링크: https://onlinelibrary.wiley.com/doi/full/10.1002/aenm.202300400 저자: Tack Ho Lee*, Sam A. J. Hillman, Soranyel Gonzalez-Carrero, Alessandro Difilippo, James R. Durrant* 제목: Long-Lived Charges in Y6:PM6 Bulk-Heterojunction Photoanodes with a Polymer Overlayer Improve Photoelectrocatalytic Performance 저널: ADVANCED ENERGY MATERIALS 출판일: 2023.07.27 초록: Photogenerating charges with long lifetimes to drive catalysis is challenging in organic semiconductors. Here, the role of a PM6 polymer overlayer on the photoexcited carrier dynamics is investigated in a Y6:PM6 bulk-heterojunction (BHJ) photoanode undergoing ascorbic acid oxidation. With the additional polymer layer, the hole lifetime is increased in the solid state BHJ film. When the photoanode is electrically coupled to a hydrogen-evolving platinum cathode, remarkably long-lived hole polaron states are observed on the timescale of seconds under operational conditions. It is demonstrated that these long-lived holes enable the organic photoanode with the polymer overlayer to show enhanced ascorbic acid oxidation performance, reaching ?7 mA cm?2 at 1.23 VRHE without a co-catalyst. An external quantum efficiency of 18% is observed using 850 nm excitation. It is proposed that the use of an organic overlayer can be an effective design strategy for generating longer charge carrier lifetimes in organic photoanodes for efficient oxidation catalysis.

링크: https://doi.org/10.1002/cssc.202300035저자: Sangram Keshari Mohanty, Lei Cao, Byeong Kil Choi, Ji Heon Ryu, Jin Kyoon Park, Hyun Deog Yoo*제목: Electrochemically Activated Expanded Graphite with Tailor­made Pores for Magnesium­Organocation Hybrid Batteries저널: ChemSusChem, 16(11), e202300035.출판일: 2023/6/9초록: Persisting limitations of lithium-ion batteries (LIBs) in terms of safety, energy and power density, natural resources, and the price call for expeditious research to develop the “beyond Li-ion” technologies. In this regard, magnesium?organocation hybrid batteries (MOHB) hold the potential to address the above issues associated with LIBs by utilizing abundant and inexpensive elements of magnesium and carbon for the anode and cathode, respectively. Moreover, magnesium metal anode is highly energy-dense yet less susceptible to the dendrite formation, enabling safer operation compared to lithium metal anodes. In this study, we targeted to increase the capacity and rate capability of porous carbon cathode of MOHB by generating tailor-made pores, which were provided by the interlayer accommodation of solvated organic cations with controlled sizes during the electrochemical activation of expanded graphite. Our electrochemically activated expanded graphite can be used as an efficient cathode in MOHB with enhanced kinetics, specific capacitance, and cycle life.

링크: https://doi.org/10.1002/ente.202300153저자: Fuead Hasan*, Ahmed Adel A Abdelazeez, Mohamed Rabia, Hyun Deog Yoo*제목: Divalent Ion Pillaring and Coating on Lithium Cobalt Oxide Cathode for Fast Intercalation of Li+ Ion with High Capacity저널: Energy Technol. 11(7), 2300153.출판일: 2023년 7월초록: The development of high-performance lithium-ion batteries (LIBs) is essential for sustainable energy storage and utilization. Lithium cobalt oxide (LiCoO2, LCO) is widely used as a cathode material in LIBs due to its excellent electrochemical properties. However, its capacity is limited by structural changes and severe side reactions at high voltage and temperature. To overcome this issue, this study combines two strategies to enhance the intercalation kinetics of the LCO cathode. First, ionic pillars of various ions (e.g., Mg2+ and Ca2+) are doped to stabilize the structure at high voltage. Second, lithium-ion conducting lithium phosphate (Li3PO4) is coated to prevent direct contact between the liquid electrolytes and LCO particles, minimizing the formation of resistive surface films. The combination of these strategies results in a synergetic effect that significantly improves the energy density, thermal stability, cycling stability, and rate capability of the cathode. A rate capability of 100?mAh?g?1 at 10C is achieved, and a stable cycle performance with 98% capacity retention after 100 cycles at 0.5C is observed. Herein, the potential pathways of enhancing the energy density of current cathode materials through a synergistic combination of surface and structural engineering are highlighted.

