| Proton exchange membrane fuel cell(PEMFC)has many unique advantages such as high power density,high energy conversion efficiency,no pollution and low operating temperature,thus gradually becoming the most promising energy conversion device in the future.With the rapid development of fuel cell catalysts and membrane materials,the output current density of proton exchange membrane fuel cells has been increasing,and the demand for commercial applications has led to a gradual increase in the activation reaction area of fuel cells,these factors have put forward higher demands on the rational design of flow field structures.The reasonable flow field design can largely improve the fuel cell performance and hydrothermal management capability,and improve the homogeneous heat-mass-electric transport performance of fuel cell,so the flow field optimization is very significant to improve the cell performance.The conventional groove-ridge structure flow field causes uneven gas and temperature distribution inside the cell,also has poor hydrothermal management capability,and severely limits the fuel cell power density increase.At present,the experimental studies on flow field design and optimization are mainly in the fuel cell with small reaction area,and there is a lack of research on the application of the designed flow field in the flow field with large reaction area such as vehicle fuel cell.In this paper,we design a novel dot block flow field with a reaction area of 108 cm~2,and the cell is tested and analyzed by combining segment characterization methods such as performance test and electrochemical impedance test.When the novel dot block flow field is used as the fuel cell cathode flow field,the effect of different structural parameters on the cell performance,electrochemical performance and pressure drop of is investigated;The performance comparison,electrochemical performance comparison and pressure drop comparison are carried out with the traditional flow field.At the same time,the effects of different working parameters(relative humidity,operating temperature,cathode stoichiometry ratio,oxygen)on the performance of the novel dot block flow field are investigated.The research shows that in terms of the edge length of dot block,the flow field with larger dot block side length at low relative humidity has better performance;however,the flow field with smaller dot block side length has better performance at high relative humidity.In terms of dot block interval,flow field with smaller interval has better performance at low relative humidity;flow field with larger dot block interval has better performance at high relative humidity.The reasonable side length and interval of the dot block need to be well balanced between ensuring the fluid domain for air delivery and providing sufficient contact area.In terms of the diversion angle of the dot block,The performance of the flow field with a smaller diversion angle is generally better at low relative humidity;The flow field with larger diversion angle has better performance at high relative humidity.The dot block diversion angle should be optimized to balance the discharge capacity of liquid water in the flow channel and the capacity of oxygen delivery to gas diffusion layer.In the high current density region,the novel dot block flow field has higher performance than the parallel flow field and better resistance to flooding,but the pressure drop is larger.The novel dot block flow field has the best performance at 60 percent relative humidity,but the performance is poor at high relative humidity.The performance is better at an operating temperature of 60℃at low relative humidity;however,a higher operating temperature can enhance the cell performance at high humidity.Increasing the cathode stoichiometry ratio also has a obvious improvement on cell performance.The polarization curve of the novel dot matrix flow field under pure oxygen condition is basically a sloping straight line,mainly dominated by the ohmic loss. |
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