To obtain the temperature sensitivity characteristics of the proton exchange membrane fuel cell under different degradation levels, accelerated durability tests and temperature sensitivity tests of the fuel cell are first performed, and the temperature characteristics under different degradation states are analyzed by electrochemical impedance spectroscopy and polarization curve. Besides, an adaptive state-of-health transient thermal model of fuel cells is developed to investigate the effect of operating temperature on the internal gas concentration and hydrothermal distribution characteristics of the fuel cell from a mechanistic perspective. The experimental results of temperature sensitivity validate that the adaptive state-of-health transient thermal model can effectively monitor the steady and transient performance of the fuel cell. Subsequently, a mathematical model is proposed to describe the relationship among the load current, state of health, and optimal temperature using the temperature sensitivity test data and the transient thermal model of the adaptive state of health, which provides important insights into the optimal temperature range tailored to the current state of health of fuel cells to ensure efficient and stable operation of fuel cells all the time and contributes to the fine design of an optimal degradation adaptive temperature control strategy.

Cathode recirculation provides a new solution to the accelerated degradation of proton exchange membrane fuel cells (PEMFCs) due to low humidity and high potential at low load conditions. Analyzing the internal impact mechanisms is basis for a more appropriate use of this technology. This paper presents a systematic investigation of the mechanisms by which key operating parameters of the cathode recirculation, including current density, cathode recirculation ratio, and stoichiometry of the fresh air path, affect the internal and external properties of PEMFCs. The voltage suppression effect and humidification effect under different cathode recirculation strategies are first analyzed. Then, as a novelty, the distribution of relaxation times (DRT) method is used to deconvolve electrochemical impedance spectra and qualitatively resolve the polarization impedance under different strategies. DRT is enabled to separate up to five polarization processes with different time constants and assign them to oxygen diffusion, oxygen reduction reaction and proton transport processes affected by the cathode recirculation. Finally, DRT quantified the change in ohmic impedance due to cathode recirculation and confirmed the effect of external humidity changes. This work provides a more in-depth insight into internal mechanisms of cathode recirculation in PEMFCs, and especially provides a comprehensive theoretical basis for the development of idle controllers for automotive PEMFCs in terms of improved durability.

Crack is always considered as a kind of defect on a catalyst layer in a proton exchange membrane fuel cell (PEMFC), and its enhancement on mass transfer ability has always been ignored. In this work, the crack effect analysis on in-plane (IP) diffusivity on a catalyst layer is numerically evaluated by a D2Q9 lattice Boltzmann method (LBM). The effects on some key parameters like crack length, width, quantity and shape are carried out. The IP concentration distribution of crack CL shows deviation from the theoretical value, and this is because of the tortuosity caused by the CL cracks. The crack shape has almost no effect on the IP effective diffusivity, and the crack length shows a little bit more influence than the crack width and quantity. The crack ratio of the CL is the dominant effect on the IP mass diffusivity enhancement, and the lower the CL porosity is, the higher this enhancement achieve.

The mitigation of water flooding in the gas diffusion layer (GDL) at relatively high current densities is indispensable for enhancing the performance of proton exchange membrane fuel cells (PEMFCs). In this paper, a 2D multicomponent LBM model is developed to investigate the effects of porosity distribution and compression on the liquid water dynamic behaviors and distribution. The results suggest that adopting the gradient GDL structure with increasing porosity along the thickness direction significantly reduces the breakthrough time and steady–state total water saturation inside the GDL. Moreover, the positive gradient structure reaches the highest breakthrough time and water saturation at 10% compression ratio (CR) when the GDL is compressed, and the corresponding values decrease with further increase of the CR. Considering the breakthrough time, total water saturation and water distribution at the entrance of the GDL at the same time, the gradient structure with continuously increasing porosity can perform better water management capacity at 30% CR. This paper is useful for understanding the two–phase process in a gradient GDL structure and provides guidance for future design and manufacturing.

Water transport through the gas diffusion layer (GDL) is vital to proton exchange membrane fuel cells (PEMFCs), especially under flooding conditions. In this paper, a twodimensional (2D) lattice Boltzmann method (LBM) is applied to reveal the water dynamic characteristics in GDL, and the computational domain is reconstructed based on the experiment. In-situ experiments, including I-V performance and electrochemical impedance spectroscopy (EIS) tests under flooding conditions, are carried out and analyzed. It is found that the porosity distribution inside the GDL is a crucial factor in water dynamic behavior research. The horizontal liquid water saturation (HSw) under the channel of real GDL (with porosity distribution) at 0.4 relative thickness are 3.2 times, 2.1 times and 3.4 times higher than the ideal GDL (without porosity distribution) in the case of 0.8 mm, 1.2 mm and 2.0 mm, respectively. The numerical simulation and experimental study show that water dynamic characteristics under the rib influence cell performance directly. In our LBM model, the GDL water distribution inconsistency (Varw) under 2.0 mm width rib is 43.1% and 28.0% higher than that under the 0.8 mm and 1.2 mm rib, respectively. With the rib wider from 0.8 mm to 2.0 mm, some parts of cell impedance such as Rmt, Rct, and Lmt increase 64.22%, 98.89%, and 47.46%, respectively. However, GDL under the channel shows no influence on water transport process.

