Investigation On Electrochemical Synthesis Of High Performance Pt-based Electrocatalysts For Oxygen Reduction Reaction In Fuel Cells

The application of scarce and precious Pt to catalyze electrochemical reactions in both electrodes of proton exchange membrane fuel cells?PEMFCs?,especially the sluggish oxygen reduction reaction?ORR?cathode,decisively impact on their high cost,which accounts for as high as43%of the fuel cell stack cost based on 500,000 systems per year,thus severely impeding the progress of PEMFC commercialization in automotive fields.To reduce the amount of Pt in the cathode,alloying Pt with other metals with various strategies have been widely developed in the last decade.However,it is noted that during some synthesis,multitudinous or long-chain organic surfactants are usually employed to assure the desired shapes,special nanostructures as well as adjusting the size.Compared with complicated chemical reduction methods,the electrochemical method gains special attention owing to some unique properties including the facile control of crystal nucleation and growth and exposure of highly clean active sites for the as-prepared catalysts.Therefore,we proposed here to investigate the electrochemical synthesis of high performance Pt-based catalysts.Firstly,we explored the electrodeposition mechanism of Pt-M alloy in aqueous solutions that employs N,N-dimethylformamide?DMF?as the selective coordinating agent to assist in the co-reduction.It is very ingenious to discovery that the selective of coordination of DMF with Pt ions rather than Co ions greatly bridges the deposition potential gap between Pt and Co as high as 200 mV,thus greatly promoting formation of PtCo alloys.The optimal Pt₄Co alloy sample exhibits a remarkable specific activity as high as 1.52 mA·cm_Pt^-2 at0.9 V?vs.RHE?towards the ORR,7 times of that for the commercial Pt/C catalyst.Secondly,electrodeposition of Pt from different organic electrolytes was carried out in order to gain a comprehensive view about the mechanism and behaviors.DFT calculation indicates that the adsorption effect of the supporting electrolytes is proved to have a significant influence on the deposition process.The Pt electrodeposits,4.72 nm in average size,gained a highest specific catalytic activity of 0.84 mA·cm^-2?3.22 times than commercial Pt/C catalyst?towards ORR when deposited at-1.7 V.Thirdly,on basis of the former experiment,we proposed to synthesize PtCo alloy catalysts in pure DMF.Highly active PtCo nanoparticles for ORR was thus prepared with a specific activity of 2.29 mA·cm^-2,nearly 10 times than commercial Pt/C catalysts.Furthermore,future plan on core-shell nanostructures have been analyzed in detail.In summary,this work not only advanced the theories of electrochemical synthesis in organic electrolytes,but also provided a solid scientific guideline for the design of high-performance ultra-low Pt loading catalysts,thus accelerating the commercialization of PEMFCs.