Study On Preparation Of Anode And Cathode Catalysts And Membrane Electrodes In Proton Exchange Membrane Water Electrolysis For H₂ Production

Proton exchange membrane（PEM）water electrolysis for hydrogen production is a green and sustainable technology.Vigorously promoting its development can effectively solve the intermittent problem of renewable energy such as wind and solar energy generation,convert low peak power into high-purity hydrogen for storage,and alleviate the global energy crisis and improve the greenhouse effect.However,PEM water electrolyzers face two important challenges,which are low cell efficiency and high stack cost.The slow kinetics of anode oxygen evolution reaction（OER）under acidic conditions is a huge obstacle,which requires higher overpotential to promote the reaction.The use of noble metal catalysts can reduce the electrode overpotential,but it is limited by the scarcity and high cost of Ir.At the same time,the high loading of Pt in catalysts for cathode hydrogen evolution reaction（HER）also limits their large-scale industrial applications.In addition,as the core component of PEM water electrolyzers,membrane electrode assembly are the site where electrochemical reactions occur,and their structural composition significantly affects the electrolyzer performance.Therefore,the thesis focuses on improving the economy and practicality of PEM water electrolysis technology for hydrogen production,and studies and optimizes the performance of cathode and anode catalysts and membrane electrodes.Firstly,aiming at the high overpotential of anode acidic oxygen evolution reaction and high loading of noble metal Ir in catalysts,amorphous Ir-Mn binary metal oxide（Ir Mn O_x）catalysts were synthesized by low-temperature calcination method,and the OER activity and stability of the catalysts with different Mn contents were studied.The experiment results indicate that amorphous Ir Mn O_x catalysts have a rich Ir surface and abundant hydroxyl oxygen defects.The high Ir^III content on the catalyst surface can promote OER to occur through lattice oxidation mechanism,thus enhancing the inherent activity of the catalyst.The Mn content affects the crystallinity and catalytic performance of the catalyst.As Mn increases from 0 to 60 at%,the activity and stability of the catalyst for OER first increase and then decrease.Among different catalysts,Ir_0.6Mn_0.4O_x catalyst has the lowest overpotential at 10 m A/cm²,which is only 212 m V,significantly lower than 370 m V of commercial Ir O₂.After the constant current stability test,the potential of the electrode with Ir_0.6Mn_0.4O_x catalyst does not significantly increase.When the Mn content reaches 60 at%,a small amount of crystallization exhibits in the catalyst.Compared with Ir O_x catalyst,the Ir content in amorphous Ir Mn O_x catalyst can be reduced to 66.98 wt%on the premise of not reducing the OER performance.In order to further reduce the loading of Ir and the cost of hydrogen production,Ir-based catalysts supported on Mn-based oxides was prepared by the two-step synthesis.The active component Ir O_x was highly dispersed on carriers with large specific surface area and excellent conductivity and fully utilized.By studing the effects of different Mn-based oxides and different calcination temperatures on the OER activity and stability of the catalyst,the appropriate catalyst carrier and the optimal preparation temperature were determined.The experiment results show that the amorphous-crystalline interface between Ir O_x and the carrier provides more active sites for the reaction,and the synergistic effect of Mn and Ir can effectively improve the inherent activity and stability of the catalyst.Among all supported catalysts,Ir O_x/β-Mn O₂ prepared at 350℃exhibits the lowest overpotential of 228 m V and the best stability.The overpotential of the electrode with Ir O_x/β-Mn O₂ only increases by 0.7 m V after the accelerated voltage test,and the Ir content of the catalyst is only about 55 wt%.Aiming at the problem of high Pt content in catalysts for cathode acidic hydrogen evolution reaction,dealloyed Pt-Ni bimetallic supported catalysts(Pt_xNi_1-x/C)were prepared by ethylene glycol reduction method.Its microstructure,crystal structure,and catalytic performance for HER were studied by various characterization methods and electrochemical analysis ways.The results indicate that the metal nanoparticles prepared is slightly smaller than that of commercial Pt/C catalyst,and they are uniformly dispersed under the anchoring effect of oxygen-containing groups on carbon black surface.The addition of Ni causes the compression of Pt lattice and formation of alloys between Pt and Ni,which can effectively enhance the intrinsic activity of Pt atoms.The increase of initial Ni feed is conducive to the formation of more Pt-rich atomic layers and the exposure of electrochemical active sites on the catalyst surface.Among all catalysts,Pt_0.25Ni_0.75/C has the best catalytic activity and stability,of which the overpotential at-10 m A/cm² is only 46.0m V,and the potential decay rate after the constant current test is only 2.7%.Both are much lower than commercial and self-made Pt/C catalysts.Finally,aiming at the high manufacturing cost and low efficiency issues of PEM electrolyzers,porous transport layer（PTL）and catalyst coating membrane（CCM）that make up the core membrane electrode were optimized.It is found that using Pt-coated Ti fiber felt on the anode side can significantly reduce the cell voltage and ohmic resistance compared with uncoated one.,while using Ti felt on the cathode side has more advantages than carbon paper.In addition,thinner PTL has better effects in improving charge and material transfer.By adjusting the loading of anode and cathode catalysts and the content of Nafion ionomers in CCM,the cell performance can be effectively improved.Higher loading of anode Ir_0.6Mn_0.4O_x catalyst can provide adequate active sites for the electrode reaction,while 0.15 mg _Pt/cm² loading of cathode Pt_0.25Ni_0.75/C catalyst reaches the lowest cell voltage.The Nafion ionomer with 11.1 wt%content can provide the best proton and gas transport channels.After optimization,the loading of noble metals in the membrane electrode significantly reduces,with Ir loading of 0.7 mg/cm² and Pt loading of 0.1mg/cm².The cell voltage is reduced to 1.840 V at 2 A/cm²,and the stability performance of the membrane electrode has also been effectively improved.Moreover,the energy consumption of hydrogen production is only 4.48 k Wh/m_H2³ at 2 A/cm²,and the electrolysis efficiency is as high as 79%,which is conducive to reducing both investment and operating costs.