Research On Energy Storage And Hydrogen Production Characteristics Of Symmetrical Double-cathode Solid Oxide Cells

As an effective energy storage device for solving the imbalance between supply and demand of renewable energy,solid oxide cell(SOC)has attracted wide attention due to its high energy-gas conversion efficiency,as well as the ability to co-electrolyze water and carbon dioxide to produce syngas of H2 and CO.In the field of water electrolysis,Solid Oxide Electrolysis Cell(SOEC)acts as the representative of high temperature water electrolysis,and demonstrates a low demand for electric energy and high electrolysis efficiency.When combining with heat engine,SOEC can effectively utilize the waste heat in industrial production.Therefore,SOEC is widely considered as an effective means of large-scale hydrogen production in the future.The shapes of common SOEC can be divided into two types:tubular and planar.For the large-scale hydrogen production,the common SOEC with planar structure is easier to be processed and cost lower.However,the traditional flat-panel batteries with asymmetric structure may warp or even rupture at high temperature.This is a serious problem that cannot be ignored.Therefore,a new type of SOEC with hollow symmetrical double cathode structure was adopted in this paper,which was designed based on the shape of planar cells and the symmetrical structure of tubular cells.In this work,researches on hydrogen production and energy storage by electrolysis of water at high temperature were carried based on the new type of SOEC.Firstly,the mechanical properties of the new type of symmetrical structure cells were simulated and analyzed.The deformation of the cells was simulated based on the expansion coefficients of different oxidation degrees.The results show that the deformation of hollow symmetrical cell is much smaller than that of conventional cell.For the preparation of the SOEC with hollow symmetrical structure,the Ni-YSZ,LSCF and YSZ were used as raw materials,and the processes of solid-liquid mixing,dry pressing and screen printing were carried in order.The electrochemical performances of the SOEC as prepared were evaluated by basic electrochemical performance tests and thermal cycle tests.The results show that the SOEC exhibits good electrochemical performance,and demonstrates a slightly attenuation in electrochemical performance after six consecutive thermal cycles,and the basic electrochemical performance still maintains.Furthermore,the battery did not break down.The water electrolysis performances for hydrogen production of the SOEC were studied.The results display a high durability and a good cycle performance at high temperature during the electrolytic water processes.Under the condition of high reaction temperature,the SOEC can be reduced to the initial state within 3 hours without any degradation.The long-term electrolysis test illustrates only 8%current loss after constant current electrolysis for 10 hours.Further,the structure of SOEC after electrolysis was characterized by scanning electron microscopy.It was found that the Ni particles in the supporting fuel pole structure were coarsened and agglomerated after a long period of electrolysis,which can be regarded as the reason for the irreversible decay of battery performance.Finally,the energy storage characteristics of Ni in the support structure of SOEC were studied.The cells was discharged without hydrogen firstly,the electricity generated during the discharge process can be considered arise from the oxidation of Ni.After discharging for a period of time,the cells were restored to observe whether the open circuit voltage can be recovered.The discharge cycle was performed 13 times and the discharge energy density was calculated.The results show that the cell can be discharged without fuel gas,after which for a period of time,the NiO can be reduced to Ni by introducing reductive gas again,and the structure of the cell would not warp obviously.Compared with the traditional planar cells,the new structure of the cells is more stable and suitable for energy storage.These results mean that the new structure of fuel electrode-support cells for energy storage cells is possible.