Churl-Hee Cho

Establishing a proton‐selective membrane, capable of completely blocking the crossover of other chemical species, has been regarded as a long‐sought‐after goal for the stable and efficient operation of electrochemical devices. Conventional polymeric membranes suffer from an inherent trade‐off between conductivity and selectivity, imposed by their water‐mediated proton‐conduction mechanism, which precludes crossover‐free proton transport. Herein, we demonstrate a unique proton shuttling mechanism of the bipolar palladium membrane that enables selective proton transport while suppressing molecular crossover. Through bipolar electrochemical proton absorption and desorption, coupled with the lattice‐channeled hydrogen diffusion in palladium, the conductivity–selectivity relationship can be fundamentally circumvented. Using the bipolar electrochemical palladium membrane, we construct a water‐fed Li‐mediated N ₂ reduction system, suppressing water crossover between an aqueous anolyte and a non‐aqueous catholyte even under continuous flow and enabling water to serve as a sustainable proton source. We achieve an ammonia Faradaic efficiency of 51% and stable operation for 12 h under potential cycling. This study introduces a new ion transport mechanism, expanding the design space for next‐generation electrochemical systems that require strict compartmentalization.

Establishing a proton-selective membrane, capable of completely blocking the crossover of other chemical species, has been regarded as a long-sought-after goal for the stable and efficient operation of electrochemical devices. Conventional polymeric membranes suffer from an inherent trade-off between conductivity and selectivity, imposed by their water-mediated proton-conduction mechanism, which precludes crossover-free proton transport. Herein, we demonstrate that a bipolar palladium membrane enables selective proton transport while suppressing molecular crossover. Through bipolar electrochemical proton absorption and desorption, coupled with the lattice-channelled hydrogen diffusion in palladium, the conductivity–selectivity relationship can be fundamentally circumvented. Using a bipolar palladium membrane, we construct a water-fed Li-mediated N2 reduction system, suppressing water crossover between an aqueous anolyte and a non-aqueous catholyte even under continuous flow and enabling water to serve as a sustainable proton source. We achieve an ammonia Faradaic efficiency of 52% and stable operation for 12 h under potential cycling. This study introduces a new ion-selective membrane paradigm, expanding the design space for next-generation electrochemical systems.

Al₂O₃, widely used in the catalytic decomposition of fluorocarbons, is known to be rapidly deactivated owing to its transformation to AlF₃. Accordingly, in this study, metal‐impregnated γ‐Al₂O₃ catalysts (M/γ‐Al₂O₃) were synthesized and their long‐term stabilities for HFC‐134a decomposition were investigated under the conditions of 10,000 ppm HFC‐134a in air balance. Although γ‐Al₂O₃ and Mg/γ‐Al₂O₃ demonstrated long‐term activities, significantly longer than those of the other catalysts, activity of γ‐Al₂O₃ rapidly decreased, whereas that of Mg/γ‐Al₂O₃ gradually decreased. Although Mg/γ‐Al₂O₃ exhibited the smallest Brunauer‐Emmett‐Teller specific surface area among those of the synthesized catalysts, it demonstrated excellent long‐term stability and the lowest deactivation rate due to the high total amount of weak acid sites. Mg/γ‐Al₂O₃ exhibited considerably smaller crystal size of AlF₃ compared to other catalysts. Additionally, after HFC‐134a decomposition, the morphology of Mg/γ‐Al₂O₃ was clearly less modified and metal agglomeration was lower than those of other catalysts. Finally, this was caused by the reaction of Mg with HF, forming MgF₂, which inhibited the complete conversion of γ‐Al₂O₃ to AlF₃ and produced AlOF_X, an intermediate compound. These results suggest that Mg impregnation in γ‐Al₂O₃‐based catalysts is a suitable method for enhancing the performances of these catalysts in the long‐term decomposition of HFC‐134a.

