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13 pages, 3256 KB

Open AccessArticle

One-Pot Synthesis of Nanostructured Ni@Ni(OH)₂ and Co-Doped Ni@Ni(OH)₂ via Chemical Reduction Method for Supercapacitor Applications

by Seungyong Eom, Jinjoo Jung and Do Hyung Kim

Materials 2023, 16(1), 380; https://doi.org/10.3390/ma16010380 - 30 Dec 2022

Cited by 6 | Viewed by 3730

Abstract

Crystalline Ni@Ni(OH)₂ (cNNH) and Co-doped cNNH were obtained via a simple one-pot hydrothermal synthesis using a modified chemical reduction method. The effect of each reagent on the synthesis of the nanostructures was investigated concerning the presence or absence of each reagent. The detailed morphology shows that both nanostructures consist of a Ni core and Ni(OH)₂ shell layer (~5 nm). Co-doping influences the morphology and suppresses the particle agglomeration of cNNH. Co-doped cNNH showed a specific capacitance of 1238 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 76%, which are significantly higher than those of cNNH. The enhanced performance of the co-doped cNNH is attributed to the reduced path length of the electrons caused by the decrease in the size of the nanostructure and the increased conductivity due to Co ions substituting Ni ions. The reported synthesis method and electrochemical behaviors of cNNH and Co-doped cNNH affirm their potential as electrochemically active materials for supercapacitor applications. Full article

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14 pages, 1510 KB

Open AccessArticle

Cobalt Nanoparticle-Embedded Nitrogen-Doped Carbon Catalyst Derived from a Solid-State Metal-Organic Framework Complex for OER and HER Electrocatalysis

by Shaik Gouse Peera, Ravindranadh Koutavarapu, Chao Liu, Gaddam Rajeshkhanna, Arunchander Asokan and Ch. Venkata Reddy

Energies 2021, 14(5), 1320; https://doi.org/10.3390/en14051320 - 1 Mar 2021

Cited by 27 | Viewed by 5158

Abstract

Electrochemical water splitting is considered a promising way of producing hydrogen and oxygen for various electrochemical energy devices. An efficient single, bi-functional electrocatalyst that can perform hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) is highly essential. In this work, Co@NC core-shell nanoparticles were synthesized via a simple, eco-friendly, solid-state synthesis process, using cobalt nitrate and with pyrazole as the N and C source. The morphological analysis of the resulting Co@NC nanoparticles was performed with a scanning and transmission electron microscope, which showed Co nanoparticles as the core and the pyrolysis of pyrazole organic ligand N-doped carbon derived shell structure. The unique Co@NC nanostructures had excellent redox sites for electrocatalysis, wherein the N-doped carbon shell exhibited superior electronic conductivity in the Co@NC catalyst. The resulting Co@NC nanocatalyst showed considerable HER and OER activity in an alkaline medium. The Co@NC catalyst exhibited HERs overpotentials of 243 and 170 mV at 10 mA∙cm⁻² on glassy carbon and Ni foam electrodes, respectively, whereas OERs were exhibited overpotentials of 450 and 452 mV at a current density of 10 and 50 mA∙cm⁻² on glassy carbon electrode and Ni foam, respectively. Moreover, the Co@NC catalyst also showed admirable durability for OERs in an alkaline medium. Full article

(This article belongs to the Special Issue Recent Advances in Electrochemical Energy Storage and Conversion Systems)

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8 pages, 2070 KB

Open AccessArticle

Self-Aligned Hierarchical ZnO Nanorod/NiO Nanosheet Arrays for High Photon Extraction Efficiency of GaN-Based Photonic Emitter

by Won-Seok Lee, Soon-Hwan Kwon, Hee-Jung Choi, Kwang-Gyun Im, Hannah Lee, Semi Oh and Kyoung-Kook Kim

