A perspective on influences of cathode material degradation on oxygen transport resistance in low Pt PEMFC

A large-scale industrial application of proton exchange membrane fuel cells(PEMFCs)greatly depends on both substantial cost reduction and continuous durability enhancement.However,compared to effects of material degradation on apparent activity loss,little attention has been paid to influences on the phenomena of mass transport.In this review,influences of the degradation of key materials in membrane electrode assemblies(MEAs)on oxygen transport resistance in both cathode catalyst layers(CCLs)and gas diffusion layers(GDLs)are comprehensively explored,including carbon support,electrocatalyst,ionomer in CCLs as well as carbon material and hydrophobic polytetrafluoroethylene(PTFE)in GDLs.It is analyzed that carbon corrosion in CCLs will result in pore structure destruction and impact ionomer distribution,thus affecting both the bulk and local oxygen transport behavior.Considering the catalyst degradation,an eventual decrease in electrochemical active surface area(ECSA)definitely increases the local oxygen transport resistance since a decrease in active sites will lead to a longer oxygen transport path.It is also noted that problems concerning oxygen transport caused by the degradation of ionomer chemical structure in CCLs should not be ignored.Both cation contamination and chemical decomposition will change the structure of ionomer,thus worsening the local oxygen transport.Finally,it is found that the loss of carbon and PTFE in GDLs lead to a higher hydrophilicity,which is related to an occurrence of water flooding and increase in the oxygen transport resistance.

Development and Challenges of Electrode Ionomers Used in the Catalyst Layer of Proton-Exchange Membrane Fuel Cells:A Review

The electrode ionomer plays a crucial role in the catalyst layer(CL) of a proton-exchange membrane fuel cell(PEMFC) and is closely associated with the proton conduction and gas transport properties,structural stability,and water management capability.In this review,we discuss the CL structural characteristics and highlight the latest advancements in ionomer material research.Additionally,we comprehensively introduce the design concepts and exceptional performances of porous electrode ionomers,elaborate on their structural properties and functions within the fuel cell CL,and investigate their effect on the CL microstructure and performance.Finally,we present a prospective evaluation of the developments in the electrode ionomer for fabricating CL,offering valuable insights for designing and synthesizing more efficient electrode ionomer materials.By addressing these facets,this review contributes to a comprehensive understanding of the role and potential of electrode ionomers for enhancing PEMFC performance.

Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the major portion of the cost.Although nonprecious metal catalysts(NPMCs)show appreciable activity and stability in the oxygen reduction reaction(ORR),the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL.Therefore,most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport.In this work,the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures,one containing low-Pt-based CCL and NPMCbased dummy catalyst layer(DCL)and the other containing only the NPMC-based CCL.Using Zn-N-C based DCLs of different thickness,the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis.Then,the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy,respectively.Results show that the ratios of local and bulk oxygen transport resistances in NPMCbased CCL are 80%and 20%,respectively,and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs.Furthermore,the activity of active sites per unit in NPMCbased CCLs was determined to be lower than that in the Pt-based CCL,thus explaining worse cell performance of NPMC-based membrane electrode assemblys(MEAs).It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.

Highly-chlorinated inert and robust interphase without mineralization of oxide enhancing high-rate Li metal batteries

Side reactions and dendrite growth triggered by the unstable interface and inhomogeneous deposition have become the biggest obstacle to the commercialization for lithium metal batteries.In this study,a highly-chlorinated organic-inorganic hybrid interfacial protective layer is developed by rationally tuning the interfacial passivation and robustness to achieve the convenient and efficient Li metal anode.The polyvinyl chloride(PVC)can effectively resist water and oxygen,which is confirmed by density functional theory.The organic-dominant solid electrolyte interphases(SEI)with lithium chloride are investigated by the X-ray photoelectron spectroscopy(XPS)with little mineralization of oxide,such as Li_(2)O and Li_(2)CO_(3).With such artificial SEI,a uniform and dense lithium deposition morphology are formed and an ultra-long stable cycle of over 500 h are achieved even at an ultra-high current density of 10 m A/cm^(2).Moreover,the simple and convenient protected anode also exhibits excellent battery stability when paired with the LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)and LiFePO_(4)(LFP)cathode,showing great potential for the commercial application of lithium metal batteries.

Microstructure and Wear Properties of Fe-based Amorphous Coatings Deposited by High-velocity Oxygen Fuel Spraying

Fe-based powder with a composition of Fe_（42.87）Cr_（15.98）Mo_（16.33）C_（15.94）B_（8.88）（at.%）was used to fabricate coatings by high-velocity oxygen fuel spraying.The effects of the spraying parameters on the microstructure and the wear properties of the Fe-based alloy coatings were systematically studied.The results showed that the obtained Fe-based coatings with a thickness of about 400μm consisted of a large-volume amorphous phase and some nanocrystals.With increasing the fuel and oxygen flow rates,the porosity of the obtained coatings decreased.The coating deposited under optimized parameters exhibited the lowest porosity of 2.8%.The excellent wear resistance of this coating was attributed to the properties of the amorphous matrix and the presence of nanocrystals homogeneously distributed within the matrix.The wear mechanism of the coatings was discussed on the basis of observations of the worn surfaces.

Effect of oxygen concentration on resistive switching behavior in silicon oxynitride film

SiOxNy films with different oxygen concentrations were fabricated by reactive magnetron sputtering,and the resistive switching characteristics and conduction mechanism of Cu/SiOxNy/ITO devices were investigated.The Cu/SiOxNy/ITO device with SiOxNy deposited in 0.8-sccm O2 flow shows a reliable resistive switching behavior,including good endurance and retention properties.As the conductivity of SiOxNy increases with the increase of the oxygen content dynamical electron trapping and detrapping is suggested to be the conduction mechanism.The temperature dependent I-V measurement indicates that the carrier transport can be ascribed to the hopping conduction rather than the metallic conductive filament.