https://scholarworks.unist.ac.kr/handle/201301/89 Wed, 08 Apr 2026 21:56:44 GMT 2026-04-08T21:56:44Z https://scholarworks.unist.ac.kr/handle/201301/91070 Title: Machine-learning based wind correction in WRF-CMAQ modeling system and its application Author(s): Kim, Seung-Mi Abstract: Accurate representation of surface wind fields is fundamental to realistic air-quality simulations in coupled meteorology–chemistry systems such as WRF–CMAQ. However, WRF systematically overestimates near-surface wind speeds, causing excessive dispersion and persistent underprediction of ozone and particulate matter. To address this limitation, this study developed an XGBoost-based machine-learning wind-correction model and incorporated the corrected 10 m winds into WRF–CMAQ through three pathways: static replacements at the WRF and MCIP stages, and a dynamic assimilation approach in which ML-corrected winds were supplied as pseudo-observations during WRF integration. The ML correction effectively reduced surface-wind overestimation across seasons, improving agreement with observations under diverse meteorological conditions. Yet its influence on the coupled system differed substantially by integration method. The static replacements improved near-surface winds and reduced local bias and RMSE, but their effects were largely confined to the lowest layers and resulted in only minor changes in pollutant fields. In contrast, the dynamic assimilation pathway propagated corrections vertically within the boundary layer while maintaining mass balance, modifying mixing height, heat fluxes, and the overall wind structure in a more coherent manner. These corrected meteorological fields were then used to drive CMAQ simulations. Unlike the static replacements—whose seasonal performance remained close to the baseline—the dynamic assimilation pathway produced meaningful changes in pollutant concentrations. ML-nudging improved primary air pollutants, enhanced O3 in all seasons except summer, and yielded superior PM2.5 performance except in spring, with further gains in high-concentration episodes. Case studies showed that ML-nudging more accurately reproduced the evolution and transport of concentration plumes and mitigated the typical underestimation during pollution events. Overall, the results highlight that the effectiveness of machine-learning wind-bias correction is strongly dependent on where and how it is integrated within the WRF–CMAQ system. Of the three approaches, the dynamic assimilation pathway offers a physically consistent and demonstrably impactful mechanism for embedding data-driven corrections into numerical models, effectively bridging statistical learning and process-based atmospheric modeling while delivering meaningful improvements in air-quality simulations. Major: Graduate School of Carbon Neutrality Carbon Neutrality(Environment) Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/91070 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91069 Title: Dual-Modification of Ammonium Vanadate Cathodes for Aqueous Zinc-Ion Batteries Author(s): Park, Jihyeon Abstract: The deployment of grid-level energy storage systems places stringent demands on battery technologies, particularly with respect to safety, cost, and long-term reliability. Aqueous zinc-ion batteries offer inherent advantages by employing nonflammable electrolytes and widely available materials. Even so, their practical operation is frequently hampered by slow electrochemical responses and progressive structural degradation of vanadium-based cathodes during repeated Zn²⁺ insertion. Layered ammonium vanadate (NH₄V₄O₁₀, NVO) possesses an interlayer-expanded architecture enabled by pre-intercalated ammonium ions, but its practical electrochemical performance remains limited by low electronic conductivity and gradual lattice deterioration. To address these challenges, nitrogen and polyvinylpyrrolidone incorporated ammonium vanadate cathode (N-NVO@PVP) was synthesized via a hydrothermal process followed by calcination. This dual modification simultaneously alters the interlayer environment and local electronic structure, leading to an expanded layered framework, as reflected by the shift of the (001) diffraction peak from 8.54° to 7.84°, and the formation of defect-associated domains. Spectroscopic characterization reveals an increased proportion of reduced vanadium species together with nitrogen-related chemical states, confirming effective modulation of the host lattice. As a result of these structural and electronic modifications, the N-NVO@PVP electrode delivers a reversible capacity of 415 mAh g⁻¹ at 0.1 A g⁻¹, along with enhanced rate capability and substantially improved cycling stability. After 2000 charge–discharge cycles, the modified electrode retains approximately 70% of its initial capacity, whereas pristine NVO retains only 35.7% under identical conditions. These findings indicate that concurrent interlayer regulation and defect engineering can effectively mitigate the intrinsic limitations of layered vanadate cathodes, suggesting N-NVO@PVP as a promising alternative cathode material for next generation energy storage applications. Major: Graduate School of Carbon Neutrality Carbon Neutrality (Energy Engineering) Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/91069 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91068 Title: Maximizing Photocurrent via Current Matching Towards Efficient All-perovskite Tandem Solar Cells Author(s): Oh, Si On Abstract: In the current age where climate change is no longer a threat of a distant future, there is a