Investigation On Membrane Electrode Assemblies (MEAs) Of Unitized Regenerative Fuel Cells

Proton Exchange Membrane Fuel Cells （PEMFCs） are a kind ofhigh-efficiency energy conversion device that has the features such asenvironmental friendly, low working temperature, fast start-up speed andhigh energy density. They are thought to be promising in the future. Basedon proton exchange membrane （PEM） electrolyte, unitized regenerativefuel cells （URFCs） can produce H₂and O₂in water electrolysis （WE）operation for energy storage, or generate electrical power in H₂/Air （O₂）fuel cell （FC） operation. Combined with solar cells or wind power systems,URFCs are potentially interesting in the application of specific situationslike spacecrafts or submarines.In this paper, novel catalyst layer preparation, hydrophobicity of gasdiffusion layers （GDLs）, WE performance with different water feedingmodes and the lifetime of WE mode were discussed separately.In novel catalyst layer preparation, in-situ grown Pt on carbon powder was compared with samples made from sputtering and commercial Pt/C.The in-situ grown Pt was well distributed onto carbon particles, and thesurface of carbon particles where Pt grows is much coarser than the others.Regional EDX result shows a similar Pt dispersion between thecommercial Pt/C and the in-situ grown Pt catalyst. The catalytic activity ofin-situ grown Pt is lower than commercial Pt/C but higher than sputteringone. In hydrogen/oxygen atmosphere, the performance of in-situ grownPt sample can achieve1.3A cm-2/0.5V and the max power output is0.64W cm-2.In electrode structure optimization for URFCs, the differencesbetween various loadings, hydrophobicity and water feeding modes arecompared and discussed. The optimum MEA is with0.20mg cm-2Pt （in50%Pt/C） for the hydrogen electrode, and a total catalyst loading of0.80mg cm-2for the oxygen electrode. And its performance can reach2.18Acm-2at1.80V in WE mode and0.64A cm-2at0.60V in FC test with airoxidant. Moreover, different water feeding modes have a great effect onWE operation. And the effect changes with different carbon paperhydrophobicity: in the orders of “OE=Dual> HE” feeding with20.68%PTFE, and “Dual> HE> OE” feeding with29.97%PTFE. It is also foundthat in different feeding modes, PTFE content shows the same effect order （in performance） as20.68%>26.95%>29.97%.The lifetime test confirms that the URFCs can at least keep workingfor over140hours in WE mode, accompanying with observable sustainedperformance loss. In the first6hours, the current density drops quickly andthen keeps an approximate constant rate in dropping.In conclusion, in-situ grown method is a highly effective and simpleway to prepare MEA catalyst layers. And through optimization combinedwith catalyst layer loading, GDL hydrophobicity and water feeding modes,MEAs with better performance and stability can be obtained. The workdescribed above may be helpful to further researches on URFCs.