Graphene-nanofiber hybrid carbon composites as support boosting tantalum oxides activity of bifunctional oxygen reduction/evolution catalysts

Carbon nanocomposites combining two or more carbon structures at the nanoscale present great potential for electrocatalysis. In this work, the combination of graphene with carbon nanofibers (CNF) is investigated as a hybrid support for tantalum-based electrocatalysts in bifunctional oxygen electrodes. Bifunctional catalysts for both the oxygen reduction and the oxygen evolution reactions (ORR and OER) are highly demanded for energy conversion devices like regenerative fuel cells or metal-air batteries. Tantalum oxides were selected as durable and promising active phases. The content of CNF in the composites was varied between 20 % and 75 %, causing an up to 5-fold increase in surface area by inhibiting the restacking of graphene sheets. Hybrid nanocomposites as catalyst support result in a relevant enhancement of ORR activity compared to the bare materials, excellent bifunctionality and exceptional stability. This novel 3-dimensional structure exposing graphene layers aided by intercalated nanofibers boosts the electroactivity and bifunctionality of the oxides. • Carbon hybrid composites are studied by growing nanofibers within graphene. • Larger surface area and pore volume since nanofibers prevent graphene restacking. • Hybrid nanocomposites are studied as support for tantalum oxides. • The new support contributes to a significant improvement of ORR activity. • Enhanced OER/ORR bifunctional activity and excellent durability attributed to new support nanostructure.