Maghemite nanoparticles decorated on carbon nanotubes as efficient electrocatalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) is a critical reaction in electrochemical water splitting and rechargeable metal-air batteries to generate and store clean energy. Therefore, the development of efficient and low cost electrocatalysts for the OER with high activity and stability is of great technological and scientific interest. We demonstrate here for the first time that maghemite (γ-Fe₂O₃) nanoparticles decorated on carbon nanotubes (CNTs) function as low cost, highly active and durable OER electrocatalysts. The material generates a current density of 10 mA cm^-2 at overpotentials of 0.38 and 0.34 V in 0.1 and 1 M NaOH, respectively. These values are comparable to those of the best OER electrocatalysts reported so far. Moreover, γ-Fe₂O₃/CNTs show a stable performance at a potential of ∼1.64 V vs. RHE during 25 h stability tests. The γ-Fe₂O₃ nanoparticles are formed from carbon encapsulated iron nanoparticles (CEINs) during the first OER measurements of the CEIN/CNT electrode. The CEIN/CNT material itself is synthesized by a fast and low cost floating catalyst chemical vapor deposition method in a one-step synthesis with a similar growth process to that of CNTs.