Applications Of Extreme-wettability Micro-structure In ?DMFC Flow Field

Micro direct methanol fuel cell??DMFC?is one of proton exchange membrane fuel cell which use methanol/water solution as the fuel directly.It is a promising power source candidate for miniaturized devices and military equipment due to its unique advantages such as high energy density,small size,abundant sources,high security,convenience in fuel replacement.However,the block of mass transportation is a key problem to restrict the?DMFC performance.To relief the problem of mass transfer including capillary blocking caused by CO₂ bubbles in anode flow field and water flooding in cathode flow field,a novel flow field containing auxiliary superhydrophilic/superhydrophobic channels and fuel channels is designed on Ti plates.And the influence of auxiliary channels on ?DMFC is studied by experiment.Based on the traditional serpentine and spiral anode flow field?AFFs?,a novel AFF structure with nested layout of fuel channels and superhydrophobic degassing channels which can remove most of CO₂ from AFF before it is released to the fuel channels was presented.A water management system consist of cathode flow field with superhydrophilic capillary network structure and carbon papers are designed for air-breathing ?DMFCs to eliminate excessive water in the cathode and avoid water flooding.The structure size of channels are determined according to the affect of channels geometric parameters on ?DMFCs performance.Ti surface will form a large number of micro-nano hybrid roughness structures after it is anodized,WCA of Ti surface can be facilely changed from hydrophilic?53°?to superhydrophilic?0°?.Then,the WCA of Ti surface changed to superhydrophobic?160°?by using the FAS modification techniques.The novel ?DMFC flow field plates are fabricated on Ti substrates by using micro photochemical etching combined with anodization and fluorination treatments.Effect of superhydrophobic degassing channels on removal process of CO₂ bubbles in anode and ?DMFC performance are studied.?DMFCs with superhydrophobic degassing channels AFFs and referenced AFFs are assembled.Performance of the ?DMFCs with different AFFs is is comparatively studied.Results show that output power density of?DMFC with superhydrophobic degassing channels in AFF is ultimately increased by 91.84%compared to those ?DMFCs with reference flow fields.Also,the results of pressure drop measurement and motion properties of anode bubbles show that most of CO₂ bubbles can be excluded from anode flow fields by superhydrophobic degassing channels without thoroughthe fuel channel,which reduced the mass-transportation resistance of the methanol and thereby lead to a solid enhancement of the ?DMFCs performance.Effect of superhydrophilic capillary network structures on eliminating ?DMFC water flood in cathode is verified by numerical simulation and prototyping experiment.The distribution condition of liquid drops in cathode flow field?CFFs?with superhydrophilic capillary network structure are simulated by COMSOL,results show that superhydrophilic capillary channels can assimilate and eliminate water from cathode.The CFFs with superhydrophilic channels are designed and fabricated and they are assembled in single?DMFCs.The degradation of ?DMFC power density caused by water flood in cathode is measured when the ?DMFCs discharged at a constant voltage of 0.15 V for 4h.Results indicate that the output power descend range of ?DMFCs applying novel CFFs after discharged for 4h is only about one third of ?DMFC with conventional CFF compared to initial discharge condition.In situ observation finds that water drops in the cathode were dragged into carbon papers by gradient capillary force and removed from cathode after water flowed into superhydrophilic channels,indicating that superhydrophilic channels and carbon papers can improve the water management ability of ?DMFCs.