Study On Construction And Performance Of The Catalytic Layer Of Membrane Electrode Assembly In PEM Electrolysis Cell

As a clean and efficient energy carrier hydrogen energy occupies an important position in the renewable energy system.Under the condition of wind and light fluctuating renewable power input proton exchange membrane electrolytic hydrogen production technology has good potential for application with its high working current density and fast response characteristics.and has become a research hotspot,The membrane electrode assembly,as the most core component in the proton exchange membrane electrolysis cell,directly affects the efficiency of the electrolysis cell.The catalytic layer,as the core site of the catalytic reaction of the membrane electrode assembly,has the problems of high noble metal catalyst loading,regional catalytic activity differences,and uneven thermoelectric distribution,which directly affect the development and popularization of the proton exchange membrane electrolytic water technology.The research focuses on the construction of the catalytic laver as follows:(1)Design the proton exchange membrane electrolysis cell fixture and build the membrane electrode assembly performance test bench,and evaluate the performance of the membrane electrode assembly under different test and thermal pressure conditions by using the electrochemical test methods of polarization curve and electrochemical impedance.Further,the proton exchange membrane and diffusion layer were investigated before and after the hot pressing process by DSC.Fourier infrared spectroscopy,and SEM electron microscopy physical characterization methods.The results show that the optimal test conditions for the membrane electrode assembly under the co-heating of feed water and cell:cell temperature of 80℃,feed water flow rate of 20 mL/min;the optimal hot pressing conditions for the membrane electrode assembly:hot pressing temperature of 135℃,hot pressing pressure of 5 Mpa and holding time of 300 s.(2)B ased on the optimal testing and hot pressing conditions of the membrane electrode assembly,the Nafion content and the catalyst Pt and Ir loadings in the cathode and anode catalytic layers were further optimized.It was found that the Nafion content and catalyst loading had an effect on the microscopic morphology of the catalytic layer and the performance of the membrane electrode,and a Nafion content of more than 30 wt%made the catalyst particles more stable.The Nafion content of more than 30 wt%will agglomerate the catalyst particles and reduce the active area of the catalyst,while the Nafion content of less than 10 wt%will make the catalyst slurry dispersion poor,and the catalyst loading affects the thickness and mass transfer resistance of the catalytic layer.The membrane electrode assembly with Ir loading of 2.0 mg/cm2 and 10 wt%Nafion content in the anode and Pt loading of 0.4 mg/cm2 and 20 wt%Nafion content in the cathode had the best performance.In addition,the parameters of the membrane electrode assembly ultrasonic spraying preparation process were optimized,and the results showed that the ultrasonic nozzle height,nozzle movement speed,vacuum heating plate temperature,and slurry flow rate were the four key parameters affecting the catalytic layer loading effect.(3)The membrane electrode assembly anode catalytic layer was further designed with regional non-uniform precision to construct membrane electrode assembly with different loadings in the transverse rib and runner regions of the catalytic layer as well as membrane electrode assembly in the longitudinal gradient catalytic layer.It is shown that the performance is better than that of the uniformly loaded membrane electrode assembly at the loading ratio of 7:3 in the flow channel and under-rib area.The stability of the gradient catalyst membrane electrode assembly was maintained at a decay rate of 60 μV/h for 100 h.The differences in thermoelectric transport,uneven gas-water distribution,and catalyst utilization in the longitudinal direction of the catalytic layer were also confirmed for the transverse rib and runner areas of the anode catalyst layer.It was found that the utilization rate of catalysts for membrane electrode assembly was as follows:the area under the transverse flow channel was higher than the subcostal region,and the longitudinal near-membrane side was higher than the near diffusion layer.