Preparation And Application Of Direct Methane Solid Oxide Fuel Cells

Due to the limited resources of fossil fuels and the environmental pollution caused by their combustion products,maximizing the utilization of fuel and achieving zero emissions are current research hotspots.It is a very attractive way to convert fossil fuels into electricity and high value-added chemicals through electrochemical process.Compared with low temperature fuel cell,SOFC has higher ionic conductivity,lower resistance and faster reaction rate,so it has higher energy conversion efficiency.Moreover,its advantages,such as strong fuel flexibility and convenient building block assembly,have been widely concerned.At present,the most commonly used SOFC anode material is nickel-based materials.Compared with perovskite-supported electrode,nickel-based electrode has better reforming catalytic activity for partial oxidation of methane,methane steam reforming and methane dry reforming reactions.In addition,the price of nickel is low,which reduces the cost of SOFC.However,when hydrocarbon fuels（such as methane,ethanol）are used on nickel-based electrodes,the cracking reaction causes carbon deposition in the nickel-based electrodes,which wraps the active sites and reduces the catalytic activity,seriously leading to the rupture of the supporting electrode.An effective anti-carbon deposition method is to impregnate the nano-catalyst in the anode.However,the traditional anode pore structure has tortuous channels and small porosity,which makes it difficult to impregnate the catalyst uniformly,resulting in catalyst agglomeration,affecting gas transmission and electrode reaction.Adding external pre-reformer is also an effective means.By adding external pre-reformer,methane and other hydrocarbon fuels are pre-reformed into syngas（H₂,CO）,and then enter the electrode for electrochemical reaction,thus avoiding the problem of carbon deposition caused by excessive methane concentration in the anode.However,this way increases the operating cost and cannot produce syngas,which ultimately reduces the utilization rate of fuel.It is a great challenge for SOFC to achieve high power output and syngas formation at the same time.Therefore,we have developed a new SOFC concept,which integrates the micro-reformer into the anode and can effectively utilize methane to generate electricity and syngas,thus solving this challenge.The anode prepared by template phase inversion method has a special dendritic pore microchannel structure,which can be filled with nanofiber catalyst to act as an independent internal catalyst bed reformer.Such SOFC reactor realizes not only the thermal coupling effect,but also the material coupling effect,thus greatly improving the electrical symbiosis performance.Experiments show that under the optimal conditions,compared with SOFC without internal catalyst bed reformer,the peak power density is increased by 25%,the syngas yield is increased by more than 3 times,and the operation stability is also improved.In addition,adding reformers（H₂O and CO₂）into methane SOFC reactor can also improve the carbon deposition resistance of SOFC.Moreover,the heat balance between the endothermic reforming reaction and the exothermic oxidation reaction in the anode can be realized after the reformer is added,thus avoiding the generation of hot spots in the anode and realizing the electrochemical autothermal reforming of methane SOFC.Compared with the traditional catalyst bed autothermal reforming reactor,SOFC autothermal reforming reactor avoids the direct contact between oxygen and methane,improves the safety of the experiment,and can adjust the proportion of syngas by adjusting the ratio of current to reformer.Nanofiber catalysts were made by electrospinning technology with high porosity（>95%）and high catalytic activity.And the dendritic microchannel anode was prepared by template phase inversion method.This anode structure with high porosity and straight channel,which is beneficial to gas transmission and heat transfer,and eliminates the concentration polarization of SOFC.This anode structure,has high porosity and straight channel,is beneficial to gas transmission and heat transfer,which eliminates the concentration polarization of SOFC.The nanofiber catalyst was combined with SOFC with dendritic microchannel anode,and the catalyst was loaded into the microchannel by ultrasonic impregnation,which not only eliminated the anode temperature gradient during SOFC operation but also realized electrochemical autothermal reforming in SOFC anode.More optimally,the existence of non-current oxygen was found and confirmed during the electrical symbiosis of methane SOFC,which can promote the electrochemical reaction process and improve the utilization rate of methane fuel.Based on this discovery,a new oxygen permeable membrane was developed,which can run stably for 20 hours under 25% CH₄.