High-Stably Confined Platinum Electrocatalysts By Carbon-Based Nanocages For Hydrogen Oxidation

With the depletion of fossil energy and the increasingly serious environmental problems,numerous efforts are devoted to exploring the clean and efficient new energy sources.Fuel cells,featuring the high energy conversion efficiency and environmental friendliness,are attracting extensive attention,especially proton exchange membrane fuel cells(PEMFCs)which fueled by gaseous hydrogen.One of the keys is the electrode catalysts for hydrogen oxidation and oxygen reduction reactions(HOR and ORR).At present,the most popular catalyst is commercial Pt/C,but there are still bottleneck issues,e.g.,the degradation of the catalytic performance in acidic conditions owing to the dissolution or migration of Pt catalysts.For the Pt HOR catalysts,some approaches have been developed to improve its stability,including to loading,anchoring,coating,and filling,but are unable to fundamentally conquer the degradation issue.Recently,our group reported the confined Pt catalysts inside the carbon-based nanocages with 0.6 nm micropores and nano-scale cavity,which exhibited the excellent ORR catalytic activity,cyclic stability,and alcohol resistance.Such excellent performance is ascribed to the seizing effects of the micropore of about 0.6 nm through the cage wall,which admit the small-sized oxygen and ions but block the large-sized alcohols into the nanocages.This dissertation focuses on the design and synthesis of the confined Pt catalysts inside carbon-based nanocages,which possess the high HOR activity and stability.The main progresses are summarized as follows:(1)The confined Pt@CNC catalysts,prepared by facile vacuum-filling method,exhibited the high HOR activity comparable to the counterparts of the supported Pt/CNC and commercial Pt/C under the acid conditions.Noticeably,the stability was far superior to those of Pt/CNC and Pt/C.The excellent performance can be attributed to:(i)the 0.6 nm micropores on the cage wall admit the small-sized species such as H2,H+,and H2O passing,which can ensure the high catalytic activity,(ii)the 0.6 nm micropore on the cage wall can also greatly block the loss of the soluble products of Pt nanoparticles etched by acid,(iii)the cage wall can effectively hinder the migration and aggregation of Pt nanoparticles,(iv)high graphitization degree of CNC can resist the electrochemical etching.(2)The confined Pt@NCNC and supported Pt/NCNC catalysts were prepared using NCNC as support.In acid medium,the two catalysts exhibited significantly better HOR catalytic activity than those of non-doped Pt@CNC,Pt/CNC and commercial Pt/C.Interestingly,N-dopants can further improve the catalytic stability of either confined or supported catalysts.The excellent catalytic activity and stability of Pt@NCNC can be ascribed to:(i)N doping conducive to highly dispersing Pt nanoparticles,decreasing the sizes of Pt nanoparticles,and thereof improving electrochemical active surface area(ECSA),(ii)N doping regulating electronic structure,enhancing the interaction between Pt and support,anchoring Pt nanoparticles,and inhibiting the etching of Pt nanoparticles,(iii)the seizing effect of the 0.6 nm micropores on cage wall and blocking effect of cage wall,similar to the case of non-doping.In addition,the co-doping of S and N can significantly degrade the HOR catalytic activity,possibly due to the poisoning of Pt catalyst by heteroatom S.These findings provide the promising strategy to explore the HOR catalysts with the high catalytic activity and stability based on carbon-based nanocages.