Rutile MnO₂ is an important material for energy storage and catalysis applications. David A. Tompsett, Stephen C. Parker, and M. Saiful Islam, University of Bath, UK, have performed a detailed density functional theory (DFT) investigation of its surfaces to find out what surface characteristics are important to electrochemical performance and catalytic activity.

A Wulff construction from relaxed surface energies indicates a rod-like equilibrium morphology that is elongated along the c-axis. This is consistent with the large number of nanowire-type structures that are obtainable experimentally. The (110) surface dominates the crystallite surface area. Higher index surfaces, for instance, the (211) and (311) surfaces, also cap the rod-like morphology.

Broken coordinations at the surface result in enhanced magnetic moments at Mn sites. These may play a role in catalytic activity.
The formation energies to form surface oxygen vacancies are considerably lower than for comparable structures like rutile TiO₂. The team thinks that this is important to the good catalytic activity of rutile MnO₂.

• Rutile (β-)MnO₂ Surfaces and Vacancy Formation for High Electrochemical and Catalytic Performance,
  David A. Tompsett, Stephen C. Parker, M. Saiful Islam,
  J. Am. Chem. Soc. 2014.
  DOI: 10.1021/ja4092962