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13 pages, 1447 KiB

Open AccessArticle

Dual-Functional Solar-to-Steam Generation and SERS Detection Substrate Based on Plasmonic Nanostructure

by Ba Thong Trinh, Hanjun Cho, Deunchan Lee, Oleksii Omelianovych, Taehun Kim, Sy Khiem Nguyen, Ho-Suk Choi, Hongki Kim and Ilsun Yoon

Nanomaterials 2023, 13(6), 1003; https://doi.org/10.3390/nano13061003 - 10 Mar 2023

Cited by 6 | Viewed by 1811

Abstract

Solar-to-steam (STS) generation based on plasmonic materials has attracted significant attention as a green method for producing fresh water. Herein, a simple in situ method is introduced to fabricate Au nanoparticles (AuNPs) on cellulose filter papers as dual-functional substrates for STS generation and [...] Read more.

Solar-to-steam (STS) generation based on plasmonic materials has attracted significant attention as a green method for producing fresh water. Herein, a simple in situ method is introduced to fabricate Au nanoparticles (AuNPs) on cellulose filter papers as dual-functional substrates for STS generation and surface-enhanced Raman spectroscopy (SERS) sensing. The substrates exhibit 90% of broadband solar absorption between 350 and 1800 nm and achieve an evaporation rate of 0.96 kg·m⁻²·h⁻¹ under 1-sun illumination, room temperature of 20 °C, and relative humidity of 40%. The STS generation of the substrate is stable during 30 h continuous operation. Enriched SERS hotspots between AuNPs endow the substrates with the ability to detect chemical contamination in water with ppb limits of detection for rhodamine 6G dye and melamine. To demonstrate dual-functional properties, the contaminated water was analyzed with SERS and purified by STS. The purified water was then analyzed with SERS to confirm its purity. The developed substrate can be an improved and suitable candidate for fresh water production and qualification. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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19 pages, 4737 KiB

Open AccessEditor’s ChoiceArticle

Effective Antibacterial/Photocatalytic Activity of ZnO Nanomaterials Synthesized under Low Temperature and Alkaline Conditions

by Sujeong Kim, Hyerim Park, Sadanand Pandey, Daewon Jeong, Chul-Tae Lee, Jeong Yeon Do, Sun-Min Park and Misook Kang

Nanomaterials 2022, 12(24), 4417; https://doi.org/10.3390/nano12244417 - 11 Dec 2022

Cited by 8 | Viewed by 1796

Abstract

The purpose of this study was to evaluate the surface properties of ZnO nanomaterials based on their ability to photodegrade methyl blue dye (MB) and to show their antibacterial properties against different types of Gram-positive bacteria (Bacillus manliponensis, Micrococcus luteus, [...] Read more.

The purpose of this study was to evaluate the surface properties of ZnO nanomaterials based on their ability to photodegrade methyl blue dye (MB) and to show their antibacterial properties against different types of Gram-positive bacteria (Bacillus manliponensis, Micrococcus luteus, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). In this study, ZnO nanomaterials were synthesized rapidly and easily in the presence of 1–4 M NaOH at a low temperature of 40 °C within 4 h. It was found that the ZnO nanomaterials obtained from the 1.0 M (ZnO–1M) and 2.0 M (ZnO–2M) aqueous solutions of NaOH had spherical and needle-shaped forms, respectively. As the concentration of NaOH increased, needle thickness increased and the particles became rod-like. Although the ZnO nanomaterial shapes were different, the bandgap size remained almost unchanged. However, as the NaOH concentration increased, the energy position of the conduction band shifted upward. Photo current curves and photoluminescence intensities suggested that the recombination between photoexcited electrons and holes was low in the ZnO–4M materials prepared in 4.0 M NaOH solution; however, charge transfer was easy. ∙O₂⁻ radicals were generated more than ∙OH radicals in ZnO–4M particles, showing stronger antibacterial activity against both Gram-positive and Gram-negative bacteria and stronger decomposition ability on MB dye. The results of this study suggest that on the ZnO nanomaterial surface, ∙O₂⁻ radicals generated are more critical for antibacterial activity than particle shape. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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19 pages, 7500 KiB

Open AccessArticle

Electrochemical Performance of Layer-Structured Ni_0.8Co_0.1Mn_0.1O₂ Cathode Active Materials Synthesized by Carbonate Co-Precipitation

by Byung Hyun Park, Taeseong Kim, Hyerim Park, Youngku Sohn, Jongmin Shin and Misook Kang

Nanomaterials 2022, 12(20), 3610; https://doi.org/10.3390/nano12203610 - 14 Oct 2022

Cited by 1 | Viewed by 2599

Abstract

The layered Ni-rich NiCoMn (NCM)-based cathode active material Li[Ni_xCo_(1−x)/2Mn_(1−x)/2]O₂ (x ≥ 0.6) has the advantages of high energy density and price competitiveness over an LiCoO₂-based material. Additionally, NCM is beneficial in terms of its [...] Read more.

