doi.org/10.3390/ma14206059 - 14 Oct 2021

Cited by 27 | Viewed by 5010

Abstract

Thermoelectric materials, which directly convert thermal energy to electricity and vice versa, are considered a viable source of renewable energy. However, the enhancement of conversion efficiency in these materials is very challenging. Recently, multiphase thermoelectric materials have presented themselves as the most promising [...] Read more.

Thermoelectric materials, which directly convert thermal energy to electricity and vice versa, are considered a viable source of renewable energy. However, the enhancement of conversion efficiency in these materials is very challenging. Recently, multiphase thermoelectric materials have presented themselves as the most promising materials to achieve higher thermoelectric efficiencies than single-phase compounds. These materials provide higher degrees of freedom to design new compounds and adopt new approaches to enhance the electronic transport properties of thermoelectric materials. Here, we have summarised the current developments in multiphase thermoelectric materials, exploiting the beneficial effects of secondary phases, and reviewed the principal mechanisms explaining the enhanced conversion efficiency in these materials. This includes energy filtering, modulation doping, phonon scattering, and magnetic effects. This work assists researchers to design new high-performance thermoelectric materials by providing common concepts. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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16 pages, 3276 KiB

Open AccessReview

A Review on Emerging Efficient and Stable Perovskite Solar Cells Based on g-C₃N₄ Nanostructures

by Konstantina Gkini, Ioanna Martinaiou and Polycarpos Falaras

Materials 2021, 14(7), 1679; https://doi.org/10.3390/ma14071679 - 29 Mar 2021

Cited by 17 | Viewed by 4495

Abstract

Perovskite solar cells (PSCs) have attracted great research interest in the scientific community due to their extraordinary optoelectronic properties and the fact that their power conversion efficiency (PCE) has increased rapidly in recent years, surpassing other 3rd generation photovoltaic (PV) technologies. Graphitic carbon [...] Read more.

Perovskite solar cells (PSCs) have attracted great research interest in the scientific community due to their extraordinary optoelectronic properties and the fact that their power conversion efficiency (PCE) has increased rapidly in recent years, surpassing other 3rd generation photovoltaic (PV) technologies. Graphitic carbon nitride (g-C₃N₄) presents exceptional optical and electronic properties and its use was recently expanded in the field of PSCs. The addition of g-C₃N₄ in the perovskite absorber and/or the electron transport layer (ETL) resulted in PCEs exceeding 22%, mainly due to defects passivation, improved conductivity and crystallinity as well as low charge carriers’ recombination rate within the device. Significant performance increase, including stability enhancement, was also achieved when g-C₃N₄ was applied at the PSC interfaces and the observed improvement was attributed to its wetting (hydrophobic/hydrophilic) nature and the fine tuning of the corresponding interface energetics. The current review summarizes the main innovations for the incorporation of graphitic carbon nitride in PSCs and highlights the significance and perspectives of the g-C₃N₄ approach for emerging highly efficient and robust PV devices. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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22 pages, 2025 KiB

Open AccessReview

Hydrogen Storage for Mobility: A Review

by Etienne Rivard, Michel Trudeau and Karim Zaghib

Materials 2019, 12(12), 1973; https://doi.org/10.3390/ma12121973 - 19 Jun 2019

Cited by 582 | Viewed by 46631

Abstract

Numerous reviews on hydrogen storage have previously been published. However, most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage [...] Read more.

Numerous reviews on hydrogen storage have previously been published. However, most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage medium should allow high volumetric and gravimetric energy densities, quick uptake and release of fuel, operation at room temperatures and atmospheric pressure, safe use, and balanced cost-effectiveness. All current hydrogen storage technologies have significant drawbacks, including complex thermal management systems, boil-off, poor efficiency, expensive catalysts, stability issues, slow response rates, high operating pressures, low energy densities, and risks of violent and uncontrolled spontaneous reactions. While not perfect, the current leading industry standard of compressed hydrogen offers a functional solution and demonstrates a storage option for mobility compared to other technologies. Full article

(This article belongs to the Special Issue Functional Materials for Energy Conversion and Storage)

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