An effective strategy to enhance phosphoric acid retention and proton conductivity stability: Construction of proton transfer channels with starch rather than H3PO4

Abstract

To enhance the phosphoric acid (PA) retention as well as maintain high proton conductivity of phosphoric acid doped proton exchange membranes at high temperature, we successfully design a series of phosphoric acid doped biobased composite membranes by incorporation of starch and graphene oxide (GO) into poly arylene ether ketones (PAEK). Proton transfer channels should be mainly built through dense hydrogen bonds formed from massive oxygen-containing groups of starch mainchain, which is confirmed by Molecular dynamics (MD) simulation, FT-IR and XRD analysis. The dense hydrogen-bond structure could construct fast proton transfer channels with extreme low doping level (0.00484 molH₃PO₄). The excellent PA retention properties with almost unchanged proton conductivity at high temperature (200 °C) for 600 min indicates that PA molecules are firmly fixed into membranes. Thus, in this study, we suggest a novel strategy for stablizing proton conductivity at high temperature and improving PA retention properties of PA doped membranes, which is building dense hydrogen-bond structure with low PA doping level.

Based on the results in this study and the Grotthuss proton transfer mechanism, dense hydrogen-bonds from oxygen-containing groups in polymer backbones should be more stable than hydrogen-bonds from massive H₃PO₄ molecules with high acid doping levels to promote proton conduction.