Carbon Nanotubes Loaded on Graphene Microfolds as Efficient Bifunctional Electrocatalysts for the Oxygen Reduction and Oxygen Evolution Reactions

Abstract

AbstractAdvanced bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are promising to improve the efficiency of fuel cells and metal–air batteries. Among the state‐of‐the‐art efficient oxygen electrocatalysts, heteroatom‐doped carbon materials are favorable candidates. However, the enriched doping requires a highly exposed carbon skeleton. Here, we report a scalable route to prepare carbon nanotubes (CNTs) loaded on graphene microfolds (CGFs) by a low‐temperature spray‐drying procedure. Molecular‐level assembly of graphene and CNTs, mesoporous structures, and large specific surface areas permit the carbon skeleton of CGFs to be highly exposed. After doping with abundant nitrogen and phosphorous (5.58 at % for N, 0.1 at % for P), CGFs exhibit excellent bifunctional electrocatalytic activity for both the ORR and OER, with superb durability and methanol tolerance. The measured variance of the ORR and OER metrics (ΔE=Ej=10−E1/2) was low at 0.9 V versus reversible hydrogen electrode (vs. RHE), being within only 20 mV of Pt‐ and Ru‐based electrodes, and superior to transition‐metal‐based catalysts and other carbon catalysts. Such efficient overall electrocatalytic activity allows CGFs to be used for high‐performance oxygen electrodes in renewable energy devices.