Construction And Performance Study Of Single Layer Fuel Cells Based On Lithium-containing Transition Metal Oxides

Owing to their high efficiency and cleanliness,solid oxide fuel cells（SOFC）are one of the most promising energy conversion technologies,however they are limited by high operating temperatures and high interfacial resistance.Single layer fuel cells（SLFC）are made from a mixture of ionic and electronic conductors and can perform the functions of the traditional SOFC three-layer structure,greatly simplifying the cell structure and fabrication process and effectively avoiding the electrode-electrolyte interface,thus significantly reducing the electrode-electrolyte interface resistance and providing a competitive advantage.However,comprehension of the working mechanism of SLFC remains restricted.It has been discovered that lithium-containing transition metal oxides（Li MO₂,M is a transition metal element,LMO）,represented as Ni_0.8Co_0.15Al_0.05Li O_2-δ（NCAL）,are the fundamental components of the SLFC functional layer,although a complete understanding of the mechanism of LMO in SLFC remains elusive.Therefore,in order to understand the working mechanism of SLFC,this thesis explores the key factors for implementing SLFC and the keys that affect the performance of SLFC in the following aspects.Firstly,the key materials to achieve SLFC functionality are investigated.The SLFC was constructed with the ionic conductor material Ce_0.8Sm_0.2O_1.9（SDC）and the electronic conductor material NCAL,and its output performance showed that the SLFC of this structure is feasible.Considering the gradual reduction of NCAL in hydrogen,five different types of SLFCs based on the online reaction products of SDC and NCAL during fuel cell operation were constructed.Microscopic morphology,electrical conductivity,catalytic activity and performance of the different cells were analysed in combination to investigate the key materials to realise the SLFC function and their effects on the cell performance.The study shows that a battery capable of SLFC functionality must contain either a lithium salt in a molten state at operating temperature or an LMO material that can be reduced by hydrogen.a certain level of porosity in the SLFC does not cause gas leakage problems,and the conductivity and catalytic activity of the material are key to the performance.Secondly,using the important parameters influencing SLFC performance identified in the preceding work,the effect of introducing SIC electrode materials on cell performance was explored from the standpoint of electrode catalytic performance augmentation.Semiconductor ionic membrane fuel cells（SIMFC）are obtained by adding an electrode catalytic layer on both sides of the functional layer SIC composite.SIC materials are more effective when applied to either electrolytes or electrodes.The Ni-7LNO-3SDC/7SDC-3LNO/7LNO-3SDC-Ni structure of the cells constructed on the basis of SIC materials achieved an OCV of 1.059 V and a P_maxof 1064 m W cm^-2at 550℃.Compared to SLFC,the duration of operation of SIMFC under discharge conditions was significantly increased.The functional layer material is the key factor to obtain more stable cell performance.Finally,based on the above study of the factors influencing the stability of the battery,this paper introduces sodium into the LMO to regulate the stability of the resulting alkali metal salt.It is shown that the introduction of sodium can significantly improve the output power and stability of the battery.The SLFC constructed with SDC-Li Co O₂was able to achieve an OCV of 0.974 V and a P_maxof 290 m W cm^-2,but was only able to operate for ten minutes,while the SLFC constructed with SDC-（Li Co O₂-Na Co O₂）achieved an OCV of 0.95V and a P_maxof 417 m W cm^-2at 550°C,and was able to operate for more than 151 h.The SLFC constructed with SDC-(Li_0.52Na_0.48)₂CO₃also achieved a sustained output performance of more than 30 h.What’s more,since Na elements are more easily detected directly using Energy Dispersive Spectrometer（EDS）than Li elements,this thesis further discusses the kinematic patterns of alkali metal elements in the LMO-based SLFC in relation to the distribution of Na elements.