Application Of Modified Carbon Support In Hydrogen Fuel Cell Cathode Catalyst

In recent years,the energy crisis is getting stronger and people urgently need a new energy source to replace traditional energy sources.It is well known that hydrogen is a clean energy source with many advantages,such as high calorific value,non-polluting products and abundant reserves.Hydrogen fuel cell is a kind of power generation device that can convert the chemical energy of hydrogen into electricity directly.Its large-scale commercialization can alleviate the environmental pollution problems caused by traditional energy use and realize the vision of future clean energy transformation.The catalyst layer in a hydrogen fuel cell is the site of the electrochemical reaction between hydrogen and oxygen to produce electric current,and can be considered the heart of the hydrogen fuel cell.At present,the most commonly used cathode and anode catalysts in hydrogen fuel cells are all Pt/C catalysts.Because of the harsh operating environment of hydrogen fuel cells,it is easy to lead to catalyst inactivation.Among the many factors affecting the catalyst electrocatalytic performance,the surface structure and composition of carbon support is one of the most important influencing factors.Commercial Vulcan XC-72R carbon black（XC）has been widely used as a support material for Pt/C catalyst because of its low price,high availability and high mesopore distribution,etc.However,its defects and edges are prone to electrochemical corrosion,and its weak interaction with Pt nanoparticles（Pt NPs）can cause Pt NPs to migrate and agglomerate during the catalytic process,all of which can lead to catalyst deactivation.In order to obtain ideal carbon carriers,in this thesis,we successfully enhanced the catalytic activity and durability of Pt/C catalyst Oxygen Reduction Reaction（ORR）by modifying XC carbon black,improving its surface structure and components,enhancing the electrochemical corrosion resistance of carbon black,changing the surface properties of carbon black and enhancing the interaction force between Pt NPs and carbon black.The main research contents and results of the paper are as follows:（1）Improving the electrochemical corrosion resistance of carbon carriers is one of the most effective strategies to extend the service life of Pt/C catalysts,and onion-like carbon（OLC）has excellent electrochemical corrosion resistance.Using Laser Irradiation in Liquids technology,a synthesis strategy of OLC was developed.In this chapter,we have successfully prepared OLC by using laser irradiation of a commercial Vulcan XC-72R carbon black（XC）dispersed in ethanol.OLC has a higher degree of graphitization than XC,and thus possesses better electrochemical corrosion resistance at extremely high potential conditions.Carrying ultrafine Pt NPs on OLC,the prepared Pt/OLC has higher catalytic activity and better long-term cycle stability of ORR.After 10,000 cycles,the electrochemical active surface area（ECSA）loss of Pt/OLC is negligible.These results suggest that laser-induced OLC is promising support for platinum-based catalysts.（2）Besides OLC,heteroatomic doping is also one of the effective means to improve the catalytic activity and stability of Pt/C catalysts for ORR.Using high temperature pyrolysis technology,the acidified XC powder,melamine and Co（NO₃）₂6H₂O were fully ground together into a tube furnace.A defective conductive carbon black（Co-N-XC）was synthesized and loaded with Pt NPs as a support.The N atoms in XC provide abundant anchoring sites for Pt NPs,enhancing the interaction between Pt NPs and conductive carbon blacks to suppress their migrating agglomerates and facilitating interfacial electron transfer.The introduction of Co species in XC not only optimizes the electronic structure of Pt,but also provides additional activity and synergy to the ORR through the Co-N-C active site.Therefore,the electrochemical test results showed that Pt/Co-N-XC has better oxygen reduction catalytic activity and stability,with ECSA reaching 29.33 m²g _Pt^?1,which is1.5 times higher than that of commercial Pt/C,and still maintaining 96.4%of the initial value after 10,000 cycles.This work provides a simple strategy for heteroatom doping with modified carbon support to help understanding the effects of heteroatom in carbon support on enhancing the ORR catalytic activity of Pt/C catalysts.（3）The effect of heteroatomic doping on the performance of membrane electrodes is also investigated in this paper.Using the high temperature heat treatment technology,the N-doped modified carbon support（N-XC）is synthesized in the ammonia atmosphere,and the Pt NPs can be evenly deposited on the surface of the modified carbon support（Pt/N-XC）.The N atoms enter the carbon skeleton,replacing the C atoms in them as the active center of the ORR.Electrochemical tests showed that the Pt/N-XC catalysts have better oxygen reduction activity and stability than the self-made Pt/C catalysts.The membrane electrode test results show that the Pt/N-XC catalyst-based hydrogen fuel cell membrane electrode has a smoother oxygen and water transport channel due to the good distribution pattern of ionic polymer on the N-XC surface,thus exhibiting higher membrane electrode output power at high current density.