Structure and spectroscopy of the supercapacitor material hydrous ruthenium oxide, RuO₂·xH₂o, by neutron scattering*

Abstract

Hydrous ruthenium dioxide, RuO₂·xH₂O, is a material of active investigation as an electrode material for supercapacitors. A combination of elastic and inelastic neutron scattering together with thermal gravimetric studies and DFT calculations have provided new insight into the nature of the surface species present on RuO₂·xH₂O. Our results confirm that hydrous ruthenium oxide is a nanocrystalline material consisting of a core of RuO₂. We show that the surface consists largely of Ru–OH with small amounts of water hydrogen-bonded to the surface. The hydroxyls are stable up to ∼200°C, i.e. over the composition range x = 0.2–2. The optimal supercapacitor material has x = 0.5–0.7, and in this range, the surface is fully hydroxylated. This provides a route for the proton transport: a proton can attach to a surface hydroxyl to generate coordinated water, proton transport then occurs along the hydrogen-bonded chain by a Grotthuss mechanism.

GRAPHICAL ABSTRACT

KEYWORDS:

• Hydrous ruthenium oxide
• neutron diffraction
• inelastic neutron scattering spectroscopy
• thermal gravimetric analysis
• density functional theory

Acknowledgements

The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. Computing resources (time on the SCARF compute cluster for the CASTEP calculations) was provided by STFC’s e-Science facility.

Disclosure statement

The authors have no conflicts of interest.

ORCID

Stewart F. Parker http://orcid.org/0000-0002-3228-2570

Silvia Imberti http://orcid.org/0000-0001-7037-6829

Additional information

Funding

This work was supported by the Science and Technology Facilities Council.