Preparation And Structural Optimization Of Membrane Electrode Assemblies For High-performance Alkaline Membrane Fuel Cells

Hydrogen energy has received extensive attention due to its wide availability,high energy density,and non-polluting combustion products,and is expected to be a key component of the future energy structure for humanity.Fuel cells,as energy conversion devices that directly convert the chemical energy stored in the fuel into electrical energy,have advantages such as high energy conversion efficiency,non-polluting product emissions,and freedom from the limitations of the Carnot cycle,making them an ideal way to utilize hydrogen energy.Currently,proton exchange membrane fuel cell technology has made significant progress,but its high reliance on precious metals makes it difficult to reduce costs significantly.In recent years,alkaline membrane fuel cells have received increasing attention due to their suitability for using non-precious metal catalysts.However,the performance of alkaline membrane fuel cells still needs to be further improved.The membrane electrode assembly（MEA）is the core component of the fuel cell,where the electrochemical reactions take place,and the performance of the MEA directly determines the performance of the fuel cell.Therefore,exploring the working mechanism of alkaline membrane fuel cell MEAs and optimizing the structure and performance of the MEA is the necessary path for the development of alkaline membrane fuel cell technology.This thesis focuses on the preparation and structural optimization of alkaline membrane fuel cell MEAs.It investigates the formation mechanism of the three-phase reaction interface structure at the ionomer-catalyst interface,adjusts and improves the catalyst ink formulation,and optimizes the internal structure of the catalyst layer to enhance the performance of the fuel cell.At the same time,the preparation methods of the MEA components are improved and optimized,with targeted catalyst layer designs for different types of catalysts,enabling them to operate with high performance in acidic or alkaline environments,providing experimental exploration and theoretical basis for improving catalyst utilization and reducing device manufacturing costs.The research content of this thesis is mainly divided into the following four aspects:（1）Optimization of the membrane electrode structure and assembly process to obtain fuel cell MEAs with high output power density.By adjusting the assembly pressure of the fuel cell,optimizing the catalyst loading and distribution in the catalyst layer of the MEA components,reducing the contact resistance of the battery devices and the internal resistance of ion conduction,the performance of the MEA is improved,and the repeatability of the MEA performance is ensured.Based on this,optimization of the MEA for non-precious metal catalysts is carried out,investigating the effects of catalyst layer thickness,assembly pressure,the proportion of dry ionomer weight in the catalyst ink,and the hydrophobicity of the catalyst layer on the performance of the MEA,and ultimately achieving the preparation of high-performance non-precious metal catalyst MEAs.The peak power density of alkaline membrane fuel cells based on Ni Cu Cr/C anodes reaches 577 m W cm^-2,and that of cells with Fe Co-NCH and Fe Co-MHs cathodes approaches 600 m W cm^-2,while the peak power density of cells with Ag Fe/CNC cathodes reaches 1.24 W cm^-2.Through the above optimizations,non-precious metal catalysts can achieve excellent performance in fuel cells,and also lay the foundation for subsequent MEA optimization exploration.（2）Study of the interaction characteristics between catalysts and ionomers in alkaline exchange membrane fuel cells and comparison with proton exchange membrane fuel cells.By adjusting the dry weight ratio of ionomer to carbon content in the catalyst,the differences in the formation process of the ionomer-catalyst interface in alkaline exchange membrane fuel cells and proton exchange membrane fuel cells are explored.It is found that the performance of alkaline membrane fuel cells is not significantly affected by the ionomer content,but proton exchange membrane fuel cells heavily rely on the ionomer content,showing a trend of first increasing and then decreasing in performance with the ionomer content.Impedance analysis and molecular dynamics simulations indicate that the interaction between the ionomer and the catalyst in alkaline membrane fuel cells is weaker and tends to be distributed on the surface of the carbon support compared to proton exchange membrane fuel cells.This indicates that developing new ionomers that can enhance the interaction with catalysts is beneficial for producing more electrochemically active three-phase points,thus further improving the performance of alkaline membrane fuel cells.（3）The pretreatment method for MEA preparation was improved,with the proposal of using an organic solvent aqueous solution for solvent annealing of the MEA to enhance the distribution of the ionomer and thereby improve the performance of the MEA.After treatment,the contact angle difference for liquid water between the internal components of the MEA was significantly reduced,the MEA components were fully hydrated,redundant ionomer films were removed,and ion transport and gas mass transfer effects were enhanced,reducing the contact impedance of the MEA components.The performance of the MEA after solvent annealing treatment exceeded that of the untreated MEA,achieving a peak power density of over 3.0 W cm^-2,and a current density of 3.1A cm^-2 at 0.65 V,with an improvement of over 40%.Additionally,based on the solvent annealing method,the preparation method for gas diffusion electrodes was improved.By applying a layer of ionomer coating on the surface of the catalyst layer and then using solvent annealing treatment,a tight connection with the ion exchange membrane could be formed,effectively reducing the contact impedance between the catalyst layer and the ion exchange membrane,and significantly reducing the performance loss of the fuel cell due to ohmic impedance.（4）High-performance anion exchange membrane fuel cells were constructed based on Ru-based catalysts.The activation phenomenon of the Ru anode during battery polarization curve testing was discovered,and analysis showed that partial oxidation of Ru was the cause of its activation.By optimizing and activating the alkaline membrane fuel cell with a Ru anode,its peak power density could reach 1.63 W cm^-2,and the current density at 0.65 V was 1.32 A cm^-2,achieving the same level as alkaline membrane fuel cells prepared with Pt Ru anodes.Furthermore,by introducing high-oxygen-affinity metals to promote the activation of the Ru anode,a highly active hydrogen oxidation reaction catalyst composed of Ru₇Cr₃ nanoclusters with surface Cr modification was prepared via an impregnation method.When the Ru₇Cr₃NCs/C catalyst was applied to the anode of an alkaline fuel cell,with an anode metal loading of 50μg _{Ru Cr} cm^-2,the cell’s peak power density could reach 2.10W cm^-2,and the current density at 0.65 V could reach 2.02 A cm^-2.This offers a potential solution for reducing the cost of catalysts.