Dissolution and Migration of Platinum in PEMFCs Investigated for Start/Stop Cycling and High Potential Degradation

Dissolution and migration of platinum due to start/stop degradation and increased cathode potentials were studied for commercial membrane electrode assemblies (MEA). The chosen conditions closely mimic real situations in automotive operation. In start/stop tests, we observed a strongly enhanced platinum dissolution due to the dynamic interplay of repeated cell start‐up and consecutive normal fuel cell operation, which is related to platinum oxidation (start‐up) and reduction (normal operation) cycles. Consequently, the performed test protocols distinguish between dynamic and static load profiles. Electrochemical investigations before and after degradation monitor the loss in cell performance. Since electron microscopy offers the unique possibility to unravel and distinguish degradation due to carbon corrosion and agglomeration or platinum dissolution, a focus was set on this method. For the start/stop MEA pronounced platinum dissolution accompanied by the formation of large platinum precipitations in the membrane was found. Carbon corrosion was also observed, but did not lead to a significantly reduced porosity and loss in platinum dispersion. In contrast, the MEA which was exposed to high constant potentials exhibited severe damage to the 3D cathode structure due to carbon corrosion. However, no pronounced platinum dissolution was observed and only few Pt precipitations were found in the membrane itself.     

Experimental analysis of SO2 effects on Molten Carbonate Fuel Cells

The aim of this work is to investigate how SO₂ can affect MCFC performance and to discover the possible mechanisms involved in cathode sulphur poisoning, specifically considering the possible use of MCFCs in CCS (Carbon Capture and Storage) application. The different contributions of cathodic, anodic and electrolyte reactions have been considered to get a complete picture of the evolution of performance degradation. Experimental tests have been performed at the Fuel Cell Centre laboratories of Korea Institute of Science and Technology (KIST) thanks to 100 cm² single cell facilities and comparing results using both an optimized gas for laboratory conditions and a gas composition that simulates MCFCs when running in a Natural Gas Combined Cycle (NGCC) power plant. Polarisation curves, endurance tests, impedance measurements and gas analyses have been carried out to support the investigation.     

二甲双胍对骨代谢的影响

二甲双胍(metformin)是2型糖尿病患者的一线用药,在50余年的临床应用中,已显示出安全、有效、全面控制血糖的效果。近年越来越多的研究发现,二甲双胍促进体外成骨细胞的增殖、分化及细胞外基质矿化,逆转高浓度葡萄糖对成骨细胞功能的损伤,抑制破骨细胞的形成;动物研究进一步证实二甲双胍增加鼠的骨矿含量以及松质骨容量,促进新骨形成,促进正常血糖大鼠及糖尿病大鼠的骨损伤修复;临床研究也发现二甲双胍影响糖尿病患者骨密度,但其对骨代谢的影响以及机制尚未完全阐明。本文综述了二甲双胍对骨代谢的影响,并探讨其可能的作用机制。     

Conformal Nano‐Sized Inorganic Coatings on Mesoporous TiO2 Films for Low‐Temperature Dye‐Sensitized Solar Cell Fabrication

Here, a new method based on sol–gel electrophoretic deposition to produce uniform high‐quality inorganic conformal coatings on mesoporous nano‐particulate films is presented. This novel sol preparation method allows for very fine control of the coating properties, thus inducing new adjustable functionalities to these electrodes. It is shown that the deposition of an amorphous TiO₂ and/or MgO shell onto photoanodes used in dye‐sensitized solar cells (DSSCs) improves their light‐to‐electric‐power conversion efficiency without the need for sintering. It is proposed that the amorphous TiO₂ coating improves the electronic inter‐particle connection and passivates the surface states. The insulating MgO coating further reduces the electron transfer from the conduction band into the electrolyte while the electron injection from the excited dye state remains unperturbed for thin coatings. Using a low‐temperature method for DSSC production on plastic substrates, a maximum efficiency of 6.2% applying pressure together with an optimized TiO₂ coating is achieved. For systems that cannot be pressed a conversion efficiency of 5.1% is achieved using a double shell TiO₂/MgO coating.     

Status and research of highly efficient hydrogen production through high temperature steam electrolysis at INET

Hydrogen generation through high temperature steam electrolysis (HTSE) using solid oxide electrolysis cells (SOEC) has recently received increasingly international interest in the large-scale, highly efficient nuclear hydrogen production field. The research and development of HTSE technology was initiated in INET of Tsinghua University from 2005 as one of the approaches in National Key Special Projects for HTGR which aims at promoting highly efficient and sustainable application of nuclear process heat in the future. In the past three years, the research team mainly focused on preliminary investigation, feasibility study, equipment development and fundamental research. Currently, two bench-scale equipments for the study of HTSE process and SOEC components have been designed and constructed. In addition, the research group made rapid progress in the development of novel anode materials, effective microstructure control of cathodes and theoretically quantitative analysis of hydrogen production efficiency through HTSE coupled with HTGR.     

