Study On Optimization Of Anode Microstructure Of Solid Oxide Fuel Cells

Solid oxide fuel cell?SOFC?is a new type of power generation device that directly converts chemical energy in fuel into electrical and thermal energy through an electrochemical process.The medium-temperature solid oxide fuel cell is currently the research hotspot.It usually uses a cermet composite made of Ni and yttria-stabilized zirconia?YSZ?as the anode material.However,Ni-YSZ as an anode,in addition to the problems of Ni particles agglomeration and growth,easy carbon deposition,but also because of different preparation process leads to different levels of performance output.In order to achieve the high performance,long life-time and other technical specifications for the commercialization of SOFC,to explore the key process steps in the preparation of SOFC cells on the structure and performance of SOFC,for improving the performance and long-term stability of SOFC is of great significance.This article mainly studyed the effects of different milling processes and reduction schemes on the anode microstructure and properties of SOFC cells.The image processing method was used to analyze the parameters of the anode microstructure,and the sizes and distributions of Ni and YSZ particles and pores were calculated.A simple model was constructed to semi-quantitatively analyze the changing trend of the Ni-YSZ bonding state and the TPB density index,establishing the link between process-structure-performance and finding suitable process parameters for improving the performance of SOFC.The following are the main research contents of this article:?1?The effect of ball-milling on anode microstructure.Preparation of SOFC anode slury requires two ball-milling processes.By designing different ball milling times,single cell anodes are prepared and NiO was reduced to Ni.Anode microstructure images are processed and the effect of two ball-milling processes on the particles dispersion and polymerization of the anode slurry are analyzed.When the first milling time is 24 h and the second milling time is 12 h,Ni particle size after reduction is the smallest.At the same time,it was also found that Ni-YSZ bonding state and TPB density are related to the Ni particle size.?2?The effect of reduction process on the microstructure of the anode.Different anode reduction conditions were designed.The isothermal reduction temperatures were 500°C,600°C,700°C,and 800°C.The reducing atmosphere was pure H2 and 5%H2/N2.The effects of temperature and atmosphere on the anode reduction kinetics and microstructure of Ni-YSZ were studied.Weight reducing method was used to draft the reduction curves of NiO-YSZ,and the kinetic model was fitted.The two main limiting factors affecting the reduction rate of NiO-YSZ have been found to be the rate of chemical reaction and the diffusion rate of reactants and products.By analyzing anode microstructure,it is found that the structure of Ni particles after reduction also has an effect on the reduction kinetics,and these results reveal the changing rule of the effect of reducing conditions on the microstructure of the anode.?3?After improving the 5%H₂ scheme,I-V curves and EIS impedance spectra of SOFC cells under various reducing conditions were tested,and the highest power density and polarization resistance of each sample were compared.It was found that the increase of reduction temperature is beneficial to reduce the ohmic resistance and the activation polarization resistance in the anode,which has an advantage to the conduction of electrons and ions,but the concentration polarization impedance at different temperature shows different effects.The analysis of the microstructure shows once again that the reduction temperature and atmosphere affect the size and distribution of Ni and pores.The size effect of Ni particles affect the bonding state of Ni-YSZ,and then affect the TPB density index;better interfacial bonding between Ni and YSZ phases reduce decrease of TPB density index loss due to the larger Ni particle size.