Preparation And Performance Of Ni Based Composite Anode Materials For Intermediate-temperature Solid Oxide Fuel Cells

Solid oxide fuel cell?SOFC?is the most effective way to solve the energy problem and environmental problems,one of has wide development prospects.But currently the cost compared to other energy conversion system is too expensive,it has become the biggest obstacle that baffles the development of SOFC commercial.Expensive cost due to its high operating temperature,the nature of the traditional based on Y2O3 stabilized Zr O2?YSZ?use of SOFC electrolyte temperature generally between 800-1000?,of which 800? such temperature need to use the new preparation process of preparation of thin film YSZ film layer to be realized.The high operating temperature,which cannot be used in SOFC system of conventional high temperature materials and sealing materials,makes the cost rise,and high operating temperature of the whole system's stability,reliability and safety has brought negative impact.Therefore,reducing the operating temperature is a major trend in the development of SOFC.However,the development of new electrolytes in intermediate temperature region and the corresponding electrode materials have become the key issues in the development of SOFC.Due to the high electrical conductivity Ni,and has higher catalytic activity for H₂ oxidation reaction,thus is widely used as a solid oxide fuel cell anode.However,due to the thermal expansion coefficient of Ni do not match with the electrolyte,high temperature operation,grain coarsening,so Ni often mixed with conductors such as yttrium oxide stable zirconia form a composite anode material.Another advantage of this composite anode materials is three-phase reaction interface can extend from anode/electrolyte interface to the anode.At the same time for Ni H₂ oxidation,electrochemical activity,anodic polarization resistance reduced.In intermediate temperature,the commonly used anode materials in addition to Ni-YSZ,as well asNi-SDC and Ni-GDC,etc.In a Ni-GDC composite anode,Ni acts as both the catalyst and electronic conducting phase,while GDC mainly acts as a matrix to support the catalyst and prohibit the metal from agglomeration under operating conditions.It is believed that ceria can also improve the anode catalytic activity,especially in SOFCs using hydrocarbon fuels.It has been demonstrated that the length of the triple-phase boundary?TPB?correlates well with the reaction rate for electrochemical oxidation of hydrogen;thus,the extension of the TPB becomes a determining factor in improving anode performance.This can be achieved mainly by optimizing the microstructure of the cermet anode through the adjustment of powder morphologies and particle sizes for the precursor Ni O and ceria,and /or developing a favorable electroding process.In this paper,the following research work was carried out on a new type of anode composite material:1.In order to increase porosity of anode,prolong three-phase reaction interface,increase conductivity of anode and power density of single cells,use transition metal part instead of Ni.Ni_1-x Cux-SDC composite anode materials were synthesized by a glycine-nitrate method,and using XRD,SEM,porosity test characterization methods are studied its morphology?structure and Ni_1-x Cux-SDC anode material and electrolyte material chemical compatibility in detail.The conductivity of Ni_1-x Cux alloy and Ni_1-x Cux-SDC was measured by a four probe dc technique.Investigation of the valence states of elements in anode materials by means of XPS characterization.Current-voltage?I-V?measurements of electrolyte-supported single cells with a Ba Co0.7Fe0.2Nb0.1O3-??BCFN?cathode and SDC electrolyte were performed.The XRD of Ni_1-x Cux O?x=0,0.10?exhibited a single face centered cubic structure and no impurity phase is found after calcinations in air at 1000 °C for 5 h.The reduced Ni_1-xCux O?x = 0,0.10?powders by hydrogen at 800 °C for 2 h can be observed that the Ni_1-x Cux O oxide is reduced to Ni_1-x Cux alloy.The reduced Ni_1-x Cux-SDC powders by hydrogen at 800 °C for 2 h can be observed fluorite SDC phase and Ni_1-x Cux alloys phase.The XPS of Ni O and Ni0.90Cu0.10 O before reduction show that Ni2+ and Cu2+existed.The XPS of Ni O ? Ni0.90Cu0.10 O ? Ni O-SDC and Ni0.90Cu0.10O-SDC after reduction show that Ni0,Cu0,Sm3+ and Ce4+existed.The Ni_1-x Cux-SDC composite anode shows a porous microstructure with a good connection between the electrode and the electrolyte.The conductivity of Ni0.90Cu0.10 is larger than that of Ni.This is because the electronegativity of Cu?1.9?is smaller than that of Ni?1.91?,so that the metallicity of Cu is stronger than that of Ni.The electrical conductivity of the Ni_1-x Cux-SDC increase with increasing Cu content?from x=0 to x=0.10?and then decrease at x=0.15.The porosity of the Ni_1-x Cux-SDC increases with increasing Cu content,while the electrical conductivity of Ni_1-x Cux-SDC?x=0-0.10?is higher than that of Ni-SDC.This is due to the electrical conductivity of Ni_1-x Cux?x=0-0.10?is higher than Ni.The reason for the decrease in conductivity of the Ni0.85Cu0.15-SDC may be due to the excessive porosity.Single cell performance test results show that the power density of the Ni0.90Cu0.10-SDC cell is the best,and the maximum power density reaches at 800 °C 483 m Wcm-2.2.By adding the appropriate Fe,can prolong the three-phase interface reaction of anode,reduce the anodic reaction activation energy.Ni_1-x Fe_x-SDC composite anode materials were synthesized by a glycine-nitrate method,and using XRD,SEM,porosity test characterization methods are studied its morphology ? structure and Ni_1-x Fe_x-SDC anode material and electrolyte material chemical compatibility in detail.The conductivity of Ni_1-x Fe_x alloy and Ni_1-x Fe_x-SDC was measured by a four probe dc technique.Current-voltage?I-V?measurements of electrolyte-supported single cells