| Proton Exchange Membrane Fuel Cell（PEMFC）is considered as one of the most promising candidates for next generation power sources due to its high power density,zero emissions and low operating temperature.Electrocatalysts play an important role in determining the performance of PEMFCs,accounting for half of the total cost,and reducing the precious metal loading is considered a key challenge for the commercialization of fuel cell,so constructing highly active,low-cost electrocatalysts for practical applications in PEMFCs is critical.nanoporous metal（NPM）materials have proven to be excellent electrodes for high performance energy conversion,and due to their high specific surface area,open framework structures,and adjustable ligament and channel sizes,NPMs have been used as the basis for active electrodes themselves or for further functionalization.In addition,these structures no longer require the use of conventional carbon carriers,avoiding this problem of carbon corrosion.In this thesis,the preparation of catalysts with high oxidation reduction reaction（ORR）performance is achieved by structurally designing and tuning the NPM to increase catalyst activity and reduce catalyst loading without compromising its performance in the cell,as follows:（1）The surface morphology of nanoporous gold（NPG）modified Palladium（Pd）was tuned to achieve high ORR activity for catalyst preparation and application on the cathode side of proton exchange membrane fuel cells.Two different Pd growth models were tuned by electrodeposition,where Pd was grown epitaxially in Frank van der Merwe（FM）mode layer by layer on the NPG ligament surface;in a layer-by-layer growth sequence followed by formation of three-dimensional islands in Stranski Krastanov（SK）mode.By comparison,the electrochemical and cell performance of the FM-mode grown catalyst is better,with the highest power density far exceeding that of commercial Pd/C,and its mass-to-power density is approximately 4.7 and 25.6times higher than that of commercial Pt/C and commercial Pd/C,respectively.It is verified that the performance of the catalyst can be improved by surface engineering strategies.（2）The effect of pore size of NPG on the performance of NPM electrode was investigated.The pore size～30 nm had the best ORR performance and cell performance with an intrinsic ORR activity of 0.46 m A·cm-2 and a mass activity of0.1 A·mg Pd-1 in electrochemistry;the cell performance reached 1068.7 m W·cm-2 at Pd loading of 20.1μg·cm-2 and 1.5 bar back pressure,and its maximum mass specific power density(53.4 k W·g Pd-1)was 25.4 times higher than the commercial Pd/C catalyst(2.1 k W·g Pd-1).The NPG-Pd electrode exhibited excellent durability in the membrane electrode polarization durability test,with losses in current density and maximum power density of about 17.1%and 17.0%,respectively.This work provides an opportunity to explore non-Platinum catalysts and to investigate the mechanism of the effect of surface configuration on the catalytic activity of ORR.（3）Considering the issue of cost,we subsequently discussed carrier-free Pt nanotubes（Platinum Nanotubes,Pt NTs）as cathode catalysts as durable electrocatalysts for PEMFC.Pt nanotubes with an average tube wall thickness of about 5.1 nm and an average tube diameter of about 30.2 nm were formed by the substitution reaction,and the thin electrode catalyst layer without carbon carriers improved the mass transfer and platinum（Platinum,Pt）utilization within the catalyst layer,reaching a maximum power density of 725.9 m W·cm-2 at the test conditions of80°C and 0.1 mg·cm-2 Pt loading with a power rating of 0.45 W·cm-2 which is 2.5times higher than that of commercial Pt/C catalysts,and a mass activity of 1.02A·mg Pt-1 in the membrane electrode,which is 1.5 times higher than that of existing commercial Pt/C catalysts.These results show the potential of Pt NTs for use in fuel cells. |
PDF Full Text Request