Study On Electrochemical Conversion And Degradation Characteristics Of Biomass In SO-DCFC

As high-efficiency electric energy conversion devices,solid oxide-direct carbon fuel cells?SO-DCFCs?can convert the chemical energy of carbon-based fuels into electrical energy directly.For its advantage of a wide range of fuels availably,high theoretical efficiency and low cost of CO₂ sequestration,SO-DCFCs offer a clean and efficient way to use carbon-based fuels.Although carbon-based fuels?such as coal,graphite,carbon black,petroleum coke,etc.?with different properties have the potential to be converted and utilized in SO-DCFCs,biomass is renewable,low sulfur/ash content compared to other carbon-based fuels,it is more practical to study its conversion and utilization in SO-DCFCs.Presently researches on biomass in SO-DCFCs are still in the basic theory and laboratory research stage,facing the problems of low peak power density?PPD?and poor discharge stability.Two scientific issues are proposed:one is the relationship between biomass fuel properties and its electrochemical properties;the other is the electrochemical contribution,degradation characteristics and carbon deposition control of biomass pyrolysis tristate products.In this paper,three aspects of research have been carried out:firstly,the electrochemical properties of biomass was studied to explore the relationship between electrochemistry and fuel properties;secondly,electrochemical behavior of biogas and toluene was studied to explore the electrochemical contribution and deterioration mechanism of biogas and toluene;thirdly,the electrochemical conversion of biomass in tin anodes was studied to explore the mechanism and effect of tin.The specific research contents and conclusions are as follows:Two typical biomasses?rice straws,sawdust?were analyzed.The electrochemical performance of biomass was test,considerable peak power density?⁰.140 W/cm²,1123 K?was obtained when raw biomass was used directly,but it showed rapid degradation.Thermal pretreatment showed that torrefraction could effectively affect the degradation?decreased by41.2%?,but the PPD had not improved;pyrolysis increased PPD significantly at 1073 and1123 K?10-20%?,it slowed down the degradation by 75.9%,the main reaction in anode was C-CO₂ gasification and electrochemical oxidation of CO.When CO₂ concentration was increased,CO concentration was diluted and the electrochemical performance was reduced.The gasification reaction rate of biochar-CO₂ was affected by its ash content.The thermodynamic equilibrium of the biogas with/without tar-containing showed that CO and H₂ increased from 0 to 65%and 40%in 373-1273 K,CO₂/CH₄/H₂O content was decreased and C content is from 50%?373 K?dropping to 0?973 K?;toluene-contained would increase C content and vanishing temperature?about 1100 K?.Theoretical open circuit voltage?OCV?of cells was between 1.22-1.32 V in 873 K-1173 K,it increased with the increase of toluene concentration.Electrochemical experiments showed that from 1023 K to 1123 K,the PPD increased by 15.4%;toluene-containing biogas increased PPD in 1023K and 1073 K by 3.74%and 3.18%respectively,but decreased by 6.40%in 1123 K;rapid cracking of toluene at high temperature leaded to serious carbon deposition,which also made anode deteriorate.Carbon deposition mainly exists in the form of graphite,C-O and O-C=O tested via SEM and XPS,high content of graphite?75%-95%?made it more difficult to remove.To investigate the feasibility of tin?Sn?in eliminating carbon deposition,electrochemical performance of biomass were explored in Sn-SOFC system.Molten tin changed the pyrolysis characteristics of biomass,so that the components of biogas changed?H₂ increased from 24%to 53%,and CO/CO₂/CH₄ decreased?.C-CO₂ gasification reaction and CO electrochemical oxidation were catalytic.Electrochemical tests showed that tin could improve the polarization performance of SO-DCFC in 1023 K?the PPD of the biomass,biochar,biogas and toluene-contained biogas increased by 47.0%,61.7%,12.5%and 20.0%respectively?,but in 1073 K and 1123 K would reduce by 30.7%,5.89%,53.2%and 37.5%respectively;it would alleviate carbon deposition,but the generation of SnO₂may destroy the anode porous structure,affecting the stable discharge process,the electrochemical performance of the SOFC would be deteriorating due to the reactions.