In Situ Fabrication Of Membrane Electrode Assembly With Low Pt Loading And Development Of Dynamic Responsive Membrane Electrode Assembly

Hydrogen,the most abundant resource on the earth and even in the universe,shows the vast potential as clean energy sources and is described as an ultimate energy alternative to fossil fuels that we rely on for hundreds of years.Around the world,efforts are being made to harness the power of hydrogen.With continuous deterioration in environmental concerns and limited use of battery,the fuel cell as an efficient and environmental friendly energy conversion device has been widely sought-after.Because of this,a new age of H2 economy is dawning.Hydrogen stations are appearing across the US,Europe,China and Japan.Toyota,Honda,Mercedes-Benz and General Motors and other companies are vigorously promoting the development of hydrogen fuel cell vehicles.Among the various typies of fuel cells,proton exchange membrane fuel cells（PEMFCs）are regarded as one of the most likely to be widely used in the field of transportation,military and other portable devices.However,the commercialization of PEMFCs is still facing many challenges:（1）the use of noble metal as catalysts;（2）perfluorosulfonic acid electrolyte membrane is expensive;（3）fuel cell system is too complex,offen eqquipped with auxiliary power module to duel with fuel starvation.These factors increase the overall cost of fuel cell system and limit the pace of its application.Based on the above three points,we explores and studies the low-platinum loading membrane electrode assemblies,the novel composite electrolyte membrane and bifunction electrode with energy storage material,aiming at pursuing the high performance and offering the flexibility for practical application while reducing the cost of fuel cell.Firslyt,we use the pulsed electrodeposition technique to prepare ultra low Pt loading membrane electrode assemblies through in-situ construction of Ir@Pt/C core-shell nanoparticles in the anode catalyst layer.The prepared Ir@Pt nanoparticles are deposited on the three-phase interface of the electrode,which greatly improves the Pt exposure and Pt utilization.In this work,we investigate effect of different duty times and Pt Ir ratios on single cell performances.The optimal duty time is ton: toff=3ms:1.5ms and ration between Ir and Pt is 2.7:1.The anode Ir@Pt/C MEA with Pt loading down to 0.012 mg cm^-2 shows the better cell performance compared to the commercial Pt/C MEA.The Pt mass activity of Ir@Pt/C MEA is 55 k W g^-1,which is 10 times that of the commercial Pt/C MEA.This demonstrates that the prepared Ir@Pt/C MEA can greatly reduce the Pt loading as well as maintaining high cell performance.Secondly,in order to further investige the cathode cell performance of Ir@Pt/C MEA,we prepared a series of Ir@Pt/C MEA by tuning of Ir core sizes at different anealing temperature.It is found that the MEA with optimal Ir particle size（4.1 nm）exhibited excellent performance in a H2/air single fuel cell and the peak power density is 0.58 W cm^-2,which is comparable to that of the MEA prepared with Pt/C catalyst（Johnson Matthey 40% Pt）,even though the Pt loading was only 44% of that of the latter.The mass activity of Ir@Pt/C-300 MEA could reach 13.04 kW g–1 Pt,which is threefold that of a JM Pt/C MEA.Combined with density function theory calculations,we confirm that there is an interaction between Pt and Ir,which can tune the energy of mediates on Pt shell leading to the enhanced ORR catalytic performance.Thirdly,ultra low platinum loadings membrane electrode assembly（MEA）is prepared by a facile synthesis process in which pulse electrodeposition is used to achieve a catalyst layer by the in situ decoration of carbon-supported Pd nanoparticles with a thin layer of Pt atoms.The novel MEA exhibits excellent performance both in hydrogen oxidation and oxygen reduction reaction,with Pt loading of as little as 0.015 mg cm^-2 at the anode and 0.04 mg cm^-2 at the cathode,outperforming the commercial Pt/C.The usage of Pt has significantly reduced.The EDS-line scan reveals the formation of core-shell structure with Pt highly-dispersed on the Pd;materials characterization results show that the strong interaction between Pt and Pd,which may attribute to the weaker binding energy of OH species on the surface of Pt and eventually reflect on the enhanced cathode cell performance.Fourthly,with the aim of reducing the cost and increasing the temperature of solid electrolyte membrane,we prepare a composite CsH2PO4/PVB as a polyer solid acid electrolyte membrane.A small amount of PVB in the CsH2PO4 composite electrolyte not only offers the required mechanical integrity but also allows high conductivity（²8 mS cm-1）at 260 °C.The results show that composite electrolyte membrane can form a dense and uniform surface structure,and the thickness can be as low as 120μm.Single cells based on the composite electrolytes demonstrated a peak power density of 108 mW cm^-2 at 260°C.Almost no degradation in electrochemical performance could be observed during the stability test for 10 h and three thermal-cycling tests,indicating the promising application of the composite electrolyte in solid acid fuel cells.Finally,in order to deal with power compensation and fuel starvation at emergency situation,we propose herein the design and synthesis of novel tungsten-based materials,and their integration as effective energy-storage electrodes at anode that enable fuel cells with dynamic response functions.Pt decorated WO₃ nanowires-based anode has been established on carbon cloth.The solid acid fuel cell system with energy storage unit is able to store proton in WO₃ during fuel cell operation by hydrogen spillover on Pt and discharged reversibly followed by WO₃ + xH+ + xe-? HxWO₃.The energy stored in the form of HxWO₃ can be released upon its oxidation to WO₃,releasing protons（H+）and electrons that cross through the electrolyte and the external electron pathways,respectively,to the cathode for oxygen reduction reaction.The responsive fuel cell device demonstrates 390 s longer discharging time with 16 mg cm^-2 WO₃ compared to fuel cell device without WO₃ energy storage anode.Through this study,we demonstrate that energy storage capability of tungsten oxide can be employed in a porous structure of solid acid fuel cell anode,may presenting a feasibility of concept for other types of fuel cells with uninterrupted power supply for practical condition.