Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Des...Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Despite extensive efforts, AD microbial ecology is still limitedly understood, especially due to the lack of quantitative information on the structures and dynamics of AD microbial communities. Such knowledge gap is particularly pronounced in sewage sludge AD processes although treating sewage sludge is among the major practical applications of AD. Therefore, we examined the microbial communities in three full-scale sewage sludge digesters using qualitative and quantitative molecular techniques in combination： denaturing gradient gel electrophoresis （DGGE） and real-time polymerase chain reaction （PCR）. Eight out of eleven bacterial sequences retrieved from the DGGE analysis were not affiliated to any known species while all eleven archaeal sequences were assigned to known methanogen species. Quantitative real-time PCR analysis revealed that, based on the 16S rRNA gene abundance, the hydrogenotrophic order Methanomicrobiales is the most dominant methanogen group （〉 94% of the total methanogen population） in all digesters. This corresponds well to the prevailing occurrence of the DGGE bands related to Methanolinea and Methanospirillum, both belonging to the order Methanomicrobiales, in all sludge samples. It is therefore suggested that hydrogenotrophic methanogens, especially Methanomicrobiales strains, are likely the major players responsible for biogas production in the digesters studied. Our observation is contrary to the conventional understanding that aceticlastic methanogens generally dominate methanogen communities in stable AD environments, suggesting the need for further studies on the dominance relationship in various AD systems.展开更多
Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction(HER)in alkaline water electrolysis,and the catalysts are produced by selective leaching of Al from Ni-Al alloys.It is well know...Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction(HER)in alkaline water electrolysis,and the catalysts are produced by selective leaching of Al from Ni-Al alloys.It is well known that chemical leaching of Ni-Al intermetallic compound(IMC)generates a high surface area in Ni(OH)_(2).However,the Ni(OH)_(2) produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction,which is attributed to its weak hydrogen adsorption energy.In this study,we controlled the chemical state of Ni using plasma vapor deposition(PVD)followed by heat treatment,selective Al leaching,and electrochemical reduction.X-ray diffraction(XRD),scanning microscopy(SEM),transmission electron microscopy(TEM),and energy-dispersive X-ray spectroscopy(EDS)were used to confirm the phase evolution of the electrocatalysts during fabrication.We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)_(2) and NiAl IMCs at the edges of the grains in the outermost surface layer.Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)_(2) to Ni(OH)_(2)/Ni in the grains during electrochemical reduction,as confirmed by X-ray photoelectron spectroscopy(XPS).An electrocatalyst containing partially reduced Ni(OH)_(2)/Ni exhibited an overpotential of 54 mV at 10 mA/cm^(2) in a half-cell measurement,and a cell voltage of 1.675 V at 0.4 A/cm2for single-cell operation.A combined experimental and theoretical study(density functional theory calculations)revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al,which facilitated water adsorption,dissociation,and finally hydrogen evolution.展开更多
The ,Aspoe Pillar Stability Experiment （APSE） is an in situ experiment for investigating the spalling mechanism under mechanical and thermal loading conditions in a crystalline rock. In this study, the thermo-mechan...The ,Aspoe Pillar Stability Experiment （APSE） is an in situ experiment for investigating the spalling mechanism under mechanical and thermal loading conditions in a crystalline rock. In this study, the thermo-mechanical behaviors in the APSE were investigated with three models： （1） a Full model with rough meshes for calculating the influence of tunnel excavation; （2） a Submodel with fine meshes for predicting the thermo-mechanical behavior in the pillar during the borehole drilling, heating, and cool- ing phases; and （3） a Thin model for modeling the effect of slot cutting for de-stressing around the pillar. In order to import the stresses calculated from the Full model to the Submodel and to define the complex thermal boundary conditions, artificial neural networks （NNs） were utilized. From this study, it was pos- sible to conclude that the stepwise approach with the application of NNs was useful for predicting the complex response of the pillar under severe thermo-mechanical loading conditions.展开更多
