The energy density of ruthenia (${\mathrm{RuO}}_2$) pseudocapacitor electrodes is critically dependent on their surface structure. To understand this dependence, we simulate the electrochemical response of ${\mathrm{RuO}}_2$(110), ${\mathrm{RuO}}_2$(100), and ${\mathrm{RuO}}_2$(101) in aqueous environments using a self-consistent continuum solvation (SCCS) model of the solid-liquid interface. The insertion of protons into the ${\mathrm{RuO}}_2$(110) sublayer is found to profoundly affect the voltage-dependent characteristics of the system, leading to a sharp transition from a battery-type to capacitor-type response. The calculated charge-voltage properties for ${\mathrm{RuO}}_2$(101) are in qualitative agreement with experiment, albeit with a pseudocapacitance that is significantly underestimated. In contrast, the ${\mathrm{RuO}}_2$(100) facet is correctly predicted to be pseudocapacitive over a wide voltage window, with a calculated pseudocapacitance in close agreement with experimental voltammetry. These results establish the SCCS model as a reliable approach to predict and optimize the facet-dependent pseudocapacitance of polycrystalline systems.

• Received 3 June 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.085405