In order to mitigate the clogging of the CO2 bubbles in the middle and export region of the flow field , a new anode flow field pattern for ��DMFC with gradual change in width along the micro channel was demonstrated in the present work. We call this type of flow field as non-equipotent flow field in order to distinguish it from the conventional flow field patterns. Transparent ��DMFC single cells with and without this flow field pattern were fabricated and comparatively studied. Preliminary results showed that the ��DMFC performance was effectively promoted using the designing concept of non-equipotent flow field.2.?Experimental details2.1. Structure of the Transparent ��DMFC Single CellIn this work, transparent ��DMFCs were designed and fabricated.
The fuel cells ran on aqueous methanol solution which was driven by a syringe pump in the anode and absorbed oxygen from the ambient air (air-breathing mechanism) in the cathode. As shown in Figure.1, the ��DMFC consists of MEA, flow field plates and end plates. The MEA with an active area of 1.4 cm �� 1.4 cm was sandwiched between two flow field plates, which were sealed with PTFE gaskets on both sides. The MEA was supplied by Dalian Institute of Chemical Physics, the fabrication process was described in our previous work . The flow field plates were made of stainless steel sheet (SS316L, 400 ��m in thickness) using double-sides photochemical micro fabrication techniques. The end plates were made from 2mm thick polymethyl methacrylate (PMMA) sheets using a laser milling method.Figure 1.Infrastructure of ��DMFC.
2.2. Flow Field Design and FabricationTwo types of anode flow field patterns were designed in this study (see Figure 2), one is the equipotent serpentine flow field (ESFF), the other is the non-equipotent serpentine Brefeldin_A flow field (NESFF). Traditional dot matrix flow field pattern was adopted on the cathode side. The detailed geometry of each anode flow field is shown in Table 1. As can be seen from Figure 2 and Table 1, the ESFF and NESFF consisted of a single meandering flow channel, each of which has a total length of 70.0 mm. The channel width of the NESFF gradually changed along the channel length. In the present work, the effects of the ESFF and NESFF patterns on the CO2 bubbles behavior were compared on the basis of the same hydraulic diameter and total length of the channels, as well as the same open ration and rib width of the flow fields.
Herein, the open ratio is defined as the ratio of the flow channel area to the total MEA area (1.96 cm2), and the hydraulic diameter of the taper channel in NESFF is an equivalent value, which can be calculated from the geometric relations shown in Figure 3.Figure 2.ESFF (a) and NESFF (b) patterns.Figure 3.Geometric relations of NESFF channel.Table 1.Geometry of the flow fields.In Figure.