As an important application scenario of proton exchange membrane fuel cell (PEMFC), the development of low-temperature proton exchange membrane fuel cell (LT-PEMFC) for drones is attracting attention. The operating conditions of the PEMFC used by drones are relatively special. The hydrogen and air used as raw materials are dry gas without humidification. To meet this requirement, it is necessary to develop a proton exchange membrane with water retention capacity. We first synthesized a polymer with high water retention (PAAAM), used the solution casting method to form composite membranes, blended it into Nafion solution, and studied the content of PAAAM. Subsequently, we characterized each composite membrane by FT-IR, SEM, proton conductivity, water uptake, swelling ratio and other properties. Then we tested the battery output performance. The final results show that the optimum operating temperature range of Nafion proton exchange membrane is 50-55℃ when the raw material is dry air and dry hydrogen. When the amount of PAAAM added is 1.0wt%, the Nafion-based composite membrane (NFPAM1) has better battery performance. When the battery temperature is 55℃, the dry hydrogen gas, and the dry air flow rate are 0.1 L·min−1 and 0.55 L·min−1, respectively, the highest power density of PEMFC using NFPAM1 composite membrane is 691 mW·cm−2.

The gas diffusion layer (GDL) plays an important role in the mass transfer process during proton exchange membrane fuel cell (PEMFC) operation. However, the GDL porosity distribution, which has often been ignored in the previous works, influences the mass transfer significantly. In this paper, a 2D lattice Boltzmann method model is employed to simulate the liquid water transport process in the real GDL (considered porosity distribution) and the ideal GDL (ignore porous distribution), respectively. It was found that the liquid water transport in the real GDL will be significantly affected by the local low porosity area. In the real GDL, a liquid water saturation threshold can be noticed when the contact angle is about 118°. The GDL porosity distribution shows a stronger influence on liquid dynamic than hydrophobicity, which needs to be considered in future GDL modelling and design.

Hydrogen isotope gases expelled from nuclear fusion reactors can be purified by a process combining catalytic deoxygenation and cryogenic adsorption (77.4 K). In the present work, a novel purification process design is proposed. The experimental result shows that the oxygen volume fraction of the purified hydrogen isotopes is below 0.1 x 10(-6) with the nitrogen volume fraction less than 1 x 10(-6). And it was discovered that the waste amount of hydrogen isotopes after purification is only 100-300 ppm which occupies just 10-30% of the amount of nitrogen impurity through the theory calculation. Therefore, the impurity content of hydrogen isotopes is removed sufficiently by the combined process and the proposed process for purification of the exhaust gases expelled from nuclear fusion reactors can be used as an alternative to the traditional method. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Unsaturated polyester resin (UPR) wastewater is highly acidic with poor biodegradability, which is difficult to treat.In this paper, the UPR wastewater was treated by distillation and cooling to solve these problems.And the effects of distillation and cooling on the parameters, such as conductivity, total dissolved solids, chemical oxygen demand (COD) Cr , biochemical oxygen demand (BOD) 5 and organic acid content of the UPR wastewater were studied.Through experiments, it was found that there is no obvious effect on the treatment of UPR wastewater by distillation or cooling.But through combination of distillation and cooling, the COD Cr , conductivity and the BOD 5 of the wastewater decreased by 22.4%, 24.6% and 30.9%, respectively, and the pH was increased from 2.23 to 4.03.A mass number of white flocs were precipitated while the irritating odor is significantly reduced, and the biodegradability of the UPR wastewater was improved.The experiment results showed that the distillation or cooling could not affect the parameters above of the UPR wastewater, but the method designed in this paper can easily and effectively treat UPR wastewater, which can be used in industry.

The caffeine production process produces a large amount of sodium methyl sulphate in the methylated mother liquor. In order to recycle this part of ingredient, we use the mother liquid of Shijiazhuang Xin Nuowei Pharmaceutical Co., Ltd. as the object of study, the use of "nanofiltration (NF) - Dish Type Reverse Osmosis (DTRO) "combination of membrane technology for desalination and concentration. The experimental results show that the concentration of sodium sulfate in the nanofiltration solution is 0.37 g . L -1, the rejection rate is 98%, and the concentration of sodium methyl sulfate in DTRO concentrated solution is 453.80 g . L -1, which meets the requirements of the enterprise.