Induced Superaerophobicity onto a Non-superaerophobic Catalytic Surface for Enhanced Hydrogen Evolution Reaction

Akbar, Kamran,Hussain, Sajjad,Truong, Linh,Roy, Sanjib Baran,Jeon, Jae Ho,Jerng, Sahng-Kyoon,Kim, Minsoo,Yi, Yeonjin,Jung, Jongwan,Chun, Seung-Hyun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.50

<P>Despite tremendous progress in the development of novel electrocatalysts for hydrogen evolution reaction (HER), the accumulation, of hydrogen gas bubbles produced on the catalyst surface has been rather poorly addressed. The bubbles block the surface of the electrode, thus resulting in poor performance even when excellent electrocatalysts are used. In this study, we show that vertically grown graphene nanohills (VGNHs) possess an excellent capability to quickly disengage the produced hydrogen gas bubbles from the electrode surface, and thus exhibit superaerophobic properties. To compensate for the poor electrolytic properties of graphene toward HER, the graphene surface was modified with WS2 nanoparticles to accelerate the water-splitting process by using this hybrid catalyst (VGNHs-WS2). For comparison purposes, WS2 nanoparticles were also deposited on the flat graphene (FG) surface. Because of its superior superaerophobic properties, VGNHs-WS2 outperformed FG-WS2 in terms of both catalytic activity toward the HER and superaerophobicity. Furthermore, VGNHs-WS2 exhibited a low onset potential (36 mV compared to 288 mV for FG-WS2) and long-term stability in the HER over an extended period of 20 h. This study provides an efficient way to utilize highly conductive and superaerophobic VGNHs as support materials for intrinsic semiconductors, such as WS2, to simultaneously achieve superaerophobicity and high catalytic activity.</P>

Superaerophobic graphene nano-hills for direct hydrazine fuel cells

Akbar, Kamran,Kim, Jung Hwa,Lee, Zonghoon,Kim, Minsoo,Yi, Yeonjin,Chun, Seung-Hyun Nature Publishing Group 2017 NPG Asia Materials Vol.9 No.-

<P>Hydrazine fuel-cell technology holds great promise for clean energy, not only because of the greater energy density of hydrazine compared to hydrogen but also due to its safer handling owing to its liquid state. However, current technologies involve the use of precious metals (such as platinum) for hydrazine oxidation, which hinders the further application of hydrazine fuel-cell technologies. In addition, little attention has been devoted to the management of gas, which tends to become stuck on the surface of the electrode, producing overall poor electrode efficiencies. In this study, we utilized a nano-hill morphology of vertical graphene, which efficiently resolves the issue of the accumulation of gas bubbles on the electrode surface by providing a nano-rough-edged surface that acts as a superaerophobic electrode. The growth of the vertical graphene nano-hills was achieved and optimized by a scalable plasma-enhanced chemical vapor deposition method. The resulting metal-free graphene-based electrode showed the lowest onset potential (-0.42 V vs saturated calomel electrode) and the highest current density of all the carbon-based materials reported previously for hydrazine oxidation.</P>

Digital image-based plant phenotyping: a review

Mohammad Kamran Omari,이재영,Mohammad Akbar Faqeerzada,Rahul Joshi,박은수,조병관 충남대학교 농업과학연구소 2020 Korean Journal of Agricultural Science Vol.47 No.1

With the current rapid growth and increase in the world’s population, the demand for nutritious food and fibers and fuel will increase. Therefore, there is a serious need for the use of breeding programs with the full potential to produce high-yielding crops. However, existing breeding techniques are unable to meet the demand criteria even though genotyping techniques have significantly progressed with the discovery of molecular markers and nextgeneration sequencing tools, and conventional phenotyping techniques lag behind. Wellorganized high-throughput plant phenotyping platforms have been established recently and developed in different parts of the world to address this problem. These platforms use several imaging techniques and technologies to acquire data for quantitative studies related to plant growth, yield, and adaptation to various types of abiotic or biotic stresses (drought, nutrient, disease, salinity, etc.). Phenotyping has become an impediment in genomics studies of plant breeding. In recent years, phenomics, an emerging domain that entails characterizing the full set of phenotypes in a given species, has appeared as a novel approach to enhance genomics data in breeding programs. Imaging techniques are of substantial importance in phenomics. In this study, the importance of current imaging technologies and their applications in plant phenotyping are reviewed, and their advantages and limitations in phenomics are highlighted.

