Pt-based Catalysts For Oxygen Reduction Reaction

Proton exchange membrane fuel cell?PEMFC?,a device that directly converts chemical energy into electrical energy,is considered to be an ideal clean power source because of its high energy conversion efficiency,fast start-up,and quiet operation.However,the slow kinetics of cathodic oxygen reduction reaction?ORR?requires a large amount of Pt-based catalyst,which has high activity for ORR.Unfortunately,the scarcity and high cost of Pt greatly increase the cost of PEMFC,which impedes its large-scale commercialization.In recent years,great progress has been achieved in the development of carbon-based non-precious metal catalysts for ORR,however,their commercial application still has a long way to go.Recently,the strategy for reducing Pt usage in Pt-based catalyst by increasing its ORR performance has attracted intensive attention.In this work,a series of carbon black-supported PdAu@Pt core-shell catalysts and Pt catalysts anchored on different supports were synthesized with the aim to increase the ORR performance so as to reduce the Pt usage.The following main conclusions were obtained.1.Pt-based core-shell catalyst was obtained by a two-step process.In the first step,carbon-supported PdAu?PdAu/C?was synthesized at 160?by using carbon black as support,palladium chloride and chloroauric acid as precursor,ethylene glycol as reducing agent,and sodium citrate as stabilizing agent.In the second step,carbon-supported PdAu@Pt core-shell?PdAu@Pt/C?catalyst was synthesized by using the above-synthesized PdAu/C as core,chloroplatinic acid as Pt precursor and anhydrous ethanol as reducing agent.The effects of the number of Pt layers in PdAu@Pt/C,which could be tuned by changing the addition amount of chloroplatinic acid,and the molar ratio of Pd to Au in PdAu@Pt/C on the catalyst's ORR performance were investigated.The results showed that the highest ORR performance was observed on the PdAu@Pt/C synthesized with the molar ratio of Pd to Au being 9:1 and the number of Pt layers being two.Pd₉Au₁@Pt-2ML/C catalyst exhibited a half-wave potential of 0.893 V vs.reversible hydrogen electrode?RHE?and a mass activity of 0.212 mA?g_Pt^-1@0.9 V.Notably,Pd₉Au₁@Pt-2ML/C catalyst exhibited a half-wave potential of 0.901 V vs.RHE and a mass activity of 0.270 mA?g_Pt^-1@0.9 V after accelerated degradation test.2.Pt-based catalyst was obtained by a two-step process.In the first step,CNT@Ti?OH?₄ gel was synthesized by using a solvothermal method with tetrabutyl titanate?300,400 or 500?L?being the precursor,and carbon nanotube-supported titanium dioxide?Ti O₂@CNT?support of different Ti O₂ loading was prepared by annealing the obtained CNT@Ti?OH?₄ gel at 400?.Pt/CNT@Ti O₂-X?X was the amount of tetrabutyl titanate added in CNT@Ti?OH?₄ gel synthesis?was synthesized by photoreduction method,and the morphology and ORR performance of the obtained Pt/CNT@Ti O₂-X was investigated.The results showed that Pt/CNT@Ti O₂-400,which showed an ORR activity larger than Pt/CNT@Ti O₂-400-EG obtained by ethylene glycol reducing method and the commercial Pt/C?JM?catalyst,exhibited a half-wave potential of 0.937 V vs.RHE and a mass activity of 0.368 mA?g_Pt^-1@0.9 V.Notably,Pt/CNT@Ti O₂-400 exhibited a half-wave potential of 0.943 V vs.RHE and a mass activity of 0.406 mA?g_Pt^-1@0.9V after accelerated degradation test.