Study On The Preparation And Performance Of Nio/YSZ Anode-Supported Planar SCFC

Solid oxide fuel cell (SOFC), as a new type of power generating device, doesnot have the problem of liquid leakage because of using solid oxide as theelectrolyte. Besides, there are many advantages of SOFC such as environmentalfriendliness, more efficienty and fuel flexibility. Therefore, SOFC attracts moreinterest in the fuel cell field nowadays.The main contents of the dissertation are manufacture of the big size anode/electrolyte composite ceramics by nonaqueous tape-casting and co-sintering,research on the possibility of Ag-CuO and silver conductive adhesive being thesealing materials of SOFC, the sealing techniques of single cell, and comparisonwith the performance of cells with hydrogen and methane as fuel gases.The NiO-YSZ/YSZ composite ceramic as the anode/electrolyte system ofplanar anode-supported SOFC was fabricated by nonaqueous tape-casting method.The formulation of the anode, anode functional layer and electrolyte slurry, and thetechnical parameters of tape-casting were identified. Based on the results of theTG-DTA, decided to use the “multistep” sintering method, using1300℃and1400℃as the presinter temperature and the final sinter temperature respectively.The products were about1.5mm thick, smooth and nondefective. Simulative cellwas fabricated and tested. The open circle voltage found to be1.05V and powerdensity to be1100mW·cm-2. Within the5h lifetime test, the working voltage wasabove0.7V.We attempted to use the Ag-CuO and silver conductive adhesive as SOFC’ssealing materials. Sealing technology of this two materials were identified. TheSEM images of connector/sealing materials and sealing materials/cell sealinginterfaces showed that the joint surfaces were well connected with no cracks andholes. The cell leakage rate achieved the working requirement. The thermal cycle,thermal stability and thermal matching performances of two materials were studied.The results showed that the thermal cycling and thermal stability performances ofboth materials acheived the working requirement, but the both thermal matchingperformances were bad. Through the experiment results, we discovered that thethermal expansion coefficient of the Ag-CuO material was difficult to change, butthe silver conductive adhesive material can be doped by Al2O3particles to reduce itsthermal expansion coefficient, optimal doping proportion was15%(w/w), thethermal expansion coefficient of silver conductive adhesive could be reduced from 20×10-6℃-1to15×10-6℃-1by this doping ratio.Single cell sealing required the use of ceramic fiber/Silver conductive adhesivecomposite sealing technique, wherein the ceramic fiber surface should be dippedwith150g/L aerosol SiO2. The silver conductive adhesive material required the useof gradient coating method with four layers which the contents of Al2O3were15mass%,10mass%,5mass%and0. The leakage rate of sealed single cell was0.045cm3·min-1·cm-1. This result became0.058cm3·min-1·cm-1after10thermal cycleswhich can fit the cell working qualification.We discovered the excessive voltage drop of conductor caused the decline ofthe cell performance. Therefore, we improved the current-collecting method andincreased the cell power from1.3W to15.47W. The influences of the single cellpower and lifetime due to the different gas flow rate were tested. We found out thatthe best flow rate of the H2and O2was2L·min-1and1L·min-1respectively. Withthis gas flow, the power of single cell was28.4W, meant the maximum powerdensity to be579.6mW·cm-2. The working voltage maintained at0.7V within the7h of the lifetime test. Fabricated the cell stack by put two cells in series, the powerof this cell stack was over50W.Performances of single cells with same flow rate of methane and hydrogen asfuel gas were compared. We found that due to carbon deposition phenomenon, thesingle cell with methane as fuel gas had the higher maximum power at the earlyworking period, however, the lifetime of this cell greatly reduced because of thedecrease of the anode working area and blocking of the gas channel by the excessivecarbon deposition. Therefore, hydrogen is a better fuel gas for the NiO-YSZ anode.