Although carbon is ubiquitously used as the basis of the cathode, its use in Li-O₂ battery is still problematic in that carbon decomposes on charge above 3 V vs. Li/Li⁺, and leads to electrolyte decomposition on both discharge and charge, rendering it unsuitable for aprotic Li-O₂ cells.  Meanwhile, a pioneering work from Bruce et al., [1] suggested that carbon be replaced with TiC which promoted reversible formation of Li₂O₂.  By the way, it is open to debate that the stability of TiC originates from the TiO₂ at the surface, and TiO₂ itself can be an air cathode, provided that the electrical conductivity is guaranteed.  For this reason, porous TiO₂ [2] with some deliberate oxygen vacancies [3] was synthesized so that the electrode exhibited large surface area with moderate electronic and ionic conductivity.  The porous black electrode showed a stable cycle-life performance, and the polarization during the decomposition of Li₂O₂ is greatly improved.  Therefore, it is expected that the electronic conductivity- and porosity-tuned TiO₂ can be a suitable substrate for Li-O₂ chemistry.  Finally, the origin of high stability of this porous black TiO₂ as an air cathode is also investigated.

[1] M. M. Ottakam Thotiyl, S. A. Freunberger, Z. Peng, Y. Chen, Z. Liu, and P.G.Bruce, Nat. Mater. 12, 1050 (2013).

[2] J.-H. Shin, J.-H. Kang, W.-M. Jin, J. H. Park, Y.-S. Cho, and J. H. Moon, Langmuir, 27, 85 (2011).

[3] X. Chen, L. Liu, and F. Huang, Chem. Soc. Rev. 44, 1861 (2015).