The layered Ni-rich NiCoMn (NCM)-based cathode active material Li[Ni_xCo_(1−x)/2Mn_(1−x)/2]O₂ (x ≥ 0.6) has the advantages of high energy density and price competitiveness over an LiCoO₂-based material. Additionally, NCM is beneficial in terms of its increasing reversible discharge capacity with the increase in Ni content; however, stable electrochemical performance has not been readily achieved because of the cation mixing that occurs during its synthesis. In this study, various layer-structured Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂ materials were synthesized, and their electrochemical performances were investigated. A NiCoMnCO₃ precursor, prepared using carbonate co-precipitation with Li₂CO₃ as the lithium source and having a sintering temperature of 850 °C, sintering time of 25 h, and metal to Li molar ratio of 1.00–1.05 were found to be the optimal parameters/conditions for the preparation of Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂. The material exhibited a discharge capacity of 160 mAhg⁻¹ and capacity recovery rate of 95.56% (from a 5.0–0.1 C-rate). Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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18 pages, 6474 KiB

Open AccessFeature PaperArticle

Interface Engineered V-Zn Hybrids: Electrocatalytic and Photocatalytic CO₂ Reductions

by Seon Young Hwang, Hye Ji Jang, Young Jun Kim, Ju Young Maeng, Go Eun Park, Seo Young Yang, Choong Kyun Rhee and Youngku Sohn

Nanomaterials 2022, 12(16), 2758; https://doi.org/10.3390/nano12162758 - 11 Aug 2022

Cited by 3 | Viewed by 1519

Abstract

V-Zn hybrids have widely been used as catalyst materials in the environment and as energy. Herein, V-Zn hybrid electrodes were prepared by the hydrothermal and sputter-deposition methods using a Zn foil support. Their electrocatalytic CO₂ reduction (EC CO₂ RR) performances were [...] Read more.

V-Zn hybrids have widely been used as catalyst materials in the environment and as energy. Herein, V-Zn hybrid electrodes were prepared by the hydrothermal and sputter-deposition methods using a Zn foil support. Their electrocatalytic CO₂ reduction (EC CO₂ RR) performances were tested under various applied potentials, different electrolytes, and concentrations before and after thermal treatment of the demonstrated electrode. Gas and liquid products were confirmed by gas chromatography and nuclear magnetic resonance spectroscopy, respectively. For V-Zn electrode by hydrothermal method produced mainly syngas (CO and H₂) with tunable ratio by varying applied potential. Minor products include CH₄, C₂H₄, and C₂H₆. A liquid product of formate showed a Faradaic efficiency (FE) of 2%. EC CO₂ RR efficiency for CO, CH₄, and formate was best in 0.2 M KHCO₃ electrolyte condition. CO and formate were further increased by photoirradiation and Nafion-treated electrode. Formate and CH₄ productions were significantly increased by thermal treatment of the V-Zn electrode. CO production was diminished for the V-Zn electrode by sputter deposition but was recovered by thermal treatment. Photocatalytic CO₂ RR was tested to find that RR products include CH₃OH, CO, CH₄, C₂H₄, and C₂H₆. Interestingly long-chain hydrocarbons (C_nH_2n and C_nH_2n+2, where n = 3–6) were first observed under mild conditions. The long-chain formation was understood by Fisher-Tropsch (F-T) synthesis. Alkenes were observed to be more produced than alkanes unlike in the conventional F-T synthesis. The present new findings provide useful clues for the development of hybrid electro-and photo-catalysts tested under various experimental conditions in energy and environment. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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19 pages, 7857 KiB

Open AccessArticle

Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO₂/Ti Nanostructures

by Hye Ji Jang, So Jeong Park, Ju Hyun Yang, Sung-Min Hong, Choong Kyun Rhee and Youngku Sohn

Nanomaterials 2021, 11(8), 1904; https://doi.org/10.3390/nano11081904 - 24 Jul 2021

Cited by 4 | Viewed by 3403

Abstract

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO₂/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started [...] Read more.

