Theoretical Modeling, Analysis And Experimental Study Of High Efficiency Energy Conversion And Storage Processes

The development of high efficiency energy conversion and storage process is a major solution for energy problem. In this work, a brief review of direct carbon fuel cell and redox flow battery is firstly presented, including background, research approach and application. A series of modeling work and theoretical analysis are developed from single carbon particle, direct carbon fuel cell anode, single cell and energy system. A novel non-aqueous vanadium acetylacetonate electrolyte for redox flow application is developed.Theoretical study of direct carbon fuel cell anode. An anode mechanism is built including series of electrochemical and chemical steps. A kinetic equation of the anode is deduced by introducing a factor of reaction time in each step based on traditional electrochemistry kinetic theory. A microstructural model of carbon particle (carbon black and graphite) is built. The concentration of active carbon site is defined. The reactivity of carbon is introduced to the open circuit voltage calculation with Nernst equation. The results show that it is consistent with the experiment results.Modeling and simulation of direct carbon single cell. The model takes account of the electrochemical reaction dynamics, mass-transfer and electrode processes. The simulation results reveal several important feathers of the very promising DCFC. The cell is under the control of anode activation polarization. The working temperature has a decisive effect on the various polarization losses, especially for the anode activation polarization, which indicates that the anode surface reaction rate is a key factor. The reaction surface area and the transportation path are among the most important factors. The power density can be as high as 200 - 500 W m^-2 with carbon particle size in the range of 1.0×10^-7 - 1.0×10^-4 m.Modeling and analysis of the high efficiency energy conversion process based on methane catalytic decomposition process and dual fuel cells. Two energy conversion systems are developed based on methane catalytic decomposition process, direct carbon fuel cell, internal reforming solid oxide fuel cell and gas turbine. The models of major units are built. Theoretical comparison study of direct carbon fuel cell and internal reforming solid oxide fuel cell is also carried out. The system has a unique loading flexibility due to the good high loading property of direct carbon fuel cell and the good low loading property of internal reforming solid oxide fuel cell. The results show that the electrical exergy efficiency of 52% and 69%, the combined power-heat exergy efficiency over 70% and 80% are achieved with the systems. The possibility of further recovery of the waste heat is discussed. The CO2 emission reduction is effective, up to 80%, can be reduced with the proposed system.Study of a novel single-element organic electrolyte for redox flow battery. The electrode kinetics of the anodic and cathodic reactions is studied using cyclic voltammetry. The V(II)/V(III) and V(III)/V(IV) couples are quasi-reversible and together yielded a cell potential of 2.2 V. The diffusion coefficient for vanadium acetylacetonate is estimated to be in the range of 1.8 - 2.9×10^-6 cm² s^-1 at room temperature. The charge-discharge characteristics of this system are evaluated in a H-type glass cell, and coulombic efficiencies near 50% are achieved.