Yunfeng Zhai

The Multiprocess Degradation of PEMFC Performance Due to Sulfur Dioxide Contamination and Its Recovery

The effects of trace concentrations of SO 2 contaminant present in the cathode feed stream on proton exchange membrane fuel cell (PEMFC) performance are studied. Contaminant concentrations of 1, 2, and 10 ppm were exposed to the cell applying a total dosage of 160 μmol of SO 2 at 80°C and a current density of 0.6 A cm ―2 . All experiments show significant cell performance degradation before the steady-state poisoning state is reached. The performance degradation shows an inflection in the cell voltage, which is attributed to at least two different poisoning processes. The overall poisoning process is shown to consist of an irreversible part and a reversible part. While the performance loss of the reversible part is dependent on the SO 2 concentration and is recoverable during a H 2 /air operation, that of the irreversible part is greatly recoverable by potential cycling in the H 2 /N 2 mode. Evidence is also presented that cathode exposure to SO 2 results in a performance impact at the anode. Furthermore, sulfur species that remain in the membrane electrode assembly accelerate the cell performance degradation during a neat H 2 /air operation and subsequent SO 2 contaminant exposure.

Modern Fuel Cell Testing Laboratory

Elements constituting a fuel cell laboratory are succinctly discussed using the experience developed at the Hawaii Sustainable Energy Research Facility. The information is expected to be useful to organizations with a desire to create or improve a fuel cell laboratory in view of the recent and anticipated fuel cell commercialization activities. Topics discussed cover a wide range with an emphasis on differentiating aspects from other types of laboratories including safety, fuel cell and test equipment, and methods used to characterize fuel cells. The use of hydrogen, oxygen and specifically introduced chemical species, and the presence of high voltages and electrical short risks constitute the most prominent hazards. Reactant purity, cleaning, test station control including data acquisition, and calibration are the most important considerations to ensure fuel cell characterization data quality. Cleanliness is also an important consideration for the fuel cell assembly and integration into the test station. The fuel cell assembly also needs to be verified for faults. Fuel cells need to be conditioned for optimum performance before a purposefully designed test plan is implemented. Many fuel cell diagnostic methods are available but novel techniques are still needed in many areas including through plane temperature distribution, stack diagnostics and mass transfer properties. The emphasis is given to commonly and sparingly used electrochemical techniques. In situ techniques include polarization, impedance spectroscopy, voltammetry and current distribution over the active area. Ex situ techniques include the rotating ring-disc electrode and the membrane conductivity cell. Other nonelectrochemical techniques are also useful to understand fuel cell behavior and include the analysis of reactant streams and condensed water, and spectroscopic measurements in combination with electrochemical cells (spectroelectrochemical cells).