Low-temperature Preparation Of Platinum Catalyst Based On Carrier Enhancement And Its Oxygen Reduction Performanc

Proton exchange membrane fuel cells（PEMFCs）are considered to be one of the most promising energy conversion systems due to their high energy density,low operating temperature and lack of pollution,which can meet the urgent need for clean and sustainable energy conversion.Currently,the development of efficient and cost-effective electrocatalysts for the cathodic oxygen reduction reaction（ORR）is one of the major challenges for the large-scale application of PEMFCs.So far,carbon-supported Pt-based materials are the most widely used ORR catalysts.However,the widespread use of this catalyst is greatly hampered by the high cost and scarcity of Pt.Moreover,under the working conditions of PEMFCs,this Pt catalyst is vulnerable to carbon support corrosion,Pt nanoparticles（NPs）dissolution,and agglomeration and sintering,resulting in poor stability.In addition,such Pt catalysts are usually synthesized using a high-temperature reduction method,which makes it easier for the Pt particles to agglomerate and lead to low catalytic activity.In response to the above problems,this paper designed a stable N-coordinated iron atom embedded carbon（Fe-NC）material as a support for Pt catalysts,starting from the regulation of the carbon support structure and the electronic structure of Pt.This Fe-NC material can not only stabilize Pt NPs and provide additional Pt-free active sites to reduce the amount of Pt in the ORR cathode,but also the synergistic effect between Pt and Fe-Nx sites can further enhance ORR activity and stability.Therefore,two kinds of stable Fe-NC supports were designed,and a method for preparing Pt NPs（catalysts）at low temperatures was developed,focusing on improving the catalytic activity and stability and reducing the cost of the catalyst in this work.The following two tasks were mainly carried out:（1）An in situ surfactant-free self-template solution reduction strategy was designed to synthesize a Fe/NC porous nanostructure using resin as a carbon-nitrogen precursor,and the Pt-Fe/NC catalyst with low Pt loading was obtained by successfully dispersing Pt nanoparticles（NPs）on Fe/NC materials by a low-temperature reduction method.The obtained Pt-Fe/NC catalysts exhibit excellent ORR performance with mass activity and specific activity of 0.42 A/mg_pt and 0.973 mA/cm² at 0.9 V,which are 2.2 and 3.53times higher than the commercial Pt/C catalysts(0.191 A/mg_pt and 0.273 mA/cm²),respectively.The stability test confirmed that the Pt-Fe/NC catalyst still maintained a high activity after 20,000 potential cycles,and its mass activity and specific activity were as high as 0.401 A/mg_pt and 0.958 mA/cm²,which were only 4.5%and 1.6%lower than the initial values.The excellent ORR performance of the Pt-Fe/NC catalyst is attributed to the electronic interaction between Pt and Fe/NC and the additional catalytically active sites provided by the Fe/NC material.This strategy of modifying the electronic structure of Pt and enhancing the catalytic performance through support enhancement provides new insights for further designing high-performance ORR electrocatalysts.（2）Based on the above work,a strategy combining stress-induced shrinkage mechanism and impregnation reduction method was further proposed to successfully disperse Pt NPs onto stress-induced shrinkage ZIF-8-derived hollow N-coordinated iron atom-embedded carbon（Fe-NC）dodecahedral nanomaterials,obtained a high-performance Pt@Fe-NC electrocatalyst for oxygen reduction reaction（ORR）.This hollow Fe-NC material is formed due to the contraction induced by the interfacial interaction between ZIF-8 and the cladding layer of PDA during high-temperature pyrolysis.The as-prepared Pt@Fe-NCs exhibit high ORR activity due to the multiple active centers and hollow porous structures favorable for mass transfer.Electrochemical tests show that the half-wave potential of Pt@Fe-NC is 0.936 V,and the mass activity and specific activity are as high as 1.34 A/mg_pt and 1.72 mA/cm²,which are 6.77 and 6.01 times that of commercial Pt/C(0.198 A/mg_pt and 0.286mA/cm²),respectively.Meanwhile,the stability test results indicated that the Pt@Fe-NC exhibited higher catalytic durability than the Pt/C catalyst.DFT calculations reveal that the electronic interaction between Pt NPs and Fe-NC substrates enhances the anchoring of Pt and weakens the adsorption of*OH intermediates on Pt and Fe sites,enhancing the intrinsic activity of ORR.This work provides a new direction to explore the synergistic effect of noble metal platinum and metal-nitrogen-carbon to realize the design of highly active ORR electrocatalysts.