| Proton exchange membrane fuel cell(Proton exchange membrane fuel cell,PEMFC)has become a new energy solution because of its high efficiency,simple structure and environmental friendliness.However,the main obstacles to its commercialization include cell performance,stability and cost.The MEAs is the core component of the PEMFC,while the catalytic layer(CL)is the core of the MEAs.Therefore,the catalytic layer directly determines the performance,stability and cost of the fuel cell.Current researchs generally focus on two aspects:1)development of highly active,low Pt or non-Pt nanocatalysts;2)construction of a new catalytic layer structure.At present,the research of catalyst has entered the deep-water-area,the improvement of catalyst activity is more difficult,and the enhancement of cell performance has been slowed down.This is mainly due to the blockage of electron,proton and mass transfer during the application of granular catalytic layer and voltage loss caused by the activation overpotential,ohmic overpotential and mass transfer overpotential in electrodes.The proton transfer in the granular catalytic layer mainly depends on the ionic polymer Nafion.However,the Nafion is an insulating material,the higher content will not only increase the electron transfer resistance,but also cover the catalyst particles,which will affect the mass transport.Electron,proton and mass transfer are difficult to coordinate for conventional granular catalytic layers.The above problems can be improved by carefully designing the electrode structure using 3D nanostructured materials such as ordered catalytic layer in MEA.Among them,ultra-thin nanoporous alloy thin film have been successfully used as electrode materials and obtained excellent cell performance.The morphological advantages of the open surface and interconnected pore structure of ultrathin nanoporous metal electrodes are manifold.Therefore,it is more important to design and improve the structure of MEA,especially the structure of catalytic layer.Thus,the specific contents of this paper are as follows:(1)The design of catalytic layers with high proton conductivity is an important topic in PEMFC.This paper first focuses on the effect of proton transport resistance of ultrathin platinum-modified nanoporous gold(NPG-Pt)catalytic layer on cell performance.In this work,A ultrathin nafion-free catalytic layer based on platinum modified nanoporous gold with a thickness of 100 nm was constructed.The proton transport resistance has great advantages over the traditional particle catalytic layer.When acting as anode and cathode alone,these integrated carbon-free electrodes can deliver maximum power density of 1.11 and 0.83 W/cm~2 when serving individually as the anode and cathode,at a Pt loading of 5.6 and 42.0?g/cm~2,respectively.Further electrochemical impedance spectroscopy and finite element analysis show that,improved proton conduction plays a key role in activation polarization,ohmic polarization,and mass transfer polarization.(2)Related studies have shown that micron pores with low tortuosity can effectively alleviate water management problems in catalytic layers.In order to further improve the water management of the cathode catalytic layer and improve the performance and stability of the MEA,we investigated the effect of platinum modified nanoporous gold catalytic layer structure based on multistage pores on cell performance.The ultra-thin micron-nanometer catalytic layer structure significantly improves the cell performance of the cathode catalytic layer.When acting as a cathode alone,the cell performance of multistage porous catalytic layer(100 nm thickness)composed of 100?m and 35 nm at a Pt load of about 50?g/cm~2 can reach1.05 W/cm~2.The stability of the MEA is 45%higher than that of the individual nanopores.Further experimental and simulation data show that the catalytic layer structure is beneficial to improve the drainage of membrane electrodes,interface problems due to water flooding in ultrathin catalytic layers,and then improve the stability.(3)Finally,we investigated the application of ultrathin platinum modified nanoporous gold in hydrazine-hydrogen peroxide fuel cells.Because of the water management problem in the PEMFC of ultrathin catalytic layer,we applied NPG-Pt catalytic layer to all liquid fuel cells to avoid the problem of PEMFC flooding.The study show that when we adopted a new hydrophilic electrode,the 100 nm thick NPG-Pt act as both anode and cathode,at a load Pt is 20?g/cm~2,and cell performance can reach 0.56 W/cm~2.At a current density 250 m A/cm~2,voltage of NPG-Pt base MEA is about 300 m V higher than that of the Pt/C.Using 400 nm thick NPG-Pt as both anode and cathode,the integrated carbon-free electrodes can reach maximum power density of 1.14 W/cm~2 when serving as both the anodes and cathodes,at a Pt loading of 56.1?g/cm~2.Further permeability experiments show that the gas/liquid transport performance of the catalytic layer is excellent and the structural advantages of ultrathin nanoporous metal electrodes are fully demonstrated in all-liquid proton exchange membrane fuel cells. |
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