WS2/CoSe2 heterostructure: A designed structure as catalysts for enhanced hydrogen evolution performance

Sajjad Hussain,Kamran Akbar,Dhanasekaran Vikraman,Hailiang Liu,천승현,정종완 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-

The development of hydrogen-evolving catalysts based on transition metal dichalchogenides (TMDs) is receiving a great attention for practical application of water-splitting devices and fuel cells due to their high electrocatalytic activity. Herein, we synthesized tungsten disulfide (WS2)/cobalt diselenide (CoSe2) hybrid catalyst for hydrogen evolution reaction (HER). CoSe2 films were first deposited via electrodeposition of Co and followed by selenization process. And, the surface of the synthesized CoSe2 films was covered with WS2 via combined process of sputtering and sulfurization. In acidic media, the WS2/CoSe2 heterostructure catalyst exhibited fast hydrogen evolution kinetics of onset potential and Tafel slope were at 95 mV and 44 mV decade−1, respectively with the excellent electrocatalytic stability over 20 h. WS2/CoSe2 heterostructure electrode demonstrates an excellent HER activity and long-term stability owing to their abundant active edge sites, and the strong chemical and electronic coupling between the CoSe2 and WS2.

Direct synthesis of thickness-tunable MoS₂ quantum dot thin layers: Optical, structural and electrical properties and their application to hydrogen evolution

Vikraman, Dhanasekaran,Akbar, Kamran,Hussain, Sajjad,Yoo, Geonwook,Jang, Ji-Yun,Chun, Seung-Hyun,Jung, Jongwan,Park, Hui Joon Elsevier 2017 Nano energy Vol.35 No.-

<P><B>Abstract</B></P> <P>We report a layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline molybdenum disulfide (MoS<SUB>2</SUB>) thin layers. For the first time, a facile, cost effective, and mass-scalable direct synthesis approach, based on a chemical bath deposition, is designed for quantum dot(QD)-based MoS<SUB>2</SUB> layers using (NH<SUB>4</SUB>)<SUB>6</SUB>Mo<SUB>7</SUB>O<SUB>24</SUB> and thiourea (CH<SUB>4</SUB>N<SUB>2</SUB>S) as precursors. Using this process, the uniformity of large area thin layer can be retained, and the applicability to various substrates can provide great opportunities in the fabrication of various atomically thin layered structures. The structural and optical properties of the MoS<SUB>2</SUB> QD layers are systematically investigated. Raman, AFM and TEM analyses confirm the formation of continuous and crystalline bi-, tri- and few-layered MoS<SUB>2</SUB>. Their electrical properties are evaluated by bottom-gate FETs, and a field-effect mobility value of ~1.06cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and a current on/off ratio in the order of ~ 10<SUP>5</SUP> are obtained. Particularly, MoS<SUB>2</SUB> prepared as a thin film consisting QD structures of grains shows novel electrocatalytic property. MoS<SUB>2</SUB> QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by Tafel slope (94mVdecade<SUP>−1</SUP>), exchange current density (1.91×10<SUP>-1</SUP> mAcm<SUP>−2</SUP>) and long-term durability for 20h. Our approach opens new avenues for the design and synthesis of functional MoS<SUB>2</SUB> layers for energy harvesting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline MoS<SUB>2</SUB> thin layers is reported. </LI> <LI> This approach is applicable to various substrates. </LI> <LI> The structural and optical properties of the synthesized MoS<SUB>2</SUB> layers are systematically investigated. </LI> <LI> The electrical properties of the synthesized MoS<SUB>2</SUB> layers are evaluated by bottom-gate FETs. </LI> <LI> MoS<SUB>2</SUB> QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

