Yi Zhang,Feng Ji,Chengwei Deng,Jing Li,Weiwei Cai,Hansong Cheng
Polytetrafluoroethylene (PTFE) is the most widely used catalyst layer (CL) binder in a polybenzimidazole phosphoric acid (PBI–PA)-based high-temperature proton exchange membrane fuel cell (HT-PEMFC) due to its great hydrophobicity. However, PTFE also limits the formation of an effective triple-phase boundary (TPB) due to its strong resistance to acid retention. To obtain the composite ionomer in the CL of HT-PEMFC, polybenzimidazole (PBI) is thus invited. Then, an in situ quaternization strategy on PBI is developed to increase the TPB concentration in CL by controlling the PA distribution and taking into account the superior PA retention capability of quaternary ammonium groups. At the same time, Pt active sites can be freed and mass transfer channels can be in situ constructed. Consequently, the corresponding HT-PEMFC fed with H2/O2 attains a maximum power density of 755 mW/cm2 and an electrochemical surface area of 35.56 cm2/mgPt, surpassing those equipped with PTFE by 10 and 30%, respectively. The electrochemical performance improvement indicates that the in-situ quaternization strategy on the ionomer has great application potential in practical HT-PEMFC manufacturing.
Zhaoxu Wang,Qiujun Liu,Qian Liu,Hao Qi,Yuesheng Li,Dong-Po Song
Microspheres bearing large pores are useful in the capture and separation of biomolecules. However, pore size is typically poorly controlled, leading to disordered porous structures with limited performances. Herein, ordered porous spheres with a layer of cations on the internal surface of the nanopores are facilely fabricated in a single step for effective loading of DNA bearing negative charges. Triblock bottlebrush copolymers (BBCPs), (polynorbornene- g -polystyrene)- b -(polynorbornene- g -polyethylene oxide)- b -(polynorbornene- g -bromoethane) (PNPS- b -PNPEO- b -PNBr), are designed and synthesized for fabrication of the positively charged porous spheres through self-assembly and in situ quaternization during an organized spontaneous emulsification (OSE) process. Pore diameter as well as charge density increase with the increase of PNBr content, resulting in a significant increase of loading density from 4.79 to 22.5 ng µg −1 within the spheres. This work provides a general strategy for efficient loading and encapsulation of DNA, which may be extended to a variety of different areas for different real applications.
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