Construction And Performance Of Sintering-and Leaching-resistant Structurally Ordered Pt-based Alloy Catalysts

Proton exchange membrane fuel cells（PEMFCs）are regarded as one of the key technologies to solve the energy and environmental problems brought by traditional power sources,owing to their high energy conversion efficiency,low environmental impact and renewable.The crucial material of fuel cell is the catalyst.At present,Pt-based catalysts are still irreplaceable catalysts.However,Pt-based catalysts still have a series of obstacles,such as high cost,low activity and poor durability.The development of high-performance,high-durability catalysts with minimal Pt are conducive to promoting commercialization of PEMFCs.Herein,two constructing methods for sintering-resistant,leaching-resistant and high-performance Pt-based alloy catalysts were explored.We report a high temperature self-assembly method that directly synthesize structurally ordered PtFe alloy being embed into thin porous N-doped carbon protective shell.The carbon support is firstly covered with a strong Pt（NH₃）₄²⁺and Fe³⁺chemical adsorption inner polydopamine（PDA）shell,and then is covered with an outer silica（SiO₂）layer.This method directly transform absorbed Pt（NH₃）₄²⁺and Fe³⁺into structurally ordered intermetallic PtFe alloys through high-temperature annealing self-assembly.TEM analysis reveals that fct-PtFe/C@NC nanoparticles with an average fine-size of 2.6 nm,indicating that sintering of PtFe alloy during high-temperature annealing can effectively be prevented by the double space-confined with the encapsulation of inner PDA and an outer SiO₂ protective shell.The electrochemical test results that fct-PtFe/C@NC catalyst exhibited excellent ORR performance,with the specific activity（SA）of 1.17 mA·cm^-2 and mass activities（MA）of 0.769 A·mg_Pt^-1 at0.9 V,which are 4.03 and 3.66 times greater than that of JM-Pt/C catalyst.After 30,000cycles of accelerated durability test,the SA and MA performance of fct-PtFe/C@NC only decreased by 23.4%and 28.6%,respectively,which are lower than that of commercial Pt/C catalyst of 41.1%and 64.8%.The enhanced durability of fct-PtFe/C@NC could be ascribed to two factors:1)the structurally ordered PtFe alloy can effectively alleviate the dissolution of Fe atoms;2)nitrogen-doped carbon layer not only can prevent the PtFe nanoparticles from migrating and aggregating on the surface of support,but also can protect the carbon support from directly expose to the harsh fuel cell working environment,further improving the durability of the catalyst.In addition to directly transform ionic precursors into structurally ordered intermetallic alloys,we report a method that directly evolved the phase single Pt nanoparticles into structurally ordered Pt₃Co alloys through assistance of solid-liquid melting space created by molten salt of CoCl₂-NaCl at high temperature.XRD analysis prove that inner the solid-liquid melting space can assist the formation of structurally ordered Pt₃Co alloy.Isolating PtCo nanoparticles function of outer solid salt,evidencd by TEM,have fine effect on inhibiting the migration,agglomeration and sintering of Pt₃Co alloy nanoparticles during high temperature reduction process.The electrochemical test results that Pt/C-CoCl₂-NaCl-500 catalyst exhibited remarkable ORR performance,with the SA of 1.56 mA·cm^-2 and MA of 1.24 A·mg_Pt^-1 at 0.9 V,which are5.38 and 5.9 times higher than that of commercial Pt/C catalyst.After 30,000cycles of accelerated durability test,the SA and MA performance of fct-PtFe/C@NC only decreased by 23.4%and 28.6%,respectively,indicating that structurally ordered Pt₃Co alloys have excellent durability.