Editorial

2 pages, 182 KiB

Open AccessEditorial

Editorial for Special Issue: Highly Efficient Energy Harvesting Based on Nanomaterials

by Seok Woo Lee

Nanomaterials 2022, 12(9), 1572; https://doi.org/10.3390/nano12091572 - 06 May 2022

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Energy-harvesting systems generate electricity or produce fuels such as hydrogen from various energy sources such as thermal energy, kinetic energy, and renewable energy [...] Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

Research

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17 pages, 2381 KiB

Open AccessArticle

Improving the Melting Duration of a PV/PCM System Integrated with Different Metal Foam Configurations for Thermal Energy Management

by Hussein M. Taqi Al-Najjar, Jasim M. Mahdi, Dmitry Olegovich Bokov, Nidhal Ben Khedher, Naif Khalaf Alshammari, Maria Jade Catalan Opulencia, Moram A. Fagiry, Wahiba Yaïci and Pouyan Talebizadehsardari

Nanomaterials 2022, 12(3), 423; https://doi.org/10.3390/nano12030423 - 27 Jan 2022

Cited by 17 | Viewed by 3035

Abstract

The melting duration in the photovoltaic/phase-change material (PV/PCM) system is a crucial parameter for thermal energy management such that its improvement can realize better energy management in respect to thermal storage capabilities, thermal conditions, and the lifespan of PV modules. An innovative and [...] Read more.

The melting duration in the photovoltaic/phase-change material (PV/PCM) system is a crucial parameter for thermal energy management such that its improvement can realize better energy management in respect to thermal storage capabilities, thermal conditions, and the lifespan of PV modules. An innovative and efficient technique for improving the melting duration is the inclusion of an exterior metal foam layer in the PV/PCM system. For detailed investigations of utilizing different metal foam configurations in terms of their convective heat transfer coefficients, the present paper proposes a newly developed mathematical model for the PV/PCM–metal foam assembly that can readily be implemented with a wide range of operating conditions. Both computational fluid dynamic (CFD) and experimental validations proved the good accuracy of the proposed model for further applications. The present research found that the average PV cell temperature can be reduced by about 12 °C with a corresponding improvement in PCM melting duration of 127%. The addition of the metal foam is more effective at low solar radiation, ambient temperatures far below the PCM solidus temperature, and high wind speeds in nonlinear extension. With increasing of tilt angle, the PCM melting duration is linearly decreased by an average value of (13.4–25.0)% when the metal foam convective heat transfer coefficient is changed in the range of (0.5–20) W/m².K. The present research also shows that the PCM thickness has a positive linear effect on the PCM melting duration, however, modifying the metal foam configuration from 0.5 to 20 W/m².K has an effect on the PCM melting duration in such a way that the average PCM melting duration is doubled. This confirms the effectiveness of the inclusion of metal foam in the PV/PCM system. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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26 pages, 6364 KiB

Open AccessArticle

Improved Melting of Latent Heat Storage Using Fin Arrays with Non-Uniform Dimensions and Distinct Patterns

by Farqad T. Najim, Hayder I. Mohammed, Hussein M. Taqi Al-Najjar, Lakshmi Thangavelu, Mustafa Z. Mahmoud, Jasim M. Mahdi, Mohammadreza Ebrahimnataj Tiji, Wahiba Yaïci and Pouyan Talebizadehsardari

Nanomaterials 2022, 12(3), 403; https://doi.org/10.3390/nano12030403 - 26 Jan 2022

Cited by 29 | Viewed by 3293

Abstract

Employing phase-change materials (PCM) is considered a very efficient and cost-effective option for addressing the mismatch between the energy supply and the demand. The high storage density, little temperature degradation, and ease of material processing register the PCM as a key candidate for [...] Read more.

Employing phase-change materials (PCM) is considered a very efficient and cost-effective option for addressing the mismatch between the energy supply and the demand. The high storage density, little temperature degradation, and ease of material processing register the PCM as a key candidate for the thermal energy storage system. However, the sluggish response rates during their melting and solidification processes limit their applications and consequently require the inclusion of heat transfer enhancers. This research aims to investigate the potential enhancement of circular fins on intensifying the PCM thermal response in a vertical triple-tube casing. Fin arrays of non-uniform dimensions and distinct distribution patterns were designed and investigated to determine the impact of modifying the fin geometric characteristics and distribution patterns in various spatial zones of the heat exchanger. Parametric analysis on the various fin structures under consideration was carried out to determine the most optimal fin structure from the perspective of the transient melting evolution and heat storage rates while maintaining the same design limitations of fin material and volume usage. The results revealed that changing the fin dimensions with the heat-flow direction results in a faster charging rate, a higher storage rate, and a more uniform temperature distribution when compared to a uniform fin size. The time required to fully charge the storage system (fully melting of the PCM) was found to be reduced by up to 10.4%, and the heat storage rate can be improved by up to 9.3% compared to the reference case of uniform fin sizes within the same fin volume limitations. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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14 pages, 3125 KiB

