Numerical Analysis on Temperature Distribution in a Single Cell of PEFC Operated at Higher Temperature by1D Heat Transfer Model and 3D Multi-Physics Simulation Model

This study is to understand the impact of operating conditions, especially initial operation temperature (Tini) which is set in a high temperature range, on the temperature profile of the interface between the polymer electrolyte membrane (PEM) and the catalyst layer at the cathode (i.e., the reaction surface) in a single cell of polymer electrolyte fuel cell (PEFC). A 1D multi-plate heat transfer model based on the temperature data of the separator measured using the thermograph in a power generation experiment was developed to evaluate the reaction surface temperature (Treact). In addition, to validate the proposed heat transfer model, Treact obtained from the model was compared with that from the 3D numerical simulation using CFD software COMSOL Multiphysics which solves the continuity equation, Brinkman equation, Maxwell-Stefan equation, Butler-Volmer equation as well as heat transfer equation. As a result, the temperature gap between the results obtained by 1D heat transfer model and those obtained by 3D numerical simulation is below approximately 0.5 K. The simulation results show the change in the molar concentration of O2 and H2O from the inlet to the outlet is more even with the increase in Tini due to the lower performance of O2 reduction reaction. The change in the current density from the inlet to the outlet is more even with the increase in Tini and the value of current density is smaller with the increase in Tini due to the increase in ohmic over-potential and concentration over-potential. It is revealed that the change in Treact from the inlet to the outlet is more even with the increase in Tini irrespective of heat transfer model. This is because the generated heat from the power generation is lower with the increase in Tini due to the lower performance of O2 reduction reaction.

Hot deformation behavior of microstructural constituents in a duplex stainless steel during high-temperature straining

The hot deformation characteristics of 1.4462 duplex stainless steel （DSS） were analyzed by considering strain partitioning between austenite and ferrite constituents. The individual behavior of ferrite and austenite in microstructure was studied in an iso-stress condition. Hot compression tests were performed at temperatures of 800-1100~C and strain rates of 0.001-1 s-1. The flow stress was modeled by a hyperbolic sine constitutive equation, the corresponding constants and apparent activation energies were determined for the studied alloys. The constitutive equation and law of mixture were used to measure the contribution factor of each phase at any given strain. It is found that the contribution factor of ferrite exponentially declines as the Zener-HoUomon parameter （Z） increases. On the contrary, the austenite contribution polynomially increases with the increase of Z. At low Z values below 2.6. x 1015 （lnZ---35.5）, a negative contribution factor is determined for austenite that is attributed to dynamic recrystallization. At high Z values, the contribution factor of austenite is about two orders of magnitude greater than that of ferrite, and therefore, austenite can accommodate more strain. Microstructural characterization via electron back-scattered diffraction （EBSD） confirms the mechanical results and shows that austenite recrystallization is possible only at high temperature and low strain rate.

Analysis on Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell When Operated in High Temperature Range

This study is to understand the impact of operating condition, especially initial operation temperature （Tini） which is set in high temperature range, on the temperature profile of the interface between PEM （polymer electrolyte membrane） and catalyst layer at the cathode （i.e., the reaction surface） in a single PEFC （polymer electrolyte fuel cell）. A 1D multi-plate heat transfer model based on the temperature data of separator measured using thermograph in a power generation experiment was developed to evaluate the reaction surface temperature （Treact）. This study investigated the effects of flow rate, relative humidity and type of supply gas as well as Tini on the temperature distribution on reaction surface. The results obtained in 02 supply case show that, the temperature rise at the segments near the outlet of cell decreases with increasing Tini irrespective of relative humidity of supply gas （RH）, while it is not seen in air supply case. Regarding the segments except near the outlet in 02 supply case, Treact - Tini increases with increasing Tini for 40% RH. The temperature distribution on reaction surface in 02 supply case is wider with increasing Tini as well as decreasing RH, though that in air supply case is relatively even.

