| Proton exchange membrane fuel cells(PEMFCs)have received extensive attention in recent years due to their high energy conversion efficiency,high stability,and low pollution characteristics.Proton exchange membrane(PEM)is the core component of a fuel cell,and its proton conductivity and stability play a decisive role in the overall performance of the cell.Currently,a large number of studies have been conducted to improve the proton conductivity of membranes through structural design effectively.However,free radicals generated during fuel cell operation lead to membrane degradation and shorten fuel cell life.Therefore,the preparation of chemically stable and high-performance proton exchange membranes is crucial.Currently,available studies focused on preparation of chemically stable PEM by directly doping free radical scavengers,but this method will sacrifice the proton conductivity of the membrane,leading to the decline in fuel cell power density.Starting from the optimization of free radical scavengers and the surface modification of proton exchange membranes,this thesis explores the interrelationship between the performance,long-term stability and the free radical quenching layer by regulating the types of free radical scavengers and the construction methods of free radical quenching layers,and achieves the improvement of the overall performance of fuel cells.The specific research work is as follows:(1)In order to improve the specific surface area and dispersion uniformity of the free radical scavenger in the free radical quenching layer.An integrated PPy/MnOx doped structure was prepared by the oxidation-reduction reaction between KMnO4 and pyrrole(Py).A PPy/MnOx thin film was uniformly fixed on the surface of the proton exchange membrane due to the in-situ growth characteristics of polypyrrole(PPy),and a free radical quenching layer was constructed.During the soaking process,some Py monomers can be embedded into the surface of the membrane through electrostatic adsorption,and polymerize with Py in solution under the oxidation of KMnO4 to form a porous PPy layer.At the same time,KMnO4 will be reduced to MnOx with a small particle size and uniformly attached to the PPy layer,which will form a stable and efficient free radical quenching layer.PPy/MnOx free radical quenching layer can not only effectively remove free radicals,but also facilitate the transmission of protons due to its porous structure.At the same time,it improves the mechanical strength of the membrane and ensures the overall performance of the fuel cell.(2)In order to further improve the proton conductivity and long-term cycle effectiveness of the free radical quenching layer,a valence cyclable free radical quenching layer PANI/Kx[Fe(CN)6]was prepared by using the oxidation-reduction reaction of the-NH-group in the polyaniline(PANI)structure with K3[Fe(CN)6].Polyaniline forms a porous layer on the surface of the proton exchange membrane through in-situ growth,and reacts with K3[Fe(CN)6]to form oxidized polyaniline and K4[Fe(CN)6].The two are uniformly mixed through electrostatic adsorption to form a free radical quenching layer.The presence of[Fe(CN)6]4-can promote the transport of H+,effectively improving the proton conductivity of modified membranes and fuel cell performance.Ionic free radical scavengers can exhibit better free radical scavenging capabilities,allowing the modified membrane to operate stably for more than 300 h in OCV stability testing.At the same time,during the operation of fuel cells,the mutual conversion of[Fe(CN)6]4-and[Fe(CN)6]3-also ensures the long-term effectiveness of free radical scavengers.This research provides a new strategy for the preparation of highly stable proton membranes and integrated MEAs.This method can improve the chemical stability of proton membranes and MEAs,and ensure that the performance of fuel cells will not be affected.The low-cost and convenient operation method makes it a prerequisite for large-scale industrial application,with high application value. |
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