Open AccessArticle

In Situ Formation of Surface-Induced Oxygen Vacancies in Co₉S₈/CoO/NC as a Bifunctional Electrocatalyst for Improved Oxygen and Hydrogen Evolution Reactions

by Khalil ur Rehman, Shaista Airam, Xiangyun Lin, Jian Gao, Qiang Guo and Zhipan Zhang

Nanomaterials 2021, 11(9), 2237; https://doi.org/10.3390/nano11092237 - 30 Aug 2021

Cited by 10 | Viewed by 2911

Abstract

Creating oxygen vacancies and introducing heterostructures are two widely used strategies in Co-based oxides for their efficient electrocatalytic performance, yet both strategies have rarely been used together to design a bifunctional electrocatalyst for an efficient overall water splitting. Herein, we propose a facile [...] Read more.

Creating oxygen vacancies and introducing heterostructures are two widely used strategies in Co-based oxides for their efficient electrocatalytic performance, yet both strategies have rarely been used together to design a bifunctional electrocatalyst for an efficient overall water splitting. Herein, we propose a facile strategy to synthesize oxygen-defect-rich Co₉S₈/CoO hetero-nanoparticles with a nitrogen-doped carbon shell (ODR-Co₉S₈/CoO/NC) through the in situ conversion of heterojunction along with surface-induced oxygen vacancies, simply via annealing the precursor Co₃S₄/Co(OH)₂/ZIF-67. The as-prepared ODR-Co₉S₈/CoO/NC shows excellent bifunctional catalytic activities, featuring a low overpotential of 217 mV at 10 mA cm⁻² in the oxygen evolution reaction (OER) and 160 mV at 10 mA cm⁻² in the hydrogen evolution reaction (HER). This performance excellency is attributed to unique heterostructure and oxygen defects in Co₉S₈/CoO nanoparticles, the current work is expected to offer new insights to the design of cost-effective, noble-metal-free electrocatalysts. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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17 pages, 7517 KiB

Open AccessArticle

Analysis of Thermoelectric Energy Harvesting with Graphene Aerogel-Supported Form-Stable Phase Change Materials

by Chengbin Yu and Young Seok Song

Nanomaterials 2021, 11(9), 2192; https://doi.org/10.3390/nano11092192 - 26 Aug 2021

Cited by 21 | Viewed by 2842

Abstract

Graphene aerogel-supported phase change material (PCM) composites sustain the initial solid state without any leakage problem when they are melted. The high portion of pure PCM in the composite can absorb or release a relatively large amount of heat during heating and cooling. [...] Read more.

Graphene aerogel-supported phase change material (PCM) composites sustain the initial solid state without any leakage problem when they are melted. The high portion of pure PCM in the composite can absorb or release a relatively large amount of heat during heating and cooling. In this study, these form-stable PCM composites were used to construct a thermoelectric power generator for collecting electrical energy under the external temperature change. The Seebeck effect and the temperature difference between the two sides of the thermal device were applied for thermoelectric energy harvesting. Two different PCM composites were used to collect the thermoelectric energy harvesting due to the different phase transition field in the heating and cooling processes. The graphene nano-platelet (GNP) filler was embedded to increase the thermal conductivities of PCM composites. Maximum output current was investigated by utilizing these two PCM composites with different GNP filler ratios. The thermoelectric energy harvesting efficiencies during heating and cooling were 62.26% and 39.96%, respectively. In addition, a finite element method (FEM) numerical analysis was conducted to model the output profiles. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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13 pages, 3453 KiB

Open AccessArticle

Copper Hexacyanoferrate Thin Film Deposition and Its Application to a New Method for Diffusion Coefficient Measurement

by Jeonghun Yun, Yeongae Kim, Caitian Gao, Moobum Kim, Jae Yoon Lee, Chul-Ho Lee, Tae-Hyun Bae and Seok Woo Lee

Nanomaterials 2021, 11(7), 1860; https://doi.org/10.3390/nano11071860 - 19 Jul 2021

Cited by 3 | Viewed by 3809

Abstract

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method [...] Read more.

