Co₃O₄ Nanocrystals on Single-Walled Carbon Nanotubes as a Highly Efficient Oxygen-Evolving Catalyst

The efficient catalytic oxidation of water to dioxygen is envisioned to play an important role in solar fuel production and artificial photosynthetic systems. Despite tremendous efforts, the development of oxygen evolution reaction (OER) catalysts with high activity and low cost under mild conditions remains a great challenge. In this work, we develop a hybrid consisting of Co₃O₄ nanocrystals supported on single-walled carbon nanotubes (SWNTs) via a simple self-assembly approach. A Co₃O₄/SWNTs hybrid electrode for the OER exhibits much enhanced catalytic activity as well as superior stability under neutral and alkaline conditions compared with bare Co₃O₄, which only performs well in alkaline solution. Moreover, the turnover frequency for the OER exhibited by Co₃O₄/SWNTs in neutral water is higher than for bare Co₃O₄ catalysts. Synergetic chemical coupling effects between Co₃O₄ nanocrystals and SWNTs, revealed by the synchrotron X-ray absorption near edge structure (XANES) technique, can be regarded as contributing to the activity, cycling stability and stable operation under neutral conditions. Use of the SWNTs as an immobilization matrix substantially increases the active electrode surface area, enhances the durability of catalysts under neutral conditions and improves the electronic coupling between Co redox-active sites of Co₃O₄ and the electrode surface.