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Initial conditioning of PEM fuel cell by temperature and potential cycling

PEM fuel cells need initial conditioning, activation or breaking-in the first time they are operated after being assembled. The exact mechanism of this initial conditioning has not been completely clarified, but it can be reasonably assumed that during the conditioning process the polymer membrane, as well as the polymer in the catalyst layer, get humidified, and the number of active catalyst sites increases. As a result the fuel cell performance gradually improves during the conditioning process. Several conditioning protocols have been applied, patented and/or proposed1, which include both on-line (such as current control, potential control, short-circuiting, temperature control, hydrogen-pumping and air-braking) and off-line (meaning before the cell is assembled) procedures. In this paper a procedure of both temperature and current cycling is proposed, described and characterized. The reasoning behind this proposed procedure is that cycling to high currents results in more water being produced inside the fuel cell, and temperature water allows the water to condense inside a fuel cell. It is well known that a membrane equilibrated with liquid water can take in more water than the same membrane equilibrated with water vapor in saturated gas. The temperature and current cycling procedure will be described, the results will be presented and compared to some conventional conditioning procedure.

PEM fuel cells; conditioning protocols; temperature cycing; potential cycling

PEM fuel cells need initial conditioning, activation or breaking-in the first time they are operated after being assembled. The exact mechanism of this initial conditioning has not been completely clarified, but it can be reasonably assumed that during the conditioning process the polymer membrane, as well as the polymer in the catalyst layer, get humidified, and the number of active catalyst sites increases. As a result the fuel cell performance gradually improves during the conditioning process. Several conditioning protocols have been applied, patented and/or proposed1, which include both on-line (such as current control, potential control, short-circuiting, temperature control, hydrogen-pumping and air-braking) and off-line (meaning before the cell is assembled) procedures. In this paper a procedure of both temperature and current cycling is proposed, described and characterized. The reasoning behind this proposed procedure is that cycling to high currents results in more water being produced inside the fuel cell, and temperature water allows the water to condense inside a fuel cell. It is well known that a membrane equilibrated with liquid water can take in more water than the