Impact of Thickness of Polymer Electrolyte Membrane on Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell Operated at High Temperature

This study is to understand the impact of operating condition, especially initial operation temperature （Tini） which is set in high temperature range, on the temperature profile of the interface between PEM （polymer electrolyte membrane） and catalyst layer at the cathode （i.e., the reaction surface） in a single PEFC （polymer electrolyte fuel cell）. A 1D multi-plate heat transfer model based on the temperature data of separator measured using thermograph in a power generation experiment was developed to evaluate the reaction surface temperature （Treact）. This study investigated the effects of Tini, flow rate and relative humidity of supply gas as well as thickness of PEM on the temperature distribution on reaction surface. As a result, the impact of flow rate of supply gas on the temperature distribution is not significant irrespective of relative humidity conditions as well as PEM type. When operated at high temperature, the temperature distribution is relatively flat in the case of thicker PEM （Nafion 115）, while Treact rises from the inlet to the outlet large and the temperature distribution is wide in the case of thin PEM （Nafion 211） irrespective of relative humidity condition. Since the water transfer through PEM in the case of Nafion 211 is better than Nafion 115 due to thin PEM, the power generation is promoted along the gas flow with the aid of humidification by water produced from electrochemical reaction.

Impact of Relative Humidity of Supply Gas on Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell When Operated at High Temperature

For improving the performance of stationary PEFC （polymer electrolyte fuel cell） system, the cell operating temperature up to 90℃ will be preferred in Japan during the period from 2020 to 2030. To understand the operation of the PEFC system under relatively high temperature conditions, detail heat and mass transfer analysis is required. The purpose of this study is to analyze the impact of relative humidity of supply gas on temperature distribution on the backside of separator in single ceil of PEFC using Nation membrane at higher temperature e.g. 90℃. The in-plane temperature distribution when power was being generated was measured using thermograph with various relative humidity of supply gases. It was found that the in-plane temperature distribution at the anode was more even than that at the cathode irrespective of the relative humidity of supply gas at the anode and the cathode. The temperature elevated along gas flow through the gas channel at the cathode irrespective of relative humidity of supply gas at the anode and the cathode. The in-plane temperature distribution at the cathode was narrower with the increase in Tini irrespective of relative humidity of supply gas at the cathode, while it was not observed when changing the relative humidity of supply gas at the anode. When the relative humidity of supply gas at cathode decreased, the in-plane temperature distribution at the anode was wider compared to decreasing the relative humidity of supply gas at the anode. The study concluded that the impact of relative humidity of supply gas at both anode and cathode had little impact on the in-plane temperature distribution at the cathode.

Regulating adsorption ability toward polysulfides in a porous carbon/Cu_(3)P hybrid for an ultrastable high-temperature lithium-sulfur battery

Lithium-sulfur batteries(LSBs)can work at high temperatures,but they suffer from poor cycle life stability due to the“shuttle effect”of polysulfides.In this study,pollen-derived porous carbon/cuprous phosphide(PC/Cu_(3)P)hybrids were rationally synthesized using a one-step carbonization method using pollen as the source material,acting as the sulfur host for LSBs.In the hybrid,polar Cu_(3)P can markedly inhibit the“shuttle effect”by regulating the adsorption ability toward polysulfides,as confirmed by theoretical calculations and experimental tests.As an example,the camellia pollen porous carbon(CPC)/Cu_(3)P/S electrode shows a high capacity of 1205.6 mAh g^(−1) at 0.1 C,an ultralow capacity decay rate of 0.038%per cycle after 1000 cycles at 1 C,and a rather high initial Coulombic efficiency of 98.5%.The CPC/Cu_(3)P LSBs can work well at high temperatures,having a high capacity of 545.9 mAh g^(−1) at 1 C even at 150℃.The strategy of the PC/Cu_(3)P hybrid proposed in this study is expected to be an ideal cathode for ultrastable high-temperature LSBs.We believe that this strategy is universal and worthy of in-depth development for the next generation energy storage devices.

