Characterization and Control of Nanoparticle Emission during 3D Printing

Kwon, Ohhun,Yoon, Chungsik,Ham, Seunghon,Park, Jihoon,Lee, Jinho,Yoo, Danbi,Kim, Yoojin American Chemical Society 2017 Environmental science & technology Vol.51 No.18

<P>This study aimed to evaluate particle emission characteristics and to evaluate several control methods used to reduce particle emissions during three-dimensional (3D) printing. Experiments for particle characterization were conducted to measure particle number concentrations, emission rates, morphology, and chemical compositions under manufacturer-recommended and consistent-temperature conditions with seven different thermoplastic materials in an exposure chamber. Eight different combinations of the different control methods were tested, including an enclosure, an extruder suction fan, an enclosure ventilation fan, and several types of filter media. We classified the thermoplastic materials as high emitter (> 10(11) #/min), medium emitters (10(9) #/min -10(11) #/min), and low emitters (< 10(9) #/min) based on nanoparticle emissions. The nanoparticle emission rate was at least 1 order of magnitude higher for all seven filaments at the higher consistent extruder temperature than at the lower manufacturer-recommended temperature. Among the eight control methods tested, the enclosure with a high-efficiency particulate air (HEPA) filter had the highest removal effectiveness (99.95%) of nanoparticles. Our recommendations for reducing particle emissions include applying a low temperature, using low-emitting materials, and instituting control measures like using an enclosure around the printer in conjunction with an appropriate filter (e.g., HEPA filter) during 3D printing.</P>

Self-assembled alloy nanoparticles in a layered double perovskite as a fuel oxidation catalyst for solid oxide fuel cells

Kwon, Ohhun,Kim, Kyeounghak,Joo, Sangwook,Jeong, Hu Young,Shin, Jeeyoung,Han, Jeong Woo,Sengodan, Sivaprakash,Kim, Guntae The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.33

<P><I>In situ</I> exsolved nanoparticles on metal oxide materials have received much attention in catalysis due to their well socketed structure and high catalytic activity. Recently, the demand for active nanoparticles with multiple functionalities in catalysis has increased, so exsolutions of intermetallic nanoparticles could be an effective strategy to meet the requirements. Herein, for the first time, we report exsolved Co-Ni alloy nanoparticles and their Gibbs free energy of alloy formation in a PrBaMn1.7Co0.1Ni0.2O5+δ layered double perovskite. These exsolved alloy nanoparticles have a high catalytic performance for fuel oxidation in fuel cells and in the dry reforming of methane. Furthermore, we probed the mechanism of the alloy formation in the exsolution using density functional theory (DFT). The theoretical calculations reveal that the Gibbs free energy of the surface alloy formation (Δ<I>G</I>aggr_surface) is more favorable than that of the bulk alloy formation (Δ<I>G</I>aggr_bulk), indicating that Co and Ni are exsolved separately from the bulk, and then aggregate to form a Co-Ni alloy on the surface.</P>

In Situ Surface Modification of Ni-YSZ with BaZrO₃ for Enhancing the Sulfur Tolerance of Ni-YSZ Anode

Kwon, Ohhun,Sengodan, Sivaprakash,Lim, Chaehyun,Jeong, Hu Young,Shin, Jeeyoung,Ju, Young-Wan,Kim, Guntae The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.9

<P>In this work, we report on a BaZrO3 (BZO) modified NiO-YSZ anode fabricated by co-sintering of NiO-YSZ and BaCO3 for SOFCs. The BZO modified Ni-YSZ anode shows stable electrochemical performance in H-2 fuel containing a high level of 100 ppm sulfur for more than 100 hours. On the other hand, an unmodified Ni-YSZ anode degrades significantly in 100 ppm sulfur containing H-2 fuel. The obtained results demonstrate that the BZO in the Ni-YSZ is an excellent catalyst for enhancing the sulfur tolerance of the conventional Ni-YSZ anode. Moreover, the surface modification strategy is simple and cost-effective, and thereby can promote commercialization of Ni-YSZ anode supported cells. (C) 2016 The Electrochemical Society. All rights reserved.</P>

Synergistic Coupling Derived Cobalt Oxide with Nitrogenated Holey Two-Dimensional Matrix as an Efficient Bifunctional Catalyst for Metal-Air Batteries

