Preparation Of Pt-based Nanoporous Films And Their Application In Oxygen Reduction Reactions

Fuel cells have attracted much attention from researchers and governments all over the world in recent years because of their clean,sustainable and high energy density.Hydrogen-oxygen proton exchange membrane fuel cells(H₂-O₂ PEMFCs)can be started at room temperature,high efficiency and safety which is more suitable for life making it becomes the hot topic of fuel cell research.Due to the high overpotential of cathode oxygen reduction reaction(ORR),most of the catalysts are based on high active platinum-based catalysts.However,platinum-based catalysts are not only expensive,but also the low storage on the earth,which makes the cost of fuel cells high and hinders their large-scale commercialization.Preparation of low cost catalyst with high performance and high stability is an effective solution.The nanoporous structure metal catalyst has high specific surface area and high porosity.Compared with the carbon-based granular catalysts,the metal porous film material is more conducive to materials transfer and can avoids the carbon corrosion.The catalyst has better activity and stability so,this can reduce the cost of catalysts.This paper mainly focuses on the research of nano-porous thin film catalyst with low platinum load.The specific research methods are as follows:(1)The ORR activity of Pt-shell was improved by adjusting the morphology and structure of nanoporous gold substrate.Nanoporous gold(NPG)with various pore sizes were prepared as substrates.From the XRD characterization,we found that NPG with different pore sizes have different lattice constants,and the degree of compressive strain increase with the decrease of pore size.Through literature investigation,we found that the compressive strain of the lattice constant on the surface of the platinum-based catalyst is beneficial to improve the ORR of the catalyst.We deposited single-atom layer Pt onto NPG by copper underpotential deposition and replacement,the Pt layer epitaxially growth on the surface of NPG and inherit the surface lattice structure of NPG.The catalyst with the largest compressive showed the best ORR,which SA and MA were 16 times and 4.4 times higher than that of commercial catalyst Pt/C,respectively.After 10000 cycles of stability test,the mass activity and area activity only decreased by 2%.(2)The ORR activity of nanoporous Pt Ni alloy was improved by adjusting the composition of nanoporous Pt Ni alloy.The composition-activity relationship between ORR performance and Pt Ni films in different proportions was systematically studied.The nanoporous structure was prepared by dealloying method,and the corrosion temperature,concentration and time were optimized.It was found that the material with an initial Pt/Ni atomic ratio of 1:3 and corroded for 10 min exhibited the best ORR activity with a half-wave potential of 0.93V(vs.RHE).The mass activity and specific activity are 14-fold and 10-fold higher than the commercial catalyst Pt/C,respectively.