jiatang wang - Academia.edu (original) (raw)

Papers by jiatang wang

International Journal of Energy Research, 2021

Nickel‐rich LiNixCoyMn1‐x‐yO2 (x ≥ 0.6, NCM) materials and in particular LiNi0.8Co0.1Mn0.1O2 (NCM... more Nickel‐rich LiNixCoyMn1‐x‐yO2 (x ≥ 0.6, NCM) materials and in particular LiNi0.8Co0.1Mn0.1O2 (NCM811) are considered as the most potential candidates for utilization in the next‐generation of high‐energy‐density lithium‐ion batteries (LIBs). However, the NCM811 materials encounter capacity fading during cycling, originating mainly from detrimental positive electrode‐electrolyte interface changes. Here, to decrease electrolyte oxidative decomposition during NCM811 cycling process, we select a partially fluorinated ether, such as 1,1,2,2‐ tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) and 1,1,1,3,3,3‐hexafluoroisopropyl methyl ether (HFPM), as a co‐solvent for fluoroethylene carbonate (FEC)‐based electrolytes and investigate theirs physicochemical and electrochemical performances in great details for their applications in NCM811 materials. Compared to the FEC‐based electrolyte solution without a fluorinated ether co‐solvent, the electrolytes with a fluorinated ether co‐solvent exhibits an obviously improved cycling and rate properties of the Li/NCM811 cells cycled between 2.7 and 4.3 V. This work also shows that the TTE solvent is prone to both suppress the decomposition of FEC to stabilize the FEC‐based electrolyte solution, and be reduced and form a stable interface layer in the highly reactive Li surface.

Energies, 2020

During development of substitute anode materials suitable for solid oxide fuel cell (SOFC), under... more During development of substitute anode materials suitable for solid oxide fuel cell (SOFC), understanding of sintering mechanisms and effects is significant for synthesized porous structures and performance. A molecular dynamics (MD) model is developed and applied in this study for the SOFC anode sintered materials to reveal the sintering condition effects. It is predicted that, for the case of two nanoparticles of electron-conducting La-doped SrTiO3 (LST), the higher the sintering temperature, the faster the aggregation of nanoparticles and the higher the sintering degree. An increase in the nanoparticle size could delay the sintering, process but does not affect the final sintering degree. The MD model is further applied for the case of the multi-nanoparticles containing LST and ion-conducting electrolyte materials of gadolinium-doped ceria (GDC), i.e., the LST-GDC particles. The sintering conditions and effects on the LST-GDC particles are evaluated, in terms of the mean square d...

Applied Energy, 2020

High-temperature fuel cells as CO 2 concentrators are presented. • Developments of high-temperatu... more High-temperature fuel cells as CO 2 concentrators are presented. • Developments of high-temperature fuel cell integrated CO 2 capture processes are reviewed. • Technical and economic evaluations on fuel cell hybrid systems with CO 2 capture are discussed. • Challenges and future prospects of fuel cell with CO 2 capture are suggested.

Energy, 2020

A new hybrid system composed of high-temperature proton exchange fuel cell and two-stage thermoel... more A new hybrid system composed of high-temperature proton exchange fuel cell and two-stage thermoelectric generator with Thomson effect: Energy and exergy analyses, Energy (2020), doi: https://doi.org/10.1016/ j.energy.2020.117000. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

International Journal of Ambient Energy, 2020

Integrating a two-stage thermoelectric generator (TTEG) with a molten carbonate fuel cell (MCFC),... more Integrating a two-stage thermoelectric generator (TTEG) with a molten carbonate fuel cell (MCFC), a new hybrid system is put forward to harvest the waste heat from the MCFC for performance improvement. Both thermodynamic and electrochemical irreversible losses in each subsystem are fully taken into account. The thermoelectric element (TEM) number ratio between hot stage and cold stage is optimally designed using power output as objective function. The mathematical relationship between MCFC operating current density and the optimized TTEG dimensionless electric current is obtained, from which the MCFC operating current density interval that allows TTEG to function is determined. The analytical expressions for equivalent power output and efficiency to evaluate the hybrid system performance are obtained. The proposed hybrid system is demonstrated to be superior to either stand-alone MCFC or MCFC/single-stage TEG hybrid system. Effects of some crucial design and operation parameters on the system performance are revealed by parametric studies.

Electrochimica Acta, 2020

Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiomet... more Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiometry can yield the positive effects on the catalytic activity of the ABO 3 perovskite toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Whereas, the universality of the deficient or excessive effects and their resulting improving mechanisms on ABO 3 perovskite are still ambiguous and need to be clarified. In this work, the simplest Mn-based perovskite (LaMnO 3) is selected to elucidate the deficient/excessive effects and improving mechanisms on both ORR and OER. We find that A-site deficient stoichiometry is favor to the catalytic activity and stability of LaMnO 3 toward both ORR and OER, whereas A-site excessive stoichiometry is deleterious to the oxygen catalytic activity and stability of LaMnO 3. The high oxygen catalytic activity of La 0$9 MnO 3 (La90) with A-site deficiency toward ORR and OER can be related to its proper Mn cation valence, large amount of oxygen vacancies, upper shift of dband center and strong adsorption capacity to oxygenated species. The results of this work highlight the A-site deficient Mn-based perovskite as the high efficient and commercially viable bifunctional catalyst for aqueous and solid-state flexible zinc-air battery (ZAB) applications.

