A Highly Effi cient Metal-Free Oxygen Reduction Electrocatalyst Assembled from Carbon Nanotubes and Graphene
The oxygen reduction reaction (ORR) at the cathode is an important process for many state-of-the-art energy storage and conversion devices that operate in alkaline (e.g., metal–air batteries, alkaline fuel cells, chlor-alkali electrolyzers, etc.) or acidic (e.g., proton-exchange-membrane fuel cells) media. However, the ORR is a kinetically sluggish reaction which greatly affects the chemical-electrical energy conversion effi ciency. [ 1–4 ] So far, Pt-based electrocatalysts are generally considered as the best catalysts for ORR. [ 5–8 ] The high cost and scarcity of Pt-based materials, however, signifi cantly limit the large-scale commercialization of the above technologies. In addition, Pt-based electrocatalysts still suffer from insuffi cient durability and poor tolerance against carbon monoxide poisoning and methanol crossover. [ 9–11 ] Therefore, much effort has been devoted to developing non-Pt materials as effi cient, durable, and low-cost electrocatalysts to substitute Pt-based materials for ORR.