Study On The Highly Efficient Utilization Of Clean Fuels Based On Proton Conductor Solid Oxide Fuel Cells

Energy has been an indispensable part of human society since ancient times.It is the material basis for human survival and development and the driving force for social and economic development.For the development of modern society,the development of a country is inseparable from energy,which drives the operation of cities.The current energy is mainly obtained by burning non-renewable fossil fuels.Due to the heavy pressure of environmental degradation and excessive consumption of fossil resources,the transformation of global energy from fossil fuel energy to clean energy has accelerated significantly in recent years.To this end,effective low-cost technologies and new pathways are urgently needed to facilitate the clean energy transition within a sustainable socio-economic framework.Solid oxide fuel cells（SOFCs）are all-solid chemical power-generation devices that can convert the chemical energy stored in fuel into electrical energy with high efficiency.Compared with the traditional oxygen ion-conducting solid oxide fuel cells,proton-conducting solid oxide fuel cells（H-SOFCs）having a lower operating temperature would decrease the degradation of the cell component due to the high-temperature oxidation of metal structures and deactivation of electrocatalyst.At a reduced temperature,the polarization loss on the cathode-electrolyte interface would be the predominant factor limiting the electricity output of H-SOFCs.Therefore,the optimization of the cathode materials could be critically important to reduce the polarization loss of the cell and increase the power output of the H-SOFC at a reduced temperature.In this paper,for the purpose of exploring proton conductor solid oxide fuel cell cathode materials,the structure,performance and other indicators of La_0.5Ba_0.5Cu_xFe_1-xO_3-d（0≤x≤1）series oxides are studied,and they are used as H-SOFC electrodes material feasibility was investigated.For the good performance of La_0.5Ba_0.5Fe O_3-d-based cathode materials,we prepared La_0.5(Ba_0.5-xCa_x)Fe O_3-d（0≤x≤0.3）by replacing Ba element with Ca²⁺at A site.A series of oxides are used in direct ammonia fuel cell（DAFC）,and its indicators and cell performance are systematically studied.（1）La_0.5Ba_0.5Cu_xFe_1-xO_3-d（0≤x≤1）perovskite was investigated as a cathode for a protonic solid oxide fuel cell（H-SOFC）using Ba Zr_0.1Ce_0.7Y_0.2O_δ（BZCY）electrolyte.A maximum electric conductivity(76.84 S cm^-1 at 700 ^oC)was achieved in the air at the composition of La_0.5Ba_0.5Cu_0.4Fe_0.6O_3-d.Comparing to La_0.5Ba_0.5Cu O_3-d（LBC）,the increase in Fe content increased the D_chem(1.07x10^-5 to 1.74x10^-5 cm² S^-1)and k_chem(1.12x10^-10 to 3.01x10^-10 cm² S^-1)at La_0.5Ba_0.5Cu_0.2Fe_0.8O_3-d（LBCF28）but decreased the proton conductivity from 7.5 to 4.3 mS cm^-1.Either Fe doping in LBC or Cu doping in La_0.5Ba_0.5Fe O_3-dincreased the thermal expansion coefficient（TEC）,but a low TEC among samples with mixed cations was achieved at La_0.5Ba_0.5Cu_0.5Fe_0.5O_3-d（LBCF55）(16.12 ppm K^-1).LBC suffered from superficial decomposition in the ambient air,causing an ohmic resistance loss of the full cell on Ni（O）-BZCY support.A high initial cell performance(820 m W cm^-2)can be achieved for the cell with LBCF55 and LBCF28 cathode but the latter was unstable under a cathodic bias owing to the increase in ohmic resistance owing to the production of intermediate layer between electrode and electrolyte.With better stability than LBCF28 and higher performance than LBC,LBCF55 was regarded as a viable cathode material for H-SOFC.This work explores systematically the behavior of a perovskite with mixed Cu and Fe cations as a cathode for H-SOFCs.（2）We report that La_0.5(Ba_0.5-xCa_x)FeO_3-d（0≤x≤0.3）series perovskites are explored as cathodes for proton-conducting direct ammonia fuel cells.The substitution of Ca²⁺for Ba²⁺can improve the D_chem and k_chem of the substance.When the Ca doping amount reaches 30%,the maximum conductivity(8.9 S cm^-1 at 700 ^oC)can be obtained,but its proton conductivity is low.For electrochemical tests,the full cell with La_0.5(Ba_0.45Ca_0.05)Fe O_3-d（LBC5F）cathode and Ba Zr_0.1Ce_0.7Y_0.2O_δ（BZCY）electrolyte has lower polarization resistances of 0.063 and 0.058Wcm² at 700 ^oC under H₂ and NH₃ fuel,which correspond to the highest cell performance of 750 and 682 m W cm^-2,respectively.In addition,LBC5F showed good stability in durability tests.This provides a possibility for proton conductor direct ammonia fuel cell cathode material.