• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.154.2-154.2
• /
• 2016

In this work, we introduce a solution-processed CdS interlayer for use in inverted bulk heterojunction (BHJ) solar cells, and compare this material to a series of standard organic and inorganic cathode interlayers. Different combinations of solution-processed CdS, ZnO and conjugated polyelectrolyte (CPE) layers were compared as cathode interlayers on ITO substrates to construct inverted solar cells based on $PTB7:PC_{71}BM$ and a $P3HT:PC_{61}BM$ as photoactive layers. Introduction of a CdS interlayer significantly improved the power conversion efficiency (PCE) of inverted $PTB7:PC_{71}BM$ devices from 2.0% to 4.9%, however, this efficiency was still fairly low compared to benchmark ZnO or CPE interlayers due to a low open circuit voltage ($V_{OC}$), stemming from the deep conduction band energy of CdS. The $V_{OC}$ was greatly improved by introducing an interfacial dipole (CPE) layer on top of the CdS layer, yielding outstanding diode characteristics and a PCE of 6.8%. The best performing interlayer, however, was a single CPE layer alone, which yielded a $V_{OC}$ of 0.727 V, a FF of 63.2%, and a PCE of 7.89%. Using $P3HT:PC_{61}BM$ as an active layer, similar trends were observed. Solar cells without the cathode interlayer yielded a PCE of 0.46% with a poor $V_{OC}$ of 0.197 V and FF of 34.3%. In contrast, the use of hybrid ZnO/CPE layer as the cathode interlayer considerably improved the $V_{OC}$ of 0.599 V and FF of 53.3%, resulting the PCE of 2.99%. Our results indicate that the CdS layer yields excellent diode characteristics, however, performs slightly worse than benchmark ZnO and CPE layers in solar cell devices due to parasitic absorption below 550 nm. These results suggest that the hybrid inorganic/organic interlayer materials are promising candidates as cathode interlayers for high efficiency inverted solar cells through the modification of interface contacts.

• Clean Technology
• /
• v.17 no.1
• /
• pp.56-61
• /
• 2011

In this study, hydrocarcking of vacuum residue was carried out in an autoclave reactor at $450^{\circ}C$ and $500^{\circ}C$ with a commercial catalyst (HDM) and the quantitative product distributions were analyzed by GC-SIMDIS method or simple distillation. During catalytic hydrocracking, thermal cracking also occurred together with catalytic cracking and the higher conversion and selectivity of gasoline and naphtha were obtained at high reaction temperature. GC-SIMDIS and simple distillation revealed different results for the analysis of products produced at different hydrocracking temperatures; almost same results were obtained for the product produced at $500^{\circ}C$ but different ones for the product produced at $450^{\circ}C$. In the analysis of product produced at $450^{\circ}C$, the GC-SIMDIS showed that a main product was VGO while a main product in the simple distillation was diesel, which implies that the simple distillation for the $450^{\circ}C$ reaction was not accurate due to thermal cracking of the product by the simple distillation.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.23 no.4
• /
• pp.40-51
• /
• 2015

This study is to estimate the viability of aerobic stabilization technology for reducing greenhouse gas (GHG) emissions from landfills in Korea. In this study, methane emissions were estimated by applying Landfill gas estimation model (LandGEM) to Y landfill in Korea. By comparison of an anaerobic condition (baseline) and an aerobic condition, the amount of $CO_2eq$ savings was calculated. The $CO_2eq$ savings take place inside the landfilled waste during aeration due to the conversion of previously anaerobic biodegradation to aerobic processes, releasing mainly $CO_2$. It was demonstrated that 86.6% of the total GHG emissions occurring under anaerobic conditions could be reduced by aerobic stabilization technology. This means the aerobic stabilization technology could reduce environmental contamination through early stabilization and GHG emissions considerably at the same time. Therefore, the aerobic stabilization technology is one of the optimal technologies that could be employed to domestic landfill sites to achieve sustainable landfill.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.18 no.1
• /
• pp.29-35
• /
• 2015

The concept design of a riser for Ocean Thermal Energy Conversion in 10 MW is proposed and its dynamic behaviour characteristics is analyzed with numerical method. A riser pipe with a hollow along its thickness in the cross-section to increase the effective modulus of its cross-section is designed considering the manufacture. The riser pipe without hollows along its thickness needs a lumped weight at the bottom end of a riser in order to keep its vertical hanging configuration from large buoyancy and the strong current. The riser is designed to control its density by inserting materials in high or low density into a hollow. The dynamic behaviour characteristics of the two designed risers is evaluated with the developed numerical analysis tool. The combined stress of the riser with a lumped weight is showed to be dominated by weight of a lumped mass. The riser with no hollow shows large combined stress near sea surface by strong current. Local structural analysis for the cross-section of a hollow riser is needed in detail.

• Journal of Korean Society of Environmental Engineers
• /
• v.34 no.12
• /
• pp.840-846
• /
• 2012

Global climate changes caused by $CO_2$ emissions are currently debated around the world; green sources of energy are being sought as alternatives to replace fossil fuels. The sustainable use of biogas for energy production does not contribute to $CO_2$ emission and has therefore a high potential to reduce them. Catalytic steam reforming of a model biogas ($CH_4:CO_2$ = 60%:40%) is investigated to produce $H_2$-rich synthesis gas. The biogas utilized 3D-IR matrix burner in which the surface combustion is applied. The ruthenium catalyst was used inside a reformer. Parametric screening studies were achieved as Steam/Carbon ratio, biogas component ratio, Space velocity and Reformer temperature. When the condition of Steam/Carbon ratio, $CH_4/CO_2$ ratio, Space velocity and Refomer temperature were 3.25, 60% : 40%, $14.7L/g{\cdot}hr$ and $550^{\circ}C$ respectively, the hydrogen concentration and methane conversion rate were showed maximum values. Under the condition mentioned above, $H_2$ yield, $H_2$/CO ratio, CO selectivity and energy efficiency were 0.65, 2.14, 0.59, 51.29%.

