Basic Research On SOFC Power Generation Application By Low Concentration CBM Internal Reforming

Solid oxide fuel cell?SOFC?is an efficient all-solid-state power generation device.Compared with low temperature fuel cell,it has the advantage of fuel diversity.Conventional nickel-based anodes degrade or even fail due to carbon deposition in SOFC fueled by low concentrations of coal-bed methane.In this paper,a catalyst NiO/BaO/CeO₂?NBC?was prepared by polymer combustion method.A catalyst NBC@SiO₂ with a core-shell structure was prepared by tetraethyl silicate?TEOS?as silicon source.The catalytic performance and stability of the catalysts for methane partial oxidation were studied.The catalysts NBC and NBC@SiO₂ were introduced into the anode of the cell by direct spraying and as an independent catalyst layer.The improvement of coking-resistance of the catalyst-modificed Ni cermet anodes was studied using a model of low concentrated coal bed gas?30 vol% methane-70 vol% air?.An anodesupported cell?denoted as Ni-YSZ?was used,with NiO-YSZ as the anode layer,yttrium-stablized zirconia?YSZ?as the electrolyte layer,Sm_0.2Ce_0.8O_1.9?SDC?as the buffer layer between electrolyte and cathode,and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-??BSCF?as the cathode layer.The main contents were as followings:1.Catalytic performance test of catalysts for methane partial oxidation using a fixed-bed reactor.The catalyst NBC had high catalytic activity and stability for methane partial oxidation.CH4 conversion efficiency was 93%with CO selectivity close to 100% at 900 ?.At 750 ?after 80 h stability test,CH₄ conversion was stable at 80% with CO selectivity of 95%.The catalyst NBC@SiO₂ had higher catalytic activity and catalytic stability than NBC for methane partial oxidation.CH₄ conversion and CO selectivity was close to 100% at 900 ?.After 200 h stability test at 750?,CH4 conversion and CO selectivity were both stable at 95%.2.The electrochemical properties and discharge stability tests of catalyst-supported SOFC?NBC//Ni-YSZ?by spraying the catalyst NBCdirectly onto the SOFC anode.When 30 vol% methane-70 vol% air was used as the fuel,the peak power densities?PPD?of NBC//Ni-YSZ were22.0% and 15.1% at 800 ?and 750 ?,respectively higher than that of Ni-YSZ?0.6254 W cm-2 and 0.5428 W cm-2?.When the discharge current was 0.16 mA at 800?,the voltage of Ni-YSZ dropped from 0.8 V to 0 V within 16 h,while the voltage of NBC// Ni-YSZ decreased from 0.8 V to 0.6V over 80 h with a drop rate of 0.0025 V h-1.The improved discharge stability of NBC//Ni-YSZ indicated that the cell anode had an improved coking-resistance.SEM-EDS showed slight sintering for the surface of NBC//Ni-YSZ after 80 h discharge stability with the carbon content increased,indicating a poor thermal stability of the NBC catalyst.3.The core-shell catalyst was introduced into the anode by direct spraying?denoted as P-@NBC//Ni-YSZ?and as an independent catalyst layer?denoted as Y-@NBC//Ni-YSZ?.The PPD of P-@NBC//Ni-YSZ and Y-@NBC//Ni-YSZ at 800? was increased by about 26.8% and 32.8%,respectively,over Ni-YSZ?0.6254 W cm-2?.When the discharge current was0.16 mA at 800?,voltage of Ni-YSZ without a catalyst layer dropped from0.8 V to 0 V after 16 h.Voltage of P-@NBC//Ni-YSZ decreased from 0.8 V to 0.6 V within 30 h with a drop rate of 0.0067 V h^-1.Voltage of Y-@NBC//Ni-YSZ decreased from 0.8 V to 0.7 V over 180 h with a drop rate of0.0006 Vh^-1.The stable discharge performance of Y-@NBC//Ni-YSZ indicated that the nickel-based anode of the cell had excellent cokingresistance.The results of SEM showed that the surface of the cell catalyst supporting the independent catalyst layer had no obvious sintering,indicating that the introduction of the catalyst layer can enhance the carbon deposition resistance of the cell anode.SEM of P-@NBC after the discharge stability test showed that catalyst particles penetrated into the anode layer and blocked the anode pores,resulting in a lower porosity and a higher diffusion resistance.