링크: https://doi.org/10.1016/j.jpowsour.2023.232657저자: Eun Jeong Moon, Jeong Ki Hong, Sangram Keshari Mohanty, Mihyun Yang, Kyuwook Ihm, Hosik Lee*, Hyun Deog Yoo*제목: Coating lithium titanate anodes with a mixed ionic-electronic conductor for high-rate lithium-ion batteries저널: J. Power Sources, 559, 232657.출판일: 2023년 3월 1일초록: Lithium titanate (Li4Ti5O12; LTO) is a promising anode material for fast (dis)charging Li-ion batteries (LIBs). However, its low Li diffusion coefficient and electronic conductivity limit its applications. Here, we uniformly coat the LTO surface with a 1.6 nm layer of partially lithiated titania (LixTiO2, x ? 0.5), which is found to be a mixed ionic-electronic conductor (MIEC), using a simple solid-state method. The MIEC layer simultaneously transfers electrons and Li-ions, facilitating efficient charge transfer to (de)lithiate LTO over the entire particle surface. MIEC-nanocoated LTO exhibits highly improved capacity retention and rate capability than pristine LTO; based on electrochemical simulations, MIEC nanocoating causes performance enhancement by maximum surface-area utilization for charge transfer. Furthermore, electrochemical impedance spectroscopy and density functional theory calculations confirm facile ionic transport and high electronic conductivity of LixTiO2 nanolayer. This general strategy of MIEC nanocoating can boost the electrochemical performances of various insulating electrodes, maximizing the materials utilization.

링크: https://doi.org/10.1002/bkcs.12651저자: Vedi Kuyil Azhagan Muniraj, Madhusudana Koratikere Srinivasa, Hyun Deog Yoo*제목: Flexible supercapacitors toward wearable energy storage devices저널: Bull. Kor. Chem. Soc., 44(2), 125-136.출판일: 2023년 2월초록: The expeditiously growing wearable, thin, and flexible electronics have created a great demand for futuristic miniaturized charge storage devices. As power sources, flexible supercapacitors (FSCs) have received huge attraction because of their reliability, compatibility, and safety within the integrated lightweight consumer device applications. Along with high specific power and durability, the FSC provides a novel platform that inspires creative applications. Thereupon, the FSCs have become one of the most favorable candidates for energy storage in various forms such as skin patches or printed/wearable fabrics that can be used in medical examination. In this review, we focus on the current progress in the development of flexible electrode materials and scalable fabrication processes for FSC devices. Prospects in developing new approaches toward improved energy and power densities are highlighted.

링크: https://doi.org/10.1016/j.jssc.2022.123464저자: Linhua Hu, Soojeong Kim, Jacob R Jokisaari, Gene M Nolis, Hyun Deog Yoo, John W Freeland, Robert F Klie, Tim T Fister, Jordi Cabana*제목: Synthesis and Mg2+ deintercalation in manganese spinel nanocrystals저널: J. Solid State Chem., 315, 123464.출판일: 2022년 11월 1일초록: Transition metal oxides are promising materials as cathodes for divalent batteries with high capacity under high voltage. A major challenge is the sluggish kinetics of intercalation of divalent cations into the oxide host. Tailoring of the size, composition and crystal structure of oxides is a necessary strategy to alleviate these barriers, which challenges our control of their synthesis. Here, we selectively synthesize spinel-type MgxMn3-xO4 nanocrystals with different Mg/Mn ratios and investigate their ability to electrochemically shuttle Mg2+ ions. Crystal-chemical characterization of the reaction outcomes was conducted with X-ray diffraction, X-ray absorption spectroscopy, electron microscopy, and elemental analysis. Both 5 nm thick MgMn2O4 nanosheets and 10 nm Mg0.41Mn2.59O4 nanocubes underwent reversible Mg2+ deintercalation, yet no obvious reaction was observed in 60 nm Mg1.2Mn1.8O4 nanocubes. Our results suggest that both the size of the spinel nanocrystals and the Mg/Mn ratios play a role in the observed behaviour. The advances in the synthesis of spinel oxide nanocrystals achieved, and their correlation with Mg2+ deintercalation, pave the way toward the precise synthesis of multivalent cathode materials that fundamentally overcome barriers to practical application.

링크: https://doi.org/10.1016/j.jelechem.2022.116828저자: Seon Hwa Lee, Ki Young Kwon, Byeong Kil Choi, Hyun Deog Yoo*제목: A kinetic descriptor to optimize Co-precipitation of Nickel-rich cathode precursors for Lithium-ion batteries저널: J. Electroanal. Chem., 924, 116828.출판일: 2022년 11월 1일초록: Nickel-rich cathodes are advantageous for lithium-ion batteries (LIBs) due to their exceptional energy densities at lower cost. In general, particles' shape and crystal structure greatly influence the electrochemical performances of cathode active materials. In this regard, co-precipitation can afford secondary particles made of highly crystalline primary particles with uniform composition. Auxiliary complexing agent such as ammonia provides sufficient time for the well-ordered nucleation and growth of primary and secondary particles by retarding the hydroxide formation. Herein we suggest the reaction quotient (Q) to equilibrium constant (K) ratio, as a kinetic descriptor for the effective nucleation and crystal growth of metal hydroxide. Based on the cumulative formation constant and the solubility product values of each metal ion, about 1.0 M NH3 concentration rendered the Q/K ratio close to 1, which implies balanced precipitation and dissolution of metal hydroxide that provides sufficient time for the crystal growth. In accordance with the theoretical expectation, co-precipitation at 1 M NH3 rendered particles with uniform shape and size. And the resultant nickel-rich cathode outperformed other samples co-precipitated at different NH3 concentrations, in terms of significantly higher discharge capacity, cycle stability, and rate capability.

