The Preparation And Performance Study Of Solid Oxide Fuel Cells Composite Anode Materials

Fuel cells are devices which can convert energy with high efficiency and low pollution. They are also called cells because they are composed of cathode,anode and electrolyte sandwiched by them, which are the same with the traditional cell, But they produce electricity by electrochemical combination of fuel gas (e.g. hydrogen) with oxidant gas (e.g. oxygen), which differs from the traditional cell used to reserve energy. So they can also be looked as a generator with an electrochemical process. But compared with the conventional generator whose efficiency of producing electricity, they are not subject to the Carnot limitation, they convert the chemical energy directly to electrical energy without intermediate of thermal energy and have excellent energy conversion efficiency as a result. In addition to high efficiency and low emissions, they have also several other advantages such as modular and distributed nature, and much lower production of pollutants. Since fuel cells just have these advantages, they will play an essential role in any future hydrogen fuel economy.As the fourth generation fuel cell, SOFC (Solid Oxide Fuel Cell) has many outstanding advantages, which is better than other fuel cells. Firstly, equipped with all solid components, it eliminates the problems that liquid electrolyte fuel cell faces, such as corrosion and leakage of liquid electrolytes. Secondly, operating at high temperatures, its electrode reaction is so fast that it is unnecessary to use noble metals as electrodes. Thus the cost of the cells can be minimized. At the same time, the high quality heat it emits can be fully used. The overall energy conversion efficiency of the thermal-electric system can be added up to 80%. The most outstanding advantage of SOFC is that it uses a large scale of fuels, from the hydrogen, carbon monoxide to the natural gas or even other combustive gases. Currently the main difficulty that the SOFC faces is the problem caused by high temperature and the ceramic components'match.Decreasing the operating temperature of SOFCs down to intermediate range( 500～800oC ) ,which is desirable due to important economical and technological advantages, requires optimization of the anode composition and microstructure in order to achieve sufficiently high performance in the intermediate temperature range.The microstructure design and the material system of the anode is varied currently. A great deal of research work still concentrated be passing an adoption to synthesize the method improvement beginning to start the powder body facial look lately, then excellent turn the microstructure of the anode, perhaps the increment mix the conductor middle layer to reduce the interface electric resistance of the anode and electrolyte between the anode and the electrolyte layer, letting up anode to turn very much, arrestment anode and the electrolyte material of reaction. For example pass to co-precipitation process, glycine- nitrate method, sol-gel method etc. The one step synthesize the NiO-YSZ or the NiO-SDC compound powder body, doing anode with this kind of material, the microstructure that discovers anode improved very greatly.The material system aspect, Gorte etc. is after the body of YSZ convenient Cu replace Ni, after of in the Ni-YSZ anode material equal battery function.. The Cu-YSZ anode function is stable, the life span extension, the Cu-YSZ metals ceramics anode function is steady after 800 oC work a week constant. The reason is the Cu to be sloth more than the Ni, the YSZ stability of the Cu is an anode to the methane fuel, not easy formation carbon deposition.. Join the function that the CeO2 can improve above- mentioned material effectively in the Cu-YSZ.In this study, the effect of Ni content on the performance of Ni-SDC has been studied and also been investigated the performance of Ni-SDC composite anode material with the temperature. Microstructure and performance of Cu or Fe doped Ni-SDC has been studied, Cu or Fe adjusted the microstructure of Ni-SDC and modified the metal phase of composite anode material. (1) Several Ni-SDC composite anode with different NiO contents were synthesized by mechanical mixed method with NiO and SDC powders, which are two kinds of powders prepared by glycine-nitrate process and sintered at 600 oC for 4h.. The results of investigation show that the conductivity has not been changed, becoming an excellent conductors after reducing; the conductivity of anode materials strongly depend on the content of Ni; its relation of the conductivity and Ni presents"S"trend. Based on the theory of percolation, it can be demonstrated that two kinds of electric mechanism are coexistent, namely the electronic channel of the Ni phase and the ionic channe2 of the SDC phase. When NiO content is around 60wt.%.The highest performance were achieved for the composite anode materials. The percolation threshold is 30vol.% Ni.. The conductivity of the anode containing 60wt.% NiO is 1021.605 Scm-1 under hydrogen atmosphere at 600 oC.(2) Composite anode material with doped Cu or Fe were synthesized by mechanical mixed method. The doped anodes'performance were measured and compared to traditional Ni-SDC anode. The weight ratio of metal oxide is 60% in all anodes material. The results show that the performance of anodes with doped Cu or Fe are superior to the traditional Ni-SDC anode materials, and optimize the microstructure of the anode. It is possible that one hand Cu or Fe formed solid solution, it has better dispersion of Ni particles; prevention of Ni small particles sintering becoming big bulk under high temperature. On the other hand, it increased the surface area; extend the triple-phase boundary. Another more fuel gas like hydrogen is easy able to adsorbed to triple-phase boundary in anode side of SOFC; enhance the catalytic of anode and reduce the anode over-potential. The maximum power density of Ni0.9Cu0.1-SDC anode is 482.95mW/cm2 at 800 oC. The maximum power density of Ni0.75Fe0.25-SDC anode with the short current 1511.85 mA/cm2 is 311.63 mW/cm2,more higher 134.13 mW/cm2 compared to that of traditional Ni-SDC at 800 oC.The bimetal anode have excellent performance on electrochemistry activity and will be a good potential anode material.(3) According to my previous work, NiO-SDC at different temperature sintering were measured and studied. The performance of anode material at 1100 oC sintering is very well. The maximum power density is 122.4 mW/cm2, the current density is 522.02 mA/cm2 at 700 oC.