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO₂/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started to thermally decompose at around 350 °C and was converted to the cubic phase Co₃O₄. The head of the bean sprout structure was observed to be Co₃O₄, while the stem showed a crystal structure of rutile TiO₂ grown from the metallic Ti support. Cu sputter-deposited Co-TiO₂/Ti nanostructures were also prepared for photocatalytic and electrocatalytic CO₂ reduction performances, as well as electrochemical oxygen reaction (OER). Gas chromatography results after photocatalytic CO₂ reduction showed that CH₃OH, CO and CH₄ were produced as major products with the highest MeOH selectivity of 64% and minor C₂ compounds of C₂H₂, C₂H₄ and C₂H₆. For electrocatalytic CO₂ reduction, CO, CH₄ and C₂H₄ were meaningfully detected, but H₂ was dominantly produced. The amounts were observed to be dependent on the Cu deposition amount. Electrochemical OER performances in 0.1 M KOH electrolyte exhibited onset overpotentials of 330–430 mV (vs. RHE) and Tafel slopes of 117–134 mV/dec that were dependent on Cu-loading thickness. The present unique results provide useful information for synthesis of bean sprout-like Co-TiO₂/Ti hybrid nanostructures and their applications to CO₂ reduction and electrochemical water splitting in energy and environmental fields. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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20 pages, 4300 KiB

Open AccessArticle

CO Oxidation at Near-Ambient Temperatures over TiO₂-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO₂ Morphology

by Abdallah F. Zedan, Safa Gaber, Amina S. AlJaber and Kyriaki Polychronopoulou

Nanomaterials 2021, 11(7), 1675; https://doi.org/10.3390/nano11071675 - 25 Jun 2021

Cited by 7 | Viewed by 2546

Abstract

Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the [...] Read more.

Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the CO oxidation reaction using a Pd-Cu/TiO₂ catalyst. Pd-Cu catalysts supported on TiO₂ were synthesized with wet chemical approaches and their catalytic activities for CO oxidation reaction were evaluated. The physicochemical properties of the prepared catalysts were studied using standard characterization tools including SEM, EDX, XRD, XPS, and Raman. The effects of the nanointerface between Pd and Cu and the morphology of the TiO₂ support were investigated using three different-shaped TiO₂ nanoparticles, namely spheres, nanotubes, and nanowires. The Pd catalysts that are modified through nanointerfacing with Cu and supported on TiO₂ nanowires demonstrated the highest CO oxidation rates, reaching 100% CO conversion at temperature regime down to near-ambient temperatures of ~45 °C, compared to 70 °C and 150 °C in the case of pure Pd and pure Cu counterpart catalysts on the same support, respectively. The optimized Pd-Cu/TiO₂ nanowires nanostructured system could serve as efficient and durable catalyst for CO oxidation at near-ambient temperature. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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10 pages, 3211 KiB

Open AccessEditor’s ChoiceArticle

Improved Photoelectrochemical Performance of MoS₂ through Morphology-Controlled Chemical Vapor Deposition Growth on Graphene

by Dong-Bum Seo, Tran Nam Trung, Sung-Su Bae and Eui-Tae Kim

Nanomaterials 2021, 11(6), 1585; https://doi.org/10.3390/nano11061585 - 17 Jun 2021

Cited by 13 | Viewed by 2915

Abstract

The morphology of MoS₂ nanostructures was manipulated from thin films to vertically aligned few-layer nanosheets on graphene, in a controllable and practical manner, using metalorganic chemical vapor deposition. The effects of graphene layer and MoS₂ morphology on photoelectrochemical (PEC) performance were [...] Read more.

The morphology of MoS₂ nanostructures was manipulated from thin films to vertically aligned few-layer nanosheets on graphene, in a controllable and practical manner, using metalorganic chemical vapor deposition. The effects of graphene layer and MoS₂ morphology on photoelectrochemical (PEC) performance were systematically studied on the basis of electronic structure and transitions, carrier dynamic behavior, and PEC measurements. The heterojunction quality of the graphene/vertical few-layer MoS₂ nanosheets was ensured by low-temperature growth at 250−300 °C, resulting in significantly improved charge transfer properties. As a result, the PEC photocurrent density and photoconversion efficiency of the few-layer MoS₂ nanosheets significantly increased upon the insertion of a graphene layer. Among the graphene/MoS₂ samples, the few-layer MoS₂ nanosheet samples exhibited shorter carrier lifetimes and smaller charge transfer resistances than the thin film samples, suggesting that vertically aligned nanosheets provide highly conductive edges as an efficient pathway for photo-generated carriers and have better electronic contact with graphene. In addition, the height of vertical MoS₂ nanosheets on graphene should be controlled within the carrier diffusion length (~200 nm) to achieve the optimal PEC performance. These results can be utilized effectively to exploit the full potential of two-dimensional MoS₂ for various PEC applications. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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8 pages, 3754 KiB

