Browsing by Author "Lin, Tzu-En"

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A solvent-resistant azide-based hole injection/transporting conjugated polymer for fluorescent and phosphorescent light-emitting diodes
(2015-01-01)
Huang, Cheng-Wei
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Chang, Feng-Chih
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Chu, Yu-Lin
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Lai, Cheng-Chang
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Lin, Tzu-En
Interfacial mixing of polymers is a critical issue when attempting to improve the charge transport and stabilize the operation of solution-processed organic light-emitting diodes (OLEDs). Herein, we describe a simple methodology for overcoming interfacial mixing, based on the use of a photo-crosslinkable hole injection/transporting material (HITM). We synthesized a conjugated polymer, PTCAzide, bearing ready crosslinking ability and investigated its suitability for use as an HITM. Photo-crosslinking of the PTCAzide copolymer gave X-PTCAzide, which exhibited much higher thermal stability (the glass transition temperature increased by 21 K relative to that of PTCAzide), remarkable electrochemical stability, and excellent solvent-resistance, thereby expanding the operation time of corresponding electronic devices. Such a tris(8-hydroxy-quinolinato) aluminum-based trilayer device reached a maximum brightness of 52 971 cd m(-2), and the maximum luminance efficiency (LE) and power efficiency (eta E) are both higher than those of the corresponding device based on commercial PEDOT:PSS. In addition, a solution-processed phosphorescent OLED device incorporating X-PTCAzide also exhibited good performance (external quantum efficiency: 7.93%; LE: 29.6 cd A(-1); eta E: 14.3 lm W-1; maximum brightness: 34484 cd m(-2)). The efficient and simple photocrosslinking without adding an initiator could facilitate the fabrication process. Thus, PTCAzide appears to be a promising next-generation HITM for the development of highly efficient and inexpensive OLEDs. Its photo-crosslinkable nature allows improvements in morphological stability and hole injection/transporting ability, leading to more stable devices with better operation, without disrupting molecular packing or charge transport.
Advanced Exergoeconomic Evaluation of Large-Scale Coal-Fired Power Plant
(2020-02-01)
Wang, Ligang
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Fu, Peng
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Yang, Zhiping
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Lin, Tzu-En
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Yang, Yongping
Conventional exergy-based analysis can only identify the location and magnitude of thermodynamic inefficiencies (exergy destruction), while an advanced analysis can further reveal their source and avoidability by splitting each inefficiency into endogenous/exogenous and avoidable/unavoidable parts and their combinations. In this paper, a framework and implementation for a comprehensive evaluation of energy systems via conventional and advanced exergoeconomic analyses are summarized and performed to a state-of-the-art pulverized-coal power plant. An easy-to-implement procedure was proposed to calculate the endogenous exergy destruction. Different from the previous analyses of such plants, the boiler subsystem of the considered plant is simulated in detail with coal combustor and a series of (radiation- or convection-dominating) heat surfaces. The exergoeconomic performances (exergy dissipation as well as the related costs) of each component and the whole system are evaluated first. Then, the splitting of all exergy destructions and costs is performed for the insights of their sources and avoidability to suggest improvement measures. The results show that large parts of the exergy destructions within most of the components are endogenous; particularly, over half of the avoidable thermodynamic inefficiencies within most of the components are endogenous with the share of the avoidable part varying significantly among different components. Most costs related to either investment or exergy destruction are endogenous, and only nearly 10% of the costs of the whole system could be avoided for such a modern power plant. Moving convection-dominating heating surfaces into the furnace and increasing air-preheating temperature are suggested for performance enhancement.
Power-to-fuels via solid-oxide electrolyzer: Operating window and techno-economics
(2019-08-01)
Wang, Ligang
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Chen, Ming
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Kungas, Rainer
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Lin, Tzu-En
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Diethelm, Stefan
Power-to-fuel systems via solid-oxide electrolysis are promising for storing excess renewable electricity by efficient electrolysis of steam (or co-electrolysis of steam and CO2) into hydrogen (or syngas), which can be further converted into synthetic fuels with plant-wise thermal integration. Electrolysis stack performance and durability determine the system design, performance, and long-term operating strategy; thus, solid-oxide electrolyzer based power-to-fuels were investigated from the stack to system levels. At the stack level, the data from a 6000-h stack testing under laboratory isothermal conditions were used to calibrate a quasi-2D model, which enables to predict practical, isothermal stack performance with reasonable accuracy. Feasible stack operating windows meeting various design specifications (e.g., specific syngas composition) were further generated to support the selection of operating points. At the system level, with the chosen similar stack operating points, various power-to-fuel systems, including power-to-hydrogen, power-to-methane, power-to-methanol (dimethyl ether) and power-to-gasoline, were compared techno-economically considering system-level heat integration. Several operating strategies of the stack were compared to address the increase in stack temperature due to degradation. The modeling results show that the system efficiency for producing H-2, methane, methanol/dimethyl ether and gasoline decreases sequentially from 94% (power-to-H-2) to 64% (power-to-gasoline), based on a higher heating value. Co-electrolysis, which allows better heat integration, can improve the efficiency of the systems with less exothermic fuel-synthesis processes (e.g., methanol/dimethyl ether) but offers limited advantages for power-tomethane and power-to-gasoline systems. In a likely future scenario, where the growing amount of electricity from renewable sources results in increasing periods of a negative electricity price, solid oxide electrolyser based power-to-fuel systems are highly suitable for levelling the price fluctuations in an economic way.
