Research On The Electrochemical Performance Of Microtubular Solid Oxide Cells（SOCs）

Solid oxide cells（SOCs）have numerous advantages in electrochemical energy conversion and have become synonymous with high efficiency,cleanliness and sustainability.Cells suffer from degradation and long-term stability issues due to high operating temperatures.The development of new materials and new structures is particularly important to improve the electrochemical performance and durability of SOCs at intermediate temperatures.Against this background,the development,simulation and testing of multi-tube stacks continued.In order to solve the key problems of low power,poor stability and short life of the stack,and promote the commercial development of the stack.The main findings are as follows,By adding insulating ceramic connectors,a co-fuel channel microtubule solid oxide fuel/electrolyte was successfully fabricated.The active electrode area of the above two cells is about 10.73 cm~2.The hydrogen-steam mixture acts as a reactant or product in the ceramic tube.The annular anode current collector is located in the middle of the anode,while the silver paste is coated on the cathode as the cathode current collector.When the cell was operated at750℃,the SOFC and SOEC reached 0.6 A cm^-2 and 1.0 A cm^-2at 0.6 V and 1.7 V,respectively.By using a common fuel channel,the SOFC generates 3.9 W of electricity,while the SOEC consumes 18.2 W at the same time.After 11 hours of operation,no microcracks were observed and no Ni agglomeration or loss of active phase was observed in the anode-electrolyte interface structure.The effect of nanohoneycomb cathodes on the performance of microtubular solid oxide fuel cells（HC-MTSOFC）was investigated.A honeycomb porous cathode with high porosity（≈64.6%）and high structural strength was successfully fabricated by freeze casting,which can effectively improve oxygen adsorption and dissociation.In the cathode material LSCF,GDC powder was added to effectively improve the low-temperature electrochemical activity of the oxygen electrode.Compared with the conventional sponge porous structure GDC-LSCF cathode,the cell performance of the nanohoneycomb structure GDC-LSCF cathode is significantly improved.At 750℃,the current density is 1450 mA/cm~2 and the power density is 475 mW/cm~2,which is much higher than that of cells with conventional cathode structures.In addition,we also discuss the effect of the honeycomb structure on the cell,including the migration of the silver paste as the cathode current collector to the GDC-LSCF interface and the improvement of the active performance of the oxygen electrode.A 3D Multiphysics coupled model was developed to calculate the temperature and thermal stress distribution of a microtubular solid oxide fuel cell（MTSOFC）stack with an external manifold structure.The stack consists of 10 tubular cells with identical cells.Models contain cells,gas distributors,metal interconnects,hermetic ceramics,and cathode/anode collectors.Analyze the flow channels with different flow directions,analyze the temperature,material distribution and discharge performance of the cell,as well as the influence of the gas distributor on the stack.The simulation results show that under the reaction conditions with the initial temperature of 700℃,the temperature of the stack is the highest distributed in the hydrogen inlet region,and further,in the air and hydrogen inlet regions.Different cathode mass transfer flow directions have obvious effects on the current distribution,temperature distribution and oxygen distribution of the cell.The stress is mainly distributed at the interface with the gas distributor,where there is a mismatch in the coefficient of thermal expansion（CTE）of the high temperature ceramic glue/glass glue and the cell.In addition,due to the influence of the expansion of the silver block of the connecting body and the cell itself,there is a stress distribution of up to 140 MPa in the intermediate connecting region.The simulation results can be used to optimize the structural design of the stack and minimize high stress concentrations in the components.The current collection window（0.4 cm~2）,without electrolyte and cathode,is located in the middle of the anode and is electrically connected to the cathode of another microtubule solid oxide fuel cell（MTSOFC）when constructing a short stack.No significant drop in open circuit voltage（OCV）was observed during 31 thermal cycles of the 8-cell cell pack using H₂and syngas.In addition,24.1,53.6 and 103.5 W power levels were achieved with this current harvesting mode in 8-tube,10-tube and 20-tube stacks,respectively.A propane-fueled 8-tube stack integrated with a catalytic partial oxidation（CPOX）reformer achieves a maximum power density（MPD）of 0.30 W cm^-2 and a flow rate of 0.32 g min^-1 propane.Pt-Ru nanoparticles were prepared by impregnation treatment of alumina honeycomb ceramic supports.The average size of the Pt-based catalyst is about 10.0 nm,and it is well distributed on the surface of the honeycomb ceramic channels.In addition,Pt-Ru/Al₂O₃ as CPOX catalyst exhibited high propane conversion（94.2%）at 700℃.