• Korean Chemical Engineering Research
• /
• v.54 no.3
• /
• pp.299-304
• /
• 2016

Characteristics of self-propagating reaction for the preparation of ZnO powder from precursors composed of nitrate and citrate compounds were examined. The ratio of C/N was maintained in range of 0.7~0.8 to initiate the self-propagating reaction between the reducing citrate and oxidizing nitrate groups. The samples were decomposed thermally by using TGA. The sudden decomposition occurred in the range of X > 0.5 in a very short time with a very sharp decrease of mass, indicating that the self-propagating reaction would occur. Friedman, Ozawa-Flynn-Wall and Vyazovkin methods were employed to predict the activation energy, reaction order and frequency factor of the reaction rate in the rate determining step of X < 0.5 range. The activation energy increased with increasing fractional conversion in the range of 46~130 (kJ/min). The reaction order decreased in the range of 2.9~0.9, while the frequency factor increased in the range of 85~278 ($min^{-1}$), respectively, with increasing the rate of temperature increase.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.4
• /
• pp.85-92
• /
• 2018

Reductions of the electricity charge are achieved by demand management of the load. The demand management method of the load using ESS involves peak shifting, which shifts from a high demand time to low demand time. By shifting the load, the peak load can be lowered and the energy charge can be saved. Electricity charges consist of the energy charge and the basic charge per contracted capacity. The energy charge and peak load are minimized by Linear Programming (LP) and Quadratic Programming (QP), respectively. On the other hand, each optimization method has its advantages and disadvantages. First, the LP cannot separate the efficiency of the ESS. To solve these problems, the charge and discharge efficiency of the ESS was separated by Mixed Integer Linear Programming (MILP). Nevertheless, both methods have the disadvantages that they must assume the reduction ratio of peak load. Therefore, QP was used to solve this problem. The next step was to optimize the formula combination of QP and LP to minimize the electricity charge. On the other hand, these two methods have disadvantages in that the charge and discharge efficiency of the ESS cannot be separated. This paper proposes an optimization method according to the situation by analyzing quantitatively the advantages and disadvantages of each optimization method.

• Transactions of the Korean hydrogen and new energy society
• /
• v.11 no.3
• /
• pp.119-125
• /
• 2000

To improve the photochemical energy conversion efficiency and the stability of CdS particulate film electrode which is used to produce hydrogen from the aqueous $H_2S$ solution photoelectrochemically, surface treatment of this film was carried out using $TiCl_4$ solution. CdS particles for preparation of the films were synthesized by precipitation reaction of $Cd({NO_3})_2{\cdot}9H_2O$ and $Na_2S{\cdot}4H_2O$. Then, the CdS sol was hydrothermally treated for 12hr in an autoclave with the variation of treatment temperature to control the crystalline phase of particles. CdS film electrode was thus prepared by annealing at $400^{\circ}C$ for 12hr of the wet-film cast at room temperature, and subsequently surface treated with $TiCl_4$ solution. The electrodes were characterized using XRD, SEM, and the photocurrent meter. The photocurrents of Cds film electrodes prepared with surface treatment were up to two times higher than the electrodes without surface treatment, indicating about $4.0mA/cm^2$. Hydrogen production rate in a continuous flow system using photoelectrochemical or photochemical cells prepared with surface treatment also increased in proportion to the increase of photocurrents.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.10
• /
• pp.985-993
• /
• 2015

Free-piston Stirling engines (FPSEs) have attracted much attention in the renewable energy field as a key device in the conversion from thermal to mechanical energy, and in the recycling of waste energy. Traditional Stirling engines consist of two pistons that are connected by a mechanical link, while FPSEs are formed as a vibration system by connecting each piston to a spring without a physical link. To ensure the correct design and control of operations, this requires elaborate dynamic-performance predictions. In this paper, we present the performance-prediction methodology using a linear and nonlinear dynamic analytical model considering the external load of FPSEs. We perform linear analyses to predict the operating point of the engine using the root locus technique. Using nonlinear analysis, we also predict the amplitude of pistons by performing numerical integration considering both the linear and nonlinear damping terms of the external load. We utilize the predicted dynamic behavior to predict the engine performance. In addition, we compare the experiment results and existing model predictions for RE-1000 to verify the reliability of the analytical model.

• Clean Technology
• /
• v.23 no.4
• /
• pp.429-434
• /
• 2017

To investigate the effect of magnesium oxide addition, $Cu/ZnO/MgO/Al_2O_3$ (CZMA) catalysts were prepared using co-precipitation method with fixed molar ratio of Cu/Zn/Mg/Al as 45/45/5/5 mol% for low-temperature water gas shift reaction. Synthesized catalysts were characterized by using BET, $N_2O$ chemisorption, XRD, $H_2-TPR$ and $NH_3-TPD$ analysis. The catalytic activity tests were carried out at a GHSV of $28,000h^{-1}$ and a temperature range of $200{\sim}320^{\circ}C$. At the same condition, magnesium oxide added catalyst (CZMA 400) showed that the lowest reduction temperature and stable presence of $Cu^+$, that is active species and abundant weak acid site. Also magnesium oxide added catalysts (CZMA) showed higher catalytic activity at temperature range above $240^{\circ}C$ than the catalyst without magnesium oxide (CZA). Consequently, CZMA 400 catalyst is considered to be excellent catalyst showing CO conversion of 77.59% without deactivation for about 75 hours at $240^{\circ}C$, GHSV $28,000h^{-1}$.