Study On Novle Oxygen Electrode For Solid Oxide Electrolysis Cells

Efficient use of fuel and the development of renewable energy are effective ways to solve the current energy crisis and environmental pollution.Solid oxide fuel cell(SOFC)is a kind of power plant converting the chemical energy of the fuel into electrical energy.Solid oxide electrolysis cell(SOEC),as the inverse process of SOFC,is a tool for storing a variety of renewable electrical energy and heat energy into chemical energy(hydrogen).When the supply of available energy is insufficient,the stored hydrogen can be used as a fuel for generating power by operating SOFC;when the wind energy,solar energy and waste heat are produced in excess,this SOEC device is provided with electrical energy and waste heat to produce hydrogen for energy storage and industrial applications.In the whole process of energy consumption and conversion,only water is the consumption in SOEC mode and only water is the products in SOFC mode,with no fossil fuel consumption and greenhouse gas emissions.Therefore,reversible solid oxide cell(RSOC)is a kind of energy conversion device,worthy of attention and study.Because SOEC and SOFC are two contrary operation modes,SOFC common oxygen electrodes with excellent oxygen reduction catalytic property tend not to show good performance of oxygen evolution under SOEC mode.Therefore,it is necessary to research novel oxygen electrode material with good performance in both the SOEC and SOFC modes.Traditional pure LSM oxygen electrode mainly conducts electrons,so the reactions sites are limited at the electrode/electrolyte interface.Thus the buildup of high oxygen pressure within the interface will lead to the oxygen electrode delamination,which ultimately causes the degradation of the cell performance.The reaction zone can be extended to the entire internal electrode by utilizing mixed ionic and electronic conductors(MIEC)materials.Co-based perovskite materials are regarded as promising SOEC oxygen electrodes materials due to their high catalytic activity and oxygen permeability.Cause perovskite LSCN(La0.8Sr0.2Co0.8Ni0.2O3-?)material in SOFC cathode can show excellent electrocatalytic activity and high electrical conductivity,the LSCN material is introduced as SOEC oxygen electrode to study the performance in SOEC mode and discuss the possibility of using LSCN material as an oxygen electrode in RSOC.The LSCN was composite modified by impregnation process,hence,the catalytic activity and long-term stability of the electrode were improved by optimizing the electrode structure.Meanwhile,the traditional SOFC/SOEC oxygen electrode LSM-YSZ was modified by impregnating Pd-based oxide to increase reaction sites and further improve the stability of the electrode.In this paper,NiO-YSZ hydrogen electrode and YSZ electrolyte were fabricated on the NiO-YSZ tape by screen-printed method,a dense electrolyte and half cell substrate were obtained after calcined at 1390°C for 4 h.To obtain hydrogen electrode-support SOECs,pure LSCN oxygen electrode was prepared by screen-printed method,LSCN-GDC oxygen electrode and PdO/ZrO2+LSM-YSZ oxygen electrode were prepared by solution impregnation method.Study on the power generation of solid oxide fuel cell and hydrogen production performance of solid oxide electrolysis,and the main research conclusions are as follows:(1)Study on the effect of powder preparation process on the properties of LSCN electrode.Compared with ball milling process,the measured size of LSCN powder by ultrasonic screening is more uniform.The prepared LSCN electrode can form a uniform porous three-dimensional network.The corresponding half cell performs better.And the Rp of electrode is almost half of electrode prepared with ball milling powder.The screen-printed LSCN oxygen electrode(SP)with GDC barrier was prepared by screen-printed method.At 800°C,for cell with SP electrode,the polarization resistance is 0.226 ? cm2 and the current density is 1.16 A cm-2 at voltage of 1.5 V with 60 vol%AH.(2)It is determined that the amount of LSCN loading in the LSCN-GDC composite electrode by solution impregnation method needs to be higher than 10 wt% to achieve performance superior to that of the SP electrode.The electrochemical performance increases with the increase of LSCN loading amount.With 60 vol%AH,for 30 wt% impregnated LSCN-GDC electrode(30LG),the R? and Rp are 0.094 ? cm2 and 0.072 ? cm2,respectively at 800°C.And the impregnated LSCN-GDC cell is fully reversible,in OCV,SOEC and SOFC modes,the polarization resistance values are almost identical.The maximum power density of 30 LG fuel cell reaches 1.336 W cm-2.(3)Both increase of the operation temperature and steam content in the hydrogen electrode can make for the current density enhancement.In the electrolysis mode,the maximum current density of 2.598 A cm-2 is obtained at 800°C with an applied voltage of 2 V at 90 vol%AH,and correspondingly hydrogen production rate reaches 1086 ml cm-2 h-1.Galvanostatic experiments are performed over 150 h at 400 mA cm-2 with 60 vol%AH at 750°C.The impregnated LSCN-GDC cell shows a very stable performance with degradation rate of 4.5×10-4 V h-1.The degradation is mainly caused by the aggregation and growth of nano-sized LSCN particles.(4)The PdO/ZrO2+LSM-YSZ oxygen electrode prepared by impregnation method was applied to the solid oxide fuel cell,and the peak power density of the cell at 750°C was 1.114 W cm-2.In the electrolysis mode,the maximum current density of 2.322 A cm-2 is obtained at 750°C with an applied voltage of 2 V at 90 vol%AH,and correspondingly hydrogen production reaches 971 ml cm-2 h-1.Tested at 750°C and 400 mA cm-2 over 150 h,the cell degradation rate is about 1.4×10-4 V h-1.It is indicated that the nanostructured PdO/ZrO2+LSM-YSZ oxygen electrode has high electrochemical performance and stability.