||In this thesis, we propose a hydrogen outflow regulation strategy for PEM fuel cells. The advantages of the proposed strategy is three-folds: to improve stability of the voltage output, to protect the fuel cell against oxygen reduction reaction (ORR) at the anode which results in water buildup, and to optimize the usage of hydrogen.|
For a conventional "open outlet" fuel cell, the hydrogen excess ratio is usually high because excessively more hydrogen is required in order to prevent fuel starvation. Even with an active feedback inflow regulator, the previous experiments indicate that the excess ratio must be at least 2 in order for the fuel cell to maintain a steady operation. Thus, at least 50\% of the hydrogen is wasted. The waste of hydrogen can be prevented if the anode outlet is closed. This, however, will results in water buildup in the anode outlet. When too much water is stacked in the fuel cell, a phenomenon referred to as "flooding", the electrochemical reaction of hydrogen and oxygen will drop significantly, or even completely shut down.
In order to reduce the waste of hydrogen and prevent the buildup of water in the anode, we propose a "semi-closed outlet" mechanism by attaching a controlled solenoid valve to the anode outlet which opens and closes the outlet in a timely fashion. More specifically, the solenoid valve is controlled by a pulse-width modulated signal, which is generated by a feedback mechanism that takes into account the current voltage/power output and the water buildup rate. The mechanism is designed in such a way to maintain stable voltage/power output while optimizing the usage of hydrogen and purging the water out of the anode in a timely fashion. The results of experiments indicate that by this approach the utilization of hydrogen is significantly improved and the hydrogen excess ratio is reduced to 1.4, comparing to the suggested value of 11 if the cell is operated in the "open outlet" condition.