Pei-Hung Chi

Numerical modeling of proton exchange membrane fuel cell with considering thermal and relative humidity effects on the cell performance

A three-dimensional (3D) model has been developed to simulate proton exchange membrane fuel cells. The model accounts simultaneously for electrochemical kinetics, current distribution, hydrodynamics, and multi-components transport. A single set of conservation equations of mass, momentum, energy, species, and electric current are developed and numerically solved using a finite-volume-based computational fluid dynamics technique (by computational fluid dynamics ACE+ commercial code). The physical model is presented for a 5 cm X 4.92 cm X 0.4479 cm 3D geometry test cell with serpentine channels and counter flow. Subsequently, the model is applied to explore cell temperature effects in the cell environment with different relative humidity of inlet. The numerical model is validated and agreed well with the experimental data. The nonuniformity of thermal and water-saturation distributions is calculated and analyzed as well as its influence on the cell performance. As the cell is operated at low voltages (or high current densities), the thermal field of fuel cell tends to be nonuniform and exists locally in hot spots. The mechanism of thermal field and water content interacted with membrane dehydration and cathode water flooding will be discussed and revealed their influences on the cell performance, stability and degradation will be revealed.

Design, Fabrication, and Performance Analysis of a Passive Micro-PEM-Fuel-Cell Stack

A micro-fuel-cell stack of six cells with an active area of 2.73 cm2 and 2.5 W output power has been designed and fabricated in-house. It can go with mini hydrogen storage and provide enough power for portable electric products. Under polarization curve measurement, when the voltage was scanning to low voltage, the performance was quickly decayed by the low fuel concentration. This result was contributed by a limited fuel supply of metal hydride hydrogen tank. The voltage declined to very low voltage in some of the cell stacks when the current output was at high current. This phenomenon is attributed to the self-breath of air in the cathode. At the higher current of 0.9 A condition, the stack voltage was decreased even though the high hydrogen flow rate was increased. The solution to prevent the decrease in voltage is adding the airflow in the cathode. The fuel cell performances respond to the transient of load changes influenced by the hydrogen flow rate and step increase in current. The flow change can decrease the high resistance in the transient of the current output, which prevents membrane electrode assembly (MEA) degradation caused by being operated for many times. After a series of experiments in this study, the micro-fuel-cell system demonstrates the ability of offering a stable power to a cell phone or robot with reliability.

Multi-Segment Foam Flow Field in Ambient Pressure Polymer Exchange Membrane Fuel Cell

In order to produce low-cost flow field plates for polymer electrolyte membrane fuel cells, we used nickel foam in this study rather than conventional flow field. Nickel foam has high electron conductivity, thermal conductivity, and mechanical strength. Electrochemical impedance spectrum analysis is carried out to evidence the use on flow field plates of nickel foam. From the impedance fitting results, the nickel foam cases showed the lower contact resistance than the serpentine. However, such plates have poor performance at low temperatures and ambient pressure. In order to overcome this, a multi-segment foam flow field is designed in this study. This increased the performance of the polarization curve by 70% from 162 to 275.5 mw cm -2 than the original nickel foam design. Also, the mass transfer resistance was reduced, and the Warburg impedance value of the operation voltage decreased by 0.4 V. The numerical analysis results demonstrate that increased segment numbers can increase the performance of the multi-segment foam flow field.