Energy, 2019

A two-dimensional mathematical model is developed for a single-cell based on the planar configura... more A two-dimensional mathematical model is developed for a single-cell based on the planar configuration and validated by relevant experimental data, with an aim to describe the coupling phenomena of the multiphysics transport processes and the meso-scale elementary reactions. It is revealed that desorption and adsorption reactions in the electrode mostly take place near the electrolyte and the channel, respectively; the distribution of the surface species depends on the gas diffusion in the porous electrode affected by the thickness and microstructure of the electrode. The electrochemical reactions are centralized in about 100 mm thick electrode from the electrolyte. Ni s and CO s are the major surface species in both fuel cell (FC) and electrolysis cell (EC) modes. O s is higher in the FC mode, particularly near the electrolyte due to the desorption and charge transfer reactions; The microscopic structure properties, including average porosity, tortuosity and particle size, are also influential on the elementary reactions due to the gas diffusion through the tortuous pathways and the active sites on the catalyst surfaces. It is also found that the performance predicted in the global models is often overestimated, because the limitations of the local elementary reactions are not considered in the global model.

Journal of Renewable and Sustainable Energy, 2019

A generic combined system composed primarily of a molten carbonate fuel cell (MCFC) and an absorp... more A generic combined system composed primarily of a molten carbonate fuel cell (MCFC) and an absorption cycle is proposed, in which the absorption cycle can operate as either an absorption heat pump (AHP) for heat amplification or an absorption refrigerator (APR) for cooling applications. The equivalent power output and efficiency expressions for the combined system are formulated by considering various electrochemical-thermodynamic irreversible losses within and between each subsystem. As a result, the generic performance characteristics are revealed, and the optimum criteria are determined. When the absorption cycle operates as an AHP or an APR, the maximum achievable power densities of the combined system are 21.23% and 10.2% higher than those of a single MCFC, respectively. Furthermore, comprehensive parametric studies are performed to show the dependency of the combined system performance on some of the important operating conditions and composite parameters.

Energy & Fuels, 2018

In a global carbon cycle, the net greenhouse gas (e.g., CO 2) emissions can be significantly redu... more In a global carbon cycle, the net greenhouse gas (e.g., CO 2) emissions can be significantly reduced if fossil fuels could be substituted with renewable and cleaner biomass-derived fuels. In the traditional iron ore sintering process, the complete replacement of coke-a coal derived fuel-with charcoal is not possible because the two fuels have very different properties and combustion behaviours, resulting in an unacceptable deterioration in sintering performance. Consequently, only low substitution ratios can be tolerated. However, research has indicated that this ratio can be increased through altering the combustion behaviour of charcoal. Most fuel particles in a sintering bed have an encapsulated layer of fine ore and flux particles. Through intentionally altering the properties of this adhering layer, combustion behaviour can be altered, leading to improved sintering performance. This work uses a newly-developed combustion model and a 2D sintering model to appropriately describe the combustion behaviour in sintering based on fuel properties and defines the optimum thickness and porosity of the adhering layer. In this study, the required properties of the adhering layer encapsulating charcoal particles-so as to match the combustion behaviour of coke particles-is determined theoretically. This study also shows that the conditions required for different fuels to have similar sintering performance are: (a) comparable ignition temperature and overall combustion rate, and (b) comparable rates of combustion at various temperatures. Matching the overall combustion rate alone does not necessarily result in comparable sintering performance. Meanwhile, the apparent density and water holding capacity of the substituting fuels should be close to the equivalent values for coke to ensure similar granulation performance and, subsequently, the properties of the bed prepared for sintering. Until these conditions are fully met, combustion efficiency, the properties of the formed flame front (e.g., width, temperature, and speed) and, consequently, sintering performance will deteriorate. In practice, fully matching all these conditions are difficult. The present work has given guidelines on which are the critical variables of the adhering fines layer that have to be considered when charcoal is introduced into sintering and also how the variable interact to determine flame front properties.

Applied Energy, 2018

• An integration of chilled ammonia process using absorption refrigerator into coal-fired power p... more • An integration of chilled ammonia process using absorption refrigerator into coal-fired power plant was proposed. • A 300 MWe subcritical coal-fired plant was selected as the baseline. • Efficiency penalties of the overall process for different steam extraction were obtained. • The absorption refrigerator was compared with the vapor compression refrigerator.

International Journal of Hydrogen Energy, 2019

A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (... more A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is proposed, where the TEG is applied to harness the generated waste heat in the HT-PEMFC for extra electricity production. The TEG considers not only the Seebeck effect and Peltier effect but also the Thomson effect. The mathematical expressions of power output, energy efficiency, exergy destruction rate and exergy efficiency for the proposed system are derived. The energetic and exergetic performance characteristics for the whole system are revealed. The optimum operating ranges for some key performance parameters of the combined system are determined using the maximum power density as the objective function. The combined system maximum power density and its corresponding energy efficiency and exergy efficiency allow 19.1%, 12.4% and 12.6% higher than that of a stand-alone HT-PEMFC, while the exergy destruction rate density is only increased by 8.6%. The system performances are compared between the TEG with and without the Thomson effect. Moreover, the impacts of comprehensive parameters on the system performance characteristics are discussed. The obtained results are helpful in developing and designing such an actual combined system for efficient and clean power production.

Energy, 2019

A new combined system consisting of a high-temperature proton exchange membrane fuel cell (HT-PEM... more A new combined system consisting of a high-temperature proton exchange membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is developed. The mathematical relationship between the HT-PEMFC operating current density and the TEG dimensionless current is derived, and the operating current density range of HT-PEMFC in which the TEG allowed to work is determined. Power output and efficiency of the combined system are formulated under different operating conditions. Compared with the stand-alone HT-PEMFC, the proposed combined system allows the equivalent power density to increase by 21%. The optimum criteria and general performance characteristics for the complete system are specified. Moreover, the effects of the operating current density, doping level, relative humidity, operating temperature, heat conductivity and figure of merit of the thermoelectric materials on the combined system performance characteristics are revealed. The obtained results may provide some theoretical insights into the design and integration of such an actual combined system.

