Aging Effects of the Cathode and Determination of Single Electrode Performance in a Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) are promising electrochemical energy conversion devices due to their advantages of high theoretical efficiency, fuel flexibility (including hydrogen and carbon monoxide), scalability, and low emission. An important problem for commercially using the SOFCs is to improve the long term stability for the SOFCs. To improve the lifetime of SOFCs and develop innovative electrode microstructures; we need to understand the individual process including the degradation processes to the cathode or the anode. To identify the independent anode and cathode contributions to the total impedance, one conventional electrochemical tool for evaluation is the reference electrode. Although reference electrode simulations predict that overpotential/current and impedance data assigned to one electrode will inevitably contain contributions from the other electrode, many current experimental reports persistently use reference electrodes. We have developed several configurations of reference electrodes and cell designs, and have experimentally examined these systems using various gas flows and two temperatures, and have also compared experimental results to simulated predictions. Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were used to collect data. The results for all of our reference electrode designs show agreement with simulation predictions. For the ring reference electrode on the anode-supported cell, the data support that the cathode impedance includes impedance from the anode in the 3-electrode measurement. On the electrolyte-supported cell, using both the ring reference electrode and a micro-reference electrode close to the cathode, the apparent inductance loops in the 3-electrode measurement show up for both reference electrode configurations. The inductive loops are artifacts which indicate the inability to accurately separate impedances for the cathode and anode.;We developed a better protocol to identify the minimum number of processes contributing to the total impedance of a SOFC associate with cathode and anode without the use of reference electrodes. The protocol is based on deconvolution combined with equivalent circuit fitting of impedance data. This protocol uses a spreadsheet program. The impedance / deconvolution technique supplies information of characteristic relaxation time distributions. This information, together with systematic changes in gas composition to the anode or cathode, is used to build the equivalent circuits. We are able to identify the impedance components associated with each electrode. The deconvolution and equivalent circuit analyses are applied successfully to three types of commercially button SOFCs including two anode-supported SOFCs and an electrolyte-supported SOFC. The results show the ability to assign the physical processes associated to cathode or anode in real electrode systems.;In the Strontium-doped lanthanum manganite (LSM) cathode of SOFCs, one special phenomenon of degradation was noticed as a changing polarization resistance over tens of hours in a cell at open circuit voltage (Aging effect). This aging effect was reversible during temperature cycles between 800ºC and 700ºC. We explored this phenomenon via electrochemical techniques (EIS and CV), with the purpose of discovering the true physical source. From the initial investigation, we proposed to relate two processes to the phenomenon we observed: (1) the wetting behavior of the LSM on the Yttria stabilized zirconia (YSZ) surface (2) the segregation of cations. Another approach for separating the processes at different frequencies is deconvolution of impedance spectra combined with complex non-linear regression fitting of the impedance spectra. We performed the extended tests with different cathode and electrolyte compositions under open circuit. This protocol provides the trends in parameters for the equivalent circuit during thermal aging for the impedance data from the extended tests, especially, the frequency ranges associated with aging. Based on results from deconvolution, a hypothesis is proposed to address the aging effect

Analysis of the thermo-elastic vibration for axially moving Euler beam

The thermo-elastic vibration response of simple supported axially moving Euler beam is investigated. The differential equation of moving beam is established by recourse to Hamilton principle and the thermal effects is considered by introducing the equivalent thermal bending moment. A 2-D transient temperature field is calculated by the alternating-directional implicit (ADI) method and the equivalent thermal moment is calculated numerically. The dimensionless equation is discretized by Galerkin method and the modal analysis of gyroscopic system is used to calculate the forced vibration response. The time-history curve of the beam’s upper middle point is obtained for thermal or non-thermal situations

Optical wireless scattering channel estimation for photon-counting and photomultiplier tube receivers

Channel estimation is conceived for optical wireless scattering channels associated with laser diode transmitters and photon-counting/photomultiplier tube receivers. The proposed channel estimation approach consists of two stages, namely, of the estimation of the channel tap second-order moments followed by the estimation of the channel taps based on the estimate of second-order moments. In the first stage, we provide the general framework of the moment estimation complemented by the conception of an estimation approach based on a sparse pilot structure, as well as by the analysis of the estimation error. We also propose a novel sparse pilot design as well as the associated low-complexity channel estimation, and prove the optimality of the proposed channel estimation. In the second stage, we conceive the associated channel tap estimation based on the eigenvalue decomposition of the matrix of estimated second-order moments, and analyze the associated performance. It is shown that as the length of the pilot sequence tends to infinity, the probability of having an estimation distortion above a certain threshold can be reduced arbitrarily small. Simulation results show that the proposed sparse pilot sequence can lead to a smaller estimation error than the pilot design using random 0-1 bits