The imperative demand for energy paradigm shift toward renewable and sustainable energy sources has intensified interest in proton exchange membrane water electrolysis(PEMWE)as a clean and efficient hydrogen productio...The imperative demand for energy paradigm shift toward renewable and sustainable energy sources has intensified interest in proton exchange membrane water electrolysis(PEMWE)as a clean and efficient hydrogen production technology.However,the practical application of PEMWE is hindered by the scarcity and high cost of iridium(Ir),the state-of-the-art electrocatalyst for the oxygen evolution reaction(OER).To reduce Ir loading without compromising performance,we report a novel hollow Bi_(2)Te_(3)(h-Bi_(2)Te_(3))nanowire as a conductive and acid-tolerant support for Ir-based OER electrocatalysts.The h-Bi_(2)Te_(3) nanowires were synthesized via a two-step wet chemical synthesis involving Te nanowire growth and subsequent Bi incorporation,with controlled hollowness induced by modulating the reducing agent concentration.Ir nanoparticles were uniformly deposited onto h-Bi_(2)Te_(3) via polyol method,forming amorphous and well-dispersed Ir catalytic layers.Ir/h-Bi_(2)Te_(3) catalyst achieved an outstanding OER overpotential of 268 mV at 10 mA/cm^(2),a mass activity of 460 mA/mgIr at 1.55 V(vs.reversible hydrogen electrode(RHE)),and superior stability over 5 h,surpassing commercial IrO_(x)/TiO_(2),commercial Ir black,and Ir/Te benchmarks.The enhanced performance was attributed to the strong metal-support interaction,improved charge transfer,and enlarged electrochemically active surface area.Moreover,Ir/h-Bi_(2)Te_(3) catalyst demonstrated outstanding single-cell performance of 1.811 V at 2.0 A/cm^(2) with extremely low Ir loading(0.1 mgIr/cm^(2))and long-term durability(a cell voltage increase of 36.6 mV during 100 h at 1.0 A/cm^(2)),confirming its strong potential as a practical anode electrocatalyst for PEMWE.This study highlights the promise of morphology-engineered h-Bi_(2)Te_(3) supports for advancing cost-effective and durable PEMWE systems.展开更多
Developing highly efficient electrochemical catalysts for carbon dioxide reduction reaction(CO_(2)RR)provides a solution to battle global warming issues resulting from ever-increasing carbon footprint due to human act...Developing highly efficient electrochemical catalysts for carbon dioxide reduction reaction(CO_(2)RR)provides a solution to battle global warming issues resulting from ever-increasing carbon footprint due to human activities.Copper(Cu)is known for its efficiency in CO_(2)RR towards value-added hydrocarbons;hence its unique structural properties along with various Cu alloys have been extensively explored in the past decade.Here,we demonstrate a two-step approach to achieve intimate atomic Cu-Ag interfaces on the surface of Cu nanowires,which show greatly improved CO_(2)RR selectivity towards methane(CH4).The specially designed Cu-Ag interfaces showed an impressive maximum Faradaic efficiency(FE)of 72%towards CH4 production at-1.17 V(vs.reversible hydrogen electrode(RHE)).展开更多
The thermal decomposition synthesis of long copper nanowires （CuNWs） was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride...The thermal decomposition synthesis of long copper nanowires （CuNWs） was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride to nickel acetylacetonate, temperature, and stirring rate on the final shape of the products. Transparent electrodes （TEs） were fabricated by wet treatment with acetic acid （AA）, without using a sintering process. The low oxidation stability and high surface roughness are the main disadvantages of the CuNW TEs, which limit their applications. In order to overcome these issues, we prepared CuNW/polymer composite TEs by partial embedding of the CuNWs into poly（methyl methacrylate） （PMMA） on poly（ethylene terephthalate） （PET） substrates. The CuNW/PMMA composite TEs exhibit excellent optoelectronic performance （91.3% at 100.7 ff2/sq）, low surface roughness （4.6 nm in height）, and good mechanical and chemical stability as compared with CuNW TEs. On the basis of these properties, we believe that CuNW-based composite TEs could serve as low-cost materials for a wide range of new optoelectronic devices.展开更多
Traditional iridium (Ir) oxide catalysts have faced significant limitations in water electrolysis, particularly under acidic conditions where instability and degradation severely restrict the efficiency of the oxygen ...Traditional iridium (Ir) oxide catalysts have faced significant limitations in water electrolysis, particularly under acidic conditions where instability and degradation severely restrict the efficiency of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). To overcome these challenges, this study successfully synthesized highly dispersed IrPtPdNi alloy nanoparticles on a graphene oxide support using a vertically moving reactor, demonstrating exceptional performance in water electrolysis. These nanoparticles, synthesized via a fast-moving bed pyrolysis method, combine iridium, platinum, palladium, and nickel. They exhibit lower overpotentials in OER and comparable performance in HER to commercial catalysts, while also offering enhanced stability. These results surpass the limitations of traditional catalysts, marking significant progress toward more efficient and sustainable hydrogen production technologies. This advancement is expected to contribute significantly to the development of sustainable energy systems by innovatively enhancing the performance of catalysts in the electrochemical water-splitting process.展开更多
