Proton exchange membrane fuel cells

Pulsing the flow of reactants in proton exchange membrane fuel cells (PEMFC) is a new frontier in the area of fuel cell research. Although power performance losses resulting from water accumulation also referred to as flooding, and power performance recovery resulting from water removal or purging, have been studied and monitored, the nexus between pulsing of reactants and power performance has yet to be established. This study introduces pulsing of reactants as a method of improving power performance. This study investigates how under continuous supply of reactants, pressure increase due to water accumulation, and power performance decay in PEMFCs. Furthermore, this study shows that power performance can be optimized through pulsing of reactants, and it investigates several variables affecting the power production under these conditions. Specifically, changes in frequency, duty cycle, and shifting of reactants as they affect performance are monitored and analyzed. Advanced data acquisition and control software allow multi-input monitoring of thermo-fluid and electrical data, while analog and digital controllers make it possible to implement optimization techniques for both discrete and continuous modes.

The incorporation of an ejector refrigeration cycle with a high temperature PEM fuel cell (HT-PEMFC) presents a novel approach to combined heat and power (CHP) applications. An ejector refrigeration system (ERS) can enhance the flexibility of a CHP system by providing an additional means of utilizing the fuel cell waste heat besides domestic hot water (DHW) heating. This study looks into the performance gains that can be attained by incorporating ejector refrigeration with HT-PEMFC micro-CHP (mCHP) systems (1 to 5kWe). The effectiveness of the ERS in utilizing fuel cell waste heat is studied as is the relulting enhancement to overall system efficiency. A test rig specially constructed to evaluate an ERS under simulated HT-PEMFC conditions is used to test the concept and verify modeling predictions. In addition, two separate analytical models were constructed to simulate the ERS test rig and a HT-PEMFC/ERS mCHP system. The ERS test rig was simulated using a Matlab based model, while two residential sized HT-PEMFC/ERS mCHP systems were simulated using a Simulink model. Using U.S. Energy Information Administration (EIA) air conditioning and DHW load profiles, as well as data collected from a large residential monitoring study in Florida, the Simulink model provides the results in system efficiency gain associated with supporting residential space cooling and water heating loads. It was found that incorporation of an ERS increased the efficiency of a HT-PEMFC mCHP system by 8 t0 10 percentage points over just using the fuel cell waste heat for DHW. In addition, results from the Matlab ERS test rig model were shown to match well with experimental results.