Micromachines 2020, 11(4), 346; https://doi.org/10.3390/mi11040346 - 26 Mar 2020

Cited by 4 | Viewed by 3382

Abstract

Advancements in nanotechnology have facilitated the increased use of ZnO nanostructures. In particular, hierarchical and core–shell nanostructures, providing a graded refractive index change, have recently been applied to enhance the photon extraction efficiency of photonic emitters. In this study, we demonstrate self-aligned hierarchical ZnO nanorod (ZNR)/NiO nanosheet arrays on a conventional photonic emitter (C-emitter) with a wavelength of 430 nm. These hierarchical nanostructures were synthesized through a two-step hydrothermal process at low temperature, and their optical output power was approximately 17% higher than that of ZNR arrays on a C-emitter and two times higher than that of a C-emitter. These results are due to the graded index change in refractive index from the GaN layer inside the device toward the outside as well as decreases in the total internal reflection and Fresnel reflection of the photonic emitter. Full article

(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)

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16 pages, 3623 KB

Open AccessArticle

Conformational Effects of Pt-Shells on Nanostructures and Corresponding Oxygen Reduction Reaction Activity of Au-Cluster-Decorated NiO_x@Pt Nanocatalysts

by Dinesh Bhalothia, Yu-Jui Fan, Yen-Chun Lai, Ya-Tang Yang, Yaw-Wen Yang, Chih-Hao Lee and Tsan-Yao Chen

Nanomaterials 2019, 9(7), 1003; https://doi.org/10.3390/nano9071003 - 11 Jul 2019

Cited by 19 | Viewed by 5008

Abstract

Herein, ternary metallic nanocatalysts (NCs) consisting of Au clusters decorated with a Pt shell and a Ni oxide core underneath (called NPA) on carbon nanotube (CNT) support were synthesized by combining adsorption, precipitation, and chemical reduction methods. By a retrospective investigation of the physical structure and electrochemical results, we elucidated the effects of Pt/Ni ratios (0.4 and 1.0) and Au contents (2 and 9 wt.%) on the nanostructure and corresponding oxygen reduction reaction (ORR) activity of the NPA NCs. We found that the ORR activity of NPA NCs was mainly dominated by the Pt-shell thickness which regulated the depth and size of the surface decorated with Au clusters. In the optimal case, NPA-1004006 (with a Pt/Ni of 0.4 and Au of ~2 wt.%) showed a kinetic current (J_K) of 75.02 mA cm⁻² which was nearly 17-times better than that (4.37 mA cm⁻²) of the commercial Johnson Matthey-Pt/C (20 wt.% Pt) catalyst at 0.85 V vs. the reference hydrogen electrode. Such a high J_K value resulted in substantial improvements in both the specific activity (by ~53-fold) and mass activity (by nearly 10-fold) in the same benchmark target. Those scenarios rationalize that ORR activity can be substantially improved by a syngeneic effect at heterogeneous interfaces among nanometer-sized NiO_x, Pt, and Au clusters on the NC surface. Full article

(This article belongs to the Special Issue Solution Synthesis, Processing, and Applications of Semiconducting Nanomaterials)

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8 pages, 2683 KB

Open AccessArticle

Improvement of Hydrogen Desorption Characteristics of MgH₂ With Core-shell Ni@C Composites

by Cuihua An and Qibo Deng

Molecules 2018, 23(12), 3113; https://doi.org/10.3390/molecules23123113 - 28 Nov 2018