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method has not been well studied. In this study, we developed the following deposition method for growing copper hexacyanoferrate (CuHCFe) thin film: copper thin film is immersed into a potassium hexacyanoferrate solution, following which the redox reaction induces the spontaneous deposition of CuHCFe thin film on the copper thin film. The film grown via this method showed compatibility with conventional photolithography processes, and the micropattern of the CuHCFe thin film was successfully defined by a lift-off process. A microelectrochemical device based on the CuHCFe thin film was fabricated via micropatterning, and the sodium ion diffusivity in CuHCFe was measured. The presented thin film deposition method can deposit PBAs on any surface, including insulating substrates, and it can extend the utilization of PBA thin films to various applications. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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14 pages, 7351 KiB

Open AccessCommunication

Optimizing K_0.5Na_0.5NbO₃ Single Crystal by Engineering Piezoelectric Anisotropy

by Weixiong Li, Chunxu Chen, Guangzhong Xie and Yuanjie Su

Nanomaterials 2021, 11(7), 1753; https://doi.org/10.3390/nano11071753 - 05 Jul 2021

Cited by 4 | Viewed by 1919

Abstract

K_0.5Na_0.5NbO₃ is considered as one of the most promising lead-free piezoelectric ceramics in the field of wearable electronics because of its excellent piezoelectric properties and environmental friendliness. In this work, the temperature-dependent longitudinal piezoelectric coefficient

d_{33}^{*}

[...] Read more.

K_0.5Na_0.5NbO₃ is considered as one of the most promising lead-free piezoelectric ceramics in the field of wearable electronics because of its excellent piezoelectric properties and environmental friendliness. In this work, the temperature-dependent longitudinal piezoelectric coefficient

d_{33}^{*}

was investigated in K_0.5Na_0.5NbO₃ single crystals via the Landau–Ginzburg–Devonshire theory. Results show that the piezoelectric anisotropy varies with the temperature and the maximum of

d_{33 m a x}^{*}

deviates from the polar direction of the ferroelectric phase. In the tetragonal phase,

d_{33 m a x}^{t^{*}}

parallels with cubic polarization direction near the tetragonal-cubic transition region, and then gradually switches toward the nonpolar direction with decreasing temperatures. The maximum of

d_{33}^{o^{*}}

in the orthorhombic phase reveals a distinct varying trend in different crystal planes. As for the rhombohedral phase, slight fluctuation of the maximum of

d_{33}^{r^{*}}

was observed and delivered a more stable temperature-dependent maximum

d_{33 m a x}^{r^{*}}

and its corresponding angle θ_max in comparison with tetragonal and orthorhombic phases. This work not only sheds some light on the temperature-dependent phase transitions, but also paves the way for the optimization of piezoelectric properties in piezoelectric materials and devices. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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10 pages, 3994 KiB

Open AccessCommunication

Triboelectric Energy Harvester Based on Stainless Steel/MoS₂ and PET/ITO/PDMS for Potential Smart Healthcare Devices

by Carlos Gallardo-Vega, Octavio López-Lagunes, Omar I. Nava-Galindo, Arxel De León, Jorge Romero-García, Luz Antonio Aguilera-Cortés, Jaime Martínez-Castillo and Agustín L. Herrera-May

Nanomaterials 2021, 11(6), 1533; https://doi.org/10.3390/nano11061533 - 10 Jun 2021

Cited by 8 | Viewed by 2911

Abstract

The smart healthcare devices connected with the internet of things (IoT) for medical services can obtain physiological data of risk patients and communicate these data in real-time to doctors and hospitals. These devices require power sources with a sufficient lifetime to supply them [...] Read more.

The smart healthcare devices connected with the internet of things (IoT) for medical services can obtain physiological data of risk patients and communicate these data in real-time to doctors and hospitals. These devices require power sources with a sufficient lifetime to supply them energy, limiting the conventional electrochemical batteries. Additionally, these batteries may contain toxic materials that damage the health of patients and environment. An alternative solution to gradually substitute these electrochemical batteries is the development of triboelectric energy harvesters (TEHs), which can convert the kinetic energy of ambient into electrical energy. Here, we present the fabrication of a TEH formed by a stainless steel substrate (25 mm × 15 mm) coated with a molybdenum disulfide (MoS₂) film as top element and a polydimethylsiloxane (PDMS) film deposited on indium tin oxide coated polyethylene terephthalate substrate (PET/ITO). This TEH has a generated maximum voltage of 2.3 V and maximum output power of 112.55 μW using a load resistance of 47 kΩ and a mechanical vibration to 59.7 Hz. The proposed TEH could be used to power potential smart healthcare devices. Full article

(This article belongs to the Special Issue Highly Efficient Energy Harvesting Based on Nanomaterials)

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