A monolithic hybrid direct methanol fuel cell & an equivalent nonlinear electric circuit model for direct methanol fuel cell.

摘要

My dissertation researches are on the field of fuel cell materials and fuel cell modeling. During my dissertation research, I authored two US patent applications and have developed several innovative approaches to new fuel cell materials, novel fuel cell hybrid power device and an original fuel cell modeling method.; A monolithic hybrid fuel cell with a novel configuration is developed in an effort to reduce the weight and size of the conventional hybrid fuel cell system. A modified direct methanol fuel cell (DMFC) with a layer of hydrous ruthenium dioxide (RuO2•xH2O) sandwiched between the anode catalyst layer and membrane has been used to demonstrate the principle of the monolithic hybrid fuel cell. Experimental results indicate that the capacitive material (e.g. RuO2•xH2O) layer is equivalent to a resistive-capacitive transmission line and functions similar to a capacitor in parallel with the anode electrode. The improvement in dynamic response of the modified DMFC has been experimentally confirmed under square current pulse operating.; A novel semi-empirical modeling method to mathematically derive a nonlinear equivalent circuit from a special group of impedance fuel cell models has also been derived in this dissertation. As an example, a 5-cm2 direct methanol fuel cell (DMFC) was modeled by this method. The derived equivalent circuit is composed of lumped nonlinear resistors, capacitors and an inductor. The nonlinear circuit has an impedance equivalent to the target fuel cell in various operating conditions and provides a good approximation of the static and transient behaviors of the fuel cell. The equivalent circuit fuel cell model was validated by comparing its numerical simulation results with its polarization curve and the dynamic behavior of the target DMFC. These comparisons were performed while the DMFC was operated under square current pulses with different upper and low current levels.; Finally, a novel resistive-capacitive-inductive transmission-line equivalent circuit was created to model a direct methanol fuel cell (DMFC). This fuel cell model was inherited and improved from existing impedance fuel cell model and transmission-line fuel cell model in many aspects. The resistive-capacitive-inductive transmission line model can properly describe the inductive and capacitive behaviors of the DMFC operating in both low and high frequency regions. The advantages of this transmission line fuel cell model have been discussed based on published experimental impedance spectrum of DMFC.