Study On Mechanical And Electrochemical Properties Based On The Anode Thickness In Solid Oxide Fuel Cell

Solid oxide fuel cell（SOFC）is an efficient energy conversion device that can directly convert the chemical energy in the fuel gas into electrical energy through an electrochemical reaction.For Ni-YSZ anode-supported SOFC,the microstructure characteristics of porous anode lead to a large concentration polarization phenomenon in the process of fuel gas diffusion,which results in the degradation of SOFC performance.Studies have shown that concentration polarization can be reduced by adjusting pores of anode and reducing the thickness of anode,but these methods also have influence on the mechanical and electrochemical properties of SOFC.This is mainly reflected in two aspects.On the one hand,the SOFC stacks formed by single cells in series need to be applied with external pressure to ensure good interface contact and sealing between stack components.On the other hand,Ni particles are prone to carbon deposition when using hydrocarbon fuel,which can be eliminated by adding appropriate amounts of steam.Therefore,to explore the influence of thickness of Ni-YSZ supporter on its mechanical and electrochemical performance,and achieve the optimal anode thickness as well as the best steam-to-carbon ratio required for CH₄ steam reforming,are of great importance for optimizing the preparation process of the SOFC and improving its electrochemical performance.This paper takes the typical Ni-YSZ anode-supported SOFC as the research object.First,influence of the thickness of anode supporter and the reduction state on the bending strength and Weibull modulus of single cell is studied,and the type of crack source that initiates the fracture is accurately determined.The influence of crack source on bending strength,Weibull modulus and fracture mode are further studied;In addition,the influence of anode supporter thickness on concentration polarization of SOFC and CH₄ steam reforming conditions are analyzed.SEM and Raman spectroscopy are adopted to characterize the microscopic morphology and carbon deposition of Ni/YSZ anode.The main contents and conclusions of this paper are as follows:（1）Influence of the thickness of Ni-YSZ anode supporter and the reduction state on mechanical properties of SOFC.The ring-on-ring method is adopted to study the correlation between the Weibull modulus of the bending strength of SOFC before and after reduction and its thickness.Single cells with the thickness of 1.1 mm,0.9 mm and 0.7 mm are studied in the paper.As the thickness of the sample before reduction decreases,Weibull modulus gradually increases,which can be explained by the reduction of internal defects in the anode.After the samples are reduced,Weibull modulus has been improved.The formation of plastic Ni phase is the main reason for suppressing the crack propagation.The single cell with 0.9 mm shows the best overall performance,and the corresponding Weibull modulus and characteristic strength are 12.49 and 122.9 MPa,respectively.The crack source of samples is mainly derived from the internal defects of Ni agglomeration in the anode supporter.According to this,different types of crack sources and three fracture modes can be summarized to explain the changes in the mechanical properties of SOFC with different thicknesses.（2）The influence of anode thickness on the electrochemical performance of SOFC.Electrochemical tests of cells with different thicknesses are performed at 750℃in H₂atmosphere.Results show that the peak power density increases with the thickness of SOFC decreasing,and it achieves a high peak power density of 2.073 W/cm² of the cell with 0.5 mm thickness.At the same time,concentration polarization is reduced,and concentration polarization shows a linear relationship with the thickness of anode.Furthermore,the long-term stability test is carried out for 24 h at a current density of 0.4A/cm² under humidified methane atmosphere at 750℃.Under the same steam-to-carbon ratio,carbon deposition decreases as the thickness of single cells decreases,and the degree of carbon deposition of a single cell increases as the steam-to-carbon ratio decreases.Study shows that it can effectively avoid the carbon deposition of Ni-YSZ anode and achieve a stable long-term operation of SOFC based on CH₄ fuel when the thickness of single cell is 0.5 mm and steam-to-carbon ratio is 2.