Optimizing nanosheet nickel cobalt oxide as an anode material for bifunctional electrochemical energy storage and oxygen electrocatalysis

Cho, Sangeun,Lee, Seongwoo,Hou, Bo,Kim, Jongmin,Jo, Yongcheol,Woo, Hyeonseok,Pawar, Sambhaji M.,Inamdar, Akbar I.,Park, Youngsin,Cha, SeungNam,Kim, Hyungsang,Im, Hyunsik Pergamon Press 2018 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>Mesoporous Ni-Co oxide (NCO) nanosheet electrodes are fabricated on Ni foam via an electrodeposition technique. Their bifunctional activities for electrochemical energy storage and electro-catalysis for water splitting in strong alkaline media are optimized by varying the ratio of concentrations of the Ni and Co precursors. The ratio-based changes vary the pore size of the NCO nanosheets between 92.5 and 200 nm, and structural analyses reveal that the electrode films have a spinel NiCo<SUB>2</SUB>O<SUB>4</SUB> structure. The obtained specific capacitance varies dramatically between 613 and 2704 Fg<SUP>−1</SUP> at 2 mA cm<SUP>−2</SUP>, with good capacity retention (80–90%) after 2000 cycles. The NCO nanosheet electrodes also exhibit a good oxygen evolution reaction at the surface. The lowest overpotential (315 mV at 10 mA cm<SUP>−2</SUP>) is obtained with a Tafel slope of 59 mV dec<SUP>−1</SUP>. The observed bifunctional activities of the new NCO nanosheet electrode are superior to those of nanostructured NCO electrodes prepared via hydrothermal and SILAR methods. The analyses regarding the electrochemically active surface area and electrochemical impedance spectroscopy, together with the observed electrochemical performance, reveal that the most-optimized Ni and Co composition produces the synergetic effects of an electrochemically active surface area and great stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mesoporous Ni-Co oxide (NCO) nanosheet electrodes are fabricated on Ni foam via an electrodeposition technique. </LI> <LI> Excellent specific capacitance and electrochemical stability are obtained. </LI> <LI> The overpotential of 315 mV at 10 mA cm<SUP>−2</SUP> is obtained with a Tafel slope of 59 mV dec<SUP>−1</SUP>. </LI> </UL> </P>

Enhanced Photosensitivity in Monolayer MoS₂ with PbS Quantum Dots

Cho, Sangeun,Jo, Yongcheol,Woo, Hyeonseok,Kim, Jongmin,Kwak, Jungwon,Kim, Hyungsang,Im, Hyunsik The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3

Photocurrent enhancement has been investigated in monolayer (1L) $MoS_2$ with PbS quantum dots (QDs). A metal-semiconductor-metal (Au-1L $MoS_2$-Au) junction device is fabricated using a standard photolithography method. Considerably improved photo-electrical properties are obtained by coating PbS QDs on the Au-1L $MoS_2$-Au device. Time dependent photoconductivity and current-voltage characteristics are investigated. For the QDs-coated $MoS_2$ device, it is observed that the photocurrent is considerably enhanced and the decay life time becomes longer. We propose that carriers in QDs are excited and transferred to the $MoS_2$ channel under light illumination, improving the photocurrent of the 1L $MoS_2$ channel. Our experimental findings suggest that two-dimensional layered semiconductor materials combined with QDs could be used as building blocks for highly-sensitive optoelectronic detectors including radiation sensors.

Distinctive Spectroscopic Characteristics Observed in Colloidal Perovskite CsPbBr₃ Quantum Dot

Sangeun Cho,Sam Kyu Noh,Hyungsang Kim,Hyunsik Im 한국진공학회(ASCT) 2021 Applied Science and Convergence Technology Vol.30 No.4

Distinctive spectroscopic characteristics are observed in colloidal perovskite CsPbBr₃ quantum dot (QD) dispersed in octane doped with PPO. As the content of CsPbBr₃-QD increases, the emission and the absorption energies decrease due to QD-cluster formed in case of the inter-QD distance smaller than diameter of QD. Spectroscopic evidences supporting QD-cluster are found in the Urbach energy and the carrier lifetime. Unusual absorption lines showing explicit QD dependence are observed in Fourier-transform infrared spectra, which is explained by vibrational modes of bound PPO hybridized with CsPbBr₃-QD.