Power-to-methane via co-electrolysis of H2O and CO2: The effects of pressurized operation and internal methanation
(2019-09-15)
Wang, Ligang
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Rao, Megha
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Diethelm, Stefan
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Lin, Tzu-En
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Zhang, Hanfei
This paper presents a model-based investigation to handle the fundamental issues for the design of co-electrolysis based power-to-methane at the levels of both the stack and system: the role of CO2 in co-electrolysis, the benefits of employing pressurized stack operation and the conditions of promoting internal methanation. Results show that the electrochemical reaction of co-electrolysis is dominated by H2O splitting while CO2 is converted via reverse water-gas shift reaction. Increasing CO2 feed fraction mainly enlarges the concentration and cathode-activation overpotentials. Internal methanation in the stack can be effectively promoted by pressurized operation under high reactant utilization with low current density and large stack cooling. For the operation of a single stack, methane fraction of dry gas at the cathode outlet can reach as high as 30 vol.% (at 30 bar and high flowrate of sweep gas), which is, unfortunately, not preferred for enhancing system efficiency due to the penalty from the pressurization of sweep gas. The number drops down to 15 vol.% (at 15 bar) to achieve the highest system efficiency (at 0.27 A/cm(2)). The internal methanation can serve as an effective internal heat source to maintain stack temperature (thus enhancing electrochemistry), particularly at a small current density. This enables the co-electrolysis based power-to-methane to.achieve higher efficiency than the steam-electrolysis based (90% vs 86% on higher heating value, or 83% vs 79% on lower heating value without heat and converter losses).
Reversible solid-oxide cell stack based power-to-x-to-power systems: Comparison of thermodynamic performance
(2020-10-01)
Wang, Ligang
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Zhang, Yumeng
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Perez-Fortes, Mar
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Aubin, Philippe
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Lin, Tzu-En
The increasing penetration of variable renewable energies poses new challenges for grid management. The economic feasibility of grid-balancing plants may be limited by low annual operating hours if they work either only for power generation or only for power storage. This issue might be addressed by a dual-function power plant with power-to-x capability, which can produce electricity or store excess renewable electricity into chemicals at different periods. Such a plant can be uniquely enabled by a solid-oxide cell stack, which can switch between fuel cell and electrolysis with the same stack. This paper investigates the optimal conceptual design of this type of plant, represented by power-to-x-to-power process chains with x being hydrogen, syngas, methane, methanol and ammonia, concerning the efficiency (on a lower heating value) and power densities. The results show that an increase in current density leads to an increased oxygen flow rate and a decreased reactant utilization at the stack level for its thermal management, and an increased power density and a decreased efficiency at the system level. The power-generation efficiency is ranked as methane (65.9%), methanol (60.2%), ammonia (58.2%), hydrogen (58.3%), syngas (53.3%) at 0.4 A/cm(2), due to the benefit of heat-to-chemical-energy conversion by chemical reformulating and the deterioration of electrochemical performance by the dilution of hydrogen. The power-storage efficiency is ranked as syngas (80%), hydrogen (74%), methane (72%), methanol (68%), ammonia (66%) at 0.7 A/cm(2), mainly due to the benefit of co-electrolysis and the chemical energy loss occurring in the chemical synthesis reactions. The lost chemical energy improves plant-wise heat integration and compensates for its adverse effect on power-storage efficiency. Combining these efficiency numbers of the two modes results in a rank of round-trip efficiency: methane (47.5%) > syngas (43.3%) hydrogen (42.6%) > methanol (40.7%) > ammonia (38.6%). The pool of plant designs obtained lays the basis for the optimal deployment of this balancing technology for specific applications.
Tape-Stripping Electrochemical Detection of Melanoma
(2019-10-15)
Darvishi, Sorour
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Pick, Horst
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Lin, Tzu-En
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Zhu, Yingdi
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Li, Xiaoyun
A noninvasive electrochemical melanoma detection approach based on using adhesive tapes for collecting and fixing cells from a suspicious skin area and transferring the cells into a scanning electrochemical microscope (SECM) is presented. The adhesive layer collects the cells reproducibly and keeps them well adhered on the tape during experiments in an electrolyte solution. A melanoma biomarker, here the intracellular enzyme tyrosinase (TYR), was imaged on the tape-collected cells without further cell lysing using antibodies that were labeled with horseradish peroxidase (HRP). The HRP labels catalyzed the oxidation of a dissolved redox-active species, which was detected at a soft microelectrode, gently brushed in contact mode over the tape. The melanoma biomarker was first detected on tape-stripped samples with murine melanoma cells of different concentrations. Thereafter, increasing levels of TYR were recorded in cells that were collected from the skin of melanoma mouse models representing three different stages of tumor growth. Additionally, SECM results of tape-stripped different human melanoma cell lines were confirmed by previous studies based on traditionally fixed and permeabilized cells.