Open AccessArticle

Efficient Visible-Light Photocatalysis of TiO_2-δ Nanobelts Utilizing Self-Induced Defects and Carbon Doping

by Dong-Bum Seo, Sung-Su Bae and Eui-Tae Kim

Nanomaterials 2021, 11(6), 1377; https://doi.org/10.3390/nano11061377 - 23 May 2021

Cited by 5 | Viewed by 2243

Abstract

Efficient visible-light photocatalysis was realized by exploring self-induced defect states, including the abundant surface states of TiO_2-δ nanobelts synthesized through metal–organic chemical vapor deposition (MOCVD). The TiO_2-δ nanobelts exhibited two strong defect-induced absorption peaks at 2.91 and 1.92 eV, overlapping with [...] Read more.

Efficient visible-light photocatalysis was realized by exploring self-induced defect states, including the abundant surface states of TiO_2-δ nanobelts synthesized through metal–organic chemical vapor deposition (MOCVD). The TiO_2-δ nanobelts exhibited two strong defect-induced absorption peaks at 2.91 and 1.92 eV, overlapping with the conduction band states so that photoexcited carriers can contribute effectively for the photocatalysis reaction. To further enhance visible-light photocatalytic activity, carbon atoms, the by-product of the MOCVD reaction, were self-doped at the judiciously determined growth conditions. The resulting visible-light photocatalysis suggests that the large surface area and consequent high concentration of the surface states of the TiO_2-δ nanobelts can be effectively utilized in a wide range of photocatalysis applications. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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17 pages, 5371 KiB

Open AccessArticle

Thermal CO Oxidation and Photocatalytic CO₂ Reduction over Bare and M-Al₂O₃ (M = Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) Cotton-Like Nanosheets

by Hee Jung Yoon, Ju Hyun Yang, So Jeong Park and Youngku Sohn

Nanomaterials 2021, 11(5), 1278; https://doi.org/10.3390/nano11051278 - 13 May 2021

Cited by 13 | Viewed by 3055

Abstract

Aluminum oxide (Al₂O₃) has abundantly been used as a catalyst, and its catalytic activity has been tailored by loading transition metals. Herein, γ-Al₂O₃ nanosheets were prepared by the solvothermal method, and transition metals (M = Co, [...] Read more.

Aluminum oxide (Al₂O₃) has abundantly been used as a catalyst, and its catalytic activity has been tailored by loading transition metals. Herein, γ-Al₂O₃ nanosheets were prepared by the solvothermal method, and transition metals (M = Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) were loaded onto the nanosheets. Big data sets of thermal CO oxidation and photocatalytic CO₂ reduction activities were fully examined for the transition metal-loaded Al₂O₃ nanosheets. Their physicochemical properties were examined by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction crystallography, and X-ray photoelectron spectroscopy. It was found that Rh, Pd, Ir, and Pt-loading showed a great enhancement in CO oxidation activity while other metals negated the activity of bare Al₂O₃ nanosheets. Rh-Al₂O₃ showed the lowest CO oxidation onset temperature of 172 °C, 201 °C lower than that of bare γ-Al₂O₃. CO₂ reduction experiments were also performed to show that CO, CH₃OH, and CH₄ were common products. Ag-Al₂O₃ nanosheets showed the highest performances with yields of 237.3 ppm for CO, 36.3 ppm for CH₃OH, and 30.9 ppm for CH₄, 2.2×, 1.2×, and 1.6× enhancements, respectively, compared with those for bare Al₂O₃. Hydrogen production was found to be maximized to 20.7 ppm during CO₂ reduction for Rh-loaded Al₂O₃. The present unique pre-screening test results provided very useful information for the selection of transition metals on Al₂O₃-based energy and environmental catalysts. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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11 pages, 3271 KiB

Open AccessArticle

Facile Strategy for Mass Production of Pt Catalysts for Polymer Electrolyte Membrane Fuel Cells Using Low-Energy Electron Beam

by Jongmin Shin, Jiho Min, Youngjin Kim, Jin Hee Lee, Geunseok Chai and Namgee Jung

Nanomaterials 2020, 10(11), 2216; https://doi.org/10.3390/nano10112216 - 6 Nov 2020

Cited by 4 | Viewed by 2274

Abstract

There are so many variables affecting the large-scale chemical synthesis of nanoparticles that mass production remains a challenge. Here, using a high-efficiency compact electron beam generator irradiating a low-energy electron beam, we fabricate carbon-supported Pt nanoparticles (Pt/C) in an open chamber to present [...] Read more.