definite imminence to the clean energy transition initiative. Solar energy has been a steadily rising candidate for the transition, with photovoltaics attracting much attention for their outstanding optical and electrical properties, allowing for fabrication of highly efficient devices. From the wide variety of photovoltaics, perovskites have been at the center of focus for their realization of highly efficient devices that have the possibility of surpassing their silicon counterparts due to their tunable bandgap and wide window of applications. The flexibility in processing, from low-temperature to solution- and solid-state manufacture, coupled with flexibility in choice of substrates make them viable for various applications, such as their incorporation into tandem structures. Therefore, researchers have researched numerous methods of raising the efficiency of perovskite-based photovoltaics, ranging from compositional engineering to additive incorporation, to reach efficiencies closer to the limit of ~33.16% power conversion efficiency (PCE) set by the Shockley-Quiesser limit (SQ Limit) for single-junction photovoltaics. While current records have made great efforts to reach the aforementioned limit, with the current record for single-junction photovoltaics set at 27% PCE, the current world record efficiency for two-junction perovskite/silicon tandem photovoltaics is set at 34.9% PCE, highlighting the immense potential of multi-junction devices toward ultra-high efficiency photovoltaics. The typical tandem structure consists of two or more sub-cells that are stacked on top of each other, for example, a sub-cell with a wide bandgap (WBG; top) paired with another sub-cell with a very narrow bandgap (NBG; bottom). The top sub-cell is typically perovskite-based, while the bottom sub-cell is interchangeable between perovskite, organic, and silicon. While perovskite/silicon and perovskite/organic tandem structures show record and moderate efficiencies, respectively, perovskite/perovskite tandem structures show most promise in attaining the best balance between high performance and low-cost manufacture, while also unlocking flexibility in applications due to the versatility in substrate choice and tunability of both sub-cells. Research is mostly focused on optimization of each sub-cell to raise the efficiency of perovskite/perovskite tandem structured photovoltaics, with the goal of achieving better current- matching and higher voltage output through various methods of engineering. Studies revolving around current matching, raising voltage output and substitution of the interconnecting layer have led to the attainment of high efficiencies reaching up to 30.1% PCE. Herein, we propose the immense significance of achieving better current matching for high quality, ultra efficient all-perovskite tandem photovoltaics using manipulation of layer thicknesses and addition of additives. Manipulating the thickness of each sub-cell through changes in the fabrication process to increase their thicknesses led to increased current output and better current matching as proved by the heightened PCE of the resultant tandem photovoltaics. Specifically, the addition of stabilizing additives in the NBG sub-cell led to a dramatic increase in voltage output, leading to greater voltage output in the resultant tandem photovoltaics. Modification of each respective layer made it possible to realize highly efficient perovskite/perovskite tandem photovoltaics and subsequent modules. This led to the fabrication of all-perovskite tandem photovoltaics with properly optimized sub-cells. Overall, this research has provided future researchers with proof-of-concept current matching capabilities and serves to emphasize the significance of this work towards the eventual development of commercializable all-perovskite tandem modules ready for real life operation. Major: Graduate School of Carbon Neutrality Carbon Neutrality (Energy Engineering) Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/91068 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91067 Title: Electrochemical Oxidation of Alcohols Using Ni-Based Catalysts Incorporating Pt-Au Nanoparticles Author(s): Park, Taeung Abstract: The continuous accumulation of plastic waste over recent decades has caused a severe environmental crisis. Among various mitigation strategies, the conversion of waste plastics into value-added products has emerged as a critical challenge. In particular, t he electrochemical refining of polybutylene terephthalate (PBT) waste—focusing on the upcycling of PBT-derived 1,4-butanediol (BDO) monomers into high-value succinic acid while simultaneously coupling hydrogen production—has attracted significant attention as a promising approach to alleviate plastic pollution. In this study, a electrocatalyst featuring a NiOOH layer and Pt–Au nanoparticles supported on nickel foam was fabricated via corrosion engineering and spontaneous redox reactions. The catalytic perfo rmance for BDO oxidation was strongly dependent on the concentrations of Pt and Au precursor ions introduced during synthesis, as evidenced by distinct differences in succinic acid production rates. This electrocatalytic upcycling strategy can be further integrated with cathodic reduction reactions, offering new insights into the energy-efficient production of value-added chemicals while addressing plastic waste challenges. Major: Graduate School of Carbon Neutrality Carbon Neutrality (Energy Engineering) Sat, 31 Jan 2026 15:00:00 GMT https://scholarworks.unist.ac.kr/handle/201301/91067 2026-01-31T15:00:00Z