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
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