Energy Conversion and Management, 2019

In addition to generate electricity, solid oxide fuel cells also produce a considerable quantity ... more In addition to generate electricity, solid oxide fuel cells also produce a considerable quantity of high-quality waste heat. To harvest the waste heat, an advanced triple-cycle system based upon solid oxide fuel cells, vacuum thermionic generators and absorption refrigerators is theoretically put forward. Assuming that the main irreversible losses within the system are thermodynamic and electrochemical losses, the performance parameters mathematically evaluating the whole system are specified under different operating conditions. The effectiveness is also demonstrated through performance comparisons between the proposed system and the stand-alone solid oxide fuel cell system. Numerical calculations show that the maximum attainable power density and its corresponding efficiency allow 20.3% and 18.4% larger than that of the stand-alone solid oxide fuel cell system, respectively. Comprehensive parametric studies are further undertaken to reveal the influences of some decisive design parameters and operating conditions on the triple-cycle system performance. Results show that the microstructure parameters of the solid oxide fuel cell and the anode temperature of the vacuum thermionic generator can be optimally designed to maximize the power density of the triple-cycle system. The vacuum thermionic generator can be treated as the alternative intermediate cycle for SOFC based triple-cycle systems.

Energies, 2019

By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse... more By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse the waste heat from a Molten Carbonate Direct Carbon Fuel Cell (MCDCFC) for additional cooling production. Various irreversible losses in each element of the system are numerically described. The operating current density span of the MCDCFC that allows the AR to work is derived. Under different operating conditions, the mathematical expressions for equivalently evaluating the hybrid system performance are derived. In comparison with the stand-alone MCDCFC, the maximum attainable power density of the proposed system and its corresponding efficiency are increased by 5.8% and 6.8%, respectively. The generic performance features and optimum operating regions of the proposed system are demonstrated. A number of sensitivity analyses are performed to study the dependences of the proposed system performance on some physical parameters and operating conditions such as operating temperature, oper...

International Journal of Energy Research, 2018

Reversible solid oxide fuel cells (rSOFCs) may be applied to store and generate electrical energy... more Reversible solid oxide fuel cells (rSOFCs) may be applied to store and generate electrical energy in a reversible mode. This technique is promising to balance the conflict between intermittent power supply and demand in a sustainable way. One of the limitations of the development of rSOFCs is the high cost of storage and usage of pure H 2 , which may be solved by employing syngas as the fuel. The performance of rSOFCs depends on the development of bifunctional materials, cell design, and operation optimization, which are often investigated and predicted by the cost-effective approach of mathematical modeling. However, the modeling of dual-mode rSOFCs involving co-redox reactions with syngas is not well developed. In this study, a two-dimensional (2D) single-channel model of an rSOFC is developed. The novelty of this model is that the multiphysics transport processes are fully coupled and solved with the reversible water-gas shift reaction with syngas and the electrochemical reactions. The effects of the operating conditions and design parameters (eg, electrode thickness) are considered, with the aim of providing guidelines to optimize the design and operation of reversible cells. It is concluded that the thickness of the electrode has a larger impact on the water-gas shift reaction than on the electrochemical reaction in both the gas diffusion and reaction regions. The C/H element ratio of syngas has a negative correlation with power output, but the distributions of current and gas species may be improved in both modes. A higher operating temperature improves the performance in both modes but has a more substantial effect in the electrolysis mode. The specific design and operating schemes favored in different modes should be balanced in the reversible mode.

International Journal of Energy Research, 2017

Proton exchange membrane fuel cells have been promoted due to improved breakthrough and increased... more Proton exchange membrane fuel cells have been promoted due to improved breakthrough and increased commercialization. The assembly pressure put on a single cell and a fuel cell stack has important influence on the geometric deformation of the gas diffusion layers (GDLs) resulting in a change in porosity, permeability, and the resistance for heat and charge transfer in proton exchange membrane fuel cells. In this paper, both the finite element method and the finite volume method are used, respectively, to predict the GDL deformation and associated effects on the geometric parameters, porosity, mass transport property, and the cell performance. It is found that based on the isotropic Young's modulus and the finite element method, the porosity and thickness under a certain assembly pressure are non-homogeneous across the fuel cell in the in-plane direction. The variations of the porosity change and compression ratio in the cross-section plane are localized by three zones, that is, a linear porosity zone, a constant porosity zone, and a nonlinear porosity zone. The results showed that the GDL porosity and compression ratios maintain linear and nonlinear changes in the zone above the shoulders and the zone under the channel but close to the shoulder, respectively. However, a constant value is kept above the middle of the channel. The obtained non-homogeneous porosity distribution is applied together with the deformed GDL for further computational fluid dynamics analysis, in which the finite volume method is implemented. The computational fluid dynamic results reveal that a higher assembly pressure decreases the porosity, GDL thickness, gas flow channel cross-sectional areas, oxygen diffusion coefficient, oxygen concentration, and cell performance. The maximum oxygen mole fraction occurs where the maximum porosity exists. A sufficient GDL thickness is required to ensure transfer of fresh gas to the reaction sites far away from the channel. However, the reduction of porosity is a dominating factor that decreases the cell performance compared with the decreased gas channel flow area and GDL thickness in the assembly condition. Therefore, the assembly pressure should be balanced to consider both the cell performance and gas sealing security.

