Investigations On Preparation Method And Performance Of MCFC Composite Cathodes Doped With Nano-particles

With the rapid development of the world economy, the energy crisis, environmentalpollution and other issues have emerged, which urged people to constantly seek new energy. Asthe fourth power generation after thermal power, hydroelectric power and nuclear power, fuelcell (FC) has advantages of high efficiency, low noise, high load capacity, etc. It is a kind ofnew energy with huge potential, whose development has draw more and more countries’attentions. Among them, the molten carbonate fuel cell (MCFC) has been initially entered thecommercialization stage, and it will become one of the main large-scale power generation in thefuture.Since NiO has excellent electrochemical properties, it is most commonly used as MCFCcathode materials. However, the dissolution of NiO cathode in the molten electrolyte shortensthe cell life-time, which limits MCFC’s commercial development. Therefore, a cathode materialwith high stability and excellent electrochemical properties is the premise and foundation forMCFC to have stable performance and long life-time.In this paper, we combined the mechanical blending method and ElectrophoreticDeposition technique (EPD) to prepare MCFC composite cathode material and further studiedits performance. In this work, the nano-particles of Co3O4, LiCoO2and LiFeO2weresynthetized by Pechini method. And then nickel powder and Co3O4nano-particles byball-milling to prepare composite-based cathodeⅠwith different doping ratio；and appropriatedoping ratios which were selected combined with home-made deformation-testing system andvarious characterization techniques. Finally, LiCoO2and LiFeO2is molar ratio of1:1, the twoparticles were modified to the surface of composite-basedcathode Ⅰ at the same time and thenmade into composite-based cathode Ⅱ. Long term stability study on the composite workingcathode transformed by complex matrix cathode and electrochemical properties were alsoinvestigated. Through the contrast analysis, ultimately determine the composite cathode material and preparation method which has excellent strength, deformation resistance,long-term stability and electrochemical properties.The results show that the content of Co3O4,doped, the electrophoresis voltage, thedeposition time and the pH value of the suspension had a greater impact on the morphology andperformance of the composite-based cathode. The nickel powder and Co3O4nano-particles byball-milling to prepare composite-based cathode Ⅰ.When the doping amount is too far, thepores of the composite-based cathode distributed unevenly, nano-particles accumulated, and thetoughness of the matrix cathode was poor.The deformation/dissolution test results showthat,compared with the traditional porous nickel,the deformation and solubility ofcomposite-based cthodes reduced in varying degrees, of which composite-based cathodes ofdoping ratio2%,4%,6%and8%display a negligible and low solubility, excellent resistance todissolve and deformation resistance. The deformation of doping ratio is10%,13%,16%islarger, and with the increase of doping ratio, the more obvious of deformation. Consideringthe morphology, material strength and toughness, resistance to deformation/dissolvingproperties of composite based cathodeⅠ, select the doping ratio of Co3O4nanoparticlesbetween2wt.%and6wt.%is better. On this basis, the better composite-based cathodes I werechoosed to prepare composite-based cathodeⅡby electrophoretic deposition technique. Theresults show that the electrophoresis voltage, the deposition time and the pH value of thesuspension had a greater impact on the morphology. When the electrophoresis voltage is45V,deposition time is about1minute and the pH value of suspension is about2.0, the preparedcomposite-based cathode II maintained a good porous structure, have an evenly distribution ofparticles deposited on its surface, and the particles coated on the substrate compactly.This stability and electrochemical properties of composite working cathodes were furtherstudied and compared in this paper paper. Under the condition of simulated MCFC workingstages, composite working cathodesⅠand Ⅱ all showed good thermal stability. Although Ni2+concentration in the molten salt electrolyte has certain differences, which is lower than thetraditional NiO. In contrast, composite working cathodesⅡshows better thermal stability, theNi2+concentration of composite cathode materialsⅡdoped with4%Co3O4was almost0. Inaddition, electrochemical performances of conventional electrodes and composite cathodematerialsⅠand Ⅱ converted into a working electrical catalytic cathode material were compared under conditions of simulated MCFC working stages. The results show that the compositecathode materialsⅠand Ⅱ possess better electrochemical performance..In conclusion, the composite cathode materials which are prepared combined with themechanical mixing method and electrophoretic deposition technique (EPD) technique possessgood strength and toughness, deformation resistance, thermal stability and electrochemicalproperties. Cathode materials are convenient for installation and sealing for actual MCFCbattery pile, and the preparation method is suitable for large-scale industrial production, isexpected to be applied in MCFC industrial production.