POLYELECTROLYTE BRUSH AS AN EFFECTIVE PROTON CONDUCTOR

摘要

Proton conducting materials having reasonable proton conductivity at low humidification conditions are critical for decrease in system complexity and improvement of power density for polymer electrolyte membrane fuel cells. Thus, construction of new materials to improve the efficiency of proton transportation is one of the very important research areas. Herein, we described a new type of proton conductors based on polyelectrolyte brushes which were synthesized through in situ free radical polymerization either from metal oxide nanotubes. The grafting density and grafted chain length can be precisely controlled by controlling the polymerization parameters. The large density of proton conducting moieties and well-distribution of ionic groups makes the free volume inside the materials relatively small and reduces the proton transporting distance. Accordingly, proton conductivity is rather less humidity-dependant. However, both grafting distance and molecular weight of surface-attached polymer electrolyte chains exhibit significant influence on proton conductivity of the formed polymer brushes. With the decrease in average grafting distance of surface-attached polymer chains, the proton conductivity of the synthesized polymer brushes initially increases and then decreases after reaching a maximum value. Non-monotonic behavior of proton conductivity with the increase in molecular weight is also observed. Under optimized conditions, the proton conductivity values of the formed polymer electrolyte brush reach 0.095 Scm~(-1) under 100% relative humidity and 0.01 Scm~(-1) under anhydrous conditions at 140 °C. Nevertheless, this kind of channelless material has the potential to low-humidity polymer electrolyte membrane applications. This work was financially supported by the National Natural Science Foundation of China (No. 51372192) and Open Foundation from State Key Laboratory of Advanced Technology for Materials Synthesis and Processing of WHUT (2014-KF-14).