Study Of New Materials And Electrochemical Performance For Semiconductor-ionic Fuel Cells

The development and application of new green energy conversion and storage technologies have received increased attention.Compared with other types of fuel cells,solid oxide fuel cells(SOFCs)hold distinct advantages of fuel flexibility higher electrical efficiency and no requirement for precious metal catalyst,which have make SOFCs the most promising Technologies for future deployment.However,the large scale application of SOFCs is still suffering from the high investment and low insufficient serving lifespan due to the low ionic conductivity of electrolyte materials and the associated complex three-component anode/electrolyte/cathode structure configuration.Semiconductor-ion conductor fuel cell(SIFC)is a new type of fuel cell device that are developed on the basis of SOFCs.Compared with pure ion conductor type batteries,SIFC based on mixed semiconductors and ion conductors has a simple cell structure,holding the potential of higher ionic conductivity and better electrochemical performance and longer lifespan.Although there is intrinsic electronic conduction in bulk SLFCs,no short circuit appears in fuel cell condition.However,the current working principle of SIFC is not yet clear and well-evidenced,and long-term stable operation is still not satisfactory.Based on the above considerations,we start from the developing of new semiconductor materials,design novel material and cell microstructure,adopt of nanotechnology to material electro catalytic activity and fuel cell performance,with the final target of improving the operational stability of SIFC,and attempting to elaborate the working mechanism.The main research contents and progress are as follows:(1)Simple SLFCs were fabricated with redox stabilized perovskite oxidesemiconductor Pr_0.4Sr_0.6Co_0.2Fe_0.7Nb_0.1O₃(P-PSCFN)and ionic conductor(Li_0.52Na_0.48)₂CO₃-Sm_0.2Ce_0.8O₂(LNSDC)to replace easily reducible semiconductor.The cell can be stably operated for 40hours,while the control cell fails in 5 hours.At the same time,the in-situ precipitation of metal/alloy nanoparticles and the associated oxygen vacancy concentration on the surface of the perovskite oxide under reducing conditions not only improves the electrode reaction kinetics,the former also constructs a nanoscale metal-semiconductor Schottky junction(SJ),and an internal electric field that facilitate the charge separation and ion conduction in SIFC.Those simultaneously improve the cell stability and electrochemical output performance.This work provides some thoughts and insights on how SIFC avoids short circuits by using the construction of SJ and P-N heterojunction methods.(2)A single-phase ionic conductor,samarium-doped cerium oxide(SDC),is used to replace of LNSDC to construct SLFC considering the possible volatilization issue of molten carbonate which may results in low durability.In order to further improve the electrochemical performance,we adopt th surface impregnation of nanosize Pr₆O₁₁.It has been confirmed that the cell can be stably operated for 120 hours at 650^oC,and the electrochemical performance was also improved after infiltration.The experimental results show that surface modification is an efficient way to improve the performance of a single cell,and also prove that SLFCs with durable performance can be achieved with a redox stable semiconductor and ionic conductor core materials..(3)The SIFC has the potential for low-temperature operation since it removes the SOFC electrolyte layer and the highly energy lose electrode/electrolyte interface.we developed a new type of SIFC with Na Co O₂as semiconductor material and SDC as the ion conductor and Ni_0.8Co_0.15Al_0.05Li O₂(NCAL)as the catalytic layer.The single cell achieved excellent electrochemical performance below 500?,The open circuit voltage was 1.06V at 450?,and the maximum power density was 450m W/cm²,which is one of the highest value in the open literature.The super low temperature operation enables the stable operation for non-stop 25hours even using the redox phase unstable Na Co O₂phase.The ionic conductivity increased significantly in Na Co O₂-SDC composite compared with pure SDC because of rapid ionic transfer interface between the semiconductor and the ion conductor and the accelerateion effect of the in situ formed physical junction.This work provides certain technical and material support for achieving ultra-low temperature operation of SOFC.