There are so many variables affecting the large-scale chemical synthesis of nanoparticles that mass production remains a challenge. Here, using a high-efficiency compact electron beam generator irradiating a low-energy electron beam, we fabricate carbon-supported Pt nanoparticles (Pt/C) in an open chamber to present the applicability of an electron beam to the mass production of metal nanocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). The amount of dispersants (glycerol) and radical scavengers (isopropyl alcohol, IPA), the most important factors in the electron beam-induced fabrication process, is systematically controlled to find the conditions for the synthesis of the particle structure suitable for PEMFC applications. Furthermore, the effects of the structural changes on the electrochemical properties of the catalysts are thoroughly investigated. Through in-depth studies, it is clearly revealed that while dispersants control the nucleation step of monomers affecting the degree of dispersion of nanoparticles, radical scavengers with strong oxidizing power have an effect on the particle growth rate. Therefore, this study is expected to present the applicability of low-energy electron beam to the mass production of metal nanocatalysts for PEMFCs, and to provide insights into the fabrication of nanoparticles using low-energy electron beams. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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14 pages, 5588 KiB

Open AccessArticle

Photocatalytic CO₂ Reduction and Electrocatalytic H₂ Evolution over Pt(0,II,IV)-Loaded Oxidized Ti Sheets

by Ju Hyun Yang, So Jeong Park, Choong Kyun Rhee and Youngku Sohn

Nanomaterials 2020, 10(10), 1909; https://doi.org/10.3390/nano10101909 - 24 Sep 2020

Cited by 10 | Viewed by 2661

Abstract

Energy recycling and production using abundant atmospheric CO₂ and H₂O have increasingly attracted attention for solving energy and environmental problems. Herein, Pt-loaded Ti sheets were prepared by sputter-deposition and Pt⁴⁺-reduction methods, and their catalytic activities on both photocatalytic [...] Read more.

Energy recycling and production using abundant atmospheric CO₂ and H₂O have increasingly attracted attention for solving energy and environmental problems. Herein, Pt-loaded Ti sheets were prepared by sputter-deposition and Pt⁴⁺-reduction methods, and their catalytic activities on both photocatalytic CO₂ reduction and electrochemical hydrogen evolution were fully demonstrated. The surface chemical states were completely examined by X-ray photoelectron spectroscopy before and after CO₂ reduction. Gas chromatography confirmed that CO, CH₄, and CH₃OH were commonly produced as CO₂ reduction products with total yields up to 87.3, 26.9, and 88.0 μmol/mol, respectively for 700 °C-annealed Ti under UVC irradiation for 13 h. Pt-loading commonly negated the CO₂ reduction yields, but CH₄ selectivity was increased. Electrochemical hydrogen evolution reaction (HER) activity showed the highest activity for sputter-deposited Pt on 400 °C-annealed Ti with a HER current density of 10.5 mA/cm² at −0.5 V (vs. Ag/AgCl). The activities of CO₂ reduction and HER were found to be significantly dependent on both the nature of Ti support and the oxidation states (0,II,IV) of overlayer Pt. The present result could provide valuable information for designing efficient Pt/Ti-based CO₂ recycle photocatalysts and electrochemical hydrogen production catalysts. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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19 pages, 6703 KiB

Open AccessArticle

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo₂O₄ Spinel Structure

by Hyerim Park, Byung Hyun Park, Jaeyoung Choi, Seyeon Kim, Taesung Kim, Young-Sang Youn, Namgyu Son, Jae Hong Kim and Misook Kang

Nanomaterials 2020, 10(9), 1727; https://doi.org/10.3390/nano10091727 - 31 Aug 2020

Cited by 43 | Viewed by 5408

Abstract

In order to improve the electrochemical performance of the NiCo₂O₄ material, Ni ions were partially substituted with Cu²⁺ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni_1−xCu_xCo₂O [...] Read more.