Social concerns regarding the safety of high-level radioactive waste have increased with growing public awareness of environmental issues and nuclear power.The performance assessment of deep geological disposal system...Social concerns regarding the safety of high-level radioactive waste have increased with growing public awareness of environmental issues and nuclear power.The performance assessment of deep geological disposal systems is crucial to reduce the uncertainties associated with high-level radioactive waste disposal and enhance the overall public confidence in nuclear safety.Accordingly,the Korea Atomic Energy Research Institute(KAERI)has undertaken various studies on the development of a deep geological disposal system for high-level waste and disposal safety evaluation.The KAERI Underground Research Tunnel(KURT),South Korea's only underground research laboratory dedicated to radioactive waste disposal,was constructed in 2006 and expanded in 2015.Since its construction,numerous in-situ experiments have been conducted and are currently underway in the KURT.The KURT plays a significant role in assessing the feasibility,safety,stability and appropriateness of a deep geological disposal system in South Korea and also provides an opportunity to revitalize industrial-academic-scientific cooperation between related institutions.This report summarizes two key in-situ experiments and international joint research conducted between 2007 and 2017 to assess the performance of the engineered and natural barriers of the KURT.The research experiences from the in-situ tests conducted at the KURT will provide crucial information on the safety and feasibility validation of the deep geological disposal system and will be an important contributor to the success of the Korean high-level radioactive waste disposal program in the future.展开更多
基金supported by the 2013 Research Fund of Ulsan National Institute of Science and Technology through a Future Challenge Project
文摘Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Despite extensive efforts, AD microbial ecology is still limitedly understood, especially due to the lack of quantitative information on the structures and dynamics of AD microbial communities. Such knowledge gap is particularly pronounced in sewage sludge AD processes although treating sewage sludge is among the major practical applications of AD. Therefore, we examined the microbial communities in three full-scale sewage sludge digesters using qualitative and quantitative molecular techniques in combination： denaturing gradient gel electrophoresis （DGGE） and real-time polymerase chain reaction （PCR）. Eight out of eleven bacterial sequences retrieved from the DGGE analysis were not affiliated to any known species while all eleven archaeal sequences were assigned to known methanogen species. Quantitative real-time PCR analysis revealed that, based on the 16S rRNA gene abundance, the hydrogenotrophic order Methanomicrobiales is the most dominant methanogen group （〉 94% of the total methanogen population） in all digesters. This corresponds well to the prevailing occurrence of the DGGE bands related to Methanolinea and Methanospirillum, both belonging to the order Methanomicrobiales, in all sludge samples. It is therefore suggested that hydrogenotrophic methanogens, especially Methanomicrobiales strains, are likely the major players responsible for biogas production in the digesters studied. Our observation is contrary to the conventional understanding that aceticlastic methanogens generally dominate methanogen communities in stable AD environments, suggesting the need for further studies on the dominance relationship in various AD systems.
基金supported by a Korea Evaluation Institute of Industrial Technology(KEIT)grant funded by the Korean government(MOTIE)(No.20022449)Commercialization Promotion Agency for R&D Outcomes(COMPA)grant funded by the Korean government(MSIT)(No.2021E100)+1 种基金supported by the Korea Electric Power Corporation(KEPCO),Open R&D(R22X004)the National Institute of Supercomputing and Network/Korea Institute of Science and Technology Information,which provided supercomputing resources,including technical support(KSC-2021-CRE-0568)。
文摘Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction(HER)in alkaline water electrolysis,and the catalysts are produced by selective leaching of Al from Ni-Al alloys.It is well known that chemical leaching of Ni-Al intermetallic compound(IMC)generates a high surface area in Ni(OH)_(2).However,the Ni(OH)_(2) produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction,which is attributed to its weak hydrogen adsorption energy.In this study,we controlled the chemical state of Ni using plasma vapor deposition(PVD)followed by heat treatment,selective Al leaching,and electrochemical reduction.X-ray diffraction(XRD),scanning microscopy(SEM),transmission electron microscopy(TEM),and energy-dispersive X-ray spectroscopy(EDS)were used to confirm the phase evolution of the electrocatalysts during fabrication.We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)_(2) and NiAl IMCs at the edges of the grains in the outermost surface layer.Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)_(2) to Ni(OH)_(2)/Ni in the grains during electrochemical reduction,as confirmed by X-ray photoelectron spectroscopy(XPS).An electrocatalyst containing partially reduced Ni(OH)_(2)/Ni exhibited an overpotential of 54 mV at 10 mA/cm^(2) in a half-cell measurement,and a cell voltage of 1.675 V at 0.4 A/cm2for single-cell operation.A combined experimental and theoretical study(density functional theory calculations)revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al,which facilitated water adsorption,dissociation,and finally hydrogen evolution.