All-in-one systems integrating solar cells and supercapacitors have recently received significant attention because of their high efficiency and portability. Unlike conventional solar photovoltaics, which require external wiring to connect to a battery for energy storage, integrated devices with solar cells and supercapacitors share one electrode, eliminating wiring resistance and facilitating charge transfer. In this work, we designed and fabricated all-in-one devices by combining a silicon solar cell and a supercapacitor with polymer gel electrolytes. Our all-in-one devices incorporating H3PO4/PVA and [BMIm]­Cl/PVA exhibited areal capacitances of 452.5 and 550 mF·cm –2 at 0.1 mA·cm–2, respectively, following 100 s of photocharging. Notably, the [BMIm]­Cl/PVA-based all-in-one device demonstrated significantly higher maximum energy density and power density compared to both the H3PO4/PVA-based all-in-one device and the values reported in literature. In addition, the cyclic photocharge/galvanostatic discharge process for the [BMIm]­Cl/PVA-based all-in-one device represented consistent retention of areal capacitance, affirming its stability across charge–discharge cycles. After 100 s of photocharging, the [BMIm]­Cl/PVA-based all-in-one device achieved a total energy efficiency of 1.85%, surpassing the 1.45% efficiency observed in the device using H3PO4/PVA. These results provide valuable insights for the design of self-charging all-in-one devices for portable and wearable applications.

Bio-SRF based on livestock waste has low heating value and high moisture content. The concentration of toxic gases such as SOx, NOx, and HCl in the flue gas is changed according to the composition of fuel, and it has been reported. Therefore, the study of fuel combustion characteristics is necessary. In this study, we investigated combustion characteristics on the blended firing of coal and Bio-SRF (bio-solid refused fuel) made from livestock waste fuel in CFBC (circulating fluidized bed combustor). The raw materials for manufacturing Bio-SRF include agricultural waste, herbaceous plants, waste wood, and vegetable residues. Bio-SRF, which is formed from organic sludge, has a low heating value and a high moisture content. Bio-SRF of livestock waste fuel is blended with different ratios of coal based on heating values when coal is completely combusted in CFBC. In the result of experiment, the combustor efficiency of calculated unburned carbon concentration in the fly ash shows 98.87%, 99.04%, 99.64%, and 99.71% when the multi co-combustion ratio of livestock waste fuel increased from 100/0 (coal/livestock waste) to 70/30 (coal/livestock waste). In addition, the boiler efficiency is shown to be 86.23%, 86.30%, 87.24% and 87.27%. Through the experimental results, we have identified that co-combustion of livestock waste fuel does not affect boiler efficiency. We have systematically investigated and discussed the temperature changes of the internal combustor, compositions of flue gases, solid ash characteristics, and the efficiency of combustion and of the boiler during co-combustion of coal and Bio-SRF.

The use of liquefied natural gas (LNG) in the transportation sector is increasing, and boil-off gas (BOG) management systems are considered viable options to increase economic efficiency and reduce greenhouse gas emissions at LNG refueling stations. The present study proposed an economically optimized method by investigating four refueling station scenarios, including different BOG management systems. Among the four scenarios, the scenario in which compressed natural gas was produced from BOG had the lowest minimum selling price (MSP) and was the most economical. Sensitivity and uncertainty analyses were conducted for the economically optimal scenario, which identified the factors with the most influential impact and their uncertainties on the MSP. Finally, to determine the feasibility of the business through profitability analysis, the net present value, discounted payback period, and present value ratio due to changes in the discount rate were presented, and the discounted cash flow rate of return was found to be 13.22%. As a result of this study, a BOG management system can contribute to improving the economic feasibility for LNG refueling stations by reliquefying BOG and re-selling it (the most efficient way is scenario 4) and will provide an economical guide for countries with much demand for LNG in the transport sector.

A CFBC (Circulating Fluidized Bed Combustor) boiler for combusted SRF (Solid Refused Fuel) is designed for solid waste combustion and power generation. The boiler consumes about 200 tons/day of SRF and generates 60 ton/h of steam or 10 MWe in electricity. The boiler is designed to burn pelletized waste fuel made of municipal solid waste collected from a town with a population of 400,000. Heat and mass balance calculations over the combustor and at each boiler section were performed and compared between the designed and measured data to analyze the boiler’s performance. After-combustion, the most significant phenomenon in low-density waste-derived fuel combustion in a CFBC boiler was monitored. The heat and mass balance were the most appropriate tools to analyze the boiler performance. The flow rate of spray water at the de-superheater was a reliable indicator to quantify the after-combustion. The design modification of the boiler unit for after-combustion control in the existing boiler was based on the quantification of spray water. The load distribution of the de-superheater decreases from 1.76% to 0.87% in 89% MCR before the installation of the evaporator and 82* % MCR load distribution of each boiler part after installation. The result was effective for the control of after-combustion in the existing boiler.

Fine-control of structural properties of WO₃. Faster and balanced charge transfer kinetics. Higher coloration efficiency.