WS₂/CoSe₂ heterostructure: A designed structure as catalysts for enhanced hydrogen evolution performance

Hussain, Sajjad,Akbar, Kamran,Vikraman, Dhanasekaran,Liu, Hailiang,Chun, Seung-Hyun,Jung, Jongwan THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.65 No.-

<P><B>Abstract</B></P> <P>The development of hydrogen-evolving catalysts based on transition metal dichalchogenides (TMDs) is receiving a great attention for practical application of water-splitting devices and fuel cells due to their high electrocatalytic activity. Herein, we synthesized tungsten disulfide (WS<SUB>2</SUB>)/cobalt diselenide (CoSe<SUB>2</SUB>) hybrid catalyst for hydrogen evolution reaction (HER). CoSe<SUB>2</SUB> films were first deposited via electrodeposition of Co and followed by selenization process. And, the surface of the synthesized CoSe<SUB>2</SUB> films was covered with WS<SUB>2</SUB> via combined process of sputtering and sulfurization. In acidic media, the WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure catalyst exhibited fast hydrogen evolution kinetics of onset potential and Tafel slope were at 95mV and 44mVdecade<SUP>−1</SUP>, respectively with the excellent electrocatalytic stability over 20h. WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure electrode demonstrates an excellent HER activity and long-term stability owing to their abundant active edge sites, and the strong chemical and electronic coupling between the CoSe<SUB>2</SUB> and WS<SUB>2</SUB>.</P> <P><B>Graphical abstract</B></P> <P>WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid structure was implemented to enhance HER electrocatalytic activity. The WS<SUB>2</SUB>/CoSe<SUB>2</SUB> catalyst exhibited low overpotentials of 95mV (@1mAcm<SUP>−2</SUP>) and 160mV (@ 10mAcm<SUP>−2</SUP>), a high exchange current density of ∼1.0×10<SUP>−2</SUP> mAcm<SUP>−2</SUP>, and a small Tafel slope of 44mVdecade<SUP>−1</SUP>. In addition, WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid electrode was stable over 20h of sustained hydrogen production in 0.5M H<SUB>2</SUB>SO<SUB>4</SUB> acidic medium.</P> <P>[DISPLAY OMISSION]</P>

High-ĸ dielectric oxide as an interfacial layer with enhanced photo-generation for Gr/Si solar cells

Bhopal, Muhammad Fahad,Akbar, Kamran,Rehman, Malik Abdul,Lee, Doo won,Rehman, Atteq ur,Seo, Yongho,Chun, Seung-Hyun,Lee, Soo Hong Elsevier 2017 Carbon Vol.125 No.-

<P>In recent years, graphene (Gr) based solar cells have attracted extensive interest because of their ability to produce low cost and highly efficient solar cells. Conventional Gr/Si Schottky junction based solar cells are mostly fabricated by transfer of graphene on silicon substrate. In current work the direct growth of graphene by using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique was demonstrated to make fabrication more practical on a large scale. Firstly Gr/Si Schottky junction based solar cells were fabricated, and by optimizing the growth process, power conversion efficiency (PCE) of about 3.5% was achieved. Additionally, we demonstrated a metal insulator semiconductor (MIS) structure by introducing hafnium oxide (HfO2), and an enriched efficiency of 6.68% was reached. Furthermore, the chemical doping of Gr grown on top of HfO2 passivated Si was done and the efficiency was further enhanced by 8.5%. This study also suggests that the Voc of the Gr/HfO2/Si solar cells strongly depends on the thickness of the HfO2 interfacial layer. These solar cells proved reliable as their efficiency was still consistent even after four months. The current study envisions the use of graphene based solar cells for commercial application. (C) 2017 Elsevier Ltd. All rights reserved.</P>

Iridium on vertical graphene as an all-round catalyst for robust water splitting reactions

Roy, Sanjib Baran,Akbar, Kamran,Jeon, Jae Ho,Jerng, Sahng-Kyoon,Truong, Linh,Kim, Kiwoong,Yi, Yeonjin,Chun, Seung-Hyun The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.36

