Effects Of Ammonia Impurities On The Hydrogen Flow In High And Low Temperature Polymer Electrolyte Fuel Cells

Fuel cells are a promising technology to use as a source of electricity and heat for buildings, and as an electrical power source for electric motors propelling vehicles. They consume hydrogen as fuel and oxygen to produce electricity, heat and water. Conventional fuels, such as natural gas, methanol, or even gasoline are reformed to produce the hydrogen required by the fuel cells. During the reforming process, impurities are inevitably obtained in the hydrogen flow. One of them is ammonia (NH3) that can result in serious damage to the fuel cell operation. In this paper, the effects produced by different concentrations of NH3 present in the hydrogen flow on the membrane electrode assembly (MEA) performance are studied, differentiating between irreversible and recoverable damages. Strictly experimental, the study includes both low and high temperature polymer electrolyte fuel cells (PEFC). The NH3 poisoning effect is analyzed and quantified by comparing the polarization curves. After the poisoning stage, the cells are subjected to a regeneration process (feeding the cell with neat H-2) with the aim of knowing the membrane's recovery capacity. The experimental results demonstrate that in low temperature (LT)-PEFCs, the cell recovers its performance almost completely with a new exposure to neat H-2, in spite of the damage previously caused by the presence of traces of NH3 in the anode feed stream. In contrast, in high temperature (HT)-PEFCs, the cell suffers irreversible damage, even with short time exposure to NH3. The paper concludes with discussing the possible chemical interactions by which NH3 affects the cell performance.