High conductivity of a fuel cell through a hydrogen bond network within an interpenetrating anion exchange membrane

Abstract

A series of anion exchange membranes (AEMs) with highly ion conductivity suitable for practical application in fuel cells were prepared in this paper. Polysulfone (PSf) was used as backbone to prepare chloromethylation polysulfone (CMPSf). Then the synthesized CMPSf was blended with tetramethyldiaminopropane (TMPDA) and polyethylene glycol (PEG 400), to construct interpenetrating polymer networks with hydrogen-bonding conduction sites. In this paper the chemical structure of the AEM is confirmed by nuclear magnetic resonance spectrum (¹H NMR) spectroscopy and fourier transform infrared spectroscopy (FT-IR). The morphologies of synthesized membranes in this paper are investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical and physical properties of AEMs are tested comprising water uptake (WU), ion exchange capacity (IEC), alkaline stability, thermal stability and mechanical stability. The introduction of hydrogen-bonding networks enhanced the OH⁻ conductivity of the membranes (from 37.03 mS·cm⁻¹ of QAPSf-PEG_0% to 104.67 mS·cm⁻¹ of QAPSf-PEG_30%). The interpenetrating polymer networks make the membranes have good mechanical property (tensile strengh is 19.61 MPa, elongation at break is 20.30 %) and anti-swelling properties (29.3 %, 80 °C). Due to the introduction of hydrogen-bonding conduction networks, the alkaline stability of the AEMs can be enhanced by reducing the modification of the polysulfone backbone. Thus, even after soaking in 6 mol·L⁻¹ KOH solution for 30 days, the retained OH⁻ conductivity of QAPSf-PEG_30% still reached 92.0 %. At the same time, the addition of PEG leads to the increased water uptake, so that the OH⁻ ions could be better transported. And the single cell performance of QAPSf-PEG_30% was also revealed that the power density increases significantly from 323.35 mW·cm⁻² at 60 °C to 514.8 mW·cm⁻² at 80 °C as the temperature increases. Overall, QAPSf-PEG_30% exhibits promising development potential in the fuel cells.