Preparation And Characterization Of Several Key Materials In Alkaline Aluminum Fuel Cells And Solid Oxide Fuel Cells

The newly developed fuel cells with high efficiency, low pollution and reliable safety have been paid more and more attention recently due to the shortage of traditional energy and deterioration of environment. However, problems such as technology and cost in the practical application of fuel cells still restrict the further development of fuel cell industry. In the research process of fuel cells, the development and application of new battery materials and their manufacturing process, which determines the efficiency and cost of the cell operation, are the core and foundation of fuel cell technology. Taking alkaline aluminum fuel cells and solid oxide fuel cells as the background, this dissertation mainly focuses on the research in preparation and characterization of inhibitors and aluminum alloy anodes in alkaline aluminum fuel cells as well as the protective coatings of metal interconnect in solid oxide fuel cells (SOFCs). All the work is aimed to improve the cell efficiency, reduce the cost and promote the progress of fuel cell industry by developing new battery materials.In term of inhibitors, effect of In(OH)3, NaSnO3, sodium citrate and resorcinol on the corrosion and electrochemical behaviors of aluminum anode in85℃, Smol·L-1NaOH electrolyte with current density of800mA·cm-2has been studied respectively. Based on the research of single inhibitors above, a modified composite inhibitor (MCI) which can help the aluminum anode to gain a well balance between corrosion resistance and electrochemical activity has been newly developed. With regard to the research of aluminum alloy anodes, effect of alloy elements, solution heat treatment and hot rolling process on the corrosion and electrochemical behaviors of aluminum anode in85℃, Smol·L-1NaOH electrolyte (containing MCI inhibitor) with current density of800mA·cm-2has been investigated comprehensively. The effect mechanism of alloy elements, heat treatment and rolling process on the micro structure and performance of aluminum alloy has been analyzed as well. In research of interconnect protective coatings, the Cu-Mn (Cu1.2Mn1.8O4) and Mn-Co (Mn1.5Co1.5O4) spinel protective coatings have been prepared on the surface of Crofer22APU stainless steel using sol-gel dip coating and electrophoretic deposition method respectively. The effect of deposition technique and sintering process on the microstructure of coated Crofer22APU alloy before and after oxidizing at800℃for up to120h has been studied. The oxidation kinetics behavior and electrical property of coated substrate during oxidation are also evaluated. The main results obtained are described as follows:1. The selected aluminum alloy anode owns the excellent electrochemical activity with negative electrode potential in85℃, Smol·L-1NaOH electrolyte with current density of800mA·cm-2. But the hydrogen evolution corrosion of the alloy in high temperature and strong alkaline electrolyte is really serious and the hydrogen evolution rate is high at0.906mL·min-1·cm-2. The aluminum alloy anode is not suitable for use in pure alkaline electrolyte and needs the assistance of inhibitor;2. The study of single inhibitors shows that In(OH)3is the best single inhibitor with favorable electrochemical comprehensive performance. When the concentration of In(OH)3is4mmol·L-1, the hydrogen evolution rate of aluminum anode is0.295mL·min-1·cm-2and the electrode potential is-1.597V. Na2SnO3is the best single inhibitor in decreasing the hydrogen evolution corrosion of the aluminum anode, however, the addition of Na2Sn03will have negative effect on the electrochemical activity of aluminum alloy anode. Sodium citrate owns the minimal impact on the electrochemical activity of aluminum alloy anode. By contrast, resorcinol has the great impact on the electrochemical activity of aluminum alloy anode;3. The modified composite inhibitor (MCI) plays a synergies effect between inorganic and organic inhibitor fiercely. With the addition of MCI, the hydrogen evolution rate of aluminum anode decreases to its lowest value at0.134mL·min-1·cm-2and the inhibition efficiency of inhibitor increases to the highest value at86.65%. Meanwhile, the electrode potential of aluminum anode is still negative at-1.589V, which reveals that MCI can help the aluminum alloy anode to gain a well balance between corrosion resistance and electrochemical activity in alkaline electrolyte perfectly. In addition, both the MCI inhibitor and the single inhibitors mentioned above are all belongs to the anode-restrained inhibitor which slows down the hydrogen evolution corrosion by restraining the anode reaction;4. The study of novel aluminum alloy anode shows that addition of high hydrogen overpotential elements Sn and In in aluminum alloy will not only enhance the corrosion resistance of alloy, but also can decrease the anodic polarization and improve the electrochemical activity of aluminum anode by reducing the ion resistance of anodic oxide films and forming low melting point alloys respectively. The addition of Ga can also improve the electrochemical activity of aluminum anode to some extent, but high content of Ga will reduce the corrosion resistance of aluminum anode. The mixed rare earth elements can enhance both the corrosion resistance and electrochemical activity of aluminum alloy anode by improving the uniformity of the microstructure;5. The electrochemical comprehensive performance of aluminum alloy anode can be improved by the solution heat treatment which can increase the solid solubility of alloy elements and decrease the aggregation of active segregation phases. The effect of rolling process on the corrosion resistance and electrochemical activity of aluminum alloy anode is achieved by the dynamic recrystallized. The uniform microstructure with homogeneous distribution of fine active segregation phases as well as the excellent electrochemical comprehensive performance of newly development aluminum alloy anode is achieved by the dynamic recrystallization under420℃with pass deformation of40%after taking heat treatment at540℃for up to5h. The optimized aluminum alloy anode has the lowest hydrogen evolution rate of0.089mL·min-1·cm-2and the most negative electrode potential of about-1.630V;6. The relatively dense, uniform and well adherent Mn1.5Co1.5O4spinel coating which could significantly improve the oxidation resistance of stainless steel substrate and effectively act as a mass barrier to the outward migration of chromium during long-term oxidation process is successfully prepared on the surface of Crofer22APU stainless steel substrate by electrophoretic deposition technique, which indicates that preparation of Mn-Co protective coatings by electrophoretic deposition technique is the effective surface modification method in improving comprehensive application performance of metal interconnects;7. The appropriate sintering process (1100℃in Ar atmosphere) of Mn-Co (2.3μm) coated Crofer22APU can not only make sure that a thin Cr2O3oxide layer and low ASR of13.1mΩ·cm2to be obtained, but also can help to form a dense Mn-Co coating layer and to get a low parabolic rate constant of6.31×10-15g2·cm-4·s-1.