Architecting side chain grafted poly (vinylidene fluoride) based graphene oxide composite polyelectrolyte membranes for hydrogen and direct methanol fuel cells

• Ozone-induced one-step grafting to produce PVDF- g -PAMPS graft copolymer . • Series of GO-incorporated PVDF- g -PAMPS membranes are fabricated. • PAG-2 exhibited excellent proton conductivity and stability. • PAG-2 showed a peak power density of 152.9 and 37.7 mW/cm 2 in PEMFC and DMFC , respectively. • PAG-2 retained 91 % of its initial OCV after an accelerated durability test. Chemically modified poly (vinylidene fluoride) (PVDF) as polyelectrolyte has generated immense interest due to its high efficiency in electrochemical energy devices. Herein, the design of a polymer electrolyte membrane (PEM) is formulated by the synergistic fusion of graphene oxide (GO) into chemically grafted PVDF with 2-acrylamido-2-methylpropane sulfonic acid (AMPS) by solution phase intercalation producing GO@PVDF- g -PAMPS composite membranes. Ozone-induced graft copolymerization technique is employed to prepare PVDF- g -PAMPS with 18.2 % (w/w) degree of grafting. Incorporation of GO into the polymeric membrane generates appropriate hydrophilic-hydrophobic phase separation and constructs well-organized sub-nano slit-like pathways that elevate the proton conduction. PAG-0 membrane without any filler shows a proton conductivity (κ) of 15.1 mS/cm at 80 °C whereas PAG-2 membrane (with 2% w/w GO loading) shows a κ of 25.9 mS/cm under similar conditions. The presence of a perfluorinated backbone furnishes excellent oxidative stability to the PEMs by retaining 95 % of total mass and 97.3 % of κ after dipping in harsh Fenton's reagent at 60 °C for 6 h. Representative PAG-2 shows a peak power density of 152.9 mW/cm 2 with a maximum current density of 480.6 mA/cm 2 (fuel cell operating conditions: 75 °C at 100 % RH) in hydrogen fuel cell and a peak power density of 37.7 mW/cm 2 in direct methanol fuel cell. Moreover, PAG-2 retains 91 % of its initial OCV and exhibits a mere 5.2 % loss in peak power density after 50 h of the durability test.