Abstract
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•Poly(bipyridine-5,5′-bibenzimidazole) polymer with a Nitrogen-rich structure.•Polymer electrolyte membrane fuel cells with enhanced proton conductivity.•Polymer functionalization of pristine-multiwalled carbon nanotube.•A membrane electrode assembly with enhanced electrochemical performance.
High density nitrogen supporters, in particular nitrogen-based polymeric supporters of metal catalysts is a topic of high interest to boost the catalytic activity of oxygen reduction reaction (ORR), and accordingly improve fuel cell (FC) performance. Here, we offer a promising membrane electrode assembly (MEA) of a nitrogen-rich and highly conductive polymer; namely, poly(bipyridine-5,5′-bibenzimidazole) (BipyPBI). The MEA comprised BipyPBI as the membrane and platinum(Pt)/BipyPBI-functionalized multiwalled carbon nanotubes as the electrodes. The fabricated materials characterized by NMR, XPS, TEM, XRD, and TGA, and catalytically evaluated by CV, LSV, current-potential, and power density measurements. The fuel cell performance diagnosed by electrochemical impedance spectroscopy (EIS). The use of BipyPBI provided highly active fuel cell electrodes with a homogenous distribution of the Pt catalyst on the surface of carbon nanotubes. Notably, the onset overpotential of ORR lowered by ∼10 mV, the half-wave potential positively shifted by a 41 mV, and the diffusion-limiting current increased by 36 mA/mgPt, when the BipyPBI-based electrode compared to the conventional PBI-based electrode. Importantly, the power density of BipyPBI-based MEA reached 0.893 W/cm2 (1.48 W/mgPt) compared to 0.549 W/cm2 (0.94 W/mgPt) for the PBI-MEA. The EIS results indicated an improvement in the ohmic and charge transfer resistances of BipyPBI-based MEA, thanks to the high density nitrogen structure of BipyPBI which enhanced the proton conduction and the reaction kinetics. These results enrich the fuel cell research, and stimulate researchers engaged in related fields.