Study On The Preparation And Oxygen Reduction Reaction Performance Of Branched Platinum And Core-shell Structured Non-precious Metal Electrocatalysts

Polymer Electrolyte Membrane Fuel Cell(PEMFC)is a power seneration device that can directly convert chemical energy into electricity,and has the advantages of being clean and highly efficient.Due to the slow reaction rate of oxygen reduction reaction(ORR)at the cathode side of PEMFC,a large quantity of commercial platinum-based electrocatalysts is usually used to accelerate ORR.However,the high cost and limited supply of precious platinum have been limiting the large-scale commercialization of PEMFC.It is a hot topic to study high-performance and low-cost electrocatalysts to replace platinum-based electrocatalysts.In this dissertation,two kinds of branched platinum electrocatalysts and two kinds of core-shell structured non-precious metal electrocatalysts(NPME)were fabricated.The main conclusions are as follows.(1)A series of spherical platinum nanodendrites with tunable average size(20-40 nm)and narrow size distribution(8-9%)were prepared by using in situ photocatalytic rapid nucleation method based on zinc(II)porphyrin(ZnP).The ORR mass activity of the platinum nanodendrites is 171 mA/mgpt(@ 0.9 V vs.RHE),which is 1.9 times of commercial platinum black.The high ORR activity is mainly due to the high electrochemical surface area(ECSA)of platinum nanodendrites(44.0 m2/gpt)that is 2.2 times of that of commercial platinum black(20.4 m2/gpt).(2)Graphene supported platinum seeds localized in-between liposomal bi-layer provides a unique supporting-seeding-templating tri-functional reaction environment that permits the synthesis of graphene supported foam-like platinum(Pt foam/G).Pt foam consists of 2-3 nm thick dendritic nanosheets.The stacking of graphene nanosheets was effectively prevented by the insertion of carbon black particles into graphene sheets.Pt foam/G showed an enhanced ORR mass activity(247 mA/mgpt @ 0.9 V vs.RHE)compared with commercial Pt/C(215 mA/mgpt @ 0.9 V vs.RHE),due to the predominant exposure of highly active Pt(110)facets.(3)Nitrogen-doped graphite(6-15 layers)coated Fe2.9Co alloy nanoparticles(11.8 ± 4.3 nm)supported on carbon black(Fe2.9Co@NG/C)were synthesized by using rotary evaporation induced deposition of complexes formed between iron acetylacetonate/cobalt acetylacetonate and melamine on carbon black,followed by carbonization and acid leaching.The electrocatalyst with a loading of 1.2 mg/cm2 on an electrode exhibits a remarkable ORR activity in alkaline solution,compared to commercial Pt/C(80 ?gpt/cm2),with a positively shifted onset potential of 50 mV and equivalent half wave potential.Density function theory(DFT)calculations and Raman spectroscopy reveal that the ORR activity of Fe2 9Co@NG/C may be related to the distortion of N-doped graphene layers.(4)Carbon black/N-doped graphene-like layers core/shell structured NPME(C@NG)was prepared for the first time by rotary evaporation induced self-assembly of iron(?)porphyrin(FeP)on carbon black,followed by carbonization and acid leaching.The thickness of graphene-like shell can be readily adjusted from 3 to 6.6 nm.Interestingly,C@NG exhibits an excellent ORR activity in both alkaline and acidic medium with half wave potential of 0.87? and 0.75 ?(vs.RHE),respectively.In particular,the core/shell structured NPME demonstrates a remarkable durability in acidic conditions superior to that of commercial Pt/C,which likely comes from the exposure of inner active sites after the outermost layer is consumed.