In-situ crosslinked, side chain polybenzimidazole-based anion exchange membranes for alkaline direct methanol fuel cells

The practical application of quaternized polybenzimidazole (PBI) as anion exchange membranes (AEMs) is limited by the crosslinking side reaction induced low hydroxide conductivity during the operation process. In this work, the in situ crosslinking side reaction is ingeniously controlled during the membrane preparation to achieve the balance between mechanical properties and ionic conductivity of quaternized PBI based AEMs with high ion exchange capacity. The results reveal that the in situ crosslinking reaction is easy to occur and the crosslinking effect is also better than the traditional crosslinking strategy. In addition, the in situ crosslinking can not only greatly improve the mechanical properties of quaternized PBI membranes, but the high substituted degree of ammonium hydroxide end-functionalized alkyl chain also guarantees the reasonable hydroxide conduction. The formed quaternized PBI based membrane with substituted degree of 95 % exhibits the tensile strength of 21.0 MPa under hydrated state with ion exchange capacity of 2.65 mmol g−1 and hydroxide conductivity of 82.4 mS cm−1 at 80 °C. In addition, the membrane maintains 79.7 % of its initial conductivity after treating with 1 M KOH at 80 °C for 360 h. The thus-assembled alkaline direct methanol fuel cell delivers a maximum power density of 152.6 mW cm−2 using 5 M KOH and 3 M methanol fuels at 80 °C. After chronopotentiometry test at 450 mA cm−2 for 150 h, the observed 8.7 % of voltage loss indicates its potential application in fuel cells.