Mid-wavelength nBn photodetector with high operating temperature and low dark current based on InAs/InAsSb superlattice absorber

In this paper,we demonstrate nBn InAs/InAsSb type II superlattice(T2SL)photodetectors with AlAsSb as the barrier that targets mid-wavelength infrared(MWIR)detection.To improve operating temperature and suppress dark current,a specific Sb soaking technique was employed to improve the interface abruptness of the superlattice with device passivation using a SiO_(2) layer.These result in ultralow dark current density of 6.28×10^(-6)A/cm^(2)and 0.31 A/cm^(2)under-600 mV at 97 K and297 K,respectively,which is lower than most reported InAs/InAsSb-based MWIR photodetectors.Corresponding resistance area product values of 3.20×10^(4)Ω·cm^(2)and 1.32Ω·cm^(2)were obtained at 97 K and 297 K.A peak responsivity of 0.39 A/W with a cutoff wavelength around 5.5μm and a peak detectivity of 2.1×10^(9)cm·Hz^(1/2)/W were obtained at a high operating temperature up to 237 K.

Numerical Analysis of Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell when Operated in Elevated Temperature Range

Abstract： The purpose of this study is to analyze the temperature distribution on the interface between the polymer electrolyte membrane and catalyst layer at the cathode in single cell of polymer electrolyte fuel cell when operated in elevated temperature range than usual. In this study, the interface between the polymer electrolyte membrane and catalyst layer at the cathode is named as reaction surface. This study has considered the 1D multi-plate heat transfer model estimating the temperature distribution on the reaction surface and verified with the 3D numerical simulation model solving many governing equations on the coupling phenomena of the polymer electrolyte fuel cell. The 3D numerical simulation model coverers a half size of actual cell including three straight parts and two turn-back corners, which can display the essential phenomena of single cell. The results from both models/simulations agreed well. The effects of initial operation temperature, flow rate, and relative humidity of supply gas on temperature distribution on the reaction surface have been investigated. Though the effect of flow rate of supply gas on temperature distribution on reaction surface has been small, low relative humidity of supply gas has caused higher temperature on the reaction surface compared to high relative humidity of the supply gas. The temperature rise of reaction surface from initial operation temperature has increased with the increasing in initial operation temperature of cell.

Injector Quantum Dot Molecule Infrared Photodetector:A Concept for Efficient Carrier Injection

Quantum dot infrared photodetectors are expected to be a competitive technology at high oper ation temperatures in the long and very long wavelength infrared spectral range.Despite the fact that they already achieved notable success,the performance suffers from the thermionic emission of electrons from the quantum dots at elevated temperatures resulting in a decreasing responsivity.In order to provide an efficient carrier injection at high temperatures,quantum dot infrared photodetectors can be separated into two parts:an injection part and a detection part,so that each part can be separately optimized.In order to integrate such functionality into a device,a new class of quantum dot infrared photodetectors using quantum dot molecules will be introduced.In addition to a general discussion simulation results suggest a possibility to realize such a device.

InAs/InAsSb type-Ⅱ superlattice with near room-temperature long-wave emission through interface engineering

Ga-free InAs/InAsSb type-Ⅱ superlattices(T2SL) have extensive application prospective in infrared photodetectors. Achieving higher operation temperature is critical to its commercial applications. Here, a fractional monolayer alloy method was used to grow InAsSb alloy with better controlled alloy composition. The as-grown T2SL gave eleven satellite peaks and a first satellite peak with a narrow full-width-half-maximum (FWHM) of 20.5arcsec (1 arcsec=0.01592°). Strain mapping results indicated limited Sb diffusion through the As-Sb exchange process at the interface. Moreover, unlike interface states caused by the As-Sb exchange effect, this relatively clear interface was distinctive with localized states with higher activation energies of the non-radiative recombination process ((18±1) meV and (84±12) meV at different temperature ranges), which means that this interface state introduced by fractional monolayer alloy growth method can effectively suppress Auger recombination process in T2SL. Through this interface engineering of InAs/InAsSb Type-Ⅱ superlattice, it achieved detective photoluminescence (PL) signal with the center wavelength of 9μm at 250K.