with a Ba Co0.7Fe0.2Nb0.1O3-??BCFN?cathode and SDC electrolyte were performed.In order to gain insight into the connection between the material internal crystal structure and conductivity,according to the numerical study first principles,using Materials Studio software?MS?based on density functional theory calculations of the band structure and density of states of the sample.The crystal structure and electrical conductivity of the material were revealed by the combination of the experiment and the first principles calculation.Finally,the relationship between the performance and the electronic structure of the material is established,and the relationship between thematerial properties and the electronic distribution is established.The XRD of the reduced Ni_1-x Fe_x-SDC powders by hydrogen at 800 °C for 2 h can be observed fluorite SDC phase and Ni_1-x Fe_x alloys phase.The Ni_1-x Fe_x-SDC composite anode shows a porous microstructure with a good connection between the electrode and the electrolyte.The electrical conductivity of Ni0.75Fe0.25 is larger than that of Ni.The electrical conductivity of Ni_1-x Fe_x-SDC increase with increasing Fe content?from x=0to x=0.25?and then decrease at x=0.30.The band structure of Ni and Ni0.75Fe0.25 calculated by the first principles calculations show that the two materials have typical metallic properties.The d-band of Ni0.75Fe0.25 is wider than Ni,the d-band fluctuations of Ni0.75Fe0.25 are larger than Ni.The results show that the electron localization of Ni0.75Fe0.25 decreases,the effective mass of Ni0.75Fe0.25 decreases,and the conductivity of Ni0.75Fe0.25 is enhanced.According to the density states of Ni and Ni0.75Fe0.25,the peak value of Ni0.75Fe0.25 electron density on the Fermi surface is larger than that of Ni.Single cell performance test results show that the power density of the Ni0.75Fe0.25-SDC cell is the best,and the maximum power density reaches at 800 °C389m Wcm-2.3.Adding stable Mg O in Ni-SDC can prevent the agglomeration of Ni particles,obtain highly dispersed Ni particles,increase the stability,and promote the interaction with reactants.Ni_1-x Mgx-SDC composite anode materials were synthesized by a glycine-nitrate method,and using XRD,SEM,porosity test characterization methods are studied its morphology ? structure and Ni_1-x Mgx-SDC anode material and electrolyte material chemical compatibility in detail.The conductivity was measured by a four probe dc technique.Current-voltage?I-V?measurements of electrolyte-supported single cells with a Ba Co0.7Fe0.2Nb0.1O3-??BCFN?cathode and SDC electrolyte were performed.XRD test results show that Ni_1-x Mgx-SDC composite anode calcined at 1000 °C for 5 h and reduced in H₂ at 800 °C for 2 h not only has the cubic fluorite structure SDC phase and Ni phase,but also Ni_1-x Mgx O solid solution phase.The addition of Mg O stabilized the Ni2+ and hindered the reduction of Ni O,which limits the sintering of the cubic phase.Ni_1-x Mgx O solid solution is a p typesemiconductor,which embodies the electronic conductivity.The Ni_1-x Mgx-SDC composite anode shows a porous microstructure with a good connection between the electrode and the electrolyte.The porosity and conductivity of the Ni_1-x Mgx-SDC decreases with increasing Mg content,mainly due to the absence of sufficient reduction of Ni_1-x Mgx O and the increase of the content of solid solution of P semiconductor Ni_1-x Mgx O.Single cell performance test results show that the power density of the Ni0.95Mg0.05-SDC cell is the best,and the maximum power density reaches at 800 °C 261 m Wcm-2.4.It is concluded that the electrochemical performance of Ni0.90Cu0.10-SDC composite anode is the best through the above studies,so a small amount of Mg O is added to further improve the microstructure of the composite anode.Ni0.90Cu0.10-x Mgx-SDC composite anode materials were synthesized by a glycine-nitrate method,and XRD and SEM by means of a detailed study of its structure and morphology,and Ni0.90Cu0.10-x Mgx-SDC anode material and electrolyte material chemical compatibility.The conductivity was measured by a four probe dc technique.Current-voltage?I-V?measurements of electrolyte-supported single cells with a Ba Co0.7Fe0.2Nb0.1O3-??BCFN?cathode and SDC electrolyte were performed.The XRD test results show that Ni0.90Cu0.10-x Mgx-SDC composite anode calcined at 1000 °C for5 h and reduced in H₂ at 800 °C for 2 h not only has the cubic fluorite structure SDC phase and Ni phase,but also Mg O phase.The reduction of Mg O style did not sufficiently.The Ni0.90Cu0.10-x Mgx-SDC composite anode shows a porous microstructure with a good connection between the electrode and the electrolyte.As a kind of stable oxide,Mg O plays an important role in inhibiting the growth of Ni and SDC in the sintering of anode material and single cell.When the content of Mg x=0.005,SDC grain size is small and uniform,Mg O particles are tightly adhered to the skeleton structure of Ni Cu-SDC ceramics,but also provides more effective power to channel,more electrons derived from the electrochemical reaction point,increase the three-phase interface,which can increase the power density of the cell.The conductivity of Ni0.90Cu0.10-x Mgx-SDC increase with increasing Mg content?from x=0to x=0.005?and then decrease at x=0.01.When the content of Mg x=0.005,SDC grain size is small and uniform,Mg O particles are tightly adhered to the skeleton structure of Ni Cu-SDC ceramics,but also provides a more effective electrical conductivity Ni0.90Cu0.095Mg0.005-SDC channel,so the maximum.Because Mg O is an insulator,when the content of Mg is x=0.01,the addition of excess leads to the decrease of the number of free electrons,so the conductivity of Ni0.90Cu0.09Mg0.01-SDC is the lowest.Single cell performance test results show that the power density of the Ni0.90Cu0.095Mg0.005-SDC cell is the best,and the maximum power density reaches at800 °C 597 m Wcm-2.