Study On The Anodic Reactions And The Performances Of Direct Carbon Fuel Cells

Direct Carbon Fuel Cells (DCFCs) attract more and more attention in recent years because they are highly efficient and favorable for carbon dioxide recovery. The setups of DCFCs with solid oxide as the electrolyte are simple and easy to be industrialized, but due to the limited research of the reaction mechanism and properties of such fuel cells, the efficiencies of such fuel cells are quite low at present. Thus, the carbon reactions in the anode of deposited carbon fuel cells and the parameters'influence on the performances of the fuel cells were studied experimentally and theoretically.Anodic reactions of deposited DCFC are quite complicate and learning the reaction mechanism is quite meaningful for the option of operating conditions and for the optimization of the cell. Deposition experiments were conducted by decomposing methane in a thermogravimetric analyzer, with NiO or YSZ powders and with small chips of an unused anode-supported SOFC button cell used separately as bed materials. Experimental results showed that the deposition position and deposited carbon particles'sizes decided the deposited carbon has little opportunity to participate in the electrochemical reactions. Meanwhile, deposited carbon particles, especially the ones after methane decomposition for a long time, will clog the micro pores inside the anode according to the analysis by the software ImageJ . Thus, it is advisable to decompose methane with higher methane concentrations and shorter time.Based on the experimental results, two two-dimensional isothermal models of the deposited DCFC and the DCFC with carbon layers outside the anode are developed and calculated at different parameters by commercial software COMSOL. The simulated results of deposited carbon fuel cells show that the probability for the deposited to improve the anodic exchange current densities is quite small. Besides, the effective diffusion coefficient of CO has the largest influence The simulated results of DCFCs with carbon layer outside the anode show that if the reactivity of carbon is not high, the carbon layer will play as the diffusion resistance. And on the conditions of natural pack, this resistance effect is not obvious. Thicker carbon layers at the same packing density can enlarger the operating time of DCFC in one period without harming the performances. When the carbon weight is settled, it is advisable to choose a proper thickness to optimize the cell's performance. Besides, the DCFCs with carbon layer outside the anode are more competitive in setups, performances, energy usage efficiencies and carbon dioxide recovery at the same carbon fuel weights.