Research On The Anode Reforming Layer Of Solid Oxide Fuel Cell Based On Methane And Carbon Dioxide Fuels

As an energy conversion device,solid oxide fuel cell(SOFC)can directly convert chemical energy in fuel into electric energy efficiently and cleanly.In particular,it can directly and efficiently use readily available and abundant hydrocarbons as fuel,which can effectively reduce system operating costs and improve energy efficiency,with huge economic benefits,and in line with the country's green sustainable development strategy.However,the most advanced Ni-based anodes of SOFC have serious carbon deposition problems when using hydrocarbon fuel directly.Therefore,how to make SOFC efficient and stable when using CH₄ for power generation is a major problem for commercial application of SOFC technology.At present,the efficient strategy is to prereform the CH₄into CO and H₂,and then pass the syngas into the SOFC anode.And the CH₄-CO₂reforming technology can consume both greenhouse gases,which also provides a solution for excessive CO₂ emissions.In this research,the efficient perovskite reforming catalyst was developed and added on the anode of SOFC as a reforming layer to elucidate the mechanism of in situ CH₄-CO₂reforming reaction on SOFC anode,which is also called on-cell reforming.First,metal Ni nanoparticles have been precipitated on the surface of perovskite by in-situ exsolution method as a catalyst for CH₄-CO₂ reforming and its catalytic performance were analyzed.Then the perovskite reforming catalyst with the best performance is selected according to the stability of the material in high temperature and reduction atmosphere,the basicity and oxygen vacancy concentration of the substrate and the conversion of CH₄.Finally,the selected catalysts are added on the anode surface of the oxygen ion-conducting(O-SOFC)and proton-conducting SOFC(H-SOFC)as reforming layer,and the effects of reforming layer on improving the electrical performance and stability in CH₄ fuel are also discussed.More details are summarized as follows:(1)A perovskite catalyst La_0.9Mn_0.8Ni_0.2O₃(LMN)with high catalytic activity has been developed and studied.In the reduced one(R-LMN),the exsolved Ni nanoparticles are embedded in the substrate,with strong interface bonding with the substract,which can effectively inhibit carbon deposition.R-LMN has much more stable and efficient performance than the supported catalyst by impregnation method with no decay at 700? after 24 hours test.However,for the R-LMN,it is not stable in high temperature and reduction atmosphere.When the temperature is higher than 750?,the perovskite structure will be decomposed,and the stable catalytic activity of the catalyst cannot be guaranteed.(2)The Sr and Ni co-doped La Cr O₃ perovskite catalysts were further studied.The stability of the catalysts in high temperature and reduction atmosphere has been improved significantly.And through the research of exsolution characteristics,it has been found that the reduction process would be mainly completed at 800? in H₂ and about 80 mol%of Ni would be exsolved finally.Furthermore,the optimum catalytic efficiency was obtained at the reduced La_0.6Sr_0.2Cr_0.85Ni_0.15O₃(R-62)by optimizing the element doping ratio and adjusting the surface basicity and oxygen vacancy concentration.After test at 750? for24 hours,the conversion rate of CH₄ and CO₂ remained above 90%.The further characterization of the interface between Ni particles and the substrate can reasonably explain the conclusion that neither the Ni particles obtained after the reduction of Ni O loaded by impregnation method nor the Ni particles obtained after the reduction of free Ni O generated in the synthesis of materials has the same catalytic activity and stability as the Ni particles exsolved.(3)La_0.6Sr_0.2Cr_0.85Ni_0.15O₃-Ce_0.9Gd_0.1O_2-?(LSCN-GDC)has been selected as the catalytic reforming layer material.The addition of a layer of LSCN-GDC catalyst on the Ni-GDC anode can improve the performance and long-term stability of the O-SOFC when50%CO₂-50%CH₄ is directly used,while ensuring that the O-SOFC does not accumulate carbon during the 36-hour long-term discharge test at 400 mA cm^-2 current density and750?.The catalytic activity of the LSCN-GDC layer for the reforming is higher than that of Ni-GDC.It can convert the majority of CH₄ and CO₂ into H₂ and CO,reducing the direct contact between CH₄ and the anode,which ensures that the SOFC can use CH₄efficiently for stable power generation.(4)After adding LSCN-GDC reforming layer and improving the current collecting mode of the anode,the lack of conductivity of the reforming layer and the problem that H-SOFC can not directly utilize CH₄have been relieved.When CH₄-CO₂ as the fuel gas,the peak power density of H-SOFC can reach 605 m W cm^-2 at 700?.Under the current density of 600 mA cm^-2 at 700?,the voltage remained stable during the 60-hours test.The LSCN-GDC catalytic reforming layer has a high reforming efficiency,which ensures the sufficient conversion of CH₄ and CO₂,eliminates the interference of carbon deposition and CO₂ poisoning for Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O_3-?(BZCYYb)in the anode,and improves the long-term stability of the single cell.The introduction of the novel catalytic reforming layer effectively solves the problem of carbon deposition caused by the direct use of CH₄ by SOFCs,enabling not only O-SOFCs but also H-SOFCs could utilize CH₄ for stable power generation efficiently.At the same time,the CH₄-CO₂ fuel reforming technology on SOFC can use CH₄ and CO₂ to reduce the emission of these two greenhouse gases,which has great economic and environmental value.