Micromachines

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12 pages, 3168 KiB

Open AccessArticle

High-Performance Flexible Energy Storage Devices Based on Graphene Decorated with Flower-Shaped MoS₂ Heterostructures

by Yongteng Qian, Zhiyi Lyu, Qianwen Zhang, Tae Hyeong Lee, Tae Kyu Kang, Minkyun Sohn, Lin Shen, Dong Hwan Kim and Dae Joon Kang

Micromachines 2023, 14(2), 297; https://doi.org/10.3390/mi14020297 - 23 Jan 2023

Cited by 6 | Viewed by 2382

Abstract

MoS₂, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and [...] Read more.

MoS₂, owing to its advantages of having a sheet-like structure, high electrical conductivity, and benign environmental nature, has emerged as a candidate of choice for electrodes of next-generation supercapacitors. Its widespread use is offset, however, by its low energy density and poor durability. In this study, to overcome these limitations, flower-shaped MoS₂/graphene heterostructures have been deployed as electrode materials on flexible substrates. Three-electrode measurements yielded an exceptional capacitance of 853 F g⁻¹ at 1.0 A g⁻¹, while device measurements on an asymmetric supercapacitor yielded 208 F g⁻¹ at 0.5 A g⁻¹ and long-term cyclic durability. Nearly 86.5% of the electrochemical capacitance was retained after 10,000 cycles at 0.5 A g⁻¹. Moreover, a remarkable energy density of 65 Wh kg⁻¹ at a power density of 0.33 kW kg⁻¹ was obtained. Our MoS₂/Gr heterostructure composites have great potential for the development of advanced energy storage devices. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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10 pages, 2763 KiB

Open AccessArticle

Effect of Ball-Milled Steatite Powder on the Latent Heat Energy Storage Properties and Heat Charging–Discharging Periods of Paraffin Wax as Phase Change Material

by Sathiyalingam Kannaiyan, Song-Jeng Huang, David Rathnaraj and S. A. Srinivasan

Micromachines 2022, 13(9), 1456; https://doi.org/10.3390/mi13091456 - 2 Sep 2022

Cited by 2 | Viewed by 1826

Abstract

Phase change materials (PCMs) serve as an advantage in thermal energy storage systems utilizing the available sensible and latent heat. The PCMs absorb the thermal energy during the charging process and release it into the environment during the discharging process. Steatite is low [...] Read more.

Phase change materials (PCMs) serve as an advantage in thermal energy storage systems utilizing the available sensible and latent heat. The PCMs absorb the thermal energy during the charging process and release it into the environment during the discharging process. Steatite is low cost and eco-friendly, with a thermal stability up to 1000 °C, and it is abundantly available in nature. This study investigates the steatite–paraffin wax-based PCM and the effect on the cyclic loads using a horizontal triplex-tube latent heat energy storage system. The thermal conductivity value of the milled steatite-based PCM composite was 7.7% higher than pure PCM. The PCM with the ball-milled steatite-fabricated composite exhibited better discharging characteristics, increasing the discharge time by 50% more than that of the pure paraffin wax. Moreover, the milled steatite-based PCM outperformed that incorporated with non-milled steatite with paraffin. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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12 pages, 3369 KiB

Open AccessArticle

Highly active N, S Co-Doped Ultramicroporous Carbon for High-Performance Supercapacitor Electrodes

by Wenjing Lu, Lina Hao and Yawei Wang

Micromachines 2022, 13(6), 905; https://doi.org/10.3390/mi13060905 - 7 Jun 2022

Cited by 6 | Viewed by 2152

Abstract

N, S-doped ultramicroporous carbons (NSUC-x) with a high nitrogen/sulfur content and a narrow pore-size distribution of around 0.55 nm were firstly prepared using L-cysteine as a nitrogen and sulfur source. The phase, graphitization degree, morphology, specific surface area, pore structure and surface condition [...] Read more.

N, S-doped ultramicroporous carbons (NSUC-x) with a high nitrogen/sulfur content and a narrow pore-size distribution of around 0.55 nm were firstly prepared using L-cysteine as a nitrogen and sulfur source. The phase, graphitization degree, morphology, specific surface area, pore structure and surface condition of NSUC-x are investigated to analyze the key role in electrochemical performance. Such an ultramicroporous structure and N, S doping not merely provide a high-specific surface area and a suitable pore size, but also induce a good wettability for the fast transport and adsorption of electrolyte ions. Due to the above strategies, the typical NSUC-0.4 exhibits a high gravimetric capacitance of 339 F g⁻¹ at 0.5 A g⁻¹ as well as a capacity retention of 91.6% after 10,000 cycles in a three-electrode system using a 6 M KOH electrolyte. More attractively, a NSUC-0.4-assembled symmetrical supercapacitor delivers an energy output of 7.4 Wh kg⁻¹ at 100 W kg⁻¹ in 6 M KOH as well as a capacity retention of 92.4% after 10,000 cycles, indicating its practical application prospect. Our findings open up new prospects for the design and electrochemical application of N, S-doped ultramicroporous carbons. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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6 pages, 2928 KiB