PNMBG: Point Neighborhood Merging with Border Grids

The special clustering algorithm is attractive for the task of grouping arbitrary shaped database into several proper classes. Up to now, a wide variety of clustering algorithms designed for this task have been proposed, the majority of these algorithms is density-based. But the effectivity and efficiency still is the great challenges for these algorithms as far as the clustering quality of such task is concerned. In this paper, we propose an arbitrary shaped clustering method with border grids (PNMBG), PNMBG is a crisp partition method. It groups objects to point neighborhoods firstly, and then iteratively merges these point neighborhoods into clusters via grids, only bordering grids are considered during the merging stage. Experiments show that PNMBG has a good efficiency especially on the database with high dimension. In general, PNMBG outperforms DBSCAN in the term of efficiency and has an almost same effectivity with the later

CFD-DEM simulation of biomass pyrolysis in fluidized-bed reactor with a multistep kinetic scheme

The pyrolysis of biomass in a fluidized-bed reactor is studied by a combination of a CFD-DEM algorithm and a multistep kinetic scheme, where fluid dynamics, heat and mass transfer, particle collisions, and the detailed thermochemical conversion of biomass are all resolved. The integrated method is validated by experimental results available in literature and a considerable improvement in predicting the pyrolysis product yields is obtained as compared to previous works using a two-fluid model, especially the relative error in the predicted tar yield is reduced by more than 50%. Furthermore, the evolution of light gas, char and tar, as well as the particle conversion, which cannot easily be measured in experiments, are also revealed. Based on the proposed model, the influences of pyrolysis temperature and biomass particle size on the pyrolysis behavior in a fluidized-bed reactor are comprehensively studied. Numerical results show that the new algorithm clearly captures the dependence of char yield on pyrolysis temperature and the influence of heating rate on light gas and tar yields, which is not possible in simulations based on a simplified global pyrolysis model. It is found that, as the temperature rises from 500 to 700 \ub0C, the light gas yield increases from 17% to 25% and char yield decreases from 22% to 14%. In addition, within the tested range of particle sizes (<1 mm), the impact on pyrolysis products from particle size is relatively small compared with that of the operating temperature. The simulations demonstrate the ability of a combined Lagrangian description of biomass particles and a multistep kinetic scheme to improve the prediction accuracy of fluidized-bed pyrolysis

Unveiling local atomic bonding and packing of amorphous nanophases via independent component analysis facilitated pair distribution function

Amorphous nanophases play a significant role for the properties of a variety of nanoscale heterogeneous materials. Experimental characterization of the atomic arrangement of the amorphous structure, including nanoscale structural variations, is one of the main challenges limiting the rational design of the materials. Here, an approach to characterize local bonding and atomic packing in complex nanomaterials is introduced. Building on scanning transmission electron microscopy (STEM) and pair distribution function analysis (PDF) to record local diffraction information with nanometer spatial resolution, we show that independent component analysis for “blind source separation” of mixed information due to projection effects in STEM-PDF, enables full separation of these signals. The unprecedented information allows determining the structure of individual nanoscale phases and identifying the compounds inside. We analyzed a FeZr/ZrO2 multilayer as proof of principle, and discovered differently coordinated FeOx in the interfacial region. The approach was applied to Fe25Sc75 nanoglass and revealed Fe–Fe bonding concealed in the Sc-rich matrix. Finally, analysis of a shear band in a deformed Cu/CuZr nanolaminate confirmed Cu enrichment and reduced medium-range order in the shear band

Rural financial development, spatial spillover, and poverty reduction: evidence from China

Rural financial development is deemed essential for eliminating poverty. In China, successive governments have initiated a series of financial development plans to reduce poverty since the launch of economic reform in the late 1970s. However, there is a rising concern about whether financial development can reduce poverty in China. This study uses a panel dataset of 30 provinces (out of 31) in mainland China from 1997 to 2015 to examine the effect of rural financial development on poverty reduction. We employ a spatial panel model to investigate whether rural financial development has a positive spatial spillover effect. Moreover, we use the instrumental variable method to address the possible bidirectional causal effect between rural financial development and poverty reduction. Our study confirms that rural financial development does reduce poverty and simultaneously widen the urban-rural income gap. We further find that rural financial development has a positive spatial spillover effect on poverty alleviation and that the conventional panel model (e.g., fixed effects method) may underestimate the effect of rural financial development, as it ignores the spatial spillover effect

Cost minimization control for electric vehicle car parks with vehicle-to-grid technology

With coordinated charging and discharging, electric vehicles (EVs) in smart car parks can be used as energy storage systems and a reserve against unexpected outrage. In this work, a modeling and control framework for EVs in a smart car park has been built up, which includes key factors such as the charging and discharging costs, the battery degradation cost, the driving probability, the feed-in tariff (FIT), and the vehicle-to-grid (V2G) rebates. Each EVs’ charging and discharging activities are scheduled through an optimization route with the purpose to minimize the car park electricity cost. Results from comprehensive simulation studies demonstrate the potential benefits of V2G for car park systems with multiple EVs subject to vehicle and battery characteristics, FIT and policy support