Design And Preparation Of Micro Fuel Cell Cathode Flow Field Based On Glassy Carbon

Depleting fossil fuels and ever-worsening environment continue to urge the development of fuel cell technology.The rapid development of micro-electromechanical system technology also provides new opportunities for the application of the micro fuel cell.Although bipolar plate is one of the key components of the fuel cell,many questions remain regarding the materials,flow field structure,Manufacturing methods,etc.,which limits the development and application of this technology.Glassy carbon has strong penetration resistance,low weight,high thermal conductivity,good mechanical properties,excellent electrical conductivity and high corrosion resistance.It is a perfect candidate material for making micro fuel cell bipolar plates.Picosecond laser processing is suitable for the micro-fabrication of all materials,which can be used for the micro-fabrication of bipolar plate flow field structure.Therefore,this dissertation presents using glassy carbon as the polar plate material and picosecond laser as the micro-channel processing method.Mixed methods combining flow field simulation and processing experiments were used to optimize the flow field structure and the process of picosecond laser etching of glassy carbon micro channels.The main discussions were provided as follows.1.The fundamental aspects on mechanisms were evaluated in a systematic study of ultrafast picosecond laser interaction with non-metallic materials.we first analyzed the characteristics of laser beam such as directionality,monochromaticity,coherence and brightness,and addressed the question of how these characteristics are utilized to realize the interaction process with the material.As well,the typical physical process of the interaction between the laser and the material was analyzed.Finally,we explored the interaction between the picosecond laser and non-metallic materials.The effect of photo-ionization and avalanche ionization on the absorption of laser energy by non-metallic materials have also been studied.2.The working process of the cathode of ?PEMFC was simulated and analyzed by using multiphysics coupling software.The model includes three parts: cathode flow field channel,cathode gas diffusion layer and cathode catalytic layer.Among them,the cathode catalyst layer is assumed to be the boundary condition at the bottom of the gas diffusion layer,and its thickness is set to be infinitely thin.The governing equations of the mass transfer process mainly involve the mass conservation equation,momentum conservation equation and electrochemical reaction equation.The model was processed under different flow field structures parameters(flow channel width,flow channel height and flow channel spacing).Performance parameters such as average current density,output voltage and power density,oxygen concentration distribution,internal pressure and speed of the flow channel of the ?PEMFC were obtained.Based on these data analysis,the optimized flow field structure parameters are obtained.The results can provide specific parameters for the following experimental research.3.According to the optimized cathode flow field structure parameters,an experimental study of picosecond laser etching glass carbon micro-channels was carried out.The effects of laser power,scanning speed,number of elements and defocusing amount on the processing dimensions(depth,width and taper)and surface morphology of glassy carbon microchannels were mainly discussed.The results show that: the combined effect of laser power and element number on the processing size of the micro-channel is the most significant,and the effects of scanning speed and defocus amount are relatively small.The quality of the surface topography of the micro channel can be effectively improved by increasing the laser power,element times,positive defocus amount or reducing the scanning speed within a certain range.As well,the aspect ratio of the microchannel and the verticality of the side wall can be improved too.However,too much laser power or too many element times will lead to a sharp deterioration of the flow channel quality.The ultimate goal of this work is to provide potential new ideas and avenues for the bipolar plate of micro fuel cell.The mechanism of the interaction between picosecond laser and glassy carbon was also deeply explored in this paper.It is of great significance from both theoretical perspective and applications...