Kim, Jeongwon,Gwon, Ohhun,Kwon, Ohhun,Mahmood, Javeed,Kim, Changmin,Yang, Yejin,Lee, Hansol,Lee, Jong Hoon,Jeong, Hu Young,Baek, Jong-Beom,Kim, Guntae American Chemical Society 2019 ACS NANO Vol.13 No.5

<P>Developing cost-effective, efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the heart of metal-air batteries as a renewable-energy technology. Herein, well-distributed nanopolyhedron (NP) Co<SUB>3</SUB>O<SUB>4</SUB> grown on iron (Fe) encapsulated in graphitic layers on a nitrogenated, porous two-dimensional (2D) structure, namely, a C<SUB>2</SUB>N matrix, (NP Co<SUB>3</SUB>O<SUB>4</SUB>/Fe@C<SUB>2</SUB>N), presents an outstanding bifunctional catalytic activity with a comparable overpotential and Tafel slope to those of benchmark Pt/C and IrO<SUB>2</SUB>. The rationally designed atomic configuration of Co<SUB>3</SUB>O<SUB>4</SUB> on the C<SUB>2</SUB>N matrix has a well-controlled NP morphology with a (111) plane, leading to bifunctional activities for the ORR and OER. Interestingly, the specific interaction between the NP Co<SUB>3</SUB>O<SUB>4</SUB> nanoparticles and the C<SUB>2</SUB>N matrix introduces synergistic coupling and changes the electronic configuration of Co atoms and the C<SUB>2</SUB>N framework. Benefiting from the synergistic coupling of Co<SUB>3</SUB>O<SUB>4</SUB> with the C<SUB>2</SUB>N matrix, the NP Co<SUB>3</SUB>O<SUB>4</SUB>/Fe@C<SUB>2</SUB>N electrocatalyst exhibits exceptionally high stability and an even lower charge-discharge overpotential gap of 0.85 V at 15 mA cm<SUP>-2</SUP> than that of the Pt/C+IrO<SUB>2</SUB> catalyst (1.01 V) in Zn-air batteries. This work provides insights into the rational design of a metal oxide on a C<SUB>2</SUB>N matrix for bifunctional, low-cost electrochemical catalysts.</P> [FIG OMISSION]</BR>

Cloud-like graphene nanoplatelets on Nd_0.5Sr_0.5CoO_3−δ nanorods as an efficient bifunctional electrocatalyst for hybrid Li–air batteries

Kim, Changmin,Gwon, Ohhun,Jeon, In-Yup,Kim, Youngsik,Shin, Jeeyoung,Ju, Young-Wan,Baek, Jong-Beom,Kim, Guntae The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.6

<▼1><P>Benefiting from the unique morphological features, NSC@IGnP provides superior bifunctional activities toward both ORR and OER for hybrid Li-air batteries.</P></▼1><▼2><P>With the recognition of metal–air batteries as promising candidates for clean and efficient energy storage, the development of inexpensive and effective bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) has become one of the most important topics in this field. Herein, we designed new composite catalysts consisting of a nanorod type Nd0.5Sr0.5CoO3−δ (NSC) perovskite and edge-iodinated graphene nanoplatelets (IGnPs) as bifunctional catalysts for ORR and OER. Interestingly, the simple application of ultrasonication endowed the catalyst with a fascinating morphology comprising cloud-like IGnPs on NSC nanorods (NSC@IGnP). Benefiting from the unique morphological features, NSC@IGnP provides superior bifunctional activities toward both ORR and OER, remarkable cell performance, and exceptionally high stability for hybrid Li–air batteries.</P></▼2>

A Highly Efficient and Robust Cation Ordered Perovskite Oxide as a Bifunctional Catalyst for Rechargeable Zinc-Air Batteries

Bu, Yunfei,Gwon, Ohhun,Nam, Gyutae,Jang, Haeseong,Kim, Seona,Zhong, Qin,Cho, Jaephil,Kim, Guntae American Chemical Society 2017 ACS NANO Vol.11 No.11

