Corrosion and Interfacial Contact Resistance of NiTi Alloy as a Promising Bipolar Plate for PEMFC.

Titanium (Ti) is generally considered as an ideal bipolar plate (BPP) material because of its excellent corrosion resistance, good machinability and lightweight nature. However, the easy-passivation property, which leads to increased interfacial contact resistance (ICR) and subsequently decreased cell performance, limits its large-scale commercial application in proton exchange membrane fuel cells (PEMFCs). In this paper, we proposed a NiTi alloy prepared by suction casting as a promising bipolar plate for PEMFCs. This NiTi alloy exhibits significantly decreased ICR values (16.8 mΩ cm2 at 1.4 MPa) compared with pure Ti (88.6 mΩ cm2 at 1.4 MPa), along with enhanced corrosion resistance compared with pure nickel (Ni). The superior corrosion resistance of NiTi alloy is accredited to the nobler open circuit potential and corrosion potential, coupled with low corrosion current densities and passive current densities. The improved ICR can be interpreted by the existence of high-proportioned metallic Ni in the passive film, which contributes to the reduced capacitance characteristic of the passive film (compared with Ti) and enhances charge conduction. This work provides a feasible option to ameliorate BPP material that may have desirable corrosion resistance and ICR.

Li+ Conduction in a Polymer/Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte and Li-Metal/Electrolyte Interface.

The solid oxide electrolyte Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with a NASICON structure has a high bulk ionic conductivity of 10-4 S cm-1 at room temperature and good stability in the air because of the strong P5+-O2- covalence bonding. However, the Ge4+ ions in LAGP are quickly reduced to Ge3+ on contact with the metallic lithium anode, and the LAGP ceramic has insufficient physical contact with the electrodes in all-solid-state batteries, which limits the large-scale application of the LAGP electrolyte in all-solid-state Li-metal batteries. Here, we prepared flexible PEO/LiTFSI/LAGP composite electrolytes, and the introduction of LAGP as a ceramic filler in polymer electrolytes increases the total ionic conductivity and the electrochemical stability of the composite electrolyte. Moreover, the flexible polymer shows good contact with the electrodes, resulting in a small interfacial resistance and stable cycling of all-solid-state Li-metal batteries. The influence of the external pressure and temperature on Li+ transfer across the Li/electrolyte interface is also investigated.

Mechanistic Study on the Corrosion of (La,Sr)(Co,Fe)O3-δ Cathodes Induced by CO2.

Solid Oxide Fuel Cell (SOFC) cathodes operating in ambient atmospheric conditions inevitably encounter CO2 contamination, leading to sustained performance deterioration. In this investigation, we examined the impact of CO2 on three variants of (La,Sr)(Co,Fe)O3-δ cathodes and employed the distribution of relaxation times method to distinguish distinct electrochemical processes based on impedance spectra analysis. We meticulously analyzed and discussed the corrosion resistance of these (La,Sr)(Co,Fe)O3-δ cathodes under high CO2 concentrations, relying on the experimental data. Electrochemical impedance spectroscopy results revealed that La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428), La0.4Sr0.6Co0.2Fe0.8O3-δ (LSCF-4628), and La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN-46271) cathodes exhibited persistent degradation when exposed to CO2 at temperatures of 650 °C or 800 °C during the durability-testing period. An increase in electrode polarization resistance was observed upon CO2 introduction to the electrode, but electrode performance recovered upon returning to a pure air environment. Furthermore, X-ray diffraction and scanning electron microscopy analyses confirmed that CO2 did not cause permanent damage to the (La,Sr)(Co,Fe)O3-δ cathodes. These findings indicate that the (La,Sr)(Co,Fe)O3-δ cathodes exhibit excellent resistance to CO2-induced corrosion.

The microstructure and property of Al-Si alloy improved by the Sc-microalloying and Y2O3 nano-particles.

The effect of Sc-microalloying and Y2O3 nano-particles on the microstructure and mechanical properties of as-cast Al-5.5Si alloy is studied by means of optical microscopy, transmission electron microscopy, hardness test and tensile test. The influence of annealing treatment on the microstructure and properties of the Al-Si alloys is also investigated as well. The results show that the addition of Sc and Y2O3 nano-particles could significantly improve the mechanical property of the Al-Si alloy. The ultimate tensile strength and yield strength of Al-Si-Sc/Y2O3 alloy are improved by around 45 and 71%, respectively, when compared to that of the Al-Si alloy. The effect of the nanosized particles (precipitated and added) on strengthening and deformation of Al-Si alloy is analyzed and discussed in detail. The results of annealing treatment indicate that the change in mechanical property of the Al-Si-Sc alloy during annealing treatment is mainly associated with the precipitation of the secondary Si phase.