https://scholar.dgist.ac.kr/handle/20.500.11750/249 2026-04-04T13:18:38Z https://scholar.dgist.ac.kr/handle/20.500.11750/59989 Title: Hydrogen Evolution via Oxygen Tolerant [NiFe]-Hydrogenase Immobilized on TiO2 Nanotubes Author(s): Kim, Hwapyong; Kim, Ki Nam; Lee, Sang-Hyeon; Nam, Chang-Hoon; Lee, Young-Sam; In, Su-Il Abstract: [FeFe]-hydrogenase has been of great interest due to its high enzymatic activity for hydrogen evolution reactions (HERs). However, the big challenge of [FeFe]-hydrogenase is a significant performance degradation in aerobic conditions. On the other hand, [NiFe]-hydrogenase of E. coli has an oxygen tolerant property. Therefore, using [NiFe]-hydrogenase is an effective solution to avoid performance degradation in aerobic conditions. Herein, we extracted [NiFe]-hydrogenases from E. coli and immobilized them on the TiO2 nanotube (TNT) electrode prepared by pyrrole-based electropolymerization for application in aerobic conditions. As a result, we can confirm that [NiFe]-hydrogenases coated TNT electrode demonstrates the increased HER activity underaerobic condition than control samples in in-vitro activity test using methylene viologen and linear sweep voltammetry. 2025-12-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59988 Title: Defect-Driven Dynamics in Gas-Phase Photocatalytic CO2 Conversion to Solar Fuels Using Ti3+/Ti4+ Containing TiO2 and Nonstoichiometric Ag2S Nanowires Author(s): Powar, Niket S.; Kwon, Soonho; Hiragond, Chaitanya B.; Lee, Junho; Gong, Eunhee; Kim, Hong Soo; Kim, Dongyun; Goddard, William A.; In, Su-Il Abstract: We studied CO2 photoreduction on nonstoichiometric surface photocatalysts using a comprehensive approach combining materials design, advanced spectroscopy, and Quantum Mechanics (QM) calculations. We developed a direct Z-scheme heterostructure, A-TiO2/Ag2S NWs, composed of amorphous TiO2 and nonstoichiometric Ag2S nanowires. This structure promotes defect-rich characteristics and a strong internal electric field (IEF), enhancing charge separation and minimizing electron-hole recombination. Employing in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and QM-simulated IR spectra revealed the CO2-to-CH4 conversion mechanism which involves H2COH* intermediate. Ti3+/Ti4+ and Ag+ defect environments were precisely characterized through X-ray photoelectron spectroscopy (XPS) and in situ extended X-ray absorption fine structure (EXAFS). Under concentrated solar illumination, this heterostructure achieved a CH4 production rate of 30.31 mu mol/g, a 5-fold enhancement over conventional 1-sun conditions. These findings provide valuable insights into solar-driven fuel synthesis through targeted defect engineering and strategic heterostructure design. 2025-10-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59985 Title: Photoelectrochemical Hydrogen Production Using TiO2/Mn-CdS Photoanode with ZnS Passivation and CoPi as Hole Transfer Relay Author(s): Kim, Hwapyong; Hiragond, Chaitanya B.; Koo, Sung Wook; Lee, Orim; In, Su-Il Abstract: To improve photoelectrochemical water splitting efficiency, it is crucial to simultaneously enhance light absorption, surface stability, and interfacial charge transfer. This work reports the rational design and fabrication of a multi-functional TiO2/Mn-CdS/ZnS/CoPi photoanode that integrates these critical aspects. TiO2 acts as a robust and conductive mesoporous film that absorbs UV light, while Mn-doped CdS broadens the absorption spectrum into the visible region owing to its narrower bandgap and suitable band alignment. To address the photocorrosion typically associated with CdS, a ZnS passivation is applied, offering chemical stability without impeding charge flow. Finally, cobalt phosphate is introduced as a surface catalyst to accelerate the oxygen evolution reaction, enhancing interfacial hole transfer and reducing the overpotential. This hierarchical architecture promotes synergistic interaction between each component, enabling efficient charge separation and transport. As a result, the TiO2/Mn-CdS/ZnS/CoPi photoanode achieves an enhanced photocurrent density under illumination. These results highlight the effectiveness of integrating light-harvesting, protective, and catalytic components to achieve high-performance and stable operation in PEC water splitting. https://scholar.dgist.ac.kr/handle/20.500.11750/59984 Title: Enhancing CO2-to-CH4 conversion efficiency of TiO2 through synergistic morphology tuning, defect engineering, and heterojunction formation Author(s): Kim, Dongyun; LEE, Kyuseok; Park, Young Ho; Lee, Junho; Murali, Guntakrinda; In, Insik; In, Su-Il; Lee, Jeonghyeon; Shin, Chaelin; Jeong, Hyeonjong; Cho, Chang-Hee; Lee, Seung Jun Abstract: The photocatalytic reduction of CO2 into valuable fuels represents a promising pathway toward sustainable energy solutions. In this study, the CO2-to-CH4 conversion efficiency of TiO2 is enhanced by implementing synergistic strategies, including morphology tuning, defect engineering, and composite construction. Reduced TiO2 nanosheet (2D-RT) morphology is employed to construct the ternary composite photocatalyst, Cu/reduced graphene oxide/2D-RT (Cu/G/2D-RT), which outperforms 2D-RT, P25 derived reduced TiO2 (P-RT), and Cu/G/P-RT. The CH4 production rate of Cu/G/2D-RT is nearly 62 times that of P-RT and 3.4 times that of Cu/G/P-RT. The optimal defect concentration in 2D-RT improves visible light absorption and charge separation, while the 2D structure enhances interaction with rGO, leading to better charge transport. Additionally, single-electron-trapped oxygen vacancies accelerate water oxidation, producing more protons to enhance the CO2 reduction on Cu cocatalyst. The CO2 reduction significantly improved under multi-sun illumination. However, the repeated cycling led to catalyst degradation, primarily driven by partial reduction of Cu. The in-situ diffuse reflectance infrared Fourier transform spectroscopy reveals the CO2 conversion pathway. Importantly, the results demonstrate that while a high defect concentration in TiO2 enhances visible light absorption, it does not necessarily ensure enhanced charge separation, optimal band alignment in heterojunctions, and improved CO2 reduction efficiency. 2025-12-31T15:00:00Z