Effect Of Catalyst Ink Additive On Fuel Cell Membrane Electrode Prepared By Doctor Blade Method

In the context of world energy crisis and environmental protection,hydrogen energy has been widely concerned by researchers for its environmental protection,high calorific value and other advantages.Currently,hydrogen fuel cell is an important application form of hydrogen energy,which can directly convert the chemical energy in hydrogen energy into electric energy.This process is not restricted by Carnot cycle,and the energy utilization rate is high.Although proton exchange membrane fuel cells have achieved initial commercialization,they still need to further reduce their cost and improve their performance to increase their market competitiveness.The optimization of membrane electrode assembly as the core component of fuel cell is the key to improve the performance of fuel cell and reduce the cost.The cost can be reduced by improving the utilization rate of catalyst,reducing the use of platinum in membrane electrode,or developing high-performance non-precious metal catalyst.By optimizing the preparation process of membrane electrode and the formulation of catalyst paste,the utilization rate of catalyst can be improved,and the performance of membrane electrode can be improved without increasing the catalyst load.Therefore,this paper focuses on the preparation process of membrane electrode by scraping and coating method and the influence of catalyst paste formula on fuel cells,namely the optimization method.The specific contents are as follows:(1)The preparation process of film electrode by scraping and coating method in the laboratory and the formulation of catalyst paste were optimized.By comparison,it is found that the cathode catalyst is loaded on the proton exchange membrane and the anode catalyst is loaded on the gas diffusion layer,and then the combination of hot pressing process can achieve higher battery performance.The effect of additives on the performance of the membrane electrode was further investigated,and four kinds of additives which can improve the performance of the membrane electrode were screened out: polytetrafluoroethylene emulsion(PTFE),nmethylpyrrolidone(NMP),potassium perfluorobutyl sulfonate(FC-98)and n-heptanol.The peak power density of the optimized membrane electrode can reach 3.12 W cm-2,which is 23.3% higher than that of the membrane electrode prepared without additives.The analysis showed that the dominant additive improved the dispersion of catalyst slurry through electrostatic action,thus increasing the number of active three-phase sites in catalyst layer,and improving the surface structure and hydrophobic effect of catalyst layer to enhance the mass transfer effect of catalyst layer.(2)The optimization effect of superior additives in catalyst slurry on different commercial Pt/C and the rule of optimal addition amount were explored.It was found that the optimization effect of the dominant additive was not related to the type of carbon carrier,but was related to the carbon content in the catalyst.With the increase of carbon content in catalyst,the optimization effect and the optimal addition amount of PTFE increased gradually.The optimization effect of NMP increased gradually,and the optimal addition amount was almost unchanged.The optimization effect of FC-98 increased gradually,but the optimal addition amount decreased gradually.The optimization effect of n-heptanol was gradually increased,and the optimal dosage was almost unchanged.Through physical characterization,it was found that catalyst agglomeration in catalyst slurry was more serious when carbon content was higher.Particle sizes of 20 wt%Pt/C,40 wt% Pt/C and 60 wt% Pt/C in non-added slurry were 276 nm,203nm and 185 nm,respectively.The particle size decreased to 255 nm,176nm and 173 nm,respectively,which showed that the dominant additive had better dispersion effect under the condition of severe agglomeration.(3)Fe-N-C catalyst was synthesized by host-guest encapsulation method using ZIF-8 nanopolyhedron as template.The membrane electrode was prepared using the catalyst,and the preparation process and catalyst slurry formula were optimized.It is found that soaking pretreatment can protect the integrity of catalyst layer and proton exchange membrane,and achieve high membrane electrode performance.Three kinds of dominant additives in Fe-N-C catalyst were selected: PTFE,2-ethoxy-ethanol(ECS)and n-heptanol.The optimal peak power density of the membrane electrode reached 850 m W cm-2,which was 15% higher than that of the membrane electrode prepared without additives.Through physical characterization,it was found that the addition of dominant additives could enhance the dispersion effect of catalyst particles and achieve the effect of increasing the number of three phases.It can also enhance the hydrophobic effect of catalyst layer,improve the surface structure of catalyst layer and enhance the mass transfer effect.