Rational synthesis of a nanocrystalline calcium phosphate cement exhibiting rapid conversion to hydroxyapatite

The rational synthesis, comprehensive characterization, and mechanical and micromechanical properties of a calcium phosphate cement are presented. Hydroxyapatite cement biomaterial was synthesized from reactive sub-micrometer-sized dicalcium phosphate dihydrate and tetracalcium phosphate via a dissolution-precipitation reaction using water as the liquid phase. As a result nanostructured, Ca-deficient and carbonated B-type hydroxyapatite is formed. The cement shows good processibility, sets in 22 ± 2 min and entirely transforms to the end product after 6 h of setting reaction, one of the highest conversion rates among previously reported for calcium phosphate cements based on dicalcium and tetracalcium phosphates. The combination of all elucidated physical-chemical traits leads to an essential bioactivity and biocompatibility of the cement, as revealed by in vitro acellular simulated body fluid and cell culture studies.The compressive strength of the produced cement biomaterial was established to be 25 ± 3 MPa. Furthermore, nanoindentation tests were performed directly on the cement to probe its local elasticity and plasticity at sub-micrometer/micrometer level. The measured elastic modulus and hardness were established to be E_s = 23 ± 3.5 and H = 0.7 ± 0.2 GPa, respectively. These values are in close agreement with those reported in literature for trabecular and cortical bones, reflecting good elastic and plastic coherence between synthesized cement biomaterial and human bones.     

Effect of Ru/CGO versus Ni/CGO Co‐Infiltration on the Performance and Stability of STN‐Based SOFCs

Electrolyte supported cells (ESC), with Sc₂O₃‐stabilized ZrO₂ (ScSZ) electrolytes, Gd‐doped ceria (CGO) or M/CGO (M = Ni, Ru) infiltrated Sr_0.94Ti_0.9Nb_0.1O₃ (STN94) anodes and LSM/YSZ cathodes, were evaluated for their initial performance and long‐term stability. Power density for the Ru/CGO infiltrated cell reached ∼0.7 W cm^–2 at 850 °C, 4% H₂O/H₂, whereas the Ni/CGO infiltrated cell reached ∼0.3 W cm^–2, with the current morphologies and loadings. Operation at 0.125 A cm^–2, 850 °C, feeding 50% H₂O/H₂ to the anode and air to the cathode, for a period >300 h, showed superior stability for the Ru/CGO infiltrated cell, with ∼0.04 mV h^–1 degradation rate, when compared to the Ni/CGO infiltrated cell (∼0.5 mV h^–1). For the Ni/CGO case, the observed degradation has been tentatively linked to initial changes in the electrochemical active area and long‐term detrimental interactions between components.     

Proton Exchange Membrane Fuel Cell Operation and Degradation in Short‐Circuit

Hybridization of proton exchange membrane fuel cells (PEMFC) and ultra capacitors (UC) are considered as an alternative way to implement high autonomy, high dynamic, and reversible energy sources. PEMFC allow high efficiency and high autonomy, however their dynamic response is limited and this source does not allow recovering energy. UC appears to be a complementary source to fuel cell systems (FCS) due to their high power density, fast dynamics, and reversibility. A direct hybridization of these sources could allow reducing the number of power converters and then the total cost of the hybridized system. Simulations show the behavior of the hybrid source when the fuel cell and ultra capacitors are interconnected and the natural energy management when a charge is connected. The results show that the magnitude of the transient current supplied by the fuel cell to charge the UC can be much higher than its nominal value. An experimental setup is implemented to study the effects of these high currents in a PEMFC. This is done by imposing a controlled short‐circuit between the electrodes. The PEMFC degradation is quantified by using electrochemical impedance spectroscopy.     

Effect of Water Transport on Swelling and Stresses in PFSA Membranes

The mechanical durability of membranes used in proton exchange membrane fuel cells (PEMFC) is directly linked to the stresses that evolve in the membrane during fuel cell operation. The stresses are primarily induced due to the swelling of the membrane as it absorbs water, within the mechanical constraints in the fuel cell assembly. Thus, in order to predict the membrane stresses, the water content in the perfluorosulphonic acid (PFSA) membranes is determined numerically via three different absorption models based on experimentally determined water uptake data from the literature. Two models are based on a single, humidity‐dependent Fickian transport coefficient for the bulk PFSA membrane. In the third, two transport properties are modeled to account for a possible difference in transport resistance between the bulk membrane and the outer surface. The membrane sorption behaviors characterized from these three models are then independently incorporated in a representative fuel cell finite element model and subjected to a standard relative humidity (RH) protocol designed for measuring mechanical durability of PEMFCs. The results show that the sorption behavior has a significant effect on the membrane stresses and therefore, may impact the lifetime of the membrane.