Synthesis And Characterization Of SO₂/NO_x Poisoning Resistance Catalysts For Oxygen Reduction Reaction

Proton exchange membrane fuel cells?PEMFCs?using platinum-based materials as electrocatalysts have achieved a desired performance,which have been considered as the most promising automobile energy source.The ideal PEMFCs consume stored pure hydrogen and ubiquitous air.However,the air feed at cathodes is challenging due to the inevitable impurities such as SO₂,NO_x,CO,O₃,etc.Given that the SO₂ and NO_x has great impact on suppressing the Pt/based catalyst towards oxygen reduction reaction?ORR?,this work is focused on developing anti-poison catalysts against the SO₂ and NO_x.Tetra-butyl titanate was used as the precursor of TiO₂ to deposit TiO₂ on XC-72 carbon to prepare TiO₂/C support.Then,Pt nanoparticles were deposited on the TiO₂/C support by microwave assisted ethylene glycol process to prepare Pt/TiO₂/C catalysts.Electrochemical tests show that Pt/TiO₂/C catalysts has certain effect on enhancing ORR activity and SO₂ toxicity resistance,but no significant improvement on NO_x.Pt/10TiO₂/C catalysts have the best performance with electrochemical activity area increases by 23.3%and the kinetic current density at 0.9 V increases by 10.4%compared with Pt/C.The electrochemical oxidation peak potential of SO₂ negatively shifts by 50mV,and the kinetic current loss after SO₂ poisoning is reduced by 23.4%compared with Pt/C.The interaction between Pt and TiO₂ as well as the abundant hydroxyl groups on the surface of TiO₂ are revealed to account for the accelerated removal of poisonous SO₂ on Pt surfaces and the improvement of catalytic activity towards ORR.However,large particle size and poor dispersibility of TiO₂ causes inadequate contact between TiO₂ and Pt.The the content of carbon is correspondingly reduced while the content of TiO₂ is increased,leading to a significant reduction in the conductivity of the catalyst.Moreover,excessive TiO₂ causes Pt aggregation in the synthesis process,resulting in a significant decrease in the performance of the catalysts.To further improve the catalytic activity of oxygen reduction reaction and the resistance to SO₂/NO_x toxicity of the catalysts,Pt/C catalysts were prepared by microwave-assisted ethylene glycol process,then Pt/C were mixed with comercial TiO₂ nanoparticles by simple ultrasonic treatment to prepare Pt/C-TiO₂ hybrid catalysts.The electrochemical behavior towards oxygen reduction reaction and resistance to toxic SO₂ and NO_x was in detail investigated.Impressively,the hybrid Pt/C-TiO₂ catalyst with 20wt.%TiO₂ shows the best ORR and anti-toxic performance:its kinetic current density at 0.9 V is 20.5%higher than Pt/C;The peak potential of SO₂ electrochemical oxidation is 50mV lower than Pt/C;The kinetic current density loss caused by SO₂ poisoning is 32.7%lower than Pt/C,and the current density loss caused by NO_x poisoning is 7.7%lower than Pt/C.The improvement of ORR performance and toxicity resistance of the catalyst can also be attributed to the synergistic effect of Pt/TiO₂ and the surface hydroxyl of.While TiO₂?30 mass%,the performance of catalyst becomes worse due to the decrease of conductivity.Compared with Pt/TiO₂/C catalyst,TiO₂ particle in Pt/C-TiO₂ hybrid catalyst prepared by ultrasonic mixing has smaller particle size,better dispersibility and more sufficient contact with Pt,and avoids the negative impact of too much TiO₂ on Pt loading process,showing better ORR activity and anti-toxicity ability.