Bendable RuO₂/graphene thin film for fully flexible supercapacitor electrodes with superior stability

Cho, Sangeun,Kim, Jongmin,Jo, Yongcheol,Ahmed, Abu Talha Aqueel,Chavan, H.S.,Woo, Hyeonseok,Inamdar, A.I.,Gunjakar, J.L.,Pawar, S.M.,Park, Youngsin,Kim, Hyungsang,Im, Hyunsik ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.725 No.-

<P><B>Abstract</B></P> <P>Ruthenium oxide (RuO<SUB>2</SUB>) is fabricated on graphene (Gr)-coated Copper (Cu) foil by using a cathodic electroplating technique for flexible supercapacitor electrode applications. The electrochemical properties of the RuO<SUB>2</SUB>/Gr/Cu electrode are investigated with a conventional three electrode configuration in 0.5 M H<SUB>2</SUB>SO<SUB>4</SUB> electrolyte. The graphene insertion layer plays a key role in improving the structural and electrochemical properties of the RuO<SUB>2</SUB> electrode film under the bent condition. The electrode exhibits a specific capacitance of 1561 F g<SUP>−1</SUP> (0.015 F cm<SUP>−1</SUP>) at a scan rate of 5 mV s<SUP>−1</SUP> and a significantly improved retention of 98% under the bent condition. The flexible RuO<SUB>2</SUB>/Gr/Cu electrode exhibits a high energy density of ∼13 Wh kg<SUP>−1</SUP> at a power density of ∼21 kW kg<SUP>−1</SUP>. The excellent capacitance retention and electrochemical stability of the flexible RuO<SUB>2</SUB>/Gr/Cu electrode are due to the improved mechanical adhesion between the RuO<SUB>2</SUB> and the current collector. This flexible RuO<SUB>2</SUB>/Gr/Cu film could be used as a supercapacitor electrode with a high capacity and long-cycle life for the next-generation flexible electronic applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A binder-free Bendable RuO<SUB>2</SUB> thin film is fabricated on a graphene/Cu substrate using an electroplating method. </LI> <LI> Electrochemical energy storage properties of RuO<SUB>2</SUB> are investigated for supercapacitor applications. </LI> <LI> Excellent capacitance retention and electrochemical stability are obtained. </LI> </UL> </P>

Enhanced Photosensitivity in Monolayer MoS₂ with PbS Quantum Dots

Sangeun Cho,Yongcheol Jo,Hyeonseok Woo,Jongmin Kim,Jungwon Kwak,Hyungsang Kim,Hyunsik Im 한국진공학회(ASCT) 2017 Applied Science and Convergence Technology Vol.26 No.3

Photosensitivity of bulk and monolayer MoS2-based two-terminal devices

Cho Sangeun,Park Wooyoung,Im Hyunsik,김형상 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.5

Transition metal dichalcogenides (TMDCs), such as MoS2, MoSe2, WS2, and WSe2, have attracted enormous attention owing to their unique electrical and optical properties. A type of material known as TMDC has the MX2 formula with a direct bandgap in ultra-thin layers and indirect bandgap properties in the bulk. TMDCs have attracted significant research interest due to their use in nano-devices, opto-electronics, and next-generation electronics. In the study, two different MoS2 devices, Au–bulk MoS2–Au and Au–monolayer MoS2–Au, were fabricated, and their photon-induced current–voltage characteristics at different wavelengths (red ≈ 650 nm, green ≈ 532 nm and blue ≈ 450 nm) and values were compared. Additionally, the time-dependent photoresponses of these devices under red light irradiation (wavelength, λex = 650 nm) were analyzed. The Au–monolayer MoS2–Au device had a higher current response compared with the Au–bulk MoS2–Au device. These results suggest that single-layer MoS2 devices could be more efficient and responsive than bulk MoS2 devices for a variety of applications.

페로브스카이트 CsPbX₃ Quantum dots 을 이용한 방사선 & 광 발광 특성 분석

Sangeun Cho,Sungwoo Kim,Jungwon Kwak,Ilhwan Ryu,Jongmin Kim,Yongcheol Jo,Jiwoo Seo,Samkyu Noh,Jaejoon Lee,Hyungsang Kim,Hyunsik Im 한국진공학회 2018 한국진공학회 학술발표회초록집 Vol.2018 No.8

