From biomass chitin to mesoporous nanosheets assembled loofa sponge-like N-doped carbon/g-C3N4 3D network architectures as ultralow-cost bifunctional oxygen catalysts

To accelerate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the field of air based energy technologies, efficient low-cost bifunctional catalysts are highly desired. In this paper, biomass chitin-derived N-doped carbon (C-Chitin)/graphitic C3N4 (g-C3N4) composites have been designed and fabricated via an ultralow-cost route including the low-temperature dissolution of biomass chitin and the subsequent carbonization. The C-Chitin/g-C3N4 composites exhibit well-designed loofa sponge-like three-dimensional (3D) network architectures assembled with massive interconnected ultrathin mesoporous nanosheets. Benefiting from the well-designed morphology and unique mesoporous structure with a high surface density of catalytic active sites, as well as the incorporation of N-doped carbon with g-C3N4, the C-Chitin/g-C3N4 composites exhibit pronounced ORR activity (4-electron pathway), superior OER activity (much lower onset potential and higher current density than Pt/C), excellent tolerance to methanol crossover and high durability toward both ORR and OER. Especially, the obtained C-Chitin/g-C3N4 composites with 20 wt % addition of g-C3N4 exhibit a potential gap of 0.90 V between the OER potential at a current density of 10 mA cm(-2) and the ORR half wave potential, which is even higher than some highly active metal catalysts including noble-metals, thus holding great promise as low-cost metal-free bifunctional catalysts for efficient ORR and OER. (C) 2016 Elsevier Inc. All rights reserved.