基金within the context of the international DECOVALEX Project (DEvelopment of COupled models and their VALidation against EXperiments)supported by Korea Atomic Energy Research Institute (KAERI) as one of the Funding Organizations of the project,through the Nuclear Research and Development Program of KOSEF with a grant funded by MEST+3 种基金supported by Inha University Research Grant (INHA-44095-1)the support by Seoul National University (SNU)Swedish Nuclear Fuel and Waste Management Co. (SKB), Swedenprovided by SKB through its sp Pillar Stability Experiment project
文摘The ,Aspoe Pillar Stability Experiment （APSE） is an in situ experiment for investigating the spalling mechanism under mechanical and thermal loading conditions in a crystalline rock. In this study, the thermo-mechanical behaviors in the APSE were investigated with three models： （1） a Full model with rough meshes for calculating the influence of tunnel excavation; （2） a Submodel with fine meshes for predicting the thermo-mechanical behavior in the pillar during the borehole drilling, heating, and cool- ing phases; and （3） a Thin model for modeling the effect of slot cutting for de-stressing around the pillar. In order to import the stresses calculated from the Full model to the Submodel and to define the complex thermal boundary conditions, artificial neural networks （NNs） were utilized. From this study, it was pos- sible to conclude that the stepwise approach with the application of NNs was useful for predicting the complex response of the pillar under severe thermo-mechanical loading conditions.
基金supported by the Technology Innovation Program(No.20026415,Development of Membrane Electrode Assembly and Stack Components for PEM Water Electrolysis)funded by the Ministry of Trade,Industry&Energy(MOTIE,Korea)supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2022M3H4A3A01083536).
文摘The imperative demand for energy paradigm shift toward renewable and sustainable energy sources has intensified interest in proton exchange membrane water electrolysis(PEMWE)as a clean and efficient hydrogen production technology.However,the practical application of PEMWE is hindered by the scarcity and high cost of iridium(Ir),the state-of-the-art electrocatalyst for the oxygen evolution reaction(OER).To reduce Ir loading without compromising performance,we report a novel hollow Bi_(2)Te_(3)(h-Bi_(2)Te_(3))nanowire as a conductive and acid-tolerant support for Ir-based OER electrocatalysts.The h-Bi_(2)Te_(3) nanowires were synthesized via a two-step wet chemical synthesis involving Te nanowire growth and subsequent Bi incorporation,with controlled hollowness induced by modulating the reducing agent concentration.Ir nanoparticles were uniformly deposited onto h-Bi_(2)Te_(3) via polyol method,forming amorphous and well-dispersed Ir catalytic layers.Ir/h-Bi_(2)Te_(3) catalyst achieved an outstanding OER overpotential of 268 mV at 10 mA/cm^(2),a mass activity of 460 mA/mgIr at 1.55 V(vs.reversible hydrogen electrode(RHE)),and superior stability over 5 h,surpassing commercial IrO_(x)/TiO_(2),commercial Ir black,and Ir/Te benchmarks.The enhanced performance was attributed to the strong metal-support interaction,improved charge transfer,and enlarged electrochemically active surface area.Moreover,Ir/h-Bi_(2)Te_(3) catalyst demonstrated outstanding single-cell performance of 1.811 V at 2.0 A/cm^(2) with extremely low Ir loading(0.1 mgIr/cm^(2))and long-term durability(a cell voltage increase of 36.6 mV during 100 h at 1.0 A/cm^(2)),confirming its strong potential as a practical anode electrocatalyst for PEMWE.This study highlights the promise of morphology-engineered h-Bi_(2)Te_(3) supports for advancing cost-effective and durable PEMWE systems.
