Synthesis And Study Of High-loading Au-doped Pt-Co/C Catalyst Toward Oxygen Reduction Reaction

Proton exchange membrane fuel cell（PEMFC）can be a practical way to utilize hydrogen energy.Due to the sluggish kinetics of the cathode oxygen reduction reaction（ORR）,catalysts,mainly platinum（Pt）,are indispensable.Pt-Co system is considered to be one of the most promising cathode catalysts.Carbon-supported Pt-Co nanoparticles（NPs）catalyst with a high Pt loading is more suitable for the practical application due to the thinner catalyst layer in the membrane electrode assembly（MEA）.It is of great significance to prepare high-loading Pt-Co/C catalysts with enhanced catalytic activity and durability.With this purpose,this thesis carried out the following work:（1）Taking the catalyst morphology,initial catalytic activity and actual Pt loading as the criterion,we chose the traditional Ethylene glycol（EG）reduction method for the preparation of high-loading carbon-supported Pt-Co catalysts.The Pt-Co NPs were totally deposited onto the carbon support through the addition of nitric acid solution at the end of the EG reduction reaction,selective acid-etching was accomplished meanwhile.The subsequent low-temperature thermal treatment promoted the formation of Pt-rich surface structure.The as-prepared catalyst Acid-EG-Pt Co/C possessed a Pt loading up to 50.3 wt.%.According to the electrochemical measurement results,the mass activity（MA）and specific activity（SA）of Acid-EG-Pt Co/C were better than commercial Pt/C.The ORR durability was also improved.The enhanced activity and durability are mainly attributed to the synergistic effect and the Pt-rich surface structure.（2）To further enhance the durability of catalysts,we tried to introduce Au into the catalyst surface through the addition of nitric acid solution containing KAu Cl₄.The Au_0.015-Pt-Co/C prepared with 0.015 mmol KAu Cl₄showed an average particle size of3.42 nm and the Pt loading of it was up to 50.2 wt.%,the atomic ratio of Au was only1%.The MA and SA were 0.386 A/mg_{（Pt）}and 0.535 m A/cm²,nearly 1.9 times and 1.6times those of commercial Pt/C,respectively.The loss of MA was only 9.4%after30000 cycles ADT.The remarkable durability is mainly attributed to the surface Au modifying,which can restrict the dissolution of Pt and Co.The thesis proposed an effective method to synthesize high Pt loading Pt-Co/C catalysts with fine morphology.Due to the selective acid-etching and the surface Au modifying,the as-prepared catalysts only need to take a thermal treatment at as low as150℃to form a Pt-rich surface structure and achieve a great improvement in durability while maintaining the morphology.We consider that it is promising for practical application.