아동특성, 부모특성, 가족특성이 아동의 사회성 발달에 미치는 영향

조상은 ( Sangeun Cho ) 사단법인 아시아문화학술원 2021 인문사회 21 Vol.12 No.4

만 3세에서 8세 기간은 사회성이 발달하고 사회적 행동이 현저히 증가하는 시기이다. 하지만 최근에는 따돌림, 부적응, 은둔형 외톨이 등 낮은 사회성과 관련된 문제들이 낮은 연령대에서도 발생되고 있어 주목이 필요하다. 이에 본 연구에서는 아동의 사회성에 미치는 요인을 아동, 부모, 가족환경 특성으로 구분하고 각 차원이 아동의 사회성에 미치는 영향과 각 차원의 설명력을 실증적으로 확인해보고자 하였다. 전국데이터인 2018 아동종합실태조사 자료를 활용하여 만 3-8세 아동(부모가 대리응답) 1,094명을 대상으로 위계적 회귀분석(hierarchical regression analysis)을 실시하였다. 연구결과를 살펴보면, 아동의 사회성에 아동 특성인 아동의 또래관계가 가장 큰 영향을 미쳤고 부모효능감, 양육스트레스, 가족건강성이 통계적으로 유의미한 영향을 미치는 것으로 나타났다. 연구결과를 토대로 본 연구에서는 아동의 긍정적인 사회성 발달을 위해 아동의 또래관계 증진, 부모효능감 강화, 양육스트레스 해소 지원, 가족건강성 제고를 위한 실천적ㆍ정책적 함의를 제언하였다. Age three to eight is a period where sociability develops and social activities increase. However, recently low sociability-related issues such as bullying, maladaptation, and social withdrawal are happening in lower age. Thus, the present study attempted to investigate the effects of child, parent and home environment factors on sociability and their explanatory power. 2018 National Survey on Child with 1,094 children aged three to eight (parent proxies) and hierarchical regression analysis were used. The findings showed children’s peer relationship was most influential in their sociability; parenting efficacy, parenting stress, and family strengths were statistically associated with children’s sociability. This study recommended practical and policy implications for enhancement of peer relationship, parenting efficacy and family strengths, and alleviation of parenting stress were discussed.

장애인에 대한 돌봄부담이 가족의 경제활동에 미치는 영향

조상은 ( Cho Sangeun ),오욱찬 ( Oh Ukchan ) 한국사회복지연구회 2021 사회복지연구 Vol.52 No.4

This study investigated whether care burden of persons with disabilities affected a family’s employment and work hours, and whether the association between care burden and employment and the association between care burden and work hours differed by gender. Existing foreign literature revealed that caring for persons with disabilities negatively affected labor force participation such as employment status and work hours of family caregivers. However, domestic studies on the caregiver’s burden family’s labor force participation were scant. People without a disability aged 18 to 64 participated as a study sample and five waves of the supplementary data for a person with a disability from the Korea Welfare Panel Study were used. The subjects were a maximum of 13,336 people (6,424 male and 6,912 female); in terms of the number of individual-year cases in five waves, they were 37,419 at a maximum size. We applied a hybrid method in conducting panel regression analysis. The findings showed, first, female had a higher burden in caring a person with a disability than male; second, in the descriptive statistics, female had a significantly lower employment rate and annual work hours than those without care burden; however, male did not show much difference. Third, the panel regression analysis showed that the level of care burden for a person with a disability did not affect employment and work hours among male; whereas female with higher care burden had a 6.5% point less employment rate and 364.8 hours less annual work hours than those without any care burden. Based on these results, practical and policy suggestions were presented.

고령장애인의 만성질환과 다차원적 장애 : 국제기능장애건강분류틀(ICF)을 적용하여

조상은 ( Cho Sangeun ) 한국사회복지연구회 2017 사회복지연구 Vol.48 No.4

This study aimed (a) to examine the association between chronic illness and multidimensional disability(i.e., psychological/emotional functions, activity capacity, and participation frequency) among older adults with disabilities, (b) to investigate the effect of formal and informal supports on multidimensional disability, and (c) to analyze the moderating effects of formal and informal supports on the association between chronic illness and multidimensional disability. This study used 2014 Korea Welfare Panel Study(the 9th wave) data and 450 older adults with disabilities aged 50 and over were selected as the study target. The research model was analyzed by structural equation modeling using IBM AMOS 22.0. Based on the ICF framework developed by WHO, health condition was measured by the level of chronic illness; psychological/emotional functions were measured by health satisfaction, self-esteem, and depression; activity capacity was measured by ADLs and IADLs; participation frequency was measured by the total number of social activities joined; formal support was measured by the total number of formal welfare services for people with disabilities utilized; informal support was measured by perceived social support. The findings showed that the level of chronic illness was negatively associated with psychological/emotional functions among the older adults with disabilities. The informal support positively affected psychological/emotional functions and activity capacity, whereas the formal support showed the opposite result. That is, the formal support negatively influenced activity capacity and showed a moderating effect on the association between the level of chronic illness and the psychological/emotional functions in a reverse way. Based on the results, practice and policy implications for alleviating disability level among the older adults with disabilities were discussed.