Open AccessArticle

Poling-Free Hydroxyapatite/Polylactide Nanogenerator with Improved Piezoelectricity for Energy Harvesting

by Wei Liu, Yunlai Shi, Zhijun Sun and Li Zhang

Micromachines 2022, 13(6), 889; https://doi.org/10.3390/mi13060889 - 31 May 2022

Cited by 5 | Viewed by 1894

Abstract

Polylactide-based piezoelectric nanogenerators were designed and fabricated with improved piezoelectric performances by blending polylactide with hydroxyapatite. The addition of hydroxyapatite significantly improves the crystallinity of polylactide and helps to form hydrogen bonds, which further improved the piezoelectric output performance of these piezoelectric nanogenerators [...] Read more.

Polylactide-based piezoelectric nanogenerators were designed and fabricated with improved piezoelectric performances by blending polylactide with hydroxyapatite. The addition of hydroxyapatite significantly improves the crystallinity of polylactide and helps to form hydrogen bonds, which further improved the piezoelectric output performance of these piezoelectric nanogenerators with over three times the open circuit voltage compared with that of pure-polylactide-based devices. Such excellent piezoelectricity of hydroxyapatite/polylactide-based nanogenerators give them great potential for energy harvesting fields. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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9 pages, 29924 KiB

Open AccessArticle

An Automated Power Evaluation Workbench for Triboelectric Nanogenerators

by Ming Yuan, Chunhui Li, Sheng Zhang and Yannan Xie

Micromachines 2022, 13(3), 444; https://doi.org/10.3390/mi13030444 - 15 Mar 2022

Cited by 2 | Viewed by 2201

Abstract

Triboelectric nanogenerators (TENGs) have high potential in self-powered sensing and energy harvesting applications. In general, TENGs’ internal source resistance is high, and their output power varies under different load resistance values. Therefore, a resistance box is required to evaluate their energy harvesting performance [...] Read more.

Triboelectric nanogenerators (TENGs) have high potential in self-powered sensing and energy harvesting applications. In general, TENGs’ internal source resistance is high, and their output power varies under different load resistance values. Therefore, a resistance box is required to evaluate their energy harvesting performance and obtain the power curve under different load values. The load tuning process is usually performed by hand. This repetitive process is time-consuming and error-prone. Consequently, an Automated Power Evaluation Workbench (APEW) is developed, making the resistance switching and power measuring process program-controlled. The resistance value is resolved using the Octal decomposition principle. In addition, a resistance synthesis algorithm is proposed to alter the resistance value with a minimum step of 1 Ohm. The target resistance value is physically synthesized by relay switching, while digital lines control the relays. The proposed APEW is then evaluated experimentally, and the obtained results are compared with those of the traditional manual switching approach. It is deduced that the two power curves are almost identical. Therefore, it is believed that the proposed APEW will play a crucial role in TENG’s further development. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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9 pages, 2346 KiB

Open AccessArticle

Cu₂S Nanoflakes Decorated with NiS Nanoneedles for Enhanced Oxygen Evolution Activity

by Le Wang, Mancong Li, Yingxin Lyu, Jiawen Liu, Jimin Du and Dae Joon Kang

Micromachines 2022, 13(2), 278; https://doi.org/10.3390/mi13020278 - 9 Feb 2022

Cited by 4 | Viewed by 2387

Abstract

Metal sulfides are considered excellent materials for oxygen evolution reaction because of their excellent conductivity and high electrocatalytic activity. In this report, the NiS-Cu₂S composites were prepared on copper foam (NiS-Cu₂S-CF) using a facile synthetic strategy. The scanning electron [...] Read more.

Metal sulfides are considered excellent materials for oxygen evolution reaction because of their excellent conductivity and high electrocatalytic activity. In this report, the NiS-Cu₂S composites were prepared on copper foam (NiS-Cu₂S-CF) using a facile synthetic strategy. The scanning electron microscopy results confirmed that the NiS nanoneedles were successfully grown on Cu₂S nanoflakes, greatly increasing the active sites. Particularly, the optimized 15% NiS-Cu₂S-CF composite demonstrated excellent oxygen evolution activity with a small overpotential of 308 mV@20 mA cm⁻², which is significantly smaller than that of noble metal-based electrocatalysts and other NiS-Cu₂S-CF composites. The enhanced oxygen evolution activity is attributed to the unique morphology that can provide ample active sites, rich ion-transfer pathways, and the synergistic effect between NiS and Cu₂S, which can boost the electron transfer rate. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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10 pages, 3055 KiB

Open AccessArticle

A Novel Triboelectric Material Based on Deciduous Leaf for Energy Harvesting

by Zhuyu Ding, Ming Zou, Peng Yao, Zhiyuan Zhu and Li Fan

Micromachines 2021, 12(11), 1314; https://doi.org/10.3390/mi12111314 - 26 Oct 2021

Cited by 5 | Viewed by 2063

Abstract

Recently, the triboelectric nanogenerator (TENG) for harvesting low-frequency energy has attracted the attention of academia. However, there are few studies on environmentally friendly triboelectric materials. Here, we propose a novel triboelectric nanogenerator based on the deciduous leaf (DL-TENG) that can harvest mechanical energy [...] Read more.

