Silvering On Anode Of SOFC For Power Generation With Microwave Pyrolysis Gas Of Sewage Sludge As Fuel Gas

As a large number of municipal sewage treatment plants have been constructedin China, the amount of sewage sludge per day in China increases with each passingday. Quantitative reduction, harmlessness and resource of sewage sludge are theproblems we must face and solve. Solid oxide fuel cell (SOFC), which is fueled bycombustible gas, can change chemical energy of fuel gas into electrical energydirectly with high energy conversion efficiency. It is a kind of promisingenvironmental energy technology. Thus, this subject put forward a conception thatusing microwave pyrolysis gas of sewage sludge as fuel gas of solid oxide fuel cellto generate electricity. One of the biggest difficulties of using microwave pyrolysisgas of sewage sludge as fuel gas is that microwave pyrolysis gas of sewage sludgecontains methane, ethane, ethylene and so on, which will lead to carbon depositionon the anode of SOFC, and it will affect the stability of SOFC and shorten theservice life of SOFC. Therefore, in order to realize the purpose of sludge resourceutilizationin, silvering on the anode of SOFC was studied in this thesis to improvethe resistance to carbon deposition of SOFC and make SOFC be able to produceelectricity stably in microwave pyrolysis gas of sewage sludge.Electroplating, microwave and electroless silver plating were used to depositsilver on SOFC anode, respectively. The results show that, the effect ofelectroplating was not very good; the effect of microwave was instable with poorreproducibility; the effect of electroless silver plating has good reproducibility witha lot of silver particles in big size. Considering comprehensive factors such as effect,reproducibility, energy consumption and the amount of silver nitrate, we selectedelectroless silver plating as the method to deposit silver on SOFC anode, because ofits good effect and reproducibility, low energy consumption and small amount ofsilver nitrate. Than the best temperature,24℃, was found, and the cells byelectroless silver plating for1min,5min and10min respectively were chose to testand characterize.The results of Scanning Electron Microscope and Energy DispersiveSpectroscopy show that silver was successfully deposited on SOFC anode and the amount and particle size were both increased with time of electroless silver plating.The mass fraction of silver on the SOFC anodes by electroless silver plating for1min,5min and10min were1.43%,10.93%and23.16%, respectively.The effects of fuel gas flow rate and temperature on the discharge performanceof cells were researched. The results show that the discharge performance of cellspromoted with the increase of the fuel gas flow rate from25mL·min-1to100mL·min-1. However, when the fuel gas flow rate was50mL·min-1, the coefficient ofutilization of cells for fuel gas was almost close to saturation. Thus, the promotionwas very small when the fuel gas flow rate was increased from50mL·min-1. Thedischarge performance of cells promoted markedly with the increase of temperaturefrom650℃to750℃. Compared with the fuel gas flow rate, the influence oftemperature on SOFC was much bigger. Finally, the SOFC working conditions wereselected: temperature was750℃and the fuel gas flow rate was50mL·min-1.The cells without electroless silver plating were used as blank cell. Blank celland the cells by electroless silver plating for1min,5min and10min were testedand characterized in H2, CH4, C2H6and simulate gas of microwave pyrolysis gas ofsewage sludge (simulate gas was consist of the main gas composition of microwavepyrolysis gas of sewage sludge such as H2, N2, CO, CH4, CO2, C2H6, C2H4)respectively. The results show that discharge performance of the cells by electrolesssilver plating improved, and the impedance and the amount of carbon depositiondecreased. The output voltage of the cells by electroless silver plating was muchmore stable than that of blank cell, and decrease of discharge performance afterstability test was much less than that of blank cell, when fueled by CH4and C2H6,respectively.It is found that, among the cells by electroless silver plating for1min,5minand10min, the discharge performance and the resistance to carbon deposition ofthe cells with more silver were much better. Therefore, blank cell and the cell byelectroless silver plating for10min were selected to test and characterize inmicrowave pyrolysis gas of sewage sludge. The results show that, after discharge atconstant current for3h, the output voltage of blank cell decreased with a widerange of fluctuation because of the destruction of carbon deposition, H2S, NH3andso on; the cell by electroless silver plating for10min was able to discharge stably atconstant current for24h relatively. After discharge at constant current for24h, the decrease of the maximum power density of blank cell was69.5%, and the maximumpower density of the cell by electroless silver plating for10min declined by26.3%,which was much less than that of blank cell. Besides, the amount of carbondeposition of the cell by electroless silver plating for10min was much less thanthat of blank cell as well. It indicated that the cell by electroless silver plating for10min already had the preliminary ability of working stably in microwave pyrolysisgas of sewage sludge.