In order to improve the electrochemical performance of the NiCo₂O₄ material, Ni ions were partially substituted with Cu²⁺ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni_1−xCu_xCo₂O₄ electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo₂O₄/GF, Ni_0.875Cu_0.125Co₂O₄/GF, Ni_0.75Cu_0.25Co₂O₄/GF, Ni_0.625Cu_0.375Co₂O₄/GF, and Ni_0.5Cu_0.5Co₂O₄/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu²⁺ ions were substituted, the electrochemical performances of the NiCo₂O₄-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni_0.75Cu_0.25Co₂O₄/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm⁻² was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec⁻¹ was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni_1−xCu_xCo₂O₄/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni_0.75Cu_0.25Co₂O₄/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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Review

Jump to: Research

23 pages, 3003 KiB

Open AccessReview

Recent Progress of Metal-Organic Frameworks and Metal-Organic Frameworks-Based Heterostructures as Photocatalysts

by Mohammad Mansoob Khan, Ashmalina Rahman and Shaidatul Najihah Matussin

Nanomaterials 2022, 12(16), 2820; https://doi.org/10.3390/nano12162820 - 17 Aug 2022

Cited by 21 | Viewed by 3839

Abstract

In the field of photocatalysis, metal-organic frameworks (MOFs) have drawn a lot of attention. MOFs have a number of advantages over conventional semiconductors, including high specific surface area, large number of active sites, and an easily tunable porous structure. In this perspective review, [...] Read more.

In the field of photocatalysis, metal-organic frameworks (MOFs) have drawn a lot of attention. MOFs have a number of advantages over conventional semiconductors, including high specific surface area, large number of active sites, and an easily tunable porous structure. In this perspective review, different synthesis methods used to prepare MOFs and MOFs-based heterostructures have been discussed. Apart from this, the application of MOFs and MOFs-based heterostructures as photocatalysts for photocatalytic degradation of different types of pollutants have been compiled. This paper also highlights the different strategies that have been developed to modify and regulate pristine MOFs for improved photocatalytic performance. The MOFs modifications may result in better visible light absorption, effective photo-generated charge carriers (e⁻/h⁺), separation and transfer as well as improved recyclability. Despite that, there are still many obstacles and challenges that need to be addressed. In order to meet the requirements of using MOFs and MOFs-based heterostructures in photocatalysis for low-cost practical applications, future development and prospects have also been discussed. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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25 pages, 3433 KiB

Open AccessReview

Transition Metal-Based 2D Layered Double Hydroxide Nanosheets: Design Strategies and Applications in Oxygen Evolution Reaction

by Birhanu Bayissa Gicha, Lemma Teshome Tufa, Sohyun Kang, Mahendra Goddati, Eneyew Tilahun Bekele and Jaebeom Lee

Nanomaterials 2021, 11(6), 1388; https://doi.org/10.3390/nano11061388 - 25 May 2021

Cited by 29 | Viewed by 5090

Abstract

Water splitting driven by renewable energy sources is considered a sustainable way of hydrogen production, an ideal fuel to overcome the energy issue and its environmental challenges. The rational design of electrocatalysts serves as a critical point to achieve efficient water splitting. Layered [...] Read more.

Water splitting driven by renewable energy sources is considered a sustainable way of hydrogen production, an ideal fuel to overcome the energy issue and its environmental challenges. The rational design of electrocatalysts serves as a critical point to achieve efficient water splitting. Layered double hydroxides (LDHs) with two-dimensionally (2D) layered structures hold great potential in electrocatalysis owing to their ease of preparation, structural flexibility, and tenability. However, their application in catalysis is limited due to their low activity attributed to structural stacking with irrational electronic structures, and their sluggish mass transfers. To overcome this challenge, attempts have been made toward adjusting the morphological and electronic structure using appropriate design strategies. This review highlights the current progress made on design strategies of transition metal-based LDHs (TM-LDHs) and their application as novel catalysts for oxygen evolution reactions (OERs) in alkaline conditions. We describe various strategies employed to regulate the electronic structure and composition of TM-LDHs and we discuss their influence on OER performance. Finally, significant challenges and potential research directions are put forward to promote the possible future development of these novel TM-LDHs catalysts. Full article

(This article belongs to the Special Issue Synthesis of Nanomaterials as Electrocatalysis, Photocatalysis and Thermal Catalysis)

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