基金TEM work was conducted using the facilities in the electron imaging center of California NanoSystems Institute at the University of California Los Angles and the Irvine Materials Research Institute at the University of California Irvine.C.C.,J.C.and Y.H.acknowledge support by the Office of Naval Research(ONR)(No.N000141712608)C.S.L.and H.M.L.acknowledge support by a National Research Foundation(NRF)of Korea grant funded by the Korean Government(Nos.NRF-2017 R1E1A1A03071049 and NRF-2020R1A5A6017701).
文摘Developing highly efficient electrochemical catalysts for carbon dioxide reduction reaction(CO_(2)RR)provides a solution to battle global warming issues resulting from ever-increasing carbon footprint due to human activities.Copper(Cu)is known for its efficiency in CO_(2)RR towards value-added hydrocarbons;hence its unique structural properties along with various Cu alloys have been extensively explored in the past decade.Here,we demonstrate a two-step approach to achieve intimate atomic Cu-Ag interfaces on the surface of Cu nanowires,which show greatly improved CO_(2)RR selectivity towards methane(CH4).The specially designed Cu-Ag interfaces showed an impressive maximum Faradaic efficiency(FE)of 72%towards CH4 production at-1.17 V(vs.reversible hydrogen electrode(RHE)).
文摘The thermal decomposition synthesis of long copper nanowires （CuNWs） was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride to nickel acetylacetonate, temperature, and stirring rate on the final shape of the products. Transparent electrodes （TEs） were fabricated by wet treatment with acetic acid （AA）, without using a sintering process. The low oxidation stability and high surface roughness are the main disadvantages of the CuNW TEs, which limit their applications. In order to overcome these issues, we prepared CuNW/polymer composite TEs by partial embedding of the CuNWs into poly（methyl methacrylate） （PMMA） on poly（ethylene terephthalate） （PET） substrates. The CuNW/PMMA composite TEs exhibit excellent optoelectronic performance （91.3% at 100.7 ff2/sq）, low surface roughness （4.6 nm in height）, and good mechanical and chemical stability as compared with CuNW TEs. On the basis of these properties, we believe that CuNW-based composite TEs could serve as low-cost materials for a wide range of new optoelectronic devices.
基金conducted within the framework of a research and development program at the Korea Institute of Energy Research(Nos.C3-2420 and C4-2403).
文摘Traditional iridium (Ir) oxide catalysts have faced significant limitations in water electrolysis, particularly under acidic conditions where instability and degradation severely restrict the efficiency of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). To overcome these challenges, this study successfully synthesized highly dispersed IrPtPdNi alloy nanoparticles on a graphene oxide support using a vertically moving reactor, demonstrating exceptional performance in water electrolysis. These nanoparticles, synthesized via a fast-moving bed pyrolysis method, combine iridium, platinum, palladium, and nickel. They exhibit lower overpotentials in OER and comparable performance in HER to commercial catalysts, while also offering enhanced stability. These results surpass the limitations of traditional catalysts, marking significant progress toward more efficient and sustainable hydrogen production technologies. This advancement is expected to contribute significantly to the development of sustainable energy systems by innovatively enhancing the performance of catalysts in the electrochemical water-splitting process.
基金supported by the Nuclear Research and Development Program of the National Research Foundation of Korea(2021M2E1A1085193).
文摘Social concerns regarding the safety of high-level radioactive waste have increased with growing public awareness of environmental issues and nuclear power.The performance assessment of deep geological disposal systems is crucial to reduce the uncertainties associated with high-level radioactive waste disposal and enhance the overall public confidence in nuclear safety.Accordingly,the Korea Atomic Energy Research Institute(KAERI)has undertaken various studies on the development of a deep geological disposal system for high-level waste and disposal safety evaluation.The KAERI Underground Research Tunnel(KURT),South Korea's only underground research laboratory dedicated to radioactive waste disposal,was constructed in 2006 and expanded in 2015.Since its construction,numerous in-situ experiments have been conducted and are currently underway in the KURT.The KURT plays a significant role in assessing the feasibility,safety,stability and appropriateness of a deep geological disposal system in South Korea and also provides an opportunity to revitalize industrial-academic-scientific cooperation between related institutions.This report summarizes two key in-situ experiments and international joint research conducted between 2007 and 2017 to assess the performance of the engineered and natural barriers of the KURT.The research experiences from the in-situ tests conducted at the KURT will provide crucial information on the safety and feasibility validation of the deep geological disposal system and will be an important contributor to the success of the Korean high-level radioactive waste disposal program in the future.
