Hartnig, C. ; Manke, I. ; Schloesser, J. ; Krüger, P. ; Kuhn, R. ; Riesemeier, H. ; Wippermann, K. ; Banhart, J.: High resolution snychrotron X-ray investigation of carbon dioxide evolution in operating direct methanol fuel cells. Electrochemistry Communications 11 (2009), p. 1559-1562
10.1016/j.elecom.2009.05.047
Abstract:
The carbon dioxide evolution and bubble formation in an operating fuel has been studied by means of synchrotron X-ray radiography. Two different observation directions have been chosen: a through plane insight has been employed to track the formation of bubbles starting at the corner of the lands of the flow field; a depth profile of the carbon dioxide evolution has been derived from cross sectional studies describing an affected area of up to 100 μm. The dynamics of the bubble formation and detachment of the bubbles from the position of formation is strongly correlated with the current density. Below a threshold value, a minimum gas pressure has to be achieved before the bubble formation starts in the flow field channel; beyond the threshold value a continuous bubbling and removal of the bubbles is observed. Cracks and breaks in the catalyst layer which result from the preparation process are visible under operating conditions and a possible swelling of the catalyst layer is not sufficient to close the open spots.