Preparation And Performance Evaluation Of Gas Diffusion Electrode Based On Metal Foam For Direct Alcohol Fuel Cells

In the context of environmental protection and energy security,vigorously developing new energy technology is an important direction for energy revolution.Direct alcohol fuel cell（DAFC）is a kind of power generation device that directly converts chemical energy stored in alcohol fuel（such as methanol,ethanol,etc.）into electric energy in a green and efficient way.Compared with hydrogen fuel cell,it has the advantages of facile fuel storage and high energy density.The core of the fuel cell is the membrane electrode assembly（MEA）,and the gas diffusion layer（GDL）is the foundation of MEA,which plays the role of transporting reactants and products,conducting electricity,conducting heat and supporting the catalyst layer.At present,the GDL mainly uses carbon fiber materials（carbon paper,carbon cloth,etc.）,which have the advantages of high porosity and good gas-liquid transmission.However,they also have disadvantages such as poor mechanical strength,complex production process,and high price.In view of the problems of carbon fiber materials,we consider using three-dimensional porous metal foam（nickel foam）with excellent physical properties（such as high porosity,high conductivity,and high specific surface area,etc.）as the electrode support material for DAFC.The main research contents of this thesis are:1.The feasibility of using nickel foam electrode in the direct methanol fuel cell（DMFC）is explored.The experimental results show that in the acidic DMFC,the nickel foam electrode has a negative impact on the cell performance.Inside the DMFC,the H⁺ions generated by the methanol oxidation reaction pass through the Nafion membrane to achieve ion conduction.Thus,the H⁺conduction path from the catalyst layer to the Nafion membrane should be as short as possible.However,the H⁺conduction path in the nickel foam electrode is longer,the charge transfer resistance increases,and the anode polarization loss is serious,resulting in poor cell performance.Therefore,for DMFC anode electrode that requires a rich three-phase interface,the three-dimensional network structure of nickel foam actually limits the use of catalysts,which is the reason why nickel foam is not suitable for acidic DMFC.2.The effect of the thickness of nickel foam electrode on the performance of alkaline direct ethanol fuel cell（ADEFC）is investigated.The experimental results show that the cell performance of the nickel foam electrode with the thickness of 0.6 mm is better than that of 0.3mm and 1.0 mm.The nickel foam thickness affects both the electron conduction and mass transfer,and the optimal thickness is a trade-off between them.The thinner the nickel foam,the better the conductivity and the shorter the mass transfer distance.However,the corresponding three-dimensional space becomes narrow,which leads to partial agglomeration of the catalyst.At the same time,the agglomerated catalyst would block the open pores of the nickel foam and hinder mass transfer.In addition,experimental parameters such as catalyst loading,cell operating temperature,and ethanol concentration are optimized.3.Aiming at the problem that the smooth skeleton surface of the original nickel foam limits its specific surface area,a mixed acid etching method is used to pretreat the nickel foam,and nickel foam with porous surface and clean inert oxide layer is obtained.This is because the strong oxidizing and corrosive nature of the mixed acid that can quickly consume part of the metallic nickel,leaving many micropores on the surface.Furthermore,a mixed acid treated nickel foam electrode with low Pd loading(0.35 mg cm^-2)is prepared.The maximum power density of the single ADEFC could reach 30 mW cm^-2,which is as twice as the performance of the hydrochloric acid treated electrode.The performance improvement is attributed to the micropores created by the etching enhance the roughness of the electrode and increase the electrochemically active surface area of the catalyst.