<P>Of the various catalysts that have been developed to date for high performance and low cost, perovskite oxides have attracted attention due to their inherent catalytic activity as well as structural flexibility. In particular, high amounts of Pr substitution of the cation ordered perovskite oxide originating from the state-of-the-art Ba<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>0.8</SUB>Fe<SUB>0.2</SUB>O<SUB>3−δ</SUB> (BSCF) electrode could be a good electrode or catalyst because of its high oxygen kinetics, electrical conductivity, oxygen capacity, and structural stability. However, even though it has many favorable intrinsic properties, the conventional high-temperature treatment for perovskite synthesis, such as solid-state reaction and combustion process, leads to the particle size increase which gives rise to the decrease in surface area and the mass activity. Therefore, we prepared mesoporous nanofibers of various cation-ordered PrBa<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>2–<I>x</I></SUB>Fe<SUB><I>x</I></SUB>O<SUB>5+δ</SUB> (<I>x</I> = 0, 0.5, 1, 1.5, and 2) perovskites <I>via</I> electrospinning. The well-controlled B-site metal ratio and large surface area (∼20 m<SUP>2</SUP> g<SUP>–1</SUP>) of mesoporous nanofiber result in high performance of the oxygen reduction reaction and oxygen evolution reaction and stability in zinc-air battery.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2017/ancac3.2017.11.issue-11/acsnano.7b06595/production/images/medium/nn-2017-06595y_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn7b06595'>ACS Electronic Supporting Info</A></P>

Hybrid-solid oxide electrolysis cell: A new strategy for efficient hydrogen production

Kim, Junyoung,Jun, Areum,Gwon, Ohhun,Yoo, Seonyoung,Liu, Meilin,Shin, Jeeyoung,Lim, Tak-Hyoung,Kim, Guntae unknown 2018 Nano energy Vol.44 No.-

<P><B>Abstract</B></P> <P>Water electrolysis based on a solid oxide electrolysis cell (SOEC) has potential to be cost-effective, environmentally friendly, and highly efficient for hydrogen production. There are two types of SOECs, depending on electrolyte materials: oxygen ion conducting SOECs (oxygen-SOECs) and proton conducting SOECs (proton-SOECs). Here we report our new findings in exploring a SOEC based on a mixed-ion conductor that can transport both oxygen ion and proton at the same time, which is denoted as “Hybrid-SOEC”. When BaZr<SUB>0.1</SUB>Ce<SUB>0.7</SUB>Y<SUB>0.1</SUB>Yb<SUB>0.1</SUB>O<SUB>3-<I>δ</I> </SUB> was used as an electrolyte, the Hybrid SOEC shows the highest efficiency, demonstrating a current density of 3.16Acm<SUP>−2</SUP> at 1.3V and 750°C in 10% humidified hydrogen at hydrogen electrode and 10% humidified air at air electrode. Moreover, the Hybrid SOEC exhibits no observable degradation in performance for more than 60h of continuous operation, implying a robust system for hydrogen production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The new concept of “Hybrid-SOEC“ based on mixed ionic conducting electrolyte is proposed. </LI> <LI> The Hybrid-SOEC shows excellent performance compared with other water-electrolysis systems. </LI> <LI> Current density of 3.16Acm<SUP>−2</SUP> at 1.3V (@750°C) is achieved based on the Hybrid-SOEC operation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Nano-perovskite oxide prepared <i>via</i> inverse microemulsion mediated synthesis for catalyst of lithium-air batteries

Lim, Chaehyun,Kim, Changmin,Gwon, Ohhun,Jeong, Hu Young,Song, Hyun-Kon,Ju, Young-Wan,Shin, Jeeyoung,Kim, Guntae Elsevier 2018 ELECTROCHIMICA ACTA Vol.275 No.-

<P><B>Abstract</B></P> <P>Perovskite oxides have received considerable attention as useful electro-catalysts for Li-air batteries due to their properties of excellent catalytic activity, electrical conductivity, and durability. The nanostructure can enhance the electrochemical performance of perovskite oxides by enlarging the catalytic active sites. In this study, nano-size Nd<SUB>0.67</SUB>Sr<SUB>0.33</SUB>CoO<SUB>3-<I>δ</I> </SUB> (NSC) perovskite particles with a particle size of 20–50 nm and a specific surface area of 12.759 m<SUP>2</SUP> g<SUP>−1</SUP> were successfully synthesized by a microemulsion method. The NSC perovskite particles exhibit excellent electrocatalytic activity particularly in the oxygen evolution reaction (OER) with a high limiting current density of 33.68 mA cm<SUP>-2</SUP> at 0.9 V <I>vs</I>. (Hg/HgO). This excellent catalytic activity can be ascribed to the existence of Co<SUP>3+</SUP> and the enlarged surface area. Co<SUP>3+</SUP> provides catalytically active site by forming Co<SUP>3+/4+</SUP> redox couple and the enlarged surface increases active sites for reactants and catalyst particles. In this regard, nano-size NSC particles prepared by the microemulsion route provide excellent and stable electrochemical performance in the hybrid Li-air battery.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A nano-structured perovskite oxide catalyst, Nd<SUB>0.67</SUB>Sr<SUB>0.33</SUB>CoO<SUB>3-<I>δ</I> </SUB> was successfully synthesized <I>via</I> inverse micro-emulsion method. </LI> <LI> The microemulsion method not only provides exensive surface area, but also increases Co<SUP>3+</SUP> and adsorbed oxygen species. </LI> <LI> The extended surface area and increased Co<SUP>3</SUP> <SUP>+</SUP> and adsorbed oxygen species enhace the electro-catalytic activity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Synergistic interaction of perovskite oxides and N-doped graphene in versatile electrocatalyst