<P>Among all noble metals, Ir has become popular for water reduction/oxidation due to its stability in both acidic and alkaline electrolytes. We find that Ir on vertical graphene (Ir_VG) is an all-round bi-functional catalyst. A high content of metallic Ir (Ir<SUP>0</SUP>) manifests as active catalytic sites supported by a superaerophobic vertical graphene surface designed to facilitate two-/four-electron transfer processes. This binder-free, nanoscale hybrid catalyst yields low overpotentials for the HER and OER in both acidic and alkaline media. With a minimal catalyst loading of 50 μg cm<SUP>−2</SUP> for the HER, the catalyst delivers a current density of 10 mA cm<SUP>−2</SUP> at overpotentials of 47 mV and 17 mV in acidic and alkaline media, respectively. For the OER, the catalyst achieves a current density of 10 mA cm<SUP>−2</SUP> at overpotentials of 300 mV and 320 mV in acidic and alkaline media, respectively. This highly active bi-functional catalyst enables total water splitting at 1.58 V (acidic) and 1.57 V (alkaline) for 10 mA cm<SUP>−2</SUP>. Unlike other catalysts, Ir_VG shows good stability against corrosion with undiminished current density even at high potential in harsh acidic or alkaline environments over 24 h. This unprecedented, versatile catalyst offers an appealing, cost-effective noble-metal-based scheme for pH-independent water electrolysis.</P>

Design and optimization of cobalt-encapsulating vertical graphene nano-hills for hydrogen evolution reaction

Roy, Sanjib Baran,Jerng, Sahng-Kyoon,Akbar, Kamran,Jeon, Jae Ho,Truong, Linh,Chun, Seung-Hyun,Noh, Min Jong,Lee, Juho,Kim, Yong-Hoon The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.28

<P>In spite of its great potential for sustainable water splitting technology, many challenges remain for the development of effective graphene-based hydrogen evolution reaction (HER) electrocatalysts. Based on mutually corroborating growth, electrochemical measurements, and density functional theory (DFT) calculations, we herein develop the HER-active vertical graphene nano-hills (VGNHs) on Co thin films such that Co atoms are introduced into the VGNH tip region. The HER activity exhibits a volcano-shaped curve with respect to the encapsulated Co density, and the best performance achieved at the nominal Co substrate thickness of 1 nm is characterized by the low onset potential, overpotential, and Tafel slope in acidic electrolyte. Especially, with this low-cost yet structurally and chemically stable Co-seeded VGNH catalyst, a record-level mass activity is achieved. The emergence of the HER activity from the combination of originally HER-inactive VGNHs and Co thin films is clarified by DFT calculations, which identifies the synergistic effects of the nanoscale curvature at the VGNH tip and the charge-transfer doping by encapsulated Co atoms.</P>

Structural investigation and improvement of microwave dielectric properties in Ca1-xBaxTiO3, low loss ceramics

Sarir Uddin,Abid Zaman,Imtiaz Rasool,Sadiq Akbar,Muhammad Kamran,Nasir Mehboob,Asad Ali,Abid Ahmad,Muhammad Farooq Nasir,Zafar Iqbal 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.6

The effects of Ba substitution on the phase analysis, microstructure and microwave dielectric properties of Ca1-xBaxTiO3ceramics were prepared through conventional solid state reaction route. The X-ray diffraction analysis of the samples showedthat the specimens Ca1-xBaxTiO3 presented single phase compound with orthorhombic structure in the range of x=0.0 to 0.7when sintered at 1300oC for 3hrs in air. From the morphological point of view, it consists of round and rod shaped grains withporous microstructure. The substitution of Ba2+ ions over Ca2+, the microwave dielectric constant (εr) diminishes from 145 to52 whereas the quality factor (Qxf) will increases from 8105 to 24305 GHz and temperature coefficient of resonant frequencydecreases from 705 to 80 ppm/oC (at 3 GHz).