링크: https://doi.org/10.1016/j.jelechem.2022.116288저자: Ji Su Kim, Sangram Keshari Mohanty, Sol Jin Kim, Kyeongmin Moon, Jiung Jeong, Ki Young Kwon, Heon-Cheol Shin, Kang Hyun Park, Hyun Deog Yoo*제목: Hanging meniscus configuration for characterizing oxygen-reduction electrocatalysts in highly concentrated electrolytes저널: J. Electroanal. Chem., 913, 116288.출판일: 2022년 5월 15일초록: Oxygen reduction reaction (ORR) in metal-air batteries or fuel cells often require highly concentrated electrolyte for higher conductivity and electrochemical stability. However, conventional rotating disk electrode (RDE) method is ineffective to evaluate ORR activity in the real systems, because the scarce dissolved oxygen in highly concentrated electrolyte fails to provide significant ORR on RDE. Herein, we report a hanging meniscus configuration method for evaluating the electrocatalytic activity in highly concentrated electrolyte solutions, utilizing atmospheric oxygen through the triple-phase boundary. The newly developed method evaluated the ORR activity of silver and platinum catalysts in highly concentrated KOH electrolyte for zinc-air batteries, enabling the characterization in more realistic experimental condition.

링크: https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.1c01548저자: Ki Young Kwon, Sol Jin Kim, Dong-Min Kim, Hyunchul Kim, Sangram Keshari Mohanty, Kyu Tae Lee, and Hyun Deog Yoo*제목: Potential-Dependent Passivation of Zinc Metal in a Sulfate-Based Aqueous Electrolyte저널: Langmuir 2021, 37, 45, 13218?13224출판일: 2021년 11월 5일초록: Owing to its abundance, high theoretical capacity, and low electrode potential, zinc is one of the most important metallic anodes for primary and secondary batteries such as alkaline and zinc?air batteries. In the operation of zinc-based batteries, passivation of the anode surface plays an essential role because the electrode potential of zinc is slightly below that of the hydrogen evolution reaction. Therefore, it is important to scrutinize the nature of the passivation film to achieve anticorrosion inside batteries. Herein, the potential-dependent formation and removal of the passivation film during the deposition and dissolution of zinc metal in aqueous electrolytes are detected via electrochemical quartz crystal microbalance analysis. Film formation was not noticeable in hydroxide-based electrolytes; however, sulfate-based electrolytes induced potential-dependent formation and removal of the passivation film, enabling a superior coulombic efficiency of 99.37% and significantly reducing the rate of corrosion of the zinc-metal anodes. These observations provide insights into the development of advanced electrolytes for safe and stable energy-storage devices based on zinc-metal anodes.

링크https://pubs.rsc.org/en/content/articlehtml/2023/ta/d2ta09793a 저자Hyungsu Jang, Hyeong Yong Lim, Chan Beom Park, Jongdeuk Seo, Jung Geon Son, Taehee Song, Jaehwi Lee, Yun Seop Shin, Jina Roe, Sang Kyu Kwak, Dong Suk Kim and Jin Young Kim 발행사항J.Mater.Chem.A (2023) 11, 10605-10611 발행일 2023.04.05 영문초록Sn-based perovskites have intrinsic defects, such as Sn vacancies, oxidised components (Sn4+), and local lattice strain in the perovskite crystalline structure. In this study, Zn metal powder (Zn0) was introduced to reduce Sn oxidation in the solution step based on the redox potential difference. Additionally, Zn2+ was introduced in the perovskite precursor, which decreased the intrinsic defects and lattice strain of the perovskite films. The diffusion length, particularly that of the hole, increased with a reduction in the lattice strain, and Zn doping led to interfacial energy-level alignment of the perovskite and hole-transporting layers. The reduced lattice strain decreased the defect density and charge carrier recombination of perovskite devices. The power conversion efficiency of the Zn-doped Sn-based perovskite solar cell was improved to 11.39% compared to the 8.56% of the reference device.