Bu, Yunfei,Jang, Haeseong,Gwon, Ohhun,Kim, Su Hwan,Joo, Se Hun,Nam, Gyutae,Kim, Seona,Qin, Yong,Zhong, Qin,Kwak, Sang Kyu,Cho, Jaephil,Kim, Guntae The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.5

<P>Multifunctional electrocatalysts with high catalytic activity and durability are needed for environmentally clean energy technologies such as water-splitting devices and metal-air batteries. Herein, we investigate a new catalyst, P-3G, consisting of a cation-ordered perovskite (PrBa0.5Sr0.5)0.95Co1.5Fe0.5O5+δ (PBSCF) and 3D porous N-doped graphene (3DNG). This new type of composite electrocatalyst simultaneously exhibited outstanding multifunctional catalytic activities and excellent stabilities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). A possible mechanism for the synergistic effects between perovskite oxides and 3DNG on ORR, OER and HER was firstly proposed by DFT calculations. The electrocatalytic activity of P-3G appeared to have great potential for a rechargeable Zn-air battery system. The operating voltage differences between the charge and discharge (Δ<I>η</I>) of P-3G and Pt/C-IrO2 after 110 cycles were 0.63 V and 0.87 V, respectively, indicating the substantial durability of P-3G. Moreover, a water-splitting device using P-3G efficiently produced H2 and O2 gases at rates of 0.859 μL s<SUP>−1</SUP> and 0.417 μL s<SUP>−1</SUP>, respectively. This study highlights extended applications of coupled perovskite oxides/carbon materials as versatile electrocatalysts for ORR, OER, and HER and unveils the cause of synergistic interactions between oxide and carbon by DFT calculation.</P>

Evaluation of Hazardous Chemicals with Material Safety Data Sheet and By-products of a Photoresist Used in the Semiconductor-Manufacturing Industry

Jang, Miyeon,Yoon, Chungsik,Park, Jihoon,Kwon, Ohhun Occupational Safety and Health Research Institute 2019 Safety and health at work Vol.10 No.1

Background: The photolithography process in the semiconductor industry uses various chemicals with little information on their constitution. This study aimed to identify the chemical constituents of photoresist (PR) products and their by-products and to compare these constituents with material safety data sheets (MSDSs) and analytical results. Methods: A total of 51 PRs with 48 MSDSs were collected. Analysis consisted of two parts: First, the constituents of the chemical products were identified and analyzed using MSDS data; second, for verification of the by-products of PR, volatile organic compounds were analyzed. The chemical constituents were categorized according to hazards. Results: Forty-five of 48 products contained trade secrets in amounts ranging from 1 to 65%. A total of 238 ingredients with multiple counting (35 ingredients without multiple counting) were identified in the MSDS data, and 48.7% of ingredients were labeled as trade secrets under the Korea Occupational Safety and Health Act. The concordance rate between the MSDS data and the analytical result was 41.7%. The by-product analysis identified 129 chemicals classified according to Chemical Abstracts Service No., with 17 chemicals that are carcinogenic, mutagenic, and reprotoxic substances. Formaldehyde was found to be released from 12 of 21 products that use novolak resin. Conclusion: We confirmed that several PRs contain carcinogens, and some were not specified in the toxicological information in the MSDS. Hazardous chemicals, including benzene and formaldehyde, are released from PRs products as by-products. Therefore, it is necessary to establish a systematic management system for chemical compounds and the working environment.