Recently, the triboelectric nanogenerator (TENG) for harvesting low-frequency energy has attracted the attention of academia. However, there are few studies on environmentally friendly triboelectric materials. Here, we propose a novel triboelectric nanogenerator based on the deciduous leaf (DL-TENG) that can harvest mechanical energy from various low-frequency motions. The deciduous leaf is an environmentally friendly triboelectric material, which has a low-cost and is easy to obtain. Using it to generate electricity can achieve the effect of waste utilization. From the experimental results, the peak value of the short-circuit current (I_sc) and the open-circuit voltage (V_oc) can reach 4.2 µA and 150 V, respectively. The fabricated DL-TENG exhibits a stable high performance, with a maximum output power of 72.2 µW, to a load of 20 MΩ. Moreover, we also designed a stacked structure, DL-TENG, to enhance the electrical output. Additionally, the stacked DL-TENG could drive 15 commercial light-emitting diodes (LEDs). This design will promote the development of low-cost and environmentally friendly triboelectric material. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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8 pages, 24245 KiB

Open AccessArticle

In Situ Sputtering Silver Induction Electrode for Stable and Stretchable Triboelectric Nanogenerators

by Jinyuan Yao, Qi Zhang, Haodong Zhang, Mengqiu Li, Xichi Lu, Yu Xiao, Rujiao Yao and Xuhong Wang

Micromachines 2021, 12(10), 1267; https://doi.org/10.3390/mi12101267 - 18 Oct 2021

Cited by 2 | Viewed by 2094

Abstract

Triboelectric nanogenerators (TENG) can convert mechanical energy into electricity and exhibit unique advantages in the field of low-frequency and discrete energy harvesting. However, the interfacial state and stability between the triboelectric layer and electrode layer influence the output and applications of TENG. Herein, [...] Read more.

Triboelectric nanogenerators (TENG) can convert mechanical energy into electricity and exhibit unique advantages in the field of low-frequency and discrete energy harvesting. However, the interfacial state and stability between the triboelectric layer and electrode layer influence the output and applications of TENG. Herein, an in situ sputtering Ag process for fabricating induction electrodes is proposed to match with TENG. The sputtering Ag process is optimized by a variety of parameters, such as sputtering power, single-cycle time, number of cycles, cycle interval, and vacuum degree. In addition, the chemical state of Ag as a function of air placement is investigated, showing the sputtered Ag has excellent conductivity and stability. Moreover, four kinds of polymers are selected for fabricating TENGs based on the sputtered Ag induction electrodes, i.e., nylon 66, polyimide (PI), fluorinated ethylene propylene (FEP), and polydimethylsiloxane (PDMS), which shows great applicability. Considering the demand of flexible power suppliers, the sputtered Ag is integrated with a PDMS substrate, and shows good adhesion, flexibility, and ductility after severe deformation of the PDMS. Finally, the developed induction electrode processing technology is used in flexible TENG and shows great prospects in self-powered electronics for practical applications. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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13 pages, 3028 KiB

Open AccessArticle

Method for QCM Resonator Device Equivalent Circuit Parameter Extraction and Electrode Quality Assessment

by Dong Liu, Xiaoting Xiao, Ziqiao Tang, Qiao Chen, Haoran Li, Xiaoxiong Wang and Yan Yan

Micromachines 2021, 12(9), 1086; https://doi.org/10.3390/mi12091086 - 9 Sep 2021

Cited by 7 | Viewed by 2774

Abstract

Quartz crystal microbalance (QCM) resonators are used in a wide range of sensors. Current QCM resonators achieve a simultaneous measurement of multiple physical quantities by analyzing lumped-element equivalent parameters, which are obtained via the introduction of external devices. This introduction of external devices [...] Read more.

Quartz crystal microbalance (QCM) resonators are used in a wide range of sensors. Current QCM resonators achieve a simultaneous measurement of multiple physical quantities by analyzing lumped-element equivalent parameters, which are obtained via the introduction of external devices. This introduction of external devices will probably increase measurement error. To realize the measurement of multiple physical quantities while eliminating the measurement error caused by external devices, this paper proposes a measurement method for the lumped-element equivalent parameters of QCM resonators without the need for extra external devices. Accordingly, a numerical method for solving nonlinear equations with fewer data points required and a higher accuracy was adopted. A standard crystal resonator parameter extraction experiment is described. The extracted parameters were consistent with the nominal parameters, which confirms the accuracy of this method. Furthermore, six QCM resonator device samples with different electrode diameters and materials were produced and used in the parameter measurement experiment. The linear relationship between the electrode material conductivity and motional resistance R₁ is discussed. The ability of this method to characterize the electrode material and to detect the rust status of the electrode is also demonstrated. These abilities support the potential utility of the proposed method for an electrode quality assessment of piezoelectric devices. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Energy Harvesting and Storage Devices)

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