Cited by 24 | Viewed by 4376

Abstract

Magnesium hydride (MgH₂) has become popular to study in hydrogen storage materials research due to its high theoretical capacity and low cost. However, the high hydrogen desorption temperature and enthalpy as well as the depressed kinetics, have severely blocked its actual utilizations. Hence, our work introduced Ni@C materials with a core-shell structure to synthesize MgH₂-x wt.% Ni@C composites for improving the hydrogen desorption characteristics. The influences of the Ni@C addition on the hydrogen desorption performances and micro-structure of MgH₂ have been well investigated. The addition of Ni@C can effectively improve the dehydrogenation kinetics. It is interesting found that: i) the hydrogen desorption kinetics of MgH₂ were enhanced with the increased Ni@C additive amount; and ii) the dehydrogenation amount decreased with a rather larger Ni@C additive amount. The additive amount of 4 wt.% Ni@C has been chosen in this study for a balance of kinetics and amount. The MgH₂-4 wt.% Ni@C composites release 5.9 wt.% of hydrogen in 5 min and 6.6 wt.% of hydrogen in 20 min. It reflects that the enhanced hydrogen desorption is much faster than the pure MgH₂ materials (0.3 wt.% hydrogen in 20 min). More significantly, the activation energy (E_A) of the MgH₂-4 wt.% Ni@C composites is 112 kJ mol⁻¹, implying excellent dehydrogenation kinetics. Full article

(This article belongs to the Special Issue Advances in Hydrogen Storage Materials Research)

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14 pages, 5163 KB

Open AccessArticle

In Situ Synthesis and Electrophoretic Deposition of NiO/Ni Core-Shell Nanoparticles and Its Application as Pseudocapacitor

by Joaquin Yus, Begoña Ferrari, Antonio Javier Sanchez-Herencia, Alvaro Caballero, Julian Morales and Zoilo Gonzalez

Coatings 2017, 7(11), 193; https://doi.org/10.3390/coatings7110193 - 8 Nov 2017

Cited by 17 | Viewed by 7751

Abstract

A simple, low cost and transferable colloidal processing method and the subsequent heat treatment has been optimized to prepare binder-free electrodes for their application in supercapacitors. NiO/Ni core–shell hybrid nanostructures have been synthetized by heterogeneous precipitation of metallic Ni nanospheres onto NiO nanoplatelets as seed surfaces. The electrophoretic deposition (EPD) has been used to shape the electroactive material onto 3D substrates such as Ni foams. The method has allowed us to control the growth and the homogeneity of the NiO/Ni coatings. The presence of metallic Nickel in the microstructure and the optimization of the thermal treatment have brought several improvements in the electrochemical response due to the connectivity of the final microstructure. The highest specific capacitance value has been obtained using a thermal treatment of 325 °C during 1 h in Argon. At this temperature, necks formed among ceramic-metallic nanoparticles preserve the structural integrity of the microstructure avoiding the employment of binders to enhance their connectivity. Thus, a compromise between porosity and connectivity should be established to improve electrochemical performance. Full article

(This article belongs to the Special Issue Electrophoretic Deposition)

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12 pages, 10590 KB

Open AccessArticle

Core/Shell Structure of Ni/NiO Encapsulated in Carbon Nanosphere Coated with Few- and Multi-Layered Graphene: Synthesis, Mechanism and Application

by Ferial Ghaemi, Luqman Chuah Abdullah and Paridah Tahir

Polymers 2016, 8(11), 381; https://doi.org/10.3390/polym8110381 - 9 Nov 2016

Cited by 9 | Viewed by 7788

Abstract

This paper focuses on the synthesis and mechanism of carbon nanospheres (CNS) coated with few- and multi-layered graphene (FLG, MLG). The graphitic carbon encapsulates the core/shell structure of the Ni/NiO nanoparticles via the chemical vapor deposition (CVD) method. The application of the resulting CNS and hybrids of CNS-FLG and CNS-MLG as reinforcement nanofillers in a polypropylene (PP) matrix were studied from the aspects of mechanical and thermal characteristics. In this research, to synthesize carbon nanostructures, nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and acetylene (C₂H₂) were used as the catalyst source and carbon source, respectively. Besides, the morphology, structure and graphitization of the resulting carbon nanostructures were investigated. On the other hand, the mechanisms of CNS growth and the synthesis of graphene sheets on the CNS surface were studied. Finally, the mechanical and thermal properties of the CNS/PP, CNS-FLG/PP, and CNS-MLG/PP composites were analyzed by applying tensile test and thermogravimetric analysis (TGA), respectively. Full article

(This article belongs to the Special Issue Polymeric Fibers)

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