Development and characterization of a quaternized polymeric anion exchange membrane reinforced with Mg–Al–NO3− LDH for direct borohydride fuel cells

Recently, direct borohydride fuel cell (DBFC) has gained widespread attention as a new type of direct liquid fuel cell due to its high theoretical voltage, high energy density, and ability to utilize non-precious metals as catalysts. In this study, a series of anion exchange composite membrane (QFPTP-x%) consisting of quaternized Poly (para-terphenyl piperidinium) (QFPTP) and Mg–Al layered double hydroxide (LDH) has been developed. Due to the hydrophilicity and OH− conductivity features of Mg–Al–NO3− LDH, QFPTP-x% exhibits enhanced ion exchange capacity, water uptake, and OH− conductivity. The interaction between LDH and copolymer at the interface between the organic and inorganic leads to the formation of hydrogen and covalent bonds, improving the mechanical properties. More importantly, the borohydride permeability can be effectively reduced by adding LDH. The optimal amount of LDH has been determined to be 1 % (QFPTP-1%) by evaluating the properties of QFPTP-x%. The assembled DBFC incorporating QFPTP-1% exhibits a remarkable peak power density, achieving 1218 mW cm−2 @ 2.9 A cm−2, which is higher than the commercial anion exchange membrane PiperION® based DBFC (1079 mW cm−2 @ 2.5 A cm−2). Such an enhancement is attributed to the superior OH− conductivity and diminished borohydride permeability presented by the QFPTP-1% membrane. Additionally, the DBFC incorporating QFPTP-1% presents excellent stability with a minimal voltage loss of 34.1 % after 10 h of operation, highlighting the potential of the composite membrane for practical DBFC applications. [Display omitted] •The mechanism behind improved OH− conductivity and reduced BH4− permeability in the composite membrane is revealed.•The incorporation of merely 1 wt% Mg–Al–NO3− LDH into the AEM exhibits the highest OH− conductivity.•The QFPTP-1% based DBFC exhibits a peak power density of 1218 mW cm−2 @ 2.9 A cm−2.•The QFPTP-1% based DBFC exhibits the lowest voltage decrease after a 10-h stability test.