Investigation On The Effect Of Gas Transport In Proton Exchange Membrane Fuel Cell And Alkaline Water Electrolysis Cell

The use and development of hydrogen energy is an important research part in the field of new energy.Proton exchange membrane fuel cells?PEMFC?and alkaline water electrolysis cells?AWE?are both carriers for hydrogen energy utilization or conversion.The transmission processes of reactive gas and generated gas respectively in PEMFC and AWE directly determines their efficiency.For the development of membrane electrodes with low Pt loading in PEMFC,the oxygen transport in the cathode is critical.Solving the coordination relationship between the hydrophobic coating and the void structure in gas diffusion layers?GDL?and the local oxygen transport problem in the catalytic layer?CL?is the key point of the research.In addition,the evolution of hydrogen and oxygen gas on the surface of the electrode to form local bubbles is also a key factor in the overpotential loss in AWE.In this paper,the oxygen transport effects in GDL and CL in PEMFC and the bubble effect in AWE are studied.The main conclusions are as follows:1.The effect of different PTFE loading on the oxygen transport in GDL shows that in the dry evaluation zone,the Fick's oxygen diffusion capacity of GDL decreased with the increase of PTFE loads,and the test temperature increased.The cathode use10 wt.%PTFE hydrophobic GDL has the best cell performance,the maximum power of 1.003 W/cm²._MEA,corresponding to 1686.6 mA/cm²@0.595V.Under high current densities,GDL with too high PTFE loading is easier to plug water,especially under relatively low temperature and high pressure operating conditions.This may be related to the uneven coating of PTFE inside the GDL.2.The results of heat treatment of low Pt loading CL show that the color of the perfluorosulfonic acid film turned yellow to deep in the heat treatment range below290°C,and the EW value increased slightly,indicating that the sulfonate detached,be not obvious.Through SEM observation,heat treatment in the range of 100-170°C has little effect on the structure of the CL.Heat treatment at 100°C,135°C,and 170°C has little effect on the reduction of oxygen transfer resistance of the low Pt?0.1 mg/cm²?CL,but for ultra-low Pt CL?0.02 mg/cm²?,the reduction is significant.The oxygen mass transfer resistance of 0.02 mg/cm² CL heat-treated at 170°C can approach the oxygen mass transfer resistance of CL of 0.1 mg/cm².The results show that heat treatment can reduce the oxygen mass transfer resistance of the whole CL by reducing the local oxygen mass transfer resistance.3.The study on the maximum mass specific power density?MMSP?of the low Pt CL shows that the lower the Pt loading in CL,the higher local oxygen mass transfer resistance increases,but the higher the maximum mass specific power density of Pt catalyst.Moreover,these changes have an inflection point at a Pt load of 0.1 mg/cm²,and the change is intensified when the Pt loading is less than 0.1 mg/cm².This indicates that the catalyst utilization in the low Pt loading CL is high,and its performance is mainly determined by the activation polarization and the local oxygen mass transfer polarization,while the catalyst utilization in the high Pt loading CL is low,and its performance is determined by the total oxygen transmission polarization.4.The study on the properties of Pt surface depolymerization in CL shows that for20 wt.%Pt/C catalyst,the Nafion content with the best electrochemical performance in the catalyst ink range from 30 wt.%to 40 wt.%.At 40°C test temperature,the hydrophilicity and hydrophobicity of nano-nafion films in CL may change at the interface,thereby affecting ORR activity and oxygen transfer.5.The cathode and anode reaction overpotential losses caused by the AWE cell bubble effect can be effectively distinguished by introducing an Hg/HgO reference electrode.At low current densities,the anode OER has a bottleneck effect on performance.A quantitative functional relationship between voltage and current density can be established by a model of bubble dynamics.This functional relationship can effectively predict and guide the energy consumption of AWE hydrogen production when AWE cell operated less than or equal to 0.5A/cm².