Preparation Of Platinum Carbon Catalysts For Proton Exchange Membrane Fuel Cell And Its Oxygen Reduction Performancel

As an important energy conversion device to solve the energy crisis and environmental degradation problems,the commercialization of Proton Exchange Membrane Fuel Cell（PEMFC）for automotive applications is imminent.The high cost,slow kinetics of cathode oxygen reduction reaction and poor stability of cathode catalysts for long time operation have become the main reasons to limit its development.Therefore,in this thesis,we address the current problems of poor durability of catalysts and optimize the modification of carbon carriers and Pt/C catalysts by different heat treatment schemes to achieve the preparation of cathode oxygen reduction catalysts with high activity and high durability.The main research contents and results are as follows:（1）High temperature heat treatment of carbon carriers was used to enhance the stability of the catalysts.The carbon carriers were annealed at 1000,1200 and 1400 ℃ to occur graphitization on the surface of the carbon carriers,which enhanced the corrosion resistance of the carbon carriers and improved the working voltage resistance of the catalysts.The test results showed that the higher the heat treatment temperature of the carbon carriers,the better the stability of the catalysts,and considering the initial activity and durability,the best oxygen reduction performance of the catalysts was obtained through 1200 ℃ heat treatment.（2）The catalysts activity and stability were enhanced by heat treatment of Pt/C catalysts with different atmospheres.The Pt/C catalysts were annealed at different temperatures by different atmospheres such as nitrogen,nitrogen-hydrogen mixture（20%H₂）and air to expose the Pt（111）crystalline surface in the catalysts and promote the transformation of Pt particles into metallic state,increasing the content of Pt⁰,which has oxygen reduction activity and stabilizing effect on the catalysts.The increase of Pt⁰ content can compensate the particle size effect to a certain extent,thus the catalysts with high activity and stability can be prepared.The test results showed that the initial activity of Pt/C-300（20%H₂）catalyst was 342 m A/mg,and the high performance of 243 m A/mg was maintained after 30,000cycles of attenuation test.Therefore,heat treatment of Pt/C catalysts not only improves its stability but also has a positive effect on its oxygen reduction activity.（3）The catalysts with high oxygen reduction activity and high durability were prepared by a combination of pre-treatment of carbon black and post-treatment of Pt/C catalysts.The dual heat treatment of the carbon carriers and the Pt/C catalysts resulted in stronger molecular forces and stronger anchoring between Pt nanoparticles and carbon carriers,which effectively inhibited Pt particles from migrating and agglomerating on the carbon carriers.The test results showed that the retention rate of electrochemically active surface area of Pt/CB₃₀₀-700 catalyst prepared by dual heat treatment was as high as 95.6%after 30,000cycles of attenuation test.