International Journal of Energy Research, 2016

A comprehensive, three-dimensional model of a proton exchange membrane (PEM) fuel cell based on a... more A comprehensive, three-dimensional model of a proton exchange membrane (PEM) fuel cell based on a steady state code has been developed. The model is validated and further be applied to investigate the effects of various porosity of the gas diffusion layer (GDL) below channel land areas, on thermal diffusivity, temperature distribution, oxygen diffusion coefficient, oxygen concentration, activation loss and local current density. The porosity variation of the GDL is caused by the clamping force during assembling, in terms of various compression ratios, that is, 0%, 10%, 20%, 30% and 40%. The simulation results show that the higher compression ratio on the GDL leads to lower porosity, and this is helpful for the heat removal from the cell. The compression effects of the GDL below the land areas have a contrary impact on the oxygen diffusion coefficient, oxygen concentration, cathode activation loss, local current density and cell performance. Generally, a lower porosity leads to a smaller oxygen diffusion coefficient, a less uniform oxygen concentration, a higher activation loss, a smaller local current density and worse cell performance. In order to have a better cell performance, the clamping force on the cell should be as low as possible but ensure gas sealing.

Proton exchange membrane (PEM) fuel cells are known as environmental friendly energy conservation... more Proton exchange membrane (PEM) fuel cells are known as environmental friendly energy conservation devices, and have the potential to be suitable alternative power sources. The cost and durability of a PEM fuel cell are strongly affected by the involved transport phenomena and reactions, which are two major challenges to be overcome before commercialization. Modeling and simulation are crucial for the cell design and operation. Various “add-on” fuel cell modules are available in commonly-used commercial CFD codes: FLUENT, STAR-CD and COMSOL Multiphysics. However, the length scale of PEM fuel cell’s main components ranges from the micro over the meso to the macro level. The various transport processes at different scales sometimes cannot be captured simultaneously by these codes. On the other hand, physical properties of functional layers used in MEA (membrane electrolyte assembly, consisting of catalyst layers, gas diffusion layers and membrane) play an important role for the cell performance. Therefore coupling of the multi-scale structural and transport characteristics in the functional layers might be an effective way to understand the electrochemical reactions and transient transport phenomena in PEM fuel cells. OpenFOAM (Open Field Operation and Manipulation) is an open source finite volume code having an object-oriented design written in C++, which allows implementation of own models and numerical algorithms. Furthermore, it is possible to integrate other models, e.g., particle-based models, with the OpenFOAM CFD Toolbox. Thus OpenFOAM has the potential to meet the requirements faced in PEM fuel cell simulations as mentioned above. In this paper, various models and applications of OpenFOAM are outlined and reviewed, focusing on the multi-phase transport processes and reactions in PEM fuel cells. The potential methods and challenges coupling OpenFOAM with other modeling techniques are also discussed and highlighted. (Less)

International Journal of Hydrogen Energy, 2019

One of advantages of solid oxide fuel cells (SOFCs) is able to utilize various hydrocarbon fuels.... more One of advantages of solid oxide fuel cells (SOFCs) is able to utilize various hydrocarbon fuels. Whereas, the classical Ni anode suffers severe carbon deposition especially operated under CH 4. Strontium titanate (SrTiO 3) perovskite anodes with strong carbon deposition resistance and good structural stability have been extensively investigated. In this work, Sr 0.88 Y 0.08-x Yb x TiO 3 and Sr 0.88 Y 0.08 Ti 1-x Yb x O 3 are synthesized by Yb 3þ doping in A-site and B-site of Sr 0.88 Y 0.08 TiO 3 perovskite, respectively. XRD results confirm that the SrTiO 3 cubic perovskite phase is formed in all the samples. Among the Yb 3þ doping samples, Sr 0.88-Y 0.06 Yb 0.02 TiO 3 exhibits the lowest thermal expansion coefficient (11.48 Â 10 À6 /K), indicating the best compatibility with the electrolyte. The ionic conductivity of Sr 0.88 Y 0.08 TiO 3 can be improved by proper Yb 3þ doping both in A-site and B-site, and the Sr 0.88 Y 0.06-Yb 0.02 TiO 3 sample has the highest ionic conductivity among all the samples. The maximum power density of SOFC with Sr 0.88 Y 0.06 Yb 0.02 TiO 3 anode is 87 mW/cm 2 under CH 4 at 800 C, which is much higher than that with Sr 0.88 Y 0.08 TiO 3 and Ni anode. This can be related to its high electrocatalytic activity to CH 4 oxidation. In addition, SOFC with the Sr 0.88 Y 0.06 Yb 0.02-TiO 3 anode shows a superior stability operated under CH 4 due to the strong carbon deposition resistances.

International Journal of Hydrogen Energy, 2017

The electric resistance is very important for the performance of a proton exchange membrane (PEM)... more The electric resistance is very important for the performance of a proton exchange membrane (PEM) fuel cell. However, the performance analysis is more complex as the cell operates under assembly conditions. At such conditions, the mass transfer is deteriorated but the electric conductivity is favored. In this paper, the electric resistance of a cell is evaluated by application of a recently developed method in the through-plane direction of the electrodes, together with consideration of the contact resistance between the gas diffusion layer (GDL) and bi-polar plates (BPP) for various assembly pressures. The predicted electric resistance and deformed GDL were implemented in an existing CFD code for evaluation of the PEM fuel cell performance. It is found that the electric current is distributed in a narrow area in the GDL under the shoulders and then redistributed into the BPP above the channels for all cases. The channel/rib structure promotes a non-homogeneous electric conductivity along the cell in the in-plane direction and a concentrated area of the current flow around the corner of the BPP close to the channels as the cell is subject to an assembly pressure. Additional contact areas are created between the GDL and BPP at the vertical interface when the cell operates at an assembly pressure above 2 MPa. Therefore, both the corner of a BPP close to the channel and the GDL region become the dominating zones, where the electric current under the middle of the channel must cross over a longer distance due to the intrusion of the GDL into the BPP. In addition, the optimized cell performance is obtained as the cell is operating below 1 MPa assembly pressure. The findings are useful for proper design of PEM fuel cells.

International Journal of Energy Research, 2021

Nickel‐rich LiNixCoyMn1‐x‐yO2 (x ≥ 0.6, NCM) materials and in particular LiNi0.8Co0.1Mn0.1O2 (NCM... more Nickel‐rich LiNixCoyMn1‐x‐yO2 (x ≥ 0.6, NCM) materials and in particular LiNi0.8Co0.1Mn0.1O2 (NCM811) are considered as the most potential candidates for utilization in the next‐generation of high‐energy‐density lithium‐ion batteries (LIBs). However, the NCM811 materials encounter capacity fading during cycling, originating mainly from detrimental positive electrode‐electrolyte interface changes. Here, to decrease electrolyte oxidative decomposition during NCM811 cycling process, we select a partially fluorinated ether, such as 1,1,2,2‐ tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) and 1,1,1,3,3,3‐hexafluoroisopropyl methyl ether (HFPM), as a co‐solvent for fluoroethylene carbonate (FEC)‐based electrolytes and investigate theirs physicochemical and electrochemical performances in great details for their applications in NCM811 materials. Compared to the FEC‐based electrolyte solution without a fluorinated ether co‐solvent, the electrolytes with a fluorinated ether co‐solvent exhibits an obviously improved cycling and rate properties of the Li/NCM811 cells cycled between 2.7 and 4.3 V. This work also shows that the TTE solvent is prone to both suppress the decomposition of FEC to stabilize the FEC‐based electrolyte solution, and be reduced and form a stable interface layer in the highly reactive Li surface.

Energies, 2020

During development of substitute anode materials suitable for solid oxide fuel cell (SOFC), under... more During development of substitute anode materials suitable for solid oxide fuel cell (SOFC), understanding of sintering mechanisms and effects is significant for synthesized porous structures and performance. A molecular dynamics (MD) model is developed and applied in this study for the SOFC anode sintered materials to reveal the sintering condition effects. It is predicted that, for the case of two nanoparticles of electron-conducting La-doped SrTiO3 (LST), the higher the sintering temperature, the faster the aggregation of nanoparticles and the higher the sintering degree. An increase in the nanoparticle size could delay the sintering, process but does not affect the final sintering degree. The MD model is further applied for the case of the multi-nanoparticles containing LST and ion-conducting electrolyte materials of gadolinium-doped ceria (GDC), i.e., the LST-GDC particles. The sintering conditions and effects on the LST-GDC particles are evaluated, in terms of the mean square d...

Applied Energy, 2020

High-temperature fuel cells as CO 2 concentrators are presented. • Developments of high-temperatu... more High-temperature fuel cells as CO 2 concentrators are presented. • Developments of high-temperature fuel cell integrated CO 2 capture processes are reviewed. • Technical and economic evaluations on fuel cell hybrid systems with CO 2 capture are discussed. • Challenges and future prospects of fuel cell with CO 2 capture are suggested.

Energy, 2020

A new hybrid system composed of high-temperature proton exchange fuel cell and two-stage thermoel... more A new hybrid system composed of high-temperature proton exchange fuel cell and two-stage thermoelectric generator with Thomson effect: Energy and exergy analyses, Energy (2020), doi: https://doi.org/10.1016/ j.energy.2020.117000. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

International Journal of Ambient Energy, 2020

Integrating a two-stage thermoelectric generator (TTEG) with a molten carbonate fuel cell (MCFC),... more Integrating a two-stage thermoelectric generator (TTEG) with a molten carbonate fuel cell (MCFC), a new hybrid system is put forward to harvest the waste heat from the MCFC for performance improvement. Both thermodynamic and electrochemical irreversible losses in each subsystem are fully taken into account. The thermoelectric element (TEM) number ratio between hot stage and cold stage is optimally designed using power output as objective function. The mathematical relationship between MCFC operating current density and the optimized TTEG dimensionless electric current is obtained, from which the MCFC operating current density interval that allows TTEG to function is determined. The analytical expressions for equivalent power output and efficiency to evaluate the hybrid system performance are obtained. The proposed hybrid system is demonstrated to be superior to either stand-alone MCFC or MCFC/single-stage TEG hybrid system. Effects of some crucial design and operation parameters on the system performance are revealed by parametric studies.

Electrochimica Acta, 2020

Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiomet... more Recently, many works have demonstrated that tuning the A-site deficient and excessive stoichiometry can yield the positive effects on the catalytic activity of the ABO 3 perovskite toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Whereas, the universality of the deficient or excessive effects and their resulting improving mechanisms on ABO 3 perovskite are still ambiguous and need to be clarified. In this work, the simplest Mn-based perovskite (LaMnO 3) is selected to elucidate the deficient/excessive effects and improving mechanisms on both ORR and OER. We find that A-site deficient stoichiometry is favor to the catalytic activity and stability of LaMnO 3 toward both ORR and OER, whereas A-site excessive stoichiometry is deleterious to the oxygen catalytic activity and stability of LaMnO 3. The high oxygen catalytic activity of La 0$9 MnO 3 (La90) with A-site deficiency toward ORR and OER can be related to its proper Mn cation valence, large amount of oxygen vacancies, upper shift of dband center and strong adsorption capacity to oxygenated species. The results of this work highlight the A-site deficient Mn-based perovskite as the high efficient and commercially viable bifunctional catalyst for aqueous and solid-state flexible zinc-air battery (ZAB) applications.

Energy, 2019

A two-dimensional mathematical model is developed for a single-cell based on the planar configura... more A two-dimensional mathematical model is developed for a single-cell based on the planar configuration and validated by relevant experimental data, with an aim to describe the coupling phenomena of the multiphysics transport processes and the meso-scale elementary reactions. It is revealed that desorption and adsorption reactions in the electrode mostly take place near the electrolyte and the channel, respectively; the distribution of the surface species depends on the gas diffusion in the porous electrode affected by the thickness and microstructure of the electrode. The electrochemical reactions are centralized in about 100 mm thick electrode from the electrolyte. Ni s and CO s are the major surface species in both fuel cell (FC) and electrolysis cell (EC) modes. O s is higher in the FC mode, particularly near the electrolyte due to the desorption and charge transfer reactions; The microscopic structure properties, including average porosity, tortuosity and particle size, are also influential on the elementary reactions due to the gas diffusion through the tortuous pathways and the active sites on the catalyst surfaces. It is also found that the performance predicted in the global models is often overestimated, because the limitations of the local elementary reactions are not considered in the global model.

Journal of Renewable and Sustainable Energy, 2019

A generic combined system composed primarily of a molten carbonate fuel cell (MCFC) and an absorp... more A generic combined system composed primarily of a molten carbonate fuel cell (MCFC) and an absorption cycle is proposed, in which the absorption cycle can operate as either an absorption heat pump (AHP) for heat amplification or an absorption refrigerator (APR) for cooling applications. The equivalent power output and efficiency expressions for the combined system are formulated by considering various electrochemical-thermodynamic irreversible losses within and between each subsystem. As a result, the generic performance characteristics are revealed, and the optimum criteria are determined. When the absorption cycle operates as an AHP or an APR, the maximum achievable power densities of the combined system are 21.23% and 10.2% higher than those of a single MCFC, respectively. Furthermore, comprehensive parametric studies are performed to show the dependency of the combined system performance on some of the important operating conditions and composite parameters.

Energy & Fuels, 2018

In a global carbon cycle, the net greenhouse gas (e.g., CO 2) emissions can be significantly redu... more In a global carbon cycle, the net greenhouse gas (e.g., CO 2) emissions can be significantly reduced if fossil fuels could be substituted with renewable and cleaner biomass-derived fuels. In the traditional iron ore sintering process, the complete replacement of coke-a coal derived fuel-with charcoal is not possible because the two fuels have very different properties and combustion behaviours, resulting in an unacceptable deterioration in sintering performance. Consequently, only low substitution ratios can be tolerated. However, research has indicated that this ratio can be increased through altering the combustion behaviour of charcoal. Most fuel particles in a sintering bed have an encapsulated layer of fine ore and flux particles. Through intentionally altering the properties of this adhering layer, combustion behaviour can be altered, leading to improved sintering performance. This work uses a newly-developed combustion model and a 2D sintering model to appropriately describe the combustion behaviour in sintering based on fuel properties and defines the optimum thickness and porosity of the adhering layer. In this study, the required properties of the adhering layer encapsulating charcoal particles-so as to match the combustion behaviour of coke particles-is determined theoretically. This study also shows that the conditions required for different fuels to have similar sintering performance are: (a) comparable ignition temperature and overall combustion rate, and (b) comparable rates of combustion at various temperatures. Matching the overall combustion rate alone does not necessarily result in comparable sintering performance. Meanwhile, the apparent density and water holding capacity of the substituting fuels should be close to the equivalent values for coke to ensure similar granulation performance and, subsequently, the properties of the bed prepared for sintering. Until these conditions are fully met, combustion efficiency, the properties of the formed flame front (e.g., width, temperature, and speed) and, consequently, sintering performance will deteriorate. In practice, fully matching all these conditions are difficult. The present work has given guidelines on which are the critical variables of the adhering fines layer that have to be considered when charcoal is introduced into sintering and also how the variable interact to determine flame front properties.

Applied Energy, 2018

• An integration of chilled ammonia process using absorption refrigerator into coal-fired power p... more • An integration of chilled ammonia process using absorption refrigerator into coal-fired power plant was proposed. • A 300 MWe subcritical coal-fired plant was selected as the baseline. • Efficiency penalties of the overall process for different steam extraction were obtained. • The absorption refrigerator was compared with the vapor compression refrigerator.

International Journal of Hydrogen Energy, 2019

A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (... more A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is proposed, where the TEG is applied to harness the generated waste heat in the HT-PEMFC for extra electricity production. The TEG considers not only the Seebeck effect and Peltier effect but also the Thomson effect. The mathematical expressions of power output, energy efficiency, exergy destruction rate and exergy efficiency for the proposed system are derived. The energetic and exergetic performance characteristics for the whole system are revealed. The optimum operating ranges for some key performance parameters of the combined system are determined using the maximum power density as the objective function. The combined system maximum power density and its corresponding energy efficiency and exergy efficiency allow 19.1%, 12.4% and 12.6% higher than that of a stand-alone HT-PEMFC, while the exergy destruction rate density is only increased by 8.6%. The system performances are compared between the TEG with and without the Thomson effect. Moreover, the impacts of comprehensive parameters on the system performance characteristics are discussed. The obtained results are helpful in developing and designing such an actual combined system for efficient and clean power production.

Energy, 2019

A new combined system consisting of a high-temperature proton exchange membrane fuel cell (HT-PEM... more A new combined system consisting of a high-temperature proton exchange membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is developed. The mathematical relationship between the HT-PEMFC operating current density and the TEG dimensionless current is derived, and the operating current density range of HT-PEMFC in which the TEG allowed to work is determined. Power output and efficiency of the combined system are formulated under different operating conditions. Compared with the stand-alone HT-PEMFC, the proposed combined system allows the equivalent power density to increase by 21%. The optimum criteria and general performance characteristics for the complete system are specified. Moreover, the effects of the operating current density, doping level, relative humidity, operating temperature, heat conductivity and figure of merit of the thermoelectric materials on the combined system performance characteristics are revealed. The obtained results may provide some theoretical insights into the design and integration of such an actual combined system.

Energy Conversion and Management, 2019

In addition to generate electricity, solid oxide fuel cells also produce a considerable quantity ... more In addition to generate electricity, solid oxide fuel cells also produce a considerable quantity of high-quality waste heat. To harvest the waste heat, an advanced triple-cycle system based upon solid oxide fuel cells, vacuum thermionic generators and absorption refrigerators is theoretically put forward. Assuming that the main irreversible losses within the system are thermodynamic and electrochemical losses, the performance parameters mathematically evaluating the whole system are specified under different operating conditions. The effectiveness is also demonstrated through performance comparisons between the proposed system and the stand-alone solid oxide fuel cell system. Numerical calculations show that the maximum attainable power density and its corresponding efficiency allow 20.3% and 18.4% larger than that of the stand-alone solid oxide fuel cell system, respectively. Comprehensive parametric studies are further undertaken to reveal the influences of some decisive design parameters and operating conditions on the triple-cycle system performance. Results show that the microstructure parameters of the solid oxide fuel cell and the anode temperature of the vacuum thermionic generator can be optimally designed to maximize the power density of the triple-cycle system. The vacuum thermionic generator can be treated as the alternative intermediate cycle for SOFC based triple-cycle systems.

Energies, 2019

By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse... more By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse the waste heat from a Molten Carbonate Direct Carbon Fuel Cell (MCDCFC) for additional cooling production. Various irreversible losses in each element of the system are numerically described. The operating current density span of the MCDCFC that allows the AR to work is derived. Under different operating conditions, the mathematical expressions for equivalently evaluating the hybrid system performance are derived. In comparison with the stand-alone MCDCFC, the maximum attainable power density of the proposed system and its corresponding efficiency are increased by 5.8% and 6.8%, respectively. The generic performance features and optimum operating regions of the proposed system are demonstrated. A number of sensitivity analyses are performed to study the dependences of the proposed system performance on some physical parameters and operating conditions such as operating temperature, oper...

International Journal of Energy Research, 2018

Reversible solid oxide fuel cells (rSOFCs) may be applied to store and generate electrical energy... more Reversible solid oxide fuel cells (rSOFCs) may be applied to store and generate electrical energy in a reversible mode. This technique is promising to balance the conflict between intermittent power supply and demand in a sustainable way. One of the limitations of the development of rSOFCs is the high cost of storage and usage of pure H 2 , which may be solved by employing syngas as the fuel. The performance of rSOFCs depends on the development of bifunctional materials, cell design, and operation optimization, which are often investigated and predicted by the cost-effective approach of mathematical modeling. However, the modeling of dual-mode rSOFCs involving co-redox reactions with syngas is not well developed. In this study, a two-dimensional (2D) single-channel model of an rSOFC is developed. The novelty of this model is that the multiphysics transport processes are fully coupled and solved with the reversible water-gas shift reaction with syngas and the electrochemical reactions. The effects of the operating conditions and design parameters (eg, electrode thickness) are considered, with the aim of providing guidelines to optimize the design and operation of reversible cells. It is concluded that the thickness of the electrode has a larger impact on the water-gas shift reaction than on the electrochemical reaction in both the gas diffusion and reaction regions. The C/H element ratio of syngas has a negative correlation with power output, but the distributions of current and gas species may be improved in both modes. A higher operating temperature improves the performance in both modes but has a more substantial effect in the electrolysis mode. The specific design and operating schemes favored in different modes should be balanced in the reversible mode.

International Journal of Energy Research, 2017

Proton exchange membrane fuel cells have been promoted due to improved breakthrough and increased... more Proton exchange membrane fuel cells have been promoted due to improved breakthrough and increased commercialization. The assembly pressure put on a single cell and a fuel cell stack has important influence on the geometric deformation of the gas diffusion layers (GDLs) resulting in a change in porosity, permeability, and the resistance for heat and charge transfer in proton exchange membrane fuel cells. In this paper, both the finite element method and the finite volume method are used, respectively, to predict the GDL deformation and associated effects on the geometric parameters, porosity, mass transport property, and the cell performance. It is found that based on the isotropic Young's modulus and the finite element method, the porosity and thickness under a certain assembly pressure are non-homogeneous across the fuel cell in the in-plane direction. The variations of the porosity change and compression ratio in the cross-section plane are localized by three zones, that is, a linear porosity zone, a constant porosity zone, and a nonlinear porosity zone. The results showed that the GDL porosity and compression ratios maintain linear and nonlinear changes in the zone above the shoulders and the zone under the channel but close to the shoulder, respectively. However, a constant value is kept above the middle of the channel. The obtained non-homogeneous porosity distribution is applied together with the deformed GDL for further computational fluid dynamics analysis, in which the finite volume method is implemented. The computational fluid dynamic results reveal that a higher assembly pressure decreases the porosity, GDL thickness, gas flow channel cross-sectional areas, oxygen diffusion coefficient, oxygen concentration, and cell performance. The maximum oxygen mole fraction occurs where the maximum porosity exists. A sufficient GDL thickness is required to ensure transfer of fresh gas to the reaction sites far away from the channel. However, the reduction of porosity is a dominating factor that decreases the cell performance compared with the decreased gas channel flow area and GDL thickness in the assembly condition. Therefore, the assembly pressure should be balanced to consider both the cell performance and gas sealing security.

International Journal of Energy Research, 2016

A comprehensive, three-dimensional model of a proton exchange membrane (PEM) fuel cell based on a... more A comprehensive, three-dimensional model of a proton exchange membrane (PEM) fuel cell based on a steady state code has been developed. The model is validated and further be applied to investigate the effects of various porosity of the gas diffusion layer (GDL) below channel land areas, on thermal diffusivity, temperature distribution, oxygen diffusion coefficient, oxygen concentration, activation loss and local current density. The porosity variation of the GDL is caused by the clamping force during assembling, in terms of various compression ratios, that is, 0%, 10%, 20%, 30% and 40%. The simulation results show that the higher compression ratio on the GDL leads to lower porosity, and this is helpful for the heat removal from the cell. The compression effects of the GDL below the land areas have a contrary impact on the oxygen diffusion coefficient, oxygen concentration, cathode activation loss, local current density and cell performance. Generally, a lower porosity leads to a smaller oxygen diffusion coefficient, a less uniform oxygen concentration, a higher activation loss, a smaller local current density and worse cell performance. In order to have a better cell performance, the clamping force on the cell should be as low as possible but ensure gas sealing.

Proton exchange membrane (PEM) fuel cells are known as environmental friendly energy conservation... more Proton exchange membrane (PEM) fuel cells are known as environmental friendly energy conservation devices, and have the potential to be suitable alternative power sources. The cost and durability of a PEM fuel cell are strongly affected by the involved transport phenomena and reactions, which are two major challenges to be overcome before commercialization. Modeling and simulation are crucial for the cell design and operation. Various “add-on” fuel cell modules are available in commonly-used commercial CFD codes: FLUENT, STAR-CD and COMSOL Multiphysics. However, the length scale of PEM fuel cell’s main components ranges from the micro over the meso to the macro level. The various transport processes at different scales sometimes cannot be captured simultaneously by these codes. On the other hand, physical properties of functional layers used in MEA (membrane electrolyte assembly, consisting of catalyst layers, gas diffusion layers and membrane) play an important role for the cell performance. Therefore coupling of the multi-scale structural and transport characteristics in the functional layers might be an effective way to understand the electrochemical reactions and transient transport phenomena in PEM fuel cells. OpenFOAM (Open Field Operation and Manipulation) is an open source finite volume code having an object-oriented design written in C++, which allows implementation of own models and numerical algorithms. Furthermore, it is possible to integrate other models, e.g., particle-based models, with the OpenFOAM CFD Toolbox. Thus OpenFOAM has the potential to meet the requirements faced in PEM fuel cell simulations as mentioned above. In this paper, various models and applications of OpenFOAM are outlined and reviewed, focusing on the multi-phase transport processes and reactions in PEM fuel cells. The potential methods and challenges coupling OpenFOAM with other modeling techniques are also discussed and highlighted. (Less)

International Journal of Hydrogen Energy, 2019

One of advantages of solid oxide fuel cells (SOFCs) is able to utilize various hydrocarbon fuels.... more One of advantages of solid oxide fuel cells (SOFCs) is able to utilize various hydrocarbon fuels. Whereas, the classical Ni anode suffers severe carbon deposition especially operated under CH 4. Strontium titanate (SrTiO 3) perovskite anodes with strong carbon deposition resistance and good structural stability have been extensively investigated. In this work, Sr 0.88 Y 0.08-x Yb x TiO 3 and Sr 0.88 Y 0.08 Ti 1-x Yb x O 3 are synthesized by Yb 3þ doping in A-site and B-site of Sr 0.88 Y 0.08 TiO 3 perovskite, respectively. XRD results confirm that the SrTiO 3 cubic perovskite phase is formed in all the samples. Among the Yb 3þ doping samples, Sr 0.88-Y 0.06 Yb 0.02 TiO 3 exhibits the lowest thermal expansion coefficient (11.48 Â 10 À6 /K), indicating the best compatibility with the electrolyte. The ionic conductivity of Sr 0.88 Y 0.08 TiO 3 can be improved by proper Yb 3þ doping both in A-site and B-site, and the Sr 0.88 Y 0.06-Yb 0.02 TiO 3 sample has the highest ionic conductivity among all the samples. The maximum power density of SOFC with Sr 0.88 Y 0.06 Yb 0.02 TiO 3 anode is 87 mW/cm 2 under CH 4 at 800 C, which is much higher than that with Sr 0.88 Y 0.08 TiO 3 and Ni anode. This can be related to its high electrocatalytic activity to CH 4 oxidation. In addition, SOFC with the Sr 0.88 Y 0.06 Yb 0.02-TiO 3 anode shows a superior stability operated under CH 4 due to the strong carbon deposition resistances.

International Journal of Hydrogen Energy, 2017

The electric resistance is very important for the performance of a proton exchange membrane (PEM)... more The electric resistance is very important for the performance of a proton exchange membrane (PEM) fuel cell. However, the performance analysis is more complex as the cell operates under assembly conditions. At such conditions, the mass transfer is deteriorated but the electric conductivity is favored. In this paper, the electric resistance of a cell is evaluated by application of a recently developed method in the through-plane direction of the electrodes, together with consideration of the contact resistance between the gas diffusion layer (GDL) and bi-polar plates (BPP) for various assembly pressures. The predicted electric resistance and deformed GDL were implemented in an existing CFD code for evaluation of the PEM fuel cell performance. It is found that the electric current is distributed in a narrow area in the GDL under the shoulders and then redistributed into the BPP above the channels for all cases. The channel/rib structure promotes a non-homogeneous electric conductivity along the cell in the in-plane direction and a concentrated area of the current flow around the corner of the BPP close to the channels as the cell is subject to an assembly pressure. Additional contact areas are created between the GDL and BPP at the vertical interface when the cell operates at an assembly pressure above 2 MPa. Therefore, both the corner of a BPP close to the channel and the GDL region become the dominating zones, where the electric current under the middle of the channel must cross over a longer distance due to the intrusion of the GDL into the BPP. In addition, the optimized cell performance is obtained as the cell is operating below 1 